Spillover sites on a 19% [formula omitted] catalyst

Abstract

Two distinct methanation sites are clearly identified on a 19% Ni Al 2O 3 catalyst by temperature-programmed reaction (TPR) employing isotope labeling. The two sites, which are present after reduction at 975 K, are due to CO adsorption on Ni crystallites and CO and H spillover onto the Al 2O 3 support. The concentration of sites on the support is 250 μmol/g Al 2O 3 (5 × 10 13 molecules/cm 2), which is the same value measured for a 5.1% Ni Al 2O 3 catalyst and for a 1.0% Ru Al 2O 3 catalyst. Temperature-programmed desorption suggests that the CO and H on the Al 2O 3 are in the form of a HCO complex. The formation of this complex is an activated process, which is related to the activated adsorption of H 2. The H 2 that adsorbs between 300 and 385 K is responsible for this spillover process onto the Al 2O 3. Isotope labeling and TPR were used to verify that a HCO complex does not form on Ni SiO 2 catalysts. Carbon monoxide adsorption on Ni SiO 2 was not activated and only one methanation site was seen.