WO2005115612A1 - Catalyst containing gold on support containing zinc oxide and production and use thereof - Google Patents

Catalyst containing gold on support containing zinc oxide and production and use thereof Download PDF

Info

Publication number
WO2005115612A1
WO2005115612A1 PCT/ZA2005/000074 ZA2005000074W WO2005115612A1 WO 2005115612 A1 WO2005115612 A1 WO 2005115612A1 ZA 2005000074 W ZA2005000074 W ZA 2005000074W WO 2005115612 A1 WO2005115612 A1 WO 2005115612A1
Authority
WO
WIPO (PCT)
Prior art keywords
gold
catalyst
carrier
zinc
metal
Prior art date
Application number
PCT/ZA2005/000074
Other languages
French (fr)
Inventor
Stephen John Roberts
Gabriele Hildegard Steinbach
Diandree Padayachee
Jason Scott Mcpherson
Gary Pattrick
Elma Van Der Lingen
Original Assignee
Mintek
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mintek filed Critical Mintek
Publication of WO2005115612A1 publication Critical patent/WO2005115612A1/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • B01J37/18—Reducing with gases containing free hydrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/005—Spinels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/005—Spinels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/48—Silver or gold
    • B01J23/52—Gold
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
    • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/8953—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with zinc, cadmium or mercury
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/03—Precipitation; Co-precipitation
    • B01J37/031—Precipitation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/06—Washing

