Catalytic hydrogenation of carbon monoxide over Rh-Mn-Li/SiO2 catalyst for the synthesis of C2+ oxygenates: the remarkable effect of urea on the particle size of Rh

A series of Rh-Mn-Li/SiO2 catalysts were prepared by the impregnation of a silica support with solutions containing metal precursors with different amounts of urea. Catalyst performance was investigated by the hydrogenation of carbon monoxide. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, hydrogen chemisorption, diffuse reflectance ultraviolet-visible (DR UV-Vis) spectroscopy, and thermogravimetric analysis. The results revealed that the amount of urea had a significant effect on the particle size of Rh, which increased from approximately 2-5 nm with the increase in urea loading from 0 to 2.0 wt%. DR UV-Vis spectra indicated that the increase in the Rh particle size with increasing urea loading might be attributed to the coordination of Rh3+ with urea or its derivatives during calcination. At a urea loading of 1.0 wt%, the particle size of Rh was 3.7 nm, and the space time yield of C2+ oxygenates reached a maximum of 560.0 g kg(-1) h(-1)