GB2182932A - Catalysts: higher alkanol synthesis from CO and H2 - Google Patents

Abstract

Carbon monoxide and hydrogen are reacted in the presence of a catalyst to give one or more alkanols, such as alkanols having more than one carbon atom per molecule (higher alkanols). The catalyst comprises rhodium in association with a metal in an oxidation state lower than that of the rhodium, the catalyst being capable of both oxygenating and chain lengthening catalytic activity. The rhodium may be in the Rh(III) or Rh(IV) state and the metal be elemental, e.g. Rh(O).

Description

SPECIFICATION Catalysis: higher alkanol synthesis This invention relates to the catalytic production ofalkanols having morethan one carbon atom permolecule.

Certain alkanols having more than one carbon atom per molecule (termed 'higher alkanols' herein) have potential use as gasoline extenders and other high value applications. Watson and Somarjai in Journal of Catalysis 74, 282-295(1982) describe the use of lanthanum rhodate as a catalyst for the hydrogenation of CO under laboratory conditions to give oxygenated products having more than one carbon atom per molecule.

However, on an industrial scale, the catalysed reaction ofcarbon monoxide and hydrogen has hitherto been used to manufacture methanol only, and US Patent No 4312955 states that lanthanum rhodate, or metal substituted lanthanum rhodate, having a perovskite structure is a highly active catalyst for the production of methanol, but not other alkanols, from hydrogen and carbon monoxide.

The invention is concerned with the catalytic production of higheralkanols, including diols,whereinthe catalyst comprises rhodium in a relatively high oxidation state in combination with a metal in a relatively low oxidation state.

The invention provides a processforthe catalytic production of one or more alkanols, the or each having morethan one carbon atom per molecule by the reaction of carbon monoxide and hydrogen in the presence of a catalyst comprising a rhodium moiety in association with a metal moiety in an oxidation state lowerthan that of the rhodium moiety, the catalyst being capable of both oxygenating and chain lengthening catalytic activity. The metal moiety may or may not be elemental.

It is believed that the rhodium moiety, for example in an oxidation state of (Ill) or (IV), provides oxygenating activity and the metal moiety, for example in an oxidation state of (0), provides chain lengthening activity with the resulting production of one or more higheralkanols as evidenced by the examples herein.The selectivity ofthe reaction may be influenced by factors such as precise electronic structure, particle size and location ofthe respective moieties.

The rhodium moiety is preferably provided in the form of a mixed metal oxide since these oxides are known to be resistant to reduction in industrial synthesis gas, i.e. H2, CO, CO2, CH4, N2, H2O. Examples of suitable mixed metal oxides are rhoditessuch as those of Cd, Co, Cu, Mg, Ni, and Zn; rhodates (IV) such as those of SrLa and Sr; LaRhO3, LiRhGeO4, LiRhMnO4, LiRha 5Sbo l504tLiRhTiO4 and Sr(Rh05Sb0.5)O3. If desired, the rhodium may be provided in a stable host matrix constituted by a sulphide or a carbide.

The metal moiety is preferably in the zero oxidation state and, as such, may be constituted by an individual metal, a mixture oftwo or more metals or an alloy oftwo or more metals. The metal or metals may be transition metals,forexample selected from thefollowing group: V, Cr, Mo,W, Mn, Re, Fe, Ru, Os, Co, Rh,lr, Ni, Pd, Pt, Cu, Ag, Au and Zn, wherein Fe, Ru, Co, Rh and Ni are preferred and Rh is particularly preferred. It is therefore noted that the metal moiety and the rhodium moiety may be ofthe same element.

The catalysts for use in the invention may be made by a number of methods such as known in the artfor "doping" salts with metal in the zero oxidation state. Examples of methods that may be used for preparing catalysts for use in the invention are as follows.

PreparationofRhfO)lLaRhO3 Catalyst Method 1 LaRhO3 is prepared by any ofthe following methods: (a) Calcination of (i) a mixture ofoxy- or hydroxy- compounds of La and Rh, e.g. a mixture of La2O3 and Rh203; (ii) a mixture of a La compound and Rh203; (iii) a mixture of La2O3 and a Rh compound; or (iv) mixed compounds of La and Rh, mixed acetates or mixed organometallics; or (b) Co-precipitation by reacting a base such as ammonia with an aqueous mixture of soluble La and Rh compounds such as their nitrates.