Definitions

  • This invention relates to a catalyst which is suitable for use in the oxidation of carbon monoxide, and to the production and use thereof.
  • Precious metals are known to act as catalysts for the conversion of carbon monoxide to carbon dioxide.
  • US-4839327 discloses catalysts for oxidising carbon monoxide to carbon dioxide comprising an ultra-fine deposit of gold upon metal oxides including MnO 2 , Fe 2 O 3 , CuO, CuMnO 2 , AI 2 O 3 , SiO 2 , TiO 2 .
  • metal oxides including MnO 2 , Fe 2 O 3 , CuO, CuMnO 2 , AI 2 O 3 , SiO 2 , TiO 2 .
  • Taylor et al disclose the use of a mixed oxide of copper and zinc for this purpose.
  • Chinese patent specification CN-1464058 discloses a complex catalyst system which has three active components (Au, Pt and Pd) and at least 2 promoters (Fe, Cu and, optionally, Zn) on a support made of alumina, silica, bentonite or molecular sieve material.
  • Carbon monoxide is a colourless, odourless and highly toxic compound which is produced in many chemical industrial processes or as a product of incomplete combustion e.g. in furnaces or internal combustion engines, as well as in mines.
  • the invention provides a catalyst formed from gold on a carrier which includes at least zinc oxide
  • the carrier may be formed from a mixed oxide of zinc and at least one metal
  • the gold has a particle size less than 100 nanometres (e g below 70 nm), advantageously less than 50 nanometres (e g below 25nm) and desirably less than 10 nanometres (e g 5 nm or lower)
  • the amount of gold is preferably at least 0 01 wt-% of the catalyst, advantageously at least 0 05 wt %, desirably at least 0 5 wt % and conveniently 1 wt-% or more
  • the catalysts tend to be more effective as the amount of gold on the carrier increases
  • the amount of gold on the carrier should not exceed 5 wt-% and is desirably no more than 4 wt-%
  • Gold is easier to deposit upon substrates that have iso-elect ⁇ c points in the pH range from 6 to 10
  • At least one other metal is therefore preferably selected so that the mixed oxide has an iso-elect ⁇ c point of from 6 to 10
  • Pure zinc oxide has an iso-electnc point of about 9, which will alter when mixed with another oxide with a different iso-electnc point
  • Suitable other metals for incorporation in the carrier therefore include aluminium (which forms the oxide AI 2 O 3 which has an iso-electnc point from 8 to 9), cerium (which forms CeO 2 with an iso-elect ⁇ c point of 7), titanium (which forms T ⁇ O 2 with an iso-electnc point of 6), zirconium (which forms ZrO 2 with an iso-electnc point of 6 7), iron (which forms Fe 2 0 3 with an ⁇ so r elect ⁇ point of 6 5-6 9), and copper (which forms cupnc oxide with an iso- elect ⁇ c point of about 6 5)
  • Effective catalysts are those in which the carrier is a mixed oxide of zinc and aluminium or a mixed oxide of copper and zinc
  • the mixed oxide may be in the form of a mixture of two oxides of metals with individual crystal structures, for example a mixture of zinc oxide and aluminium oxide
  • the relative quantities of zinc and the other metal may vary widely
  • the weight ratio of zinc to the other metal in the mixed metal oxide may vary from 100 1 to 1 100, but preferably the range is from 80 1 to 1 80
  • the weight ratios of zinc to the other metal will be at least 5 and preferably at least 6 5 parts of zinc to 80 parts of the other metal
  • Higher relative amounts of zinc can be used, e g 10, 20, 30, 40, 50, 60, 70, or 80 parts of zinc to 80 of the other metal Zinc may be present in greater weight proportions than the other metal, for example in ratios of 2, 5, 10, 20, 30, 40 50, 60, 70 or 80 parts to 1 of the other metal
  • Zinc to other metal weight ratios in the range of 80-20 1 are typically useful, preferably 25-65 1, desirably 35 45:1, especially weight ratios of about 40 1
  • the other metal is at least one of aluminium, graphite, silicon, titanium, zirconium, copper and iron
  • the aforementioned ranges also apply to possible molar ratios of zinc to the other metal
  • the molar ratio of zinc to the other metal may be in the range of 80-1 to 1 80, and intermediate values, eg 2 1 to 1 2
  • the molar ratio of zinc to the other metal is greater than 1 1
  • zinc is the more important metallic element although it may be present in amounts as low as 2% by weight of the catalyst, it is preferably present in amounts of at least 5% by weight, preferably at least 10%, desirably at least 15% and advantageously at least 20%, 25 wt% or 30 wt-%
  • the carrier may be composed predpminantly of zinc oxide, and may contain up to 80% by weight of zinc, for example 75 wt-% or preferably 70 wt-%, or conveniently 65 wt-%, or less, such as 50 wt-%, 45 wt-% or 40 wt-%.
  • the preferred catalysts may be prepared in any appropriate way e.g. by using co- precipitation, impregnation or inverse deposition-precipitation techniques, as described in the specification of South African patent application No 2003/8981.
  • the invention also extends to a method of producing a catalyst of the aforementioned kind wherein an aqueous solution containing at least one water soluble gold compound (for example tetrachloroauric acid, gold cyanide or sodium tetrachloroaurate and other such complexes or compounds) and water soluble salts (for example the nitrates) of zinc and at least one other metal is prepared, using quantities required to produce a desired ratio of gold, zinc and the other metal in the finished mixed metal oxide.
  • the pH of the solution may be increased by the addition of a base such as ammonium or an alkali metal carbonate or hydroxide (e.g.
  • NH 4 OH, NaOH, KOH, Na 2 CO 3 , K 2 CO 3 or Li 2 CO 3 ) or urea to a point at which gold is precipitated simultaneously with the hydroxides, carbonates, hydroxy- carbonates, oxides (or a combination thereof) of zinc and the at least one other metal.
  • This will normally be in the pH range of 7 to 10, depending on the precursors used for the gold and the other metal of the carrier.
  • the resulting gold-bearing catalyst material is separated from the aqueous liquor, washed and dried. Washing is particularly important where the gold is deposited from chloride-containing solutions.
  • the gold catalyst is produced by depositing gold on a carrier material.
  • the carrier may be prepared in a variety ways including, but not limited to, co- precipitation of metal precursors and physical mixing of metal oxides.
  • any commercially available zinc containing carrier can be used with no particular restriction thereon
  • the carrier material generally has a surface area of from 4 to 180 m 2 /g (as determined by the BET/N 2 method (ASTM D3037)
  • Gold may be deposited upon the carrier by treating the carrier with an aqueous solution of a gold precursor compound The amount of gold deposited may be varied by varying the relative proportions of gold solution and carrier.
  • the gold precursor compound may be selected at least from, gold (I) cyanide [AuCN], sodium tetrachloroaurate (III) [NaAuCI 4 ], potassium dicyanoaurate (I) [KAu(CN) 2 ], gold (III) acethylacetonate [(CH 3 ) 2 Au(CH 3 COCH 2 COCH 3 ) and tetrachloroauric (III) acid
  • the gold precursor may be dissolved to form a treatment solution with a gold content in the range of from 1x10 "1 to 1x10 "4 , preferably in the range 1x10 "2 to 5x10 "3 M.
  • the treatment solution may initially have a pH below 7, preferably in the range of from 1 to 3.
  • the pH of the treatment solution may be adjusted to a desired value, e g. from 2 to 8.5, by adding a suitable alkali such as sodium carbonate solution.
  • the relative proportion of these species is dependent on the degree of hydrolysis that the HAuCI 4 species undergoes. As such, the degree of hydrolysis is in part a function of solution pH, with higher pH's promoting further hydrolysis
  • the treatment solution and the carrier are preferably brought into contact at an elevated temperature, preferably in the range 20-90°C , ideally 40-80°C, conveniently 65- 75°C
  • the solution is contacted with the carrier Gold is then precipitated from the solution, for example by increasing the pH of the solution to a desired value by adding an alkaline solution of, for example sodium, potassium or ammonium hydroxide or carbonate, or urea This will normally be in the pH range of 4 to 11.
