In Situ Preparation of Highly Stable Ni-Based Supported Catalysts by Solution Combustion Synthesis

Solution combustion synthesis (SCS) is typically used to produce nanostructured oxides and bulk metallic materials for a variety of application including catalysis. Here, we report in situ, one-step SCS of high surface area (155 m(2)/g) Ni catalysts supported on fumed silica (SiO2). Time-resolved X-ray diffraction is used to investigate the dynamics of phase formation during combustion of nickel nitrateglycineammonium nitrate reactive gels impregnated onto porous SiO2. It is shown that highly dispersed nickel nanoparticles (5 nm) formed in the reaction front are followed by their rapid oxidation by air oxygen. To prevent the undesired oxidation process, the synthesis was conducted in an inert atmosphere (argon, helium). It is demonstrated that low concentration oxygen impurity (less than 0.001 wt %) in the inert gas passivates the Ni nanoparticles through the formation of a thin amorphous oxide layer. The thus prepared Ni/SiO2 supported catalyst possesses high activity during the ethanol decomposition toward hydrogen at low temperatures (200 degrees C) and excellent stability toward deactivation with essentially no change of catalyst activity over 100 h of operation.