Deactivation Mechanism of Palladium Catalysts for Ethanol Conversion to Butanol

A Pd/Al2O3 catalyst (Pd = 0.1 wt %) for ethanol conversion to butanol deactivates within 10 h of service, despite its high initial activity at 275 degrees C. Probable deactivation mechanisms were explored, including poisoning of Pd/Al2O3 due to adsorption of by-products on Pd, sintering of Pd phases, leaching of Pd from the catalyst, changes in the Pd electronic state, changes in the catalyst's porous structure, and blockage of Al2O3 active sites. The Pd/Al2O3 deactivation was found to be mainly caused by CO molecules that evolved during side reactions. These molecules can either block Pd active sites due to the formation of strong Pd-CO complexes, or enter a CO disproportionation reaction to form carbon deposits on Pd phases. The knowledge gained from this study can be used for the targeted modification of Pd/Al2O3 and the creation of selective systems operating stably in the presence of by-products.