  • an alkaline solution of, for example sodium, potassium or ammonium hydroxide or carbonate, or urea
  • the pH at which precipitation will occur similarly depends on the nature of the precipitate. [Au(OH) n CI .
  • Gold hydroxide however precipitates at higher pH values, (typically from 7 to 10, preferably 8 to 9.5, ideally about 8.5). This is advantageous because high pH values lead to well-dispersed gold with a low particle size in the nanometre range.
  • the gold species prevalent at high pH values contain less chloride. The presence of chloride species is believed to increase the formation of larger gold particles, thereby decreasing catalytic activity, due to the sintering of the gold particles as a result of the formation of CI-Au-CI bridges.
  • Residual chloride may also serve to poison the catalytic active site.
  • the contacting time of the gold containing solution and the carrier material is performed for a suitable period, for example 0.5 to 3 hours, preferably about 1 hour.
  • the solid material is then separated and washed.
  • the washing is preferably carried out with a base, such as aqueous ammonia solution, NaOH or urea, which also assists in the removal of chloride ions.
  • the catalyst material is dried, preferably at a temperature of from 20 to 150°C, e.g. at 120°C. Further washing with an alkaline solution can be performed on the dried catalyst material to remove excess chloride and other undesired ions, if required.
  • the activity of the catalyst may be modified by further treatment of the gold-bearing carrier.
  • the catalytic mechanism of gold is not fully understood, but may depend upon the presence of both metallic gold (Au°) species and positively charged gold species (Au ⁇ + ).
  • Au° metallic gold
  • Au ⁇ + positively charged gold species
  • the presence of these gold species can be affected by further treatment of the catalyst material.
  • catalyst material obtained by a co-precipitation, impregnation or inverse deposition-precipitation technique may be calcined before use, typically by heating the catalyst material to a temperature from 50 to 500°C (preferably from 100 to 300°C) for a period of from 1 to 5 hours.
  • the effect of calcining is to reduce Au(OH) 3 species present in the catalyst to metallic gold
  • the catalyst material may be treated in a reducing atmosphere, for example hydrogen or, preferably, carbon monoxide Such treatment also affects the nature of the gold species on the surface of the catalyst
  • a 1 34M aqueous solution of zinc nitrate [Zn(NO 3 ) 2 6H 2 O] and a 0 081 M aqueous solution of aluminium nitrate [AI(NO 3 ) 3 9H 2 O] were mixed together in proportions such that the weight ratio zinc aluminium was 40 1
  • the solution was heated to a temperature of approximately 80°C, and the pH of the solution was adjusted from an initial value of 1 1 to a value of 9 1 by adding an aqueous solution of sodium carbonate while stirring, thereby producing a precipitate of the hydroxides of zinc and aluminium
  • the pH and temperature of the solution were maintained to allow the precipitate to age in contact with the solution for about 5 hours
  • the precipitate was filtered from the solution, washed with high-purity water to remove unwanted ions, and dried in air at approximately 120°C for 16 hours
  • the dried precipitate was then calcined by heating in air at 400°C for four hours
  • the resulting earner material (A) was then ground into
  • a volume of deionised water sufficient to support a sample of carrier A in suspension was heated to 70°C.
  • a solution of tetrachloroauric [HAuCU] acid containing sufficient gold was added to the water.
  • the pH of the solution was adjusted from an initial pH of 2 to 5.5 by adding a solution of Na 2 CO 3 . Having stabilised the temperature and pH, the carrier was added, and the suspension agitated for a period of 1 hour. The solid material was separated, washed with a ammonia solution of a desired concentration and dried in air at 120°C.
  • gold, deposited upon alumina alone, does not function as a catalyst for oxidation of CO under the conditions tested.
  • Gold deposited upon zinc oxide shows some catalytic function, but the best catalytic function is exhibited by gold when deposited upon a carrier composed of the mixed oxides of zinc and aluminium, especially when the ratio of zinc to aluminium in the carrier is over 20:1. Also the catalysts with higher gold loading (2% by weight or more) perform more effectively.
  • Examples 9 - 14 Au/CuZnOx catalyst Samples of catalyst material comprising gold on a carrier material consisting of the mixed oxides of copper and zinc were prepared. Carrier Preparation
  • Gold catalysts were produced on the aforementioned carriers by means of inverse deposition precipitation using an aqueous solution of HAuCI 4 of desired concentration. This solution was preheated to 70°C and the pH adjusted to 8.5 by adding Na 2 CO 3 solution. The carrier materials were then added to separate batches of the gold solution and each was aged for 1 hour at 70°C with pH control. Thereafter, the catalyst materials were filtered, washed several times with deionised water, dried in an oven at 120°C for 16 hours and calcined if necessary.
  • a batch of support material was prepared using the method described for Examples 1 to 8, with a Zn:AI ratio of 40:1.
  • the resulting material was treated with gold as described in Examples 9 - 14, with the exception that the solid-liquid contacting (ageing) time and temperatures were varied as shown in Table 4.
  • Supports with zinc to aluminium ratios of 20:1, 40:1 , 80:1 as well as 100% ZnO and 100% AI 2 O 3 were prepared according to the method highlighted in Examples 1 - 8.
  • Gold was deposited onto these carriers as described in Examples 9 - 14. Effect of zinc to aluminium ratio on catalyst activity and gold loading
  • the gold adsorption is also affected by Zn to Al ratios and the highest gold loading was obtained at Zn/AI ratios of 40:1.
  • the alumina catalyst had very low gold loading. This trend is shown in
  • catalysts prepared on G72D are more active than the gold catalysts prepared on the individual metal oxide carriers alone.
  • Gold loading from solution onto the all the carriers is higher at low pH when compared to high pH preparation, the inverse is true for CO oxidation activity.
  • Examples 29 - 37 Au/ZnO impregnated on AbOs
  • gold was deposited or impregnated onto an AI 2 O 3 carrier impregnated with ZnO.
  • a support was prepared comprising a ZnO layer on Al 2 0 3 using one of the following techniques:
  • the mixture was subjected to impregnation described in method (b). Washing, drying and calcining followed as described in method (a).
  • the gold catalyst was prepared by the inverse deposition precipitation method highlighted in Examples 1 - 8.
  • Catalysts were prepared by contacting the necessary amount of carrier material and gold containing solution to obtain a maximum gold loading of 1 wt%.
  • the deposition- precipitation conditions employed are similar to those described in Examples 9 - 14.
  • Catalytic activity was determined using 0.05 - 0.1 g of catalyst in a micro fixed-bed reactor under conditions identical to those described in Examples 9 - 14.
  • Catalysts prepared using the recycled gold solution compare well in terms of gold loading and catalytic activity to their freshly prepared counterpart. Recycling of the gold solution used in catalyst synthesis is possible.
  • a commercially available zinc- aluminium oxide (supplied by S ⁇ d-Chemie under product reference No G72D) was used as the carrier material.
  • Gold catalysts were prepared by depositing gold onto two carriers composed of a commercially available zinc-aluminium oxide (supplied by S ⁇ d-Chemie under product reference No G72D) and a commercially available copper-zinc oxide (supplied by S ⁇ d- Chemie under product reference No G66B). In each case the carrier was crushed and sieved to a particle size in the range 500-1000 ⁇ m. Gold was deposited onto the carrier by an inverse deposition precipitation technique as described in Example 9 - 14.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Catalysts (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

