Temperature-programmed methanation on Pd/La2O3 and Pd/SiO2 catalysts

Temperature-programmed reaction and desorption (TPR, TPD) spectra are compared for Pd/La2O3 and Pd/SiO2 catalysts for CO methanation and CO and H2 coadsorption. A methoxy (CH3O) species readily forms on the La2O3 surface of Pd/La2O3 by spillover, and this CH3O hydrogenates to CH4 at a higher rate than CO adsorbed on Pd. Carbon also deposits on the catalyst surface during TPR, and then hydrogenates at a slower rate than CH3O. In contrast, CH3O does not form on Pd/SiO2 from CO and H2, and correspondingly Pd/SiO2 has a lower methanation activity than Pd/La2O3. Isotope labeling, interrupted reaction, activated adsorption, high-temperature TPD/TPR, and CH3OH adsorption are used to study the surface processes on Pd/La2O3. The high methanation activity of Pd/La2O3 catalysts during steady-state methanation may be related to the formation and hydrogenation of CH3O.