Increased productivity in ethylene carbonylation by zeolite-supported molybdenum carbonyls

Abstract

Ethylene carbonylation to propionic acid is a powerful route to the synthesis of oxygenates. Mo(CO)6 is a known homogenous catalyst for this reaction. When supported on HY zeolite, prepared by incipient wetness impregnation from pentane or by vapor deposition, turnover numbers dramatically increase to over 40,000 in 5h of reaction, particularly for the supports with lower Si/Al ratios. Diffuse reflectance UV–visible spectra and thermogravimetric analysis indicate that lower Si/Al ratios promote more and stronger interactions between Mo(CO)6 and the support, leading to higher reactivity under liquid-phase reaction conditions. Although some leaching occurs under these conditions, the active catalyst is the supported Mo(CO)x/HY, and the recovered catalysts are still stable and active for ethylene carbonylation with turnover numbers exceeding 30,000mol propionic acid/mol of Mo over 5h at 190°C. FTIR provides evidence for the formation and stabilization of under-coordinated carbonyl species during heat treatment, and such sub-carbonyls are known to be relevant in previously-established catalytic mechanisms.