Atomically Dispersed Rh Active Sites on Oxide Supports with Controlled Acidity for Gas-Phase Halide-Free Methanol Carbonylation to Acetic Acid

Abstract

Acetic acid (AA) is an important bulk commodity chemical produced primarily via methanol carbonylation using homogeneous organometallic catalysts in liquid phase reactors with halides that participate in each catalytic turnover. Here we report a heterogeneous, halide-free, gas-phase process for methanol carbonylation to AA using a catalyst consisting of atomically dispersed rhodium (Rh) active sites on an acidic support. It is demonstrated that active site pairs consisting of atomically dispersed Rh and support acid sites enable highly selective AA production, whereas Rh clusters drive methanol decomposition to CO and CO2. Through a comparison of methanol carbonylation over atomically dispersed Rh species on γ-Al2O3, ZrO2, and Na-modified ZrO2, it was identified that by decreasing the concentration of acidic sites, the production of byproduct dimethyl ether could be minimized. After the acidity of the support was tuned by depositing 5 wt % Na on ZrO2 that contained atomically dispersed Rh, AA selectivity ...