A catalyst for use in the oxidation of carbon monoxide to carbon dioxide which includes gold on a carrier of a mixed oxide of zinc and at least one other metal.

Description

CATALYST AND PRODUCTION AND USE THEREOF
BACKGROUND OF THE INVENTION
[0001] This invention relates to a catalyst which is suitable for use in the oxidation of carbon monoxide, and to the production and use thereof.
[0002] Precious metals are known to act as catalysts for the conversion of carbon monoxide to carbon dioxide. For example, US-4839327 discloses catalysts for oxidising carbon monoxide to carbon dioxide comprising an ultra-fine deposit of gold upon metal oxides including MnO2, Fe2O3, CuO, CuMnO2, AI2O3, SiO2, TiO2. In Che . Commun., 1999, 1373-1374, Taylor et al disclose the use of a mixed oxide of copper and zinc for this purpose.
[0003] International patent publication WO 2004/002247 discloses several catalysts including zinc aluminate, and gold deposited upon a rare earth oxide such as cerium oxide. US-2003/0075193 discloses catalysts in the form of nanoparticles of metal oxides such as Fe2O3, CuO, TiO2, CeO2, Ce2O3, AI2O3, Y2O3 doped with Zr and MnO2 doped with Pd. Chinese patent specification CN-1464058 discloses a complex catalyst system which has three active components (Au, Pt and Pd) and at least 2 promoters (Fe, Cu and, optionally, Zn) on a support made of alumina, silica, bentonite or molecular sieve material.
[0004] Other documents which relate to gold catalysts for the oxidation of carbon monoxide to carbon dioxide include US patent 5,068,217, where the catalyst comprises gold on a porous ceramic carrier material which contains Fe2O3', US publication No. 2003/099586 which focuses on gold Fe2O3; and US patent 4,698,324 which describes the deposition of gold or a mixture of gold with a catalytic metal oxide (Cr2O3, MnO, NiO, Fe2O3, Co3O4, CuO) on a carrier of silica, alumina or magnesia.
[0005] Carbon monoxide is a colourless, odourless and highly toxic compound which is produced in many chemical industrial processes or as a product of incomplete combustion e.g. in furnaces or internal combustion engines, as well as in mines. [0006] A need exists for a catalyst which can be used for the oxidation of carbon monoxide to carbon dioxide at ambient temperature, often in conditions with high humidity, e g in CO2 lasers, submarines, fuel cells, sensors, breathing masks, respirators, motor vehicle ventilation and filters for air conditioners These potential applications are given merely as non-limiting examples of the use of the catalyst of the invention
SUMMARY OF THE INVENTION
[0007] The invention provides a catalyst formed from gold on a carrier which includes at least zinc oxide
[0008] The carrier may be formed from a mixed oxide of zinc and at least one metal
[0009] Preferably, the gold has a particle size less than 100 nanometres (e g below 70 nm), advantageously less than 50 nanometres (e g below 25nm) and desirably less than 10 nanometres (e g 5 nm or lower)
[0010] The amount of gold is preferably at least 0 01 wt-% of the catalyst, advantageously at least 0 05 wt %, desirably at least 0 5 wt % and conveniently 1 wt-% or more The catalysts tend to be more effective as the amount of gold on the carrier increases Preferably, however, for reasons of cost, the amount of gold on the carrier should not exceed 5 wt-% and is desirably no more than 4 wt-%
[0011] Gold is easier to deposit upon substrates that have iso-electπc points in the pH range from 6 to 10 At least one other metal is therefore preferably selected so that the mixed oxide has an iso-electπc point of from 6 to 10 Pure zinc oxide has an iso-electnc point of about 9, which will alter when mixed with another oxide with a different iso-electnc point Suitable other metals for incorporation in the carrier therefore include aluminium (which forms the oxide AI2O3 which has an iso-electnc point from 8 to 9), cerium (which forms CeO2 with an iso-electπc point of 7), titanium (which forms TιO2 with an iso-electnc point of 6), zirconium (which forms ZrO2 with an iso-electnc point of 6 7), iron (which forms Fe203 with an ιsorelectπς point of 6 5-6 9), and copper (which forms cupnc oxide with an iso- electπc point of about 6 5)
[0012] Effective catalysts are those in which the carrier is a mixed oxide of zinc and aluminium or a mixed oxide of copper and zinc
[0013] The mixed oxide may be in the form of a mixture of two oxides of metals with individual crystal structures, for example a mixture of zinc oxide and aluminium oxide
[0014] The relative quantities of zinc and the other metal may vary widely For example, the weight ratio of zinc to the other metal in the mixed metal oxide may vary from 100 1 to 1 100, but preferably the range is from 80 1 to 1 80 Typically the weight ratios of zinc to the other metal will be at least 5 and preferably at least 6 5 parts of zinc to 80 parts of the other metal Higher relative amounts of zinc can be used, e g 10, 20, 30, 40, 50, 60, 70, or 80 parts of zinc to 80 of the other metal Zinc may be present in greater weight proportions than the other metal, for example in ratios of 2, 5, 10, 20, 30, 40 50, 60, 70 or 80 parts to 1 of the other metal [0015] Zinc to other metal weight ratios in the range of 80-20 1 are typically useful, preferably 25-65 1, desirably 35 45:1, especially weight ratios of about 40 1 These ranges are applicable particularly where the other metal is at least one of aluminium, graphite, silicon, titanium, zirconium, copper and iron
[0016] The aforementioned ranges also apply to possible molar ratios of zinc to the other metal For example the molar ratio of zinc to the other metal may be in the range of 80-1 to 1 80, and intermediate values, eg 2 1 to 1 2 Preferably the molar ratio of zinc to the other metal is greater than 1 1
[0017] In carriers composed of oxides of zinc and another metal, zinc is the more important metallic element Although it may be present in amounts as low as 2% by weight of the catalyst, it is preferably present in amounts of at least 5% by weight, preferably at least 10%, desirably at least 15% and advantageously at least 20%, 25 wt% or 30 wt-% The carrier may be composed predpminantly of zinc oxide, and may contain up to 80% by weight of zinc, for example 75 wt-% or preferably 70 wt-%, or conveniently 65 wt-%, or less, such as 50 wt-%, 45 wt-% or 40 wt-%.
[0018] The preferred catalysts may be prepared in any appropriate way e.g. by using co- precipitation, impregnation or inverse deposition-precipitation techniques, as described in the specification of South African patent application No 2003/8981.
[0019] Where co-precipitation is used, gold and the metal oxides, or precursors thereof, are simultaneously precipitated from solution.
[0020] The invention also extends to a method of producing a catalyst of the aforementioned kind wherein an aqueous solution containing at least one water soluble gold compound (for example tetrachloroauric acid, gold cyanide or sodium tetrachloroaurate and other such complexes or compounds) and water soluble salts (for example the nitrates) of zinc and at least one other metal is prepared, using quantities required to produce a desired ratio of gold, zinc and the other metal in the finished mixed metal oxide. The pH of the solution may be increased by the addition of a base such as ammonium or an alkali metal carbonate or hydroxide (e.g. NH4OH, NaOH, KOH, Na2CO3, K2CO3 or Li2CO3) or urea to a point at which gold is precipitated simultaneously with the hydroxides, carbonates, hydroxy- carbonates, oxides (or a combination thereof) of zinc and the at least one other metal. This will normally be in the pH range of 7 to 10, depending on the precursors used for the gold and the other metal of the carrier. The resulting gold-bearing catalyst material is separated from the aqueous liquor, washed and dried. Washing is particularly important where the gold is deposited from chloride-containing solutions.
[0021] In a different approach, which makes use of inverse deposition-precipitation or impregnation techniques, the gold catalyst is produced by depositing gold on a carrier material. The carrier may be prepared in a variety ways including, but not limited to, co- precipitation of metal precursors and physical mixing of metal oxides. Alternatively, any commercially available zinc containing carrier can be used with no particular restriction thereon
[0022] The carrier material generally has a surface area of from 4 to 180 m2/g (as determined by the BET/N2 method (ASTM D3037)
[0023] Gold may be deposited upon the carrier by treating the carrier with an aqueous solution of a gold precursor compound The amount of gold deposited may be varied by varying the relative proportions of gold solution and carrier.
[0024] The gold precursor compound may be selected at least from, gold (I) cyanide [AuCN], sodium tetrachloroaurate (III) [NaAuCI4], potassium dicyanoaurate (I) [KAu(CN)2], gold (III) acethylacetonate [(CH3)2Au(CH3COCH2COCH3) and tetrachloroauric (III) acid
[HAuCI4] The gold precursor may be dissolved to form a treatment solution with a gold content in the range of from 1x10"1 to 1x10"4, preferably in the range 1x10"2to 5x10"3M. The treatment solution may initially have a pH below 7, preferably in the range of from 1 to 3. The pH of the treatment solution may be adjusted to a desired value, e g. from 2 to 8.5, by adding a suitable alkali such as sodium carbonate solution. Upon altering the pH the gold species in solution may undergo chemical changes. For example, HAuCI4 produces gold species of the general formula [Au(OH)nCI4-n]" (where n = 1 - 4). The relative proportion of these species is dependent on the degree of hydrolysis that the HAuCI4 species undergoes. As such, the degree of hydrolysis is in part a function of solution pH, with higher pH's promoting further hydrolysis
[0025] The treatment solution and the carrier are preferably brought into contact at an elevated temperature, preferably in the range 20-90°C , ideally 40-80°C, conveniently 65- 75°C
