Journal of Catalysis, Vol.381, 193-203, 2020
The role of H-2 on the stability of the single-metal-site Ir-1/AC catalyst for heterogeneous methanol carbonylation
Supported single-metal-site catalysts are well known for their 100% atom utilization efficiency, uniformly isolated active sites and well-defined coordination environment. Methanol carbonylation is a classic homogeneous reaction for acetic acid production. Here, we present the crucial role of H-2 on the stability of single-metal-site Ir-1/AC catalyst for heterogeneous methanol carbonylation. Metal leaching and carbon deposition are verified to be the main reasons of catalyst deactivation. Metal leaching is probably due to the formation of volatile [Ir(CO)(3)I] species, and carbon deposition is supposed to arise from the high energy barrier rate-determining step of CH3COI reductive elimination. However, hydrogenation of the surface intermediate species alleviates the carbon forming problem greatly and competitive adsorption of H-2 with CO on active species inhibits the formation of [Ir(CO)(3)I]. Consequently, H-2 is essential to avoid the activity decay of the Ir-1/AC catalyst. (C) 2019 Elsevier Inc. All rights reserved.