CeO_2-promoted Ni/activated carbon catalysts for the water-gas shift (WGS) reaction

摘要

The low temperature water-gas shift (WGS) reaction has been studied over carbon-supported nickel catalysts promoted by ceria. To this end, cerium oxide has been dispersed (at different loadings: 10, 20, 30 and 40 wt.%) on the activated carbon surface with the aim of obtaining small ceria particles and a highly available surface area. Furthermore, carbon- and ceria-supported nickel catalysts have also been studied as . A combination of N_2 adsorption analysis, powder X-ray diffraction, temperature-programmed reduction with H_2, X-ray photoelectron spectroscopy and TEM analysis were used to characterize the Ni-CeO_2 interactions and the CeO_2 dispersion over the activated carbon support. Catalysts were tested in the low temperature WGS reaction with two different feed gas mixtures: the idealized one (with only CO and H_2O) and a slightly harder one (with CO, CO_2, H_2, and H_2O). The obtained results show that there is a clear effect of the ceria loading on the catalytic activity. In both cases, catalysts with 20 and 10 wt.% CeO_2 were the most active materials at low temperature. On the other hand, Ni/C shows a lower activity, this assessing the determinant role of ceria in this reaction. Methane, a product of side reactions, was observed in very low amounts, when CO_2 and H_2 were included in the WGS feed. Nevertheless, our data indicate that the methanation process is mainly due to CO_2, and no CO consumption via methanation takes place at the relevant WGS temperatures. Finally, a stability test was carried out, obtaining CO conversions greater than 40% after 150 h of reaction.