Development of Ni catalysts for gas production from biomass gasification. Reactivity in steam- and dry-reforming

Biomass gasification can be optimised in a fluidised bed by the use of metallic nickel as active phase grafted on olivine. Natural olivine ((Mg, Fe)(2)SiO4) has been chosen as catalyst support because of its activity in biomass steam gasification and tar cracking, its high attrition resistance. After impregnation of nickel oxide on olivine and calcination at 900, 1100 or 1400 degreesC, different interactions between the precursor and the support have been revealed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy coupled to energy dispersive X-ray spectroscopy. Temperature programmed reduction has completed this study and permitted to control the reducibility of the catalysts. The most promising catalyst determined after these different characterisation studies contained 2.8 wt.% of Ni and was calcined at 1100 degreesC. It exhibited strong nickel-olivine interaction but the grafted nickel oxide particles stayed reducible under catalytic test conditions. Already at 750 degreesC, this catalyst presented a high activity in dry-reforming (95% methane conversion) and steam-reforming (88% methane conversion) and yield in syngas (80% and 75% CO yield, respectively). An excess of water content in steam-reforming inhibited the catalytic activation which could be retrieved by addition of a reducer like H-2. No sintering of nickel particles and very little carbon deposition has been observed on this catalytic system by characterisation studies after catalytic tests. This can explain its very good ageing behaviour (at least 260 h at 800 degreesC) and justifies its use in a fluidised bed pilot plant. (C) 2000 Elsevier Science B.V. All rights reserved.