Rhodium Electronic State in Catalysts Based on Rh/НZSM-5 for Oxidative Carbonylation of Methane into Acetic Acid: Effect of Copper and Zinc Doping

Diffuse reflectance infrared Fourier transform spectroscopy of adsorbed carbon monoxide is used along with X-ray absorption spectroscopy to study the effect a second alloying metal (Zn, Cu) has on the electronic state and local structure of rhodium on the surfaces of Rh/HZSM-5 zeolite catalyst. It is established that introducing copper and zinc helps improve the stability of rhodium toward aggregation (the formation of clusters) under conditions of the oxidative carbonylation of methane into acetic acid. Compared to monometallic catalyst Rh/HZSM-5, where single atom rodium sites are partially aggregated into clusters, the proportion of Rh° is halved in the case of Rh–Zn/HZSM-5, and Rh clustering does not occur in the case of Rh‒Cu/HZSM-5. The stabilizing effect of Cu is due to the interaction between copper and rhodium cations on the surface of zeolite.