Heterogeneous catalyst for alcohol oxycarbonylation to dialkyl oxalates

A titanium-promoted palladium-vanadium pentoxide catalyst for oxycarbonylation of alcohols (ROH) to dialkyl oxalates has been developed. Dialkyl oxalates may be hydrogenated to ethylene glycol and ROH and the latter can be recycled. Optimum oxalate selectivity is 90%, with CO₂, methylal, and methyl formate as major by-products. The oxycarbonylation reaction involves a surface Pd(II) Pd⁰ couple. The V(V) V(IV) couple serves as a co-oxidant for Pd. Molecular oxygen reoxidizes V(IV) to V(V). The titanium promoter improves overall catalyst activity by a factor of 5. Oxycarbonylation kinetics are first order in ROH and CO. Relative rates of oxalate ester formation with methanol, ethanol, 1-propanol, and 1-butanol are consistent with nucleophilic attack of alcohol on a surface oxalate species. The effect of Pd loading on activity suggests Pd is associated with two surface V sites.