Role of the Support in Syngas Conversion over Pd/Cu–KL Zeolite Catalysts

Abstract

Infrared spectra are reported for a KL zeolite and copper and palladium-containing KL zeolites at high temperatures and under high pressures of CO/H2and the results discussed with reference to parallel reaction studies. Particular attention has been given to the role of the zeolite surface in the further conversion of methanol produced in the metallic function. The initial steps in the reaction are the formation of formyl type species from adsorbed H atoms and associatively adsorbed CO which generate methanol or spillover to produce adsorbed formate at potassium sites in the zeolite. These formate species undergo further reaction with adsorbed methanol to produce methyl formate. The formation of methyl formate from methanol contrasts with the established route for methanol to hydrocarbons over acidic zeolites where methanol is initially dehydrated to give dimethylether. This has been attributed to the failure to generate surface methoxy species on the basic zeolite. Acetate species located on the zeolite surface are produced from acetyl species on the metal surface followed by transfer to the support in the same manner as formate and are not generated via isomerisation of methyl formate. The alloying of Pd and Cu leads to enhanced hydrogenation behavior compared to the individual metals as reflected in the alkane/alkene ratios.