The LaRhO3 is then impregnated with an easily reducible metal compound, e.g. Rh(NO3)3(H2O)2, RhCl3(H2O)3, Rh4(CO)2. followed by reduction under conditions to give Rh(O) and such that Rh"+ components are retained in the LaRhO3.

Method 2 An aqueous solution of soluble salts of La and of Rh wherein the La is present in a super-stoichiometric proportion is prepared and a base added to co-precipitate La and Rh components. The catalyst is prepared by reducing the co-precipitate in H2/Ar attemperatures of less than 350"C.

Method3 A high surface area catalyst support such as y-AI203 or SiO2 is impregnated with a solution of a bimetallic compound of La and Rh with a Rh : La atomic ratio ofgreaterthan 1. Calcination followed by reduction provides the catalyst in an intimately mixed, highly dispersed form on the support.

Method 4 La2O3 or La(OH)3 or an oxy-compound of La as a support is impregnated with an aqueous solution of a rhodium compound such as Rh(NO3)3(H2O)2 or RhCl3(H2O)3. Calcination induces a surface reaction to yield highly dispersed LaRhO3 on the support. Subsequent impregnation with a Rh compound followed by reduc- tiongivesa Rh(O)/LaRhO3catalystonthesupportmaterial.

Preparation of Rh(O)lMgRh204 Catalyst The above described methods for preparing Rh/La RhO3 catalysts may be used, with appropriate modifica tion, for prepa ring Rh/MgRh204 catalysts. Also, MgO may be impregnated with RhCI3 at 650"C to give highly dispersed Mg Rh204 on MgO. Subsequent impregnation with a suitable Rh compound followed by reduction gives highly dispersed Rh/MgRh204/MgO.

In the above-mentioned methods, substituted LaRhO3 compounds may be used in place of LaRhO3 where appropriate, metal(O) species otherthan Rh(O) may be provided, and alkali metal salts such as Na3[RhCl6] may be used in place of simple metal salts. The latter could be advantageous since alkali metals are known to facilitate oxygenate production in association with metal(O) species.

Several ways of carrying out the invention will now be described by way of example.

The catalysts were tested in powder form and, before testing, were characterised by: (a) X-ray diffraction (XRD); (b) BET surface area; and (c) thermogravimetric analysis (TGA).

The general testing procedure involved placing a catalyst (Ig) in a quartz reaction tube, which was then heated to 280"C in aflowing mixture (25 ml/min) of CO and H2 in the volume ratio of 70% H2: 30% CO. This temperature was maintained for 24 hours. The product gases were bubbled through distilled water (5 ml) which was later analysed for alcohol content. During testing, gas samples weretaken attwo-hourly intervals and analysed for hydrocarbons and CO2.

The above liquid product was analysed by gas chromatographywherein samples (2 FI) were injected onto a chromosorb 102 column at 140"C on a Perkin Elmer(P.E.) sigma gas chromatograph, calibrated using standard solutions. The above gas samples were also analysed by gas chromatography using a spherecomb column, P.E. F30 gaschromatograph. The results are summarised in the table below.

EX CATALYST + PRODUCTS %Rh (byweight); Rh/Rh ratio; BETsurface area CM OOH CHOH OTHER (mug) (moles/ (moles/ OXYGENATES g catalystl g catalyst/ secxl0 sec x 10 1 Rh/MgRhO/MgO 0.30 0.30 0.33 None (14.3; 0.71; not detected measured) 2 Rh/MgRh O/MgO 0.24 0.80 Detected (24.1;2.27; 16.4) 3 Na RhCI/MgRh O/MgO 0.33 0.74 None (17.0; 1.35; 15.1) detected The results show that catalysts of the invention give rise to alkanols having morethan one carbon atom per molecule.

Claims (5)

1. A processforthe catalytic production of one or more alkanols,the or each having morethan one carbon atom per molecule, by the reaction of carbon monoxide and hydrogen in the presence of a catalyst comprising a rhodium moiety in association with a metal moiety in an oxidation state lowerthan thatofthe rhodium moiety, the catalyst being capable of both oxygenating and chain lengthening catalytic activity.

2. A process according to claim 1 wherein the rhodium moiety is in an oxidation state of (Ill) or (lV) and the metal moiety is in an oxidation state of(O).

3. A process according to claim 1 or claim 2 wherein the metal moiety is selected from Fe, Ru, Co, Rh and Ni.

4. A process according to anyofthe preceding claims wherein the rhodium moiety is in the form of a mixed metal oxide.

5. A process forthe catalytic production of one or more alkanols substantially as described herein with reference to any of the examples.