Oxidative dehydrogenation of ethane over Ni–W–O mixed metal oxide catalysts

Ni–W–O mixed oxides were prepared through the evaporation of aqueous solutions of nickel nitrate and ammonium tungstate and calcined in air at 500 °C for 2 h. The catalysts were characterized by several techniques (N2 adsorption, X-ray diffraction, temperature-programmed reduction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO, and 18O/16O isotope exchange) and tested in the oxidative dehydrogenation of ethane. The catalytic activity and catalyst reducibility decrease when the W content increases. Thus, nickel sites seem to be the active centers for ethane activation in these catalysts. However, the selectivity to ethylene strongly changes depending on the Ni/W ratio. In W-rich catalysts, in which NiWO4 and WO3 are mainly observed, a strong influence of ethane conversion on the selectivity to ethylene is observed. However, in Ni-rich catalysts, in which NiO crystallites and WOx nanoparticles are mainly observed, ethane conversion hardly influences the selectivity to ethylene. It has been demonstrated that the nature of the Ni sites and the characteristics and number of the acid sites determine the catalytic behavior of these catalysts. The presence of Lewis acid sites with high acid strength in W-rich catalysts facilitates the decomposition of ethylene during ethane oxidation.

Ni–W–O mixed oxides have been tested in the oxidative dehydrogenation of ethane: ethane conversion influences ethylene selectivity in W-rich catalysts, while it hardly influences ethylene selectivity in Ni-rich catalysts. Figure optionsDownload high-quality image (80 K)Download as PowerPoint slideHighlights
► Ni–W–O mixed oxides have been prepared, characterized and tested in the ODH of ethane.
► Ni-rich catalysts show high selectivity to ethylene.
► In Ni-rich catalysts, the ethane conversion hardly influences the selectivity to ethylene.
► The incorporation of W modifies the NiO crystals reducing non-selective sites.