Ethanol Dehydration and Dehydrogenation on γ-Al2O3: Mechanism of Acetaldehyde Formation

Abstract

Steady state kinetics and measured pyridine inhibition of ethanol dehydration and dehydrogenation rates on γ-alumina above 623 K show that ethanol dehydrogenation can be described with an indirect hydrogen transfer mechanism to form acetaldehyde and ethane and that this mechanism proceeds through a shared surface intermediate with ethylene synthesis from ethanol dehydration. Ethane is produced at a rate within experimental error of acetaldehyde production, demonstrating that ethane is a coproduct of acetaldehyde synthesis from ethanol dehydrogenation. Steady state kinetic measurements indicate that acetaldehyde synthesis rates above 623 K are independent of co-fed water partial pressure up to 1.7 kPa and possess an ethanol partial pressure dependence between 0 and 1 (Pethanol = 1.0–16.2 kPa), consistent with ethanol dehydrogenation rates being inhibited only by ethanol monomer surface species. The surface density of catalytically active sites for ethylene and diethyl ether production were estimated from i...