CN108311139B - Method for improving thermal stability of noble metal nano catalyst - Google Patents

Method for improving thermal stability of noble metal nano catalyst Download PDF

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CN108311139B
CN108311139B CN201810222359.1A CN201810222359A CN108311139B CN 108311139 B CN108311139 B CN 108311139B CN 201810222359 A CN201810222359 A CN 201810222359A CN 108311139 B CN108311139 B CN 108311139B
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catalyst
noble metal
thermal stability
metal nano
improving
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CN108311139A (en
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张桂臻
李瑶瑶
何洪
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Beijing University of Technology
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    • 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
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/44—Palladium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/62—Carbon oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • 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
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/42—Platinum
    • 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
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/46—Ruthenium, rhodium, osmium or iridium
    • B01J23/464—Rhodium
    • 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
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/50—Carbon oxides
    • B01D2257/502—Carbon monoxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases

Abstract

A method for improving the thermal stability of a noble metal nano catalyst belongs to the field of industrial catalysis. The method utilizes the characteristic that low-cost plant polyphenol forms a film by self polymerization under an alkaline condition, forms an organic polymerization film with a certain structure on the surface of the catalyst, and sequentially treats the organic film at high temperature in an inert atmosphere and an air atmosphere, so that the interaction between metal nanoparticles and a carrier is enhanced, and the sintering resistance of noble metal is improved. Tests show that compared with a catalyst which is not subjected to organic polymeric membrane treatment, the catalyst obtained by the invention is aged for 2 hours at 900 ℃ in the air, the Pd nanoparticles do not grow obviously, the CO oxidation activity of the catalyst is higher than that of the traditional catalyst, and the catalyst has higher thermal stability. The method is simple to operate, is suitable for powder catalysts or molded catalysts, has obvious effect and has good industrial application prospect.

