Thermal processing of biomass in the presence of a catalyst is a promising technology to generate H 2 -rich gases for fuelling the future. Metal particles loaded on porous supports have been widely used for biomass gasification. However, no detailed research has been designed for describing the catalytic performance of nickel particles located inside compared to outside the pores of the supports. In this work, two groups of Ni/MCM-41 catalysts were prepared: Iseries catalysts where most of the NiO particles were located inside the mesopores of MCM-41 and O-series catalysts where most of the NiO particles were located outside the pores of MCM-41. The prepared catalysts were used in the pyrolysiscatalytic gasification of wood sawdust using a two-stage fixedbed reaction system. Gasification on the I-series catalysts generated more gas and hydrogen and lower oil, compared with the Oseries catalysts. Hydrogen production was increased from 16.46 to 21.26 (mmol H 2 g −1 wood) when the catalyst was changed from 20%Ni−O to 20%Ni−I. The better performance of the I-series catalysts in relation to hydrogen production is suggested to be due to the longer residence time of pyrolysis reactants inside the pores of the MCM-41 and thus a longer contact time between reactants and active Ni sites. In addition, the high dispersion of the fine NiO particles inside the pores of the MCM-41 support enhances the catalytic performance of the I-series catalyst during the pyrolysis/gasification of biomass.

Abstract:The production of hydrogen-enriched syngas from the thermo-chemical conversion of biomass was studied using Ni/CaAlO x catalysts prepared by coprecipitation method. The effect of Ca addition with different molar ratios of Ca:Al (1:3, 1:2, 1:1, 2:1, 3:1) on the properties and catalytic behaviour in relation to syngas production and the coke formation on the surface of the catalysts were investigated.Catalysts were characterized by BET, XRD, TPR, SEM, and TEM. The SEM and TEM results showed that rod-shaped nano-particles were highly dispersed on the surface of the catalyst. The particle size of NiO was slightly affected with the increase of Ca content in the catalyst. It appeared that the selectivity of CO was increased and the selectivity of CO 2 was reduced with the increase of Ca addition to the catalyst. For example, CO 2 concentration was reduced from 20 to 12 Vol.%, when the molar ratio of Ca/Al was increased from 1:3 to 3:1 for the Ni/CaAlO x catalyst; it is suggested that the water gas shift reaction was inhibited and CO 2 reforming reactions were promoted in the presence of the catalyst with higher Ca content. The CO/H 2 molar ratio could be manipulated by changing the Ca content in the catalyst, while the H 2 concentration remained almost constant (around 45 Vol.%). Thus, using the Ni/CaAlO x catalyst developed in this work could provide a promising route to control the syngas composition, which is an important factor for syngas applications.

Hydrogen production from the thermochemical conversion of biomass was carried out with nano-sized NiZnAlOx catalysts using a two-stage fixed bed reactor system. The gases derived from the pyrolysis of wood sawdust in the first stage were catalytically steam reformed in the second stage. The NiZnAlOx catalysts were synthesized by a co-precipitation method with different Ni molar fractions (5, 10, 15, 25 and 35%) and a constant Zn:Al molar ratio of 1:4. The catalysts were characterized by a wide range of techniques, including N2 adsorption, SEM, XRD, TEM and temperature-programmed oxidation (TPO) and reduction (TPR). Fine metal particles of size around 10-11 nm were obtained and the catalysts had high stability characteristics, which improved the dispersion of active centers during the reaction and promoted the performance of the catalysts. The yield of gas was increased from 49.3 to 74.8 wt.%, and the volumetric concentration of hydrogen was increased from 34.7 to 48.1 vol.%, when the amount of Ni loading was increased from 5 to 35%. Meanwhile, the CH4 fraction decreased from 10.2 to 0.2 vol.% and the C2-C4 fraction was reduced from 2.4 vol.% to 0.0 vol.%. During the reaction, the crystal size of all catalysts was successfully maintained at around 10-11 nm with lowered catalyst coke formation, (particularly for the 35NiZn4Al catalyst where negligible coke was found) and additionally no obvious catalyst sintering was detected. The efficient production of hydrogen from the thermochemical conversion of renewable biomass indicates that it is a promising sustainable route to generate hydrogen from biomass using the NiZnAl metal oxide catalyst prepared in this work via a two-stage reaction system.

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ABSTRACT:The production of renewable hydrogen enriched gas from biomass waste is a promising technology for the development of a sustainable economy and society. Until now, there are still challenges of the technology in terms of the efficiency of hydrogen production. Catalyst is known and has been tested to enhance hydrogen production from biomass gasification. In particular using Ni-based catalysts, which have high reactivity for hydrogen production and are cost effective. However, developing a Ni-based catalyst with high thermal stability and resistance of coke deposition on the surface of the catalyst is still a challenging topic. In this work, Ni-Al catalysts doped with low-cost Fe metal were investigated for hydrogen enriched syngas production from gasification of biomass using a two-stage fixed bed reactor. NiOFe2O3-Al2O3 catalysts with various Ni:Fe molar ratios (9:1, 8:2, 6:4, 5:5, 4:6, 2:8 and 1:9) were studied aiming to understand the influence of Fe addition on the production of hydrogen and the catalyst stability in terms of coke deposition on surface. X-ray diffraction, temperature programme reduction and Transmission electron microscopy analysis of the fresh catalysts showed that nanoparticles (mainly NiAl2O4 spinel phase and Al2O3, ~5 nm) were identified in the catalysts. High dispersion of metal particles was obtained using a co-precipitation method of catalyst preparation. With the increase of Fe addition, hydrogen production was reduced from around 11 to 8 (mmol H2 g -1 biomass). However, the addition of Fe into the Ni-based catalyst significantly reduced the amount of coke deposited on the surface of the catalyst.H2/CO molar ratio was maximized to 1.28 when Ni:Fe molar ratio was 1:1. In addition, sintering of metal particles was not observed through the TEM analysis of the fresh and reacted catalysts.2