HYDROGEN EFFECTS ON NICKEL-CATALYZED VAPOR-PHASE METHANOL CARBONYLATION

The influence of hydrogen on the reaction orders of CO and methanol, with respect to the formation of acyl compounds, methane, and dimethyl ether, was investigated. Although hydrogen-promoted methane formation, experiments with deuterium and methanol-d1 (MeOD) clarified that the hydrogen of the methanol hydroxyl group is the exclusive hydrogen source of the CH4 formation and that this reaction occurs at nickel centers, which are also involved in the acyl compound formation. Temperature-programmed reaction (TPR) and X-ray diffraction (XRD) experiments suggested that the hydrogen effect is caused by changes in the number of active sites and that neither methanol carbonylation nor methane formation proceeds at the larger nickel[0] crystallites detectable by XRD. Furthermore, it has been demonstrated that under certain reaction conditions, hydrogen can induce a remarkable deactivation of the catalyst by promoting nickel aggregation. A mechanism that accounts for the hydrogen effects has been postulated. © 1992.