[0026] When the pH and temperature of the treatment solution are stabilised the solution is contacted with the carrier Gold is then precipitated from the solution, for example by increasing the pH of the solution to a desired value by adding an alkaline solution of, for example sodium, potassium or ammonium hydroxide or carbonate, or urea This will normally be in the pH range of 4 to 11. The form in which the gold is precipitated will depend upon the precursor used to form the precipitation mixture. For example, it may be precipitated as the hydroxide or deposited as [Au(OH)nCI .n (where n = 1-4). The pH at which precipitation will occur similarly depends on the nature of the precipitate. [Au(OH)nCI .n]" (where n = 1 ,2) adsorbs/impregnates at lower pH values (typically in the range 4 to 6.5, preferably 4.5 to 6, e.g. about pH 5). Gold hydroxide however precipitates at higher pH values, (typically from 7 to 10, preferably 8 to 9.5, ideally about 8.5). This is advantageous because high pH values lead to well-dispersed gold with a low particle size in the nanometre range. In addition, the gold species prevalent at high pH values contain less chloride. The presence of chloride species is believed to increase the formation of larger gold particles, thereby decreasing catalytic activity, due to the sintering of the gold particles as a result of the formation of CI-Au-CI bridges. Residual chloride may also serve to poison the catalytic active site. The contacting time of the gold containing solution and the carrier material is performed for a suitable period, for example 0.5 to 3 hours, preferably about 1 hour. The solid material is then separated and washed. The washing is preferably carried out with a base, such as aqueous ammonia solution, NaOH or urea, which also assists in the removal of chloride ions. After washing, the catalyst material is dried, preferably at a temperature of from 20 to 150°C, e.g. at 120°C. Further washing with an alkaline solution can be performed on the dried catalyst material to remove excess chloride and other undesired ions, if required.
[0027] The activity of the catalyst may be modified by further treatment of the gold-bearing carrier. The catalytic mechanism of gold is not fully understood, but may depend upon the presence of both metallic gold (Au°) species and positively charged gold species (Auδ+). Without wishing to be limited by any theory, the presence of these gold species can be affected by further treatment of the catalyst material. For example, catalyst material obtained by a co-precipitation, impregnation or inverse deposition-precipitation technique may be calcined before use, typically by heating the catalyst material to a temperature from 50 to 500°C (preferably from 100 to 300°C) for a period of from 1 to 5 hours. The effect of calcining is to reduce Au(OH)3 species present in the catalyst to metallic gold Alternatively the catalyst material may be treated in a reducing atmosphere, for example hydrogen or, preferably, carbon monoxide Such treatment also affects the nature of the gold species on the surface of the catalyst
DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] The invention is further described with reference to the following examples
Examples 1 - 8 Au-ZnAIOx Catalysts
Carrier Preparation
[0029] A 1 34M aqueous solution of zinc nitrate [Zn(NO3)2 6H2O] and a 0 081 M aqueous solution of aluminium nitrate [AI(NO3)39H2O] were mixed together in proportions such that the weight ratio zinc aluminium was 40 1 The solution was heated to a temperature of approximately 80°C, and the pH of the solution was adjusted from an initial value of 1 1 to a value of 9 1 by adding an aqueous solution of sodium carbonate while stirring, thereby producing a precipitate of the hydroxides of zinc and aluminium The pH and temperature of the solution were maintained to allow the precipitate to age in contact with the solution for about 5 hours The precipitate was filtered from the solution, washed with high-purity water to remove unwanted ions, and dried in air at approximately 120°C for 16 hours The dried precipitate was then calcined by heating in air at 400°C for four hours The resulting earner material (A) was then ground into a powder Examination of the crystal structure of the material indicated that it consisted of hexagonal zincite, ZnO and amorphous alumina, AI2O3 with traces of zinc aluminium carbonate hydroxy hydrate
[0030] The aforementioned procedure was repeated with different quantities of zinc and aluminium nitrates, and different reaction conditions, shown in Table 1 to produce catalyst carriers B and C with properties as specified in Table 1 For the purposes of comparison, carriers D and E, consisting of zinc oxide and aluminium oxide alone, were prepared by a similar process Table 1: Varying Zir.Al ratio
Figure imgf000009_0001
Catalyst preparation
[0031] A volume of deionised water sufficient to support a sample of carrier A in suspension was heated to 70°C. A solution of tetrachloroauric [HAuCU] acid containing sufficient gold was added to the water. The pH of the solution was adjusted from an initial pH of 2 to 5.5 by adding a solution of Na2CO3. Having stabilised the temperature and pH, the carrier was added, and the suspension agitated for a period of 1 hour. The solid material was separated, washed with a ammonia solution of a desired concentration and dried in air at 120°C.
[0032] This procedure was repeated using carriers A to E with different quantities of tetrachloroauric acid, and wash solutions of different ammonium concentration, as tabulated in Table 2 to produce the catalysts in Examples 1 to 8 in accordance with the invention, and comparative catalysts in Examples I to V.
[0033] In order to test their catalytic activities, 0.25g samples of the catalysts of Examples 1 to 8, and of Examples I to V, having a particle size fraction of from 700 to 1400μm were loaded into a continuous fixed-bed micro-reactor and tested under adiabatic conditions, through which a test gas consisting of a 1% by volume mixture of CO in air with 100% relative humidity vyas passed at a flow rate of 495 ml/min, equivalent to a space velocity (SV) of 118,800 ml.g'Vh"1 (millilitres of test gas per gram of catalyst per hour). The activity of the catalyst was obtained by measuring the micro-mols of CO converted per second per gram of gold on the catalyst (μmol CO.gAu "1.s"1). The resulting rates of conversion of CO to CO2 are set forth in Table 2.
Table 2: Catalyst preparation on carrier materials
Figure imgf000010_0001
[0034] As can be seen from Table 2 gold, deposited upon alumina alone, does not function as a catalyst for oxidation of CO under the conditions tested. Gold deposited upon zinc oxide shows some catalytic function, but the best catalytic function is exhibited by gold when deposited upon a carrier composed of the mixed oxides of zinc and aluminium, especially when the ratio of zinc to aluminium in the carrier is over 20:1. Also the catalysts with higher gold loading (2% by weight or more) perform more effectively.
Examples 9 - 14: Au/CuZnOx catalyst Samples of catalyst material comprising gold on a carrier material consisting of the mixed oxides of copper and zinc were prepared. Carrier Preparation
[0035] To prepare the carrier materials, solutions of Cu(NO3)2.3H2O and Zn(NO3)2.6H2O with various copperzinc molar ratios, as set forth in Table 3, were mixed and heated to 80°C, and the pH was adjusted to a value of 8.5 with an aqueous Na2CO3 solution. The pH and temperature were maintained for 5 hours during precipitation. Thereafter, the resulting precipitates were filtered, washed several times with deionised water and dried overnight at 120°C. The powders were then calcined either at 200°C for 1 hour, or at 300°C for 5 hours. The calcined material was then pelletised, crushed and sieved to a particle size range of 500 to 1000 μm.
Catalyst Preparation
[0036] Gold catalysts were produced on the aforementioned carriers by means of inverse deposition precipitation using an aqueous solution of HAuCI4 of desired concentration. This solution was preheated to 70°C and the pH adjusted to 8.5 by adding Na2CO3 solution. The carrier materials were then added to separate batches of the gold solution and each was aged for 1 hour at 70°C with pH control. Thereafter, the catalyst materials were filtered, washed several times with deionised water, dried in an oven at 120°C for 16 hours and calcined if necessary.
[0037] Activity tests were performed analogously to those of Examples 1 - 8, with the exception that catalyst samples of 0.5g were tested under both 0 and 100% humidity with a gas flowrate of 60 ml/min.
Effect of Cu:Zn ratios and calcination temperature
[0038] For the purposes of comparison, tests were also carried out on samples of the carrier material, with Cu:Zn ratios of 1:2, 1:1 and 2:1, that had not been treated with gold. Each sample had a very low catalytic activity under dry and humid conditions, less than 0.02
Figure imgf000011_0001
Table 3:. Effect of calcination temperature and Cn.Zn ratio
Figure imgf000012_0001
[0039] All the samples carrying gold exhibited significant catalytic activity, especially those that contained zinc in the form of zincite (ZnO) rather than rosasite or aurichalcite as a result of calcination of the carrier material at higher temperatures. Also, the activity of the catalysts is increased by 50% to 100% under humid conditions.
Examples 15 - 17: Au/ZnAIOx catalyst
Carrier and catalyst preparation
[0040] A batch of support material was prepared using the method described for Examples 1 to 8, with a Zn:AI ratio of 40:1. The resulting material was treated with gold as described in Examples 9 - 14, with the exception that the solid-liquid contacting (ageing) time and temperatures were varied as shown in Table 4.
Ageing
[0041] The effect of ageing time and temperature on catalytic activity is shown in Table 4. The activity of the catalysts was tested in a CO/CO2 system, as described with reference to Examples 1 - 8.
[0042] Satisfactory results were obtained for ageing at 70°C for a duration of 1 hour. It was found that the ageing conditions strongly influenced the activity of the catalysts. When the ageing step was omitted almost no activity was observed. Catalyst preparation and ageing (1 hour) at room ternperature produced an inactive catalyst. The gold loading of the catalysts was also much lower than that of catalysts aged for 1 hour at 70°C.
Table 4: Effect of ageing
Figure imgf000013_0001
Examples 18 - 22: Au/ZnAIOx catalyst
Carrier and catalyst preparation
[0043] Supports with zinc to aluminium ratios of 20:1, 40:1 , 80:1 as well as 100% ZnO and 100% AI2O3 were prepared according to the method highlighted in Examples 1 - 8. Gold was deposited onto these carriers as described in Examples 9 - 14. Effect of zinc to aluminium ratio on catalyst activity and gold loading