Description

Method for improving thermal stability of noble metal nano catalyst
Technical Field
The invention relates to a method for improving the thermal stability of a noble metal nano catalyst, belonging to the field of industrial catalysis.
Background
The technology for controlling the pollution of the tail gas emission of the motor vehicle is a great requirement of the environment-friendly industry in China, and the preparation technology of the three-way catalyst is a key technology for controlling the pollution of gasoline vehicles. Precious metal nanocatalysts are widely used for automobile exhaust purification due to their excellent catalytic performance (Lampert et al, 1997; Centi, 2001; Huang et al, 2009; Fan et al, 2012). However, the temperature of the tail gas of gasoline vehicles can reach 900 ℃, and sintering phenomena such as migration and aggregation of noble metals are easy to occur, thereby causing the deactivation of the catalyst (Campbell C T. science,2002,298(5594): 811-. Therefore, it is important to improve the thermal stability of the noble metal catalyst.
In recent years, researchers have resorted to a number of methods for stabilizing metal nanoparticles. People design a core-shell structure catalyst, namely, a layer of oxide shell is coated outside a nano metal core, so that the thermal stability of the catalyst is improved to a certain extent. For example, the Smorjai (Science 2004,304, 711) -714 topic group reported that Pt nanoparticles (Pt @ mSiO) were coated with mesoporous silica2) The nano catalytic material is stable in air atmosphere at a high temperature of 750 ℃. However, the oxide protective layer on the metal surface covers the active sites on the metal surface, resulting in a decrease in catalytic activity. Thin layers of oxide-anchored metal nanoparticles are also deposited on the catalyst surface using Atomic Layer Deposition (ALD) techniques. Onn et Al (ACS Catal.2015,5,5696-2O3Surface deposition of 1nm ZrO2And the thin film inhibits high-temperature sintering of PdO particles. However, the ALD technique is difficult to be widely used in industry due to expensive raw materials and equipment limitations. Zhan (J.Am.chem.Soc.2016,138,16130-16139) et al in Au/TiO2The stable Au particles are obtained by a method of coating a layer of dopamine on the surface of the catalyst. However, dopamine is expensive, limiting its practical utility. It is found that organic phenols and polyphenols widely present in plant tissues have similar properties to dopamine, and aqueous solution thereof can be rapidly autoxidized under alkaline conditions to form high polymers, and the high polymers are adsorbed on surfaces of nano particles and bulk phase substances (J.W.Drynan, M.N.Clifford, J.Obuchowicz, N.Kuhnert, Nat.prod.Rep.2010,27, 417-containing 462), and the plant polyphenols are widely available and low in cost.
Disclosure of Invention
In the treatment of automobile exhaust, the catalyst system may undergo a high temperature process, resulting in a severe reduction in catalytic performance. Aiming at the technical problem, the invention provides an improved method of the catalyst, which improves the catalytic performance of the catalyst after high-temperature treatment. The invention utilizes the characteristic that low-cost plant polyphenol can form a film by self polymerization under the alkaline condition, forms an organic polymerization film with a certain structure on the surface of the catalyst, and sequentially treats the organic film at high temperature in inert atmosphere and air atmosphere, thereby enhancing the interaction between metal nano particles and a carrier and improving the anti-sintering property of noble metal. The catalyst system can be used for preparing three-way catalysts for CO exhaust emission control and automobile exhaust purification.
In order to achieve the above object, the present invention provides a method for improving thermal stability of a noble metal nanocatalyst, comprising the steps of:
(1) dispersing a noble metal nano catalyst into tris-HCl buffer solution, carrying out water bath at 30-45 ℃ and continuously stirring until the noble metal nano catalyst is uniformly mixed;
(2) adding plant polyphenol into the mixed solution obtained in the step (1), and stirring for 2-24 hours; along with the reaction time, the solution is changed into yellow brown firstly, gradually turns green after a few minutes, and is changed into yellow brown to dark brown after a few hours, and the longer the reaction time is, the darker the color is;
(3) then, the product is centrifugally washed, washed with water and alcohol until no Cl is formed-Drying at 80 ℃ for 8-12 h, grinding into powder, treating in inert atmosphere, and burning off a carbon layer in air to obtain the improved noble metal nano catalyst.
The noble metal can be one or more of Pt, Rh, Pd and the like, and the carrier in the catalyst can be Al2O3、CeO2One or more of the following;
the tris-HCl buffer was 10mM, pH 8.5.
The water bath temperature in the step (1) is further preferably 45 ℃, and the stirring time is 24 hours after the plant polyphenol is added in the step (2).
The plant polyphenol may be one or more of pyrogallol, epicatechin gallate (ECG), epigallocatechin gallate (EGCG), and tannic acid ((TA).
The concentration of the plant polyphenol in the tris-HCl buffer solution is 0.5mg/ml to 1.5mg/ml, and the preferable concentration is 1 mg/ml.
The process of treatment under inert atmosphere is N2Roasting for 1-3 h at 600-800 ℃, wherein the heating rate is 1-10 ℃/min, and the preferred process is N2Roasting at 700 deg.C for 2h at a heating rate of 5 deg.C/min。
Has the advantages that:
the invention has cheap and easily obtained raw materials and simple preparation process.
The preparation method for improving the noble metal nano catalyst provided by the invention has good thermal stability and wide application prospect.
Description of the drawings:
FIG. 1 is a graph showing the catalytic activity curves of catalysts # 1, # 2 and # 3 for CO oxidation reaction in example 1 of the process of the present invention
FIG. 2 shows XRD spectra of catalysts # 1, # 2 and # 3 in example 1 of the process of the present invention.
FIGS. 3(a), (b), (c) and (d) show No. 1#, No. 2# and Pd/Al in example 1, respectively2O3TEM photograph of @ polyphenol, catalyst # 3.
Detailed Description
The following examples are given for the purpose of illustration of the present invention and are not intended to limit the scope of the invention in any way.
Example 1:
(1) 6.000mL of 1mg/mL PVA solution was weighed into a round-bottomed flask, stirred for 5min under ice-water bath, and 4.699mL of 0.01mL/L Na was added2PdCl4The aqueous solution was added to the PVA aqueous solution, stirred for 20min until well mixed, followed by rapid addition of 4.450ml of 2mg/ml NaBH4The solution is quickly stirred for 30min to obtain the Pd nano particle sol. 1g of Al was added2O3Stirring the carrier for 12h, standing for 12h, centrifugally washing, drying at 80 ℃ for 8h, grinding, placing in a muffle furnace, heating to 350 ℃ from room temperature at a heating rate of 5 ℃/min, and maintaining at the temperature for 2h to obtain a No. 1 catalyst sample (Pd/Al)2O3Nano-catalyst).
(2) The 1# catalyst sample was aged: a part of the No. 1 catalyst sample was placed in a muffle furnace and heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min under an air atmosphere, and the temperature was maintained for 2h, and the sample was recorded as the No. 2 catalyst sample.
Example 2:
(1) weigh 0.5g of the 1# catalyst obtained in the step (1) of example 1The reagent was dissolved in 100ml of tris-HCl buffer (10mM, pH 8.5), and the mixture was stirred in a water bath at 45 ℃ until uniform mixing, followed by addition of 0.1g of pyrogallol acid and stirring for 24 hours. Then, the product is centrifugally washed, washed with water and alcohol until no Cl is formed-Drying at 80 deg.C for 8h, grinding into powder, and recording as Pd/Al2O3@ polyphenol. Placing it in a tube furnace at N2Raising the temperature from room temperature to 700 ℃ at a temperature raising rate of 5 ℃/min under the atmosphere and keeping the temperature for 2 hours, and recording the Pd/Al2O3@Carbon。
(2) For Pd/Al2O3@ Carbon for aging: the catalyst was placed in a muffle furnace and heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min under an air atmosphere and held at that temperature for 2 hours to obtain a modified catalyst, which was designated as a # 3 catalyst sample.
Test example 1:
the catalysts # 1, # 2 and # 3 in example 1 were evaluated for CO oxidation activity, and the reaction gas compositions were CO and O2And N2(CO/O2/N 21/20/79) and the space velocity is 20040 mL/(g.h).
As shown in fig. 1 and 2. The test results show that the catalyst 1 has good catalytic activity, CO is completely converted at the temperature of 130 ℃, the temperature for completely converting CO is 190 ℃ for 2#, the temperature for completely converting CO is 150 ℃ for 3#, and the temperature for completely converting CO is lower than 2# for 3#, which shows that the catalytic performance is reduced after high-temperature treatment, but the catalyst 3 has better catalytic activity compared with the catalyst 2#, which shows that the improved catalyst has better catalytic activity, namely higher thermal stability.
Test example 2:
phase structure analysis was performed on the catalyst samples # 1, # 2, and # 3 in example 1 by X-ray powder diffraction. The test results show that the main diffraction peak in all samples is attributed to tetragonal phase Al2O3(JCPDS PDF #46-1215), no PdO phase is detected in the 1# sample, but trace PdO species are detected in the 2# and 3# catalysts, and the PdO peak intensity of the 3# catalyst is weaker, which indicates that the noble metal nanoparticles of the 2# and 3# catalyst samples are aggregated and grown to different degrees, but the nanoparticles of the 3# sampleThe aggregation is slow, which shows that the method slows down the aggregation growth of the Pd NPs.
Test example 3:
1#, 2#, Pd/Al in example 1 were subjected to transmission electron microscopy2O3And carrying out TEM characterization on @ polyphenenol and 3# catalyst, wherein the test result shows that: for catalyst # 1 (fig. 3.(a)), the Pd nanoparticles were uniformly dispersed in spherical Al2O3The particle size is 2 to 3 nm. After high-temperature treatment (fig. 3.(b)), the 2# catalyst Pd nanoparticles were long and about 63nm in size. The 2# catalyst (figure 3.(d)) has partial Pd nano-particles with the particle size of about 5mn, and no obvious aggregation growth occurs.
For Pd/Al2O3@ polyphenol (fig. 3.(c)), the pyro-acid forms a thin coating on the catalyst surface.

