Catalyst and a process for the production of ethylenically unsaturated carboxylic acids or esters
A catalyst has a modified silica support and comprises a modifier metal, zirconium and/or hafnium, and a catalytic metal on the modified support. The catalyst has at least a proportion, typically, at least 25%, of modifier metal present in moieties having a total of up to 2 modifier metal atoms. The moieties may be derived from a monomeric and/or dimeric cation source. A method of production:— provides a silica support with isolated silanol groups with optional treatment to provide isolated silanol groups (—SiOH) at a level of <2.5 groups per nm 2 ; contacting the optionally treated silica support with a monomeric zirconium or hafnium modifier metal compound to effect adsorption onto the support; optionally calcining the modified support for a time and temperature sufficient to convert the monomeric zirconium or hafnium compound adsorbed on the surface to an oxide or hydroxide of zirconium or hafnium in preparation for catalyst impregnation.
1. A catalyst comprising
a) a silica support modified with a modifier metal present on a surface thereof, and
b) a catalytic metal on the silica support,
wherein the modifier metal is selected from the group consisting of zirconium and hafnium with at least a proportion of the modifier metal present as a monomeric and/or dimeric metal moiety, wherein the catalytic metal is at least one alkali metal.
2. A catalyst according to claim 1 , wherein the modifier metal is present in the silica support in an effective amount to reduce sintering and improve selectivity of the catalyst.
3. A catalyst according to claim 1 , wherein the catalytic metal is caesium.
4. A catalyst according to claim 1 , wherein catalytic metal is present in the range 0.5-7.0 mol/mol modifier metal.
5. A modified silica support for a catalyst having at least one alkali metal comprising a silica support modified with a modifier metal present on a surface thereof, wherein the modifier metal is selected from the group consisting of zirconium and/or hafnium with at least a proportion of the modifier metal present as a monomeric and/or dimeric metal oxide moiety.
6. A modified silica support according to claim 5 , wherein the modifier metal is an adsorbate adsorbed on the silica support surface.
7. A modified silica support according to claim 5 , wherein the silica support is in the form of a silica gel.
8. A modified silica support according to claim 5 , wherein the modifier metal is present in the support in the form of a co-gel.
9. A modified silica support according to claim 5 , wherein at least 25% of the modifier metal in the modified silica support is present as the monomeric and/or dimeric metal oxide moiety.
10. A modified silica support according to claim 5 , wherein the level of modifier metal present is up to 7.6×10−2 mol/mol of silica.
11. A modified silica support according to claim 5 , wherein the level of modifier metal is between 0.067×10−2 and 7.3×10−2 mol/mol of silica.
12. A modified silica support according to claim 5 , wherein the level of modifier metal present is at least 0.1×10−2 mol/mol of silica.
13. A modified silica support according to claim 5 , wherein the modified silica support is a calcined modified silica support.