Combined Temperature-Programmed Processes, Pulse Reactions, and On-Line Mass Spectroscopy Study of CH4, CO, and H2Interaction with Ni/Al2O3Catalysts

Abstract

The interactions of CH4, CO, and CH4/O2 with Ni/Al2O3 catalysts were examined by the pulse reaction technique and the transient response technique. The adsorption and dissociation of CH4, CO, CH4/CO2, and CH4/O2 on nickel alumina catalysts were also extensively investigated by temperature-programmed hydrogenation (TPH) and temperature-programmed desorption (TPD). The phase structure and nickel oxidation states of Ni/Al2O3 samples were examined by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. XRD, TPR, and XPS results demonstrated that nickel is mainly present as NiO and NiAl2O4 in the as-prepared catalyst, while around 83%−90% nickel is Ni0 after the catalyst is reduced at 700 °C. Methane pulse reactions and transient response analysis demonstrate that the methane oxidation mechanism changes as the nickel oxidation state changes over Ni/Al2O3 when there is no gaseous oxygen present. CH4 is efficiently oxidized into CO and H2 via a direct oxidation mechanism when Ni/...