[0044] The catalysts were tested for CO oxidation in 100% relative humidity conditions as described in Examples 1 - 8. Very high CO conversions were obtained when the catalysts contained zinc and aluminium at a ratio of 40:1. A synergistic effect appears to exist when the catalyst contains some aluminium. The investigation revealed the optimum zinc to aluminium ratio to be approximately 40 to 1. Gold on AI2O3 showed poor activity, while gold supported on zinc oxide performed well — see . Table 5.
Table 5: Effect of varying Zn to Al ratios on catalyst activity
Figure imgf000015_0001
[0045] The gold adsorption is also affected by Zn to Al ratios and the highest gold loading was obtained at Zn/AI ratios of 40:1. The alumina catalyst had very low gold loading. This trend is shown in
Table 5.
Examples 23 - 28: Au/ZnYALO7 catalysts
Carrier and catalyst preparation
[0046] Gold catalysts were prepared by the inverse deposition precipitation method at both high (pH=8.5, Examples 9 - 14) and low (pH=5.5, Examples 1 - 8) pH values on three carriers composed of commerciallly available zinc-aluminium oxide (supplied by Sud-Chemie under product reference No G72D), zinc-oxide (supplied by Zinchem under product reference No B.P. grade ZnO), and γ-AI2O3 (supplied by Degussa under product reference No 2010). Various washing techniques were employed and are shown in Table 6. All catalysts were tested as per the method shown in Examples 9 - 14.
Table 6: Effect of washing at high and low pH preparation on Au/ZnA10x
Figure imgf000016_0001
Figure imgf000017_0001
[0047] As can be seen in Tables 6 to 8, catalysts prepared on G72D (Zn/AI 40:1) are more active than the gold catalysts prepared on the individual metal oxide carriers alone. Gold loading from solution onto the all the carriers is higher at low pH when compared to high pH preparation, the inverse is true for CO oxidation activity.
[0048] Ammonia washing is needed to induce reasonable catalytic activity for catalysts prepared at low pH.
Examples 29 - 37: Au/ZnO impregnated on AbOs [0049] In another example of the invention gold was deposited or impregnated onto an AI2O3 carrier impregnated with ZnO. A support was prepared comprising a ZnO layer on Al203 using one of the following techniques:
Deposition of Zn as fZn(NH3) 12+ on AI7O3
(a) 19.2 g Zn(NO3)2 were dissolved in 296 ml of 2M NH4OH to form the zinc amine complex [Zn(NH3)4]2+ before adding 30 g γ-alumina (particle size between 500 and 1000 μm). The solution was left standing for 24 hours. (pHi = 10.60, pHf = 11.30). After filtration the support was washed with 1 I high-purity water, dried at 120°C overnight and calcined at 400°C for 4 hours to ensure complete conversion to ZnO.
(b) The procedure was repeated with 1x (see method (a)), 2x and 5x stoichiometric amounts of zinc nitrate. In addition to contacting the zinc complex/alumina by standing, an 'impregnation' method as follows was also used.
19.2 g Zn(NO3)2 were dissolved in 296 ml of 2M NH4OH to form the zinc amine complex [Zn(NH3)4]2+, before adding 30 g γ-alumina (particle size between 500 and 1000 μm). The slurry was contacted at 73 °C and an initial vacuum of 200 mbar (decreasing over time), using a Bϋchi rotary evaporator, until it was dry (approximately 2 hours). Washing, drying and calcining were carried out as described in method (a).
Deposition of Zn as Zn(NO3)2 (c) Zn(NO3)2 was dissolved in 200 ml high - purity water (1x (pHi = 3.78) and 2x (pHf = 3.42) stoichiometric amounts) before addition of AI2O3 (pH values of 4.74 and 4.53 respectively). The mixture was subjected to impregnation described in method (b). Washing, drying and calcining followed as described in method (a).
Deposition of Zn as Zn(OH)? (d) A stoichiometric amount of Zn(NO3)2 was dissolved in 200 ml high - purity water (pH = 3.30). Alumina was added (pH = 4.56) followed by pH-adjustment to pH = 7 with 2 M NaOH (-55 ml) to precipitate Zn(OH)2. The mixture was contacted with Al 03 for 24 hours, decanted, followed by washing, drying and calcining as described in method (a).
(e) A stoichiometric amount of Zn(NO3)2 was dissolved in 200 ml high - purity water (pH = 3.81); alumina was added (pH = 4.71) followed by pH-adjustment to pH = 7 with 2 M NaOH (50 ml) to precipitate Zn(OH)2. The mixture was impregnated for approximately 2 hours at 74°C (vacuum 300mbar, decreasing to 200 mbar), followed by washing, drying and calcination as described in method (a).
Preparation of gold onto support comprising of ZnO on AI7O3
[0050] The gold catalyst was prepared by the inverse deposition precipitation method highlighted in Examples 1 - 8.
Table 9: Activity and gold loading on Zn impregnated AhO 3
Figure imgf000019_0001
Figure imgf000020_0001
[0051] The results indicate that impregnation with [Zn(NH3)4]2+ gave the highest catalytic activity. Higher catalytic activity was obtained with the presence of ZnO than for Au deposited onto Al203 alone. Examples 38 - 40: Au/ZnAIOx catalyst
Gold Solution Recycling
[0052] Reuse/recycle of the gold containing solution is required, from a cost point of view, as only a portion of the gold is loaded from solution onto the carrier material. Several catalysts (Zn:AI=40:1 , mass ratio) were prepared by recycling the gold solution. The virgin solution consists of tetrachloroauric acid, with the subsequent catalysts synthesised using the spent solution. Prior to each catalyst synthesis the spent solution was adjusted with fresh tetrachloroauric acid, to maintain a constant solution volume and gold concentration (3.94x10"3M).
[0053] Catalysts were prepared by contacting the necessary amount of carrier material and gold containing solution to obtain a maximum gold loading of 1 wt%. The deposition- precipitation conditions employed are similar to those described in Examples 9 - 14. Catalytic activity was determined using 0.05 - 0.1 g of catalyst in a micro fixed-bed reactor under conditions identical to those described in Examples 9 - 14.
Table 10: Activity and loading of catalysts prepared with recycled gold solution
Figure imgf000020_0002
Figure imgf000021_0001
[0054] Catalysts prepared using the recycled gold solution compare well in terms of gold loading and catalytic activity to their freshly prepared counterpart. Recycling of the gold solution used in catalyst synthesis is possible.
Examples 41 - 43: Au/ZnAIOx catalyst
Effect of Gold Concentration
[0055] Catalysts (Zn:AI=40:1 , mass ratio) were prepared using various gold concentrations by an inverse-deposition-precipitation technique, and tested for CO oxidation activity, under conditions similar to those described in Examples 9-14. A commercially available zinc- aluminium oxide (supplied by Sϋd-Chemie under product reference No G72D) was used as the carrier material.
Table 11: Effect of gold cone, on activity and gold loading
Figure imgf000021_0002
[0056] It appears that an increase in gold concentration results not only in a higher gold loading but in an increase in the relative amount of gold loaded from solution onto the carrier material. Conversely an increase in gold concentration results in a decrease in activity on a per gram gold and per gram catalyst basis. Preparation at relatively low gold concentrations (1x10"2 and 5x10'3M) is therefore advantageous in producing highly active material, although the uptake of gold from solution is poor at these low concentrations.
Examples 44 - 49: Au/ZnAIOx and Au/CuZnOx Pre-treatment in reducin atmospheres
[0057] Gold catalysts were prepared by depositing gold onto two carriers composed of a commercially available zinc-aluminium oxide (supplied by Sϋd-Chemie under product reference No G72D) and a commercially available copper-zinc oxide (supplied by Sϋd- Chemie under product reference No G66B). In each case the carrier was crushed and sieved to a particle size in the range 500-1000μm. Gold was deposited onto the carrier by an inverse deposition precipitation technique as described in Example 9 - 14.
[0058] 5g samples of each catalyst were then contacted in a fluidised bed reactor with reducing atmospheres consisting of a dry 1.45% carbon monoxide-air mixture; a humidified 1.45% carbon monoxide-air mixture, a 10% hydrogen-argon mixture and, for comparison purposes, air, at flow rates of 10 litres/min for the periods and at the temperatures indicated in Table 12. The reductive process caused a change in colour of the catalyst from light yellow or white in the oxidised state, to purple in the reduced state, which can be attributed to the change in oxidation state of the deposited gold from the oxidised state to a mixture of species comprising metallic gold and oxidised species:
AuJ Auu + Au δ+
[0059] The activities of the resulting catalysts on the oxidation of CO were compared by using a piston to draw a specific volume of 1.45% CO in air mixture for a duration of two seconds from a pre-filled gas-tight bag over a bed of 200mg of the catalyst packed in a glass tube and retained therein by glass wool plugs. Gas samples were taken at one minute intervals. The emerging gas was analysed using a commercially available carbon monoxide infra-red analyser sold under the trade name Signal 7000GFG. The % conversions of CO to C02 in the 1st and 8th gas sample are shown in Table 12.
Table 12: Effect of gas treatment
Figure imgf000022_0001
Figure imgf000023_0001
[0060] As can be seen from Table 12, whilst the activities of the untreated catalysts and catalysts treated in air increase over the 8-gas sample test period, the activities of the catalysts that were pre-treated in a reducing atmosphere are significantly enhanced in comparison. This enhancement of activity correlates with an increase in Au(0) species present in gold deposited upon the carrier.
Examples 50 - 52: Au/ZnAIOx and Au/CuZnOx
Pre-treatment by calcination
[0061] 5g samples of each of the catalysts prepared for Examples 70 - 72 were subject to calcinations at 200 and 300°C for 2 hours in static air. Temperature programmed reduction tests on the resulting catalysts confirmed that at 300°C, the gold species are almost completely reduced to the Au(0) state whereas, after calcination at 200°C, approximately half the original Au(lll) remains.
[0062] The catalytic effects of the samples upon carbon monoxide were tested according to the procedure used in Examples 70 - 72. The results are shown in Table 13.
Table 13: Effect of heat treatment
Figure imgf000023_0002
Figure imgf000024_0001
[0063] As can be seen from Table 13, heat treatment, especially at a higher temperature, enhances the activities of the catalysts and sustains their performances over the 8-gas sample cycle in comparison with the untreated samples, although low temperature reductive treatments still yield higher activity which is also consistent with the transformation of Au(lll) species to Au(0) caused by calcination.

