Porous nickel-based catalysts for combined steam and carbon dioxide reforming of methane

Abstract

X-ray diffraction, low-temperature nitrogen adsorption, and electron microscopy combined with energy dispersive X-ray microanalysis were used for studying the effect of synthesis conditions on the phase composition and texture of a porous nickel ribbon with a MgO underlayer and of nickel catalysts supported on it. The MgO underlayer was prepared by impregnation of a nickel ribbon with a Mg(NO3)2 solution and subsequent calcination at 550°C in air or H2. Catalysts were synthesized by additional supporting of nickel onto supports by its impregnation with a solution of Ni(NO3)2 or a mixture of solutions Ni(NO3)2 and Mg(NO3)2. In supported reduced catalysts (750–900°C, H2), the phase of nickel and the solid solution of NiO in MgO were observed. A considerable part of nickel crystallites was epitaxially bound with MgO. The nickel-based catalysts were tested in combined steam and carbon dioxide reforming of methane to synthesis gas (750°C, CH4/CO2/H2O/N2=35/23/39/3, GHSV=62.5L/gh). The catalysts with the MgO underlayer completely covering the nickel ribbon showed stable activity throughout the test period (18h). After the reaction, in these catalysts on the large crystallites of nickel ribbon, dispersed nickel crystallites (5–10nm) epitaxially bound with MgO appeared; no carbon deposits were found in them. The resistance of these catalysts to carbonization was attributed both to the formation of nickel crystallites epitaxially bound with MgO and to the formation of the MgO underlayer that covers the nickel ribbon and prevents its contact with the reaction medium.