Chemisorption and interaction of hydrogen and oxygen on Ni/SiO 2 catalysts

Abstract

The interaction at room temperature of hydrogen with preadsorbed oxygen on the surface of a Ni/SiO 2 catalyst was studied using volumetric, low-field magnetic, and infrared spectroscopic measurements. Oxygen was adsorbed ( T = 22 °C) by dissociative chemisorption of O 2 or by decomposition of N 2O according to N 2O(g) → N 2(g) + O(ads). The chemisorption of O 2 always exceeded the monolayer coverage, which was defined as the amount of hydrogen taken up at 22 °C and p H 2 = 30 Torr. With N 2O the monolayer coverage could be surpassed with sufficiently large exposures. After admission of hydrogen at room temperature to samples that previously had taken up more than a monolayer of oxygen, a surface reaction that led to formation of physisorbed H 2O proceeded. Adsorption of H 2 and subsequent surface reaction were found to occur only when sites that could dissociate hydrogen molecules were present; on completely oxidized NiO no hydrogen adsorption was observed at 30 °C.