Cellulose assisted combustion synthesis of high surface area Ni-MgO catalysts: Mechanistic studies

Abstract

The objective of this study was to determine the combustion mechanism of cellulose paper impregnated with Mg(NO3)2, Ni(NO3)2, glycine solutions, and their different combinations. It was established that the combustion mechanism changes as a function of the impregnated media composition. In the Mg(NO3)2-cellulose system, Mg2+ ions strongly catalyze cellulose pyrolysis; hence no atmospheric oxygen is needed for the self-sustained combustion reaction. In the Ni(NO3)2-cellulose system, Ni2+ ions catalyze pyrolysis at a lower rate, and atmospheric oxygen assists the combustion wave propagation. In glycine containing systems, glycine blocks the ability of metal cations to catalyze the early cellulose pyrolysis, and the combustion front propagates due to the exothermic reactions between metal nitrates and glycine. The above mechanisms influence the microstructure of the combustion products. Due to the near-complete degradation of cellulose fibers during the Mg2+ catalyzed pyrolytic combustion, the resulting materials had a highly porous, sponge-like microstructure with a BET surface area of up to 152 m2/g. After the reduction in hydrogen, Ni segregates to the surface of NiO-MgO solid solution, and the resulting catalysts exhibited near-equilibrium methane conversion during the dry reforming of methane reaction at 600°C with low carbon formation and no deactivation for 24 h of time on stream.