Claims

1 A catalyst which includes gold on a carrier which is formed, at least, from zinc oxide
2 A catalyst according to claim 1 wherein the carrier is formed from a mixed oxide of zinc and at least one other metal
3 A catalyst according to claim 2 wherein the at least one other metal is selected from aluminium, graphite, silicon, titanium, zirconium, iron and copper
4 A catalyst according to claim 2 or 3 wherein the mixed weight ratio of zinc to the at least one other metal is in the range of from 100 1 to 1 100
5 A catalyst according to claim 4 wherein the mixed weight ratio is in the range of from 80 1 to 1 80
6 A catalyst according to any one of claims 1 to 5 wherein the carrier contains from 2% to 80% by weight of zinc
7 A catalyst according to any one of claims 1 to 5 wherein the gold has a particle size less than 100 nanometres 8 A catalyst according to any one of claims 1 to 7 wherein the carrier has a surface area of from 4 to 180 m2/g
9 A catalyst according to any one of claims 1 to 8 wherein the gold includes metallic gold (Au°) species and positively charged gold species Auδ+)
10 A catalyst according to any one of claims 1 to 9 wherein the carrier has an iso-electnc point of from 6 to 10
11 A method of preparing a catalyst which includes the step of depositing gold on a carrier which contains at least zinc
12. A method according to claim 11 wherein the carrier is formed by a technique selected from the following: precipitation; co-precipitation; impregnation; oxidation of metal vapours; and physical mixing of zinc oxide and at least one other metal oxide.
13. A method according to claim 11 wherein the catalyst is formed using a co-precipitation technique which includes the step of preparing an aqueous solution containing at least one water soluble gold compound and water soluble salts of zinc and at least one other metal.
14. A method according to claim 13 which includes the steps of depositing gold from the solution onto a carrier, of zinc and the at least other metal, which is precipitated from the solution, and separating the gold-bearing carrier from the solution.
15. A method according to any one of claims 11 to 14 wherein the gold-bearing carrier is exposed to a reducing agent to enhance initial catalytic activity of the gold.
16. A method according to any one of claims 11 to 15 wherein the gold-bearing carrier is calcined. 17. A method of oxidizing carbon monoxide to carbon dioxide which includes the step of contacting the carbon monoxide with a catalyst which is according to any one of claims 1 to 10.
PCT/ZA2005/000074 2004-05-28 2005-05-24 Catalyst containing gold on support containing zinc oxide and production and use thereof WO2005115612A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ZA200404125 2004-05-28
ZA2004/4125 2004-05-28

Publications (1)

Publication Number Publication Date
WO2005115612A1 true WO2005115612A1 (en) 2005-12-08

Family

ID=35063386

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/ZA2005/000074 WO2005115612A1 (en) 2004-05-28 2005-05-24 Catalyst containing gold on support containing zinc oxide and production and use thereof

Country Status (6)

Country Link
AR (1) AR051171A1 (en)
MY (1) MY149330A (en)
PE (1) PE20060386A1 (en)
UY (1) UY28921A1 (en)
WO (1) WO2005115612A1 (en)
ZA (1) ZA200610870B (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008169054A (en) * 2007-01-09 2008-07-24 National Institute Of Advanced Industrial & Technology Zno nanoparticle immobilized in aluminum-containing amorphous matrix, and method for producing the same
WO2008107445A1 (en) * 2007-03-05 2008-09-12 Institut Català D'investigació Química (Iciq) Gold-based catalysts for selective hydrogenation of unsaturated compounds
WO2009087040A2 (en) * 2008-01-11 2009-07-16 H.C. Starck Gmbh Catalyst powder
WO2009091389A1 (en) * 2008-01-14 2009-07-23 3M Innovative Properties Company Multifunctional oxidation catalysts and methods of making
US8058202B2 (en) 2005-01-04 2011-11-15 3M Innovative Properties Company Heterogeneous, composite, carbonaceous catalyst system and methods that use catalytically active gold
US8137750B2 (en) 2006-02-15 2012-03-20 3M Innovative Properties Company Catalytically active gold supported on thermally treated nanoporous supports
CN103084185A (en) * 2013-01-25 2013-05-08 天津大学 Multi-element metal oxide load gold catalyst and preparation method thereof
WO2015027031A1 (en) * 2013-08-23 2015-02-26 Basf Corporation Catalysts for oxidation of carbon monoxide and/or volatile organic compounds

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0454022A1 (en) * 1990-04-23 1991-10-30 Phillips Petroleum Company Catalyst and process for dehydrogenation and dehydrocyclization
DE4238640A1 (en) * 1991-12-06 1993-06-09 Agency Of Industrial Science & Technology, Ministry Of International Trade & Industry, Tokio/Tokyo, Jp Highly reactive metal oxide and gold catalyst for low temps. - useful for hydrogenation of carbon mono or di:oxide in synthesis of methanol
EP0794006A1 (en) * 1996-03-08 1997-09-10 Ykk Corporation Metal-metal oxide catalyst and method for production thereof by mechanical alloying treatment
FR2841438A1 (en) * 2002-06-26 2004-01-02 Rhodia Elect & Catalysis CIGARETTE COMPRISING A CATALYST FOR THE TREATMENT OF SMOKE

