Effect of a Hydrogen Pretreatment on the Mechanism of Deuterium Addition and Exchange of Propene over Ni–Cu Alloy Catalysts

Abstract

Abstract The effects of a hydrogen pretreatment on the activity and reaction intermediate in a C3H6–D2 reaction over a Ni–Cu alloy as well as Ni metal catalysts were investigated in detail by applying an isotope tracer technique. Ni metal and Ni-rich alloy catalysts, cooled down to the reaction temperature under a hydrogen atmosphere (D-surface), exhibited low activity compared to that of a surface evacuated before cooling (E-surface). For Cu-rich alloy catalysts, however, the E-surface exhibited a lower activity and a higher activation energy than did the D-surface. A comparison of the TPD spectra of adsorbed hydrogen with the dependence of the activity upon the evacuation temperature suggests that strongly adsorbed hydrogen retards the reaction over Ni and Ni-rich alloy catalysts at lower temperature. Microwave spectroscopic analysis demonstrated that the reaction intermediates over D- and E-surfaces of Cu-rich alloy catalysts were similar to those over Cu and Ni metals, respectively. This result suggests that a hydrogen pretreatment of Cu-rich alloys forms a specific surface structure which is destroyed by evacuation at elevated temperatures.