Influence of metal particle size on the hydrogenation of maleic anhydride over Pd/C catalysts in scCO2

Hydrogenation of maleic anhydride (MAH) with Pd/C catalysts in supercritical carbon dioxide (scCO2) was investigated. The selectivity for γ-butyrolactone (GBL) reached 97.3% in scCO2 at 100% conversion of MAH, which was notably higher than that of 77.4% obtained in organic solvent of ethylene glycol dimethyl ether (EGDME). The particle size of Pd exhibited large influence on the reaction rate and selectivity of GBL. Higher selectivity of GBL was obtained with Pd/C catalyst of smaller Pd particle size, and the rate of GBL selectivity increase as a function of CO2 pressure was found to be significantly correlated with Pd particle size.