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0454022A1 (en) * 1990-04-23 1991-10-30 Phillips Petroleum Company Catalyst and process for dehydrogenation and dehydrocyclization
DE4238640A1 (en) * 1991-12-06 1993-06-09 Agency Of Industrial Science & Technology, Ministry Of International Trade & Industry, Tokio/Tokyo, Jp Highly reactive metal oxide and gold catalyst for low temps. - useful for hydrogenation of carbon mono or di:oxide in synthesis of methanol
EP0794006A1 (en) * 1996-03-08 1997-09-10 Ykk Corporation Metal-metal oxide catalyst and method for production thereof by mechanical alloying treatment
FR2841438A1 (en) * 2002-06-26 2004-01-02 Rhodia Elect & Catalysis CIGARETTE COMPRISING A CATALYST FOR THE TREATMENT OF SMOKE

Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8664149B2 (en) 2005-01-04 2014-03-04 3M Innovative Properties Company Heterogeneous, composite, carbonaceous catalyst system and methods that use catalytically active gold
US8518854B2 (en) 2005-01-04 2013-08-27 3M Innovative Properties Company Heterogeneous, composite, carbonaceous catalyst system and methods that use catalytically active gold
US8314046B2 (en) 2005-01-04 2012-11-20 3M Innovative Properties Company Heterogeneous, composite, carbonaceous catalyst system and methods that use catalytically active gold
US8058202B2 (en) 2005-01-04 2011-11-15 3M Innovative Properties Company Heterogeneous, composite, carbonaceous catalyst system and methods that use catalytically active gold
US8137750B2 (en) 2006-02-15 2012-03-20 3M Innovative Properties Company Catalytically active gold supported on thermally treated nanoporous supports
JP2008169054A (en) * 2007-01-09 2008-07-24 National Institute Of Advanced Industrial & Technology Zno nanoparticle immobilized in aluminum-containing amorphous matrix, and method for producing the same
WO2008107445A1 (en) * 2007-03-05 2008-09-12 Institut Català D'investigació Química (Iciq) Gold-based catalysts for selective hydrogenation of unsaturated compounds
EP1970117A1 (en) * 2007-03-05 2008-09-17 Institut Catala D'Investigacio Quimica Gold-based catalysts for selective hydrogenation of unsaturated compounds
WO2009087040A3 (en) * 2008-01-11 2012-03-29 H.C. Starck Gmbh Catalyst powder
WO2009087040A2 (en) * 2008-01-11 2009-07-16 H.C. Starck Gmbh Catalyst powder
EP2253377A3 (en) * 2008-01-14 2010-12-29 3M Innovative Properties Co. Multifunctional oxidation catalysts
US8236725B2 (en) 2008-01-14 2012-08-07 3M Innovative Properties Company Gold carbon monoxide oxidation catalysts with etched substrate
AU2008348197B2 (en) * 2008-01-14 2011-09-01 3M Innovative Properties Company Multifunctional oxidation catalysts and methods of making
JP2011509824A (en) * 2008-01-14 2011-03-31 スリーエム イノベイティブ プロパティズ カンパニー Multifunctional oxidation catalyst and production method
CN101952035B (en) * 2008-01-14 2013-11-06 3M创新有限公司 Multifunctional oxidation catalysts and methods of making
WO2009091389A1 (en) * 2008-01-14 2009-07-23 3M Innovative Properties Company Multifunctional oxidation catalysts and methods of making
KR101414428B1 (en) 2008-01-14 2014-07-01 쓰리엠 이노베이티브 프로퍼티즈 컴파니 Multifunctional oxidation catalysts and methods of making
CN103084185A (en) * 2013-01-25 2013-05-08 天津大学 Multi-element metal oxide load gold catalyst and preparation method thereof
WO2015027031A1 (en) * 2013-08-23 2015-02-26 Basf Corporation Catalysts for oxidation of carbon monoxide and/or volatile organic compounds
US9399208B2 (en) 2013-08-23 2016-07-26 Basf Corporation Catalysts for oxidation of carbon monoxide and/or volatile organic compounds

Also Published As

Publication number Publication date
MY149330A (en) 2013-08-30
PE20060386A1 (en) 2006-05-15
AR051171A1 (en) 2006-12-27
UY28921A1 (en) 2005-06-30
ZA200610870B (en) 2007-11-28

Similar Documents

Publication Publication Date Title
KR100237812B1 (en) Catalytic Composition Based on Cerium Oxide and Manganese, Iron or Praseodymium Oxide, Method for Preparing Same and Use Thereof in Motor Vehicle Post-Combustion Catalysis
WO2005115612A1 (en) Catalyst containing gold on support containing zinc oxide and production and use thereof
EP2558199B1 (en) Process for preparing supported noble metal catalysts via hydrothermal deposition
RU2730496C2 (en) Rhodium-containing catalysts for treating automotive exhausts
US5134109A (en) Catalyst for reforming hydrocarbon with steam
US5397758A (en) Alumina-based compositions and catalysts having high specific surface area
US9409149B2 (en) Sulfur resistant cladded titania—alumina supports
AU2005224127B2 (en) Gold and reducible oxide-based composition, method for the preparation and the use thereof in the form of a catalyst, in particular for carbon monoxide oxidation
KR101976161B1 (en) Sulfur tolerant alumina catalyst support
EP0234745A1 (en) Catalysts
WO2002016026A2 (en) Adsorbent and/or catalyst compounds promoted with halide ions and methods of making and using thereof
US20070190347A1 (en) Gold-and cerium-oxide-based composition, method for the preparation and the use thereof in the form of a catalyst, in particular for carbon monoxide oxidation
JP2001504078A (en) Cerium oxide wash coat
Reddy et al. “PdO vs. PtO”—The influence of PGM oxide promotion of Co3O4 spinel on direct NO decomposition activity
Zhai et al. TiO 2-nanosheet-assembled microspheres as Pd-catalyst support for highly-stable low-temperature CO oxidation
KR20140111132A (en) Catalyst For Hydrocarbon Oxidation, Odor Removal And Its Preparation Method
RU2501605C2 (en) Method of producing fischer-tropsh synthesis oxide cobalt-zinc catalyst
KR20190040491A (en) Methane oxidation catalyst, a process for producing the same, and a method for using the same
JP4972868B2 (en) Surface-modified ceria / zirconia hydrated oxide, oxide thereof, production method thereof, and use thereof
EP1126914A1 (en) Preparation of nanocrystalline and dispersible supported metal catalysts
EP3384985A1 (en) Steam reforming catalyst for hydrocarbons
EP1928788B1 (en) Method for preparing metal oxide containing precious metals
Mul et al. Preparation of supported metal catalysts
JPH0925119A (en) Production of heat resistant transition alumina
CN115427144B (en) Material for N2O decomposition

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BW BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE EG ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KM KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NA NG NI NO NZ OM PG PH PL PT RO RU SC SD SE SG SK SL SM SY TJ TM TN TR TT TZ UA UG US UZ VC VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): BW GH GM KE LS MW MZ NA SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LT LU MC NL PL PT RO SE SI SK TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
DPEN Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed from 20040101)
NENP Non-entry into the national phase

Ref country code: DE

WWW Wipo information: withdrawn in national office

Country of ref document: DE

122 Ep: pct application non-entry in european phase