Claims (8)

1. A method for improving the thermal stability of a noble metal nano catalyst is characterized by comprising the following steps:
(1) dissolving a noble metal nano catalyst into tris-HCl buffer solution, carrying out water bath at 30-45 ℃ and continuously stirring until the noble metal nano catalyst is uniformly mixed;
(2) adding plant polyphenol pyromucic acid into the solution, and stirring for 2-24 hours; along with the reaction time, the solution is changed into yellow brown firstly, gradually turns green after a few minutes, and is changed into yellow brown to dark brown after a few hours, and the longer the reaction time is, the darker the color is;
(3) then, the product is centrifugally washed, washed with water and alcohol until no Cl is formed-And drying at 80 ℃ for 8-12 h, grinding into powder, treating in an inert atmosphere, and burning off a carbon layer in air to obtain the improved noble metal nano catalyst.
2. The method for improving the thermal stability of a noble metal nano-catalyst according to claim 1, wherein the noble metal is one or more of Pt, Rh and Pd, and the carrier of the catalyst is Al2O3、CeO2One or two of them.
3. The method for improving the thermal stability of a noble metal nanocatalyst according to claim 1, wherein the tris-HCl buffer has a concentration of 10mM and a pH = 8.5.
4. The method for improving the thermal stability of the noble metal nano-catalyst according to claim 1, wherein the water bath temperature in the step (1) is 45 ℃, and the stirring time after the plant polyphenol is added in the step (2) is 24 hours.
5. The method for improving the thermal stability of the noble metal nano-catalyst according to claim 1, wherein the concentration of the plant polyphenol in the tris-HCl buffer is 0.5mg/mL to 1.5 mg/mL.
6. The method of claim 1, wherein the concentration of plant polyphenol in tris-HCl buffer is 1 mg/mL.
7. The method for improving the thermal stability of the noble metal nano-catalyst according to claim 1, wherein the process of treatment under the inert atmosphere is roasting at 600-800 ℃ for 1-3 h, and the temperature rise rate is 1-10 ℃/min.
8. The method for improving the thermal stability of the noble metal nano-catalyst according to claim 7, wherein the process of treatment under the inert atmosphere is calcination at 700 ℃ for 2h, and the heating rate is 5 ℃/min.
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CN109794241B (en) * 2019-01-26 2022-01-28 北京工业大学 Cerium oxide selective coating supported palladium catalyst and preparation method thereof
CN112536042A (en) * 2020-11-19 2021-03-23 福州大学 Preparation method of methanol catalytic oxidation photoelectric catalyst

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