Effects of Fe promoter on desorption and hydrogenation of CO adsorbed on Rh-Mn-Li/SiO2 catalyst

The effects of Fe promoter on the desorption and hydrogenation of adsorbed CO over a series of silica-supported Rh-based catalysts were investigated by means of temperature-programmed desorption of adsorbed CO (CO-TPD) and temperature-programmed surface reaction (TPSR) of adsorbed CO with hydrogen. There were three peaks of CO desorption in the CO-TPD spectra over the Rh/SiO2, catalyst. The low-temperature peak of CO desorption was unchanged and the two high-temperature peaks shifted simultaneously toward lower temperature and became narrower when 0.05% of Fe was added into Rh/SiO2. In contrast, the desorption peaks at high temperature moved to higher temperature when 0.05% of Fe was added into the Rh-Mn-Li/SiO2 catalyst, and the amount of CO desorption was more than that over Rh/SiO2. However, the amount of CO desorption decreased with increasing amount of Fe added. The temperature of maximum methane formation in the TPSR spectra was found to be in the following order: Rh/SiO2(482 K) <Rh-Mn-Li/SiO2, (489 K) <Rh-Fe/SiO2(494 K) < Rh-Mn-Li-Fe/SiO2 (501 K). It was interesting to find that the amount of CH4 formation ran parallel to the amount of CO desorption at high temperature, implying that the CO adsorbed strongly on the surface of Rh-based catalysts was hydrogenated to methane