Highly dispersion single Rh species on CoMn2O4 spinel oxides nanosphere for water gas shift reaction

Abstract

Spinel oxides have garnered significant attention owing to their exceptional physicochemical characteristics. Herein, single Rh species were deposited onto CoMn₂O₄ spinel oxides using a deposition-precipitation method for the water gas shift (WGS) reaction. Structural characterization results indicate that the Rh species predominantly exist as single Rh atoms (xRh/CoMn₂O₄, x = 0.21, 0.52, 0.86). However, as the loading increase, Rh species tend to agglomerate and formation of Rh nanoparticles over the 1.11Rh/CoMn₂O₄ sample. Experimental analysis has demonstrated that the presence of Rh single atoms promotes creation of oxygen vacancies and enhances the ratios of Co³⁺/Co²⁺, Mn⁴⁺/Mn³⁺, and O_ads/O_lat, consequently improving the catalyst's reducibility at low temperatures. 0.52Rh/CoMn₂O₄ demonstrated 100 % CO conversion at 350 °C, achieved a specific reaction rate of 0.78 mol_CO g_Rh⁻¹ h⁻¹ and a turnover frequency (TOF) of 2.2×10⁻² s⁻¹. In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) results indicate that carbonate serves as a significant intermediate product for Rh single atom catalysts, while formates and carboxylates are the primary intermediate products for Rh nanoparticle catalysts. The projected density of states (PDOS) and adsorption energy calculations collectively demonstrate that Rh₁/CoMn₂O₄(111) exhibits superior catalytic activity for the WGS reaction compared to Rh₄/CoMn₂O₄(111). Moreover, the presence of Rh single atoms significantly enhances the formation of oxygen vacancies. This study provides both experimental and theoretical insights into the rational development of spinel-supported Rh catalysts aimed at enhancing activity in the WGS reaction.