Performance Of Nickel-based Nanocatalysts In Hydrodeoxygenation Of Vanillin

Bio-oil is an important carbon source of liquid hydrocarbon fuel,but it is difficult to be used because of its high oxygen content.Hydrodeoxygenation is the most promising method for upgrading bio-oil.Vanillin,as a common component of bio-oil,is considered to be an important platform molecule.2-methoxy-4-methylphenol（MMP）,which is generated from its hydrodeoxygenation,is a potential biofuel.The hydrodeoxygenation of vanillin is mainly studied with noble metal catalysts.However,the cost of noble metal catalyst is high,and some non-noble metals,such as Cu and Co,have been applied for vanillin hydrodeoxygenation.However,these catalysts need harsh reaction conditions and high feedstock.Therefore,a series of highly efficient and stable nickel-based nanocatalysts were prepared for the hydrodeoxygenation of vanillin.Firstly,Ni/Nb-Si catalysts with different Nb:Si ratios were prepared.It was found that Ni/Nb-Si-3 had the best catalytic performance,with the conversion of vanillin being above99.9%and the selectivity for MMP being 91.1%.Furthermore,Ni/Nb-Si-3 could be used stably for five times.XRD,TEM and BET showed that the addition of Si O₂ could increase the specific surface area of these catalysts and promote the dispersion of Ni nanoparticles,thus improving the activity and stability of Ni/Nb-Si-X.NH₃-TPD and XPS showed that the addition of Nb₂O₅ increased the acid sites on the surface of the catalyst,and Nb₂O₅ was partially reduced to Nb O_x during the process of catalyst reduction,thus improving the selectivity of MMP.Secondly,Al was impregnated in mesoporous silica prepared by an improved St?ber method to form mesoporous aluminosilicate（Si Al）,and Ni was loaded on Si Al by the deposition-precipitation method to form mesoporous nickel aluminosilicate catalyst（Ni/Si-Al-DP）.This catalyst has the structure of both mesoporous aluminosilicate and nickel silicate.The influence of the catalyst structure on its hydrodeoxygenation performance was explained by BET and H₂-TPD.Through ICP,TEM,TG-MS and other characterizations,it was found that the catalyst deactivation was caused by the collapse of catalyst structure and the adsorption of raw material or products on the catalyst surface.Finally,Ni/MSA catalysts were prepared by an impregnation method and an in-situ method,respectively.A Ni/MSA-0.05g Na F catalyst,which is prepared by the in-situ method with the addition of small amount Na F,showed excellent activity and the best stability under mild reaction conditions.Moreover,it can be used stably for five times.XRD,TEM and other characterizations showed that the Ni nanoparticles prepared by the in-situ method had good dispersion.The stability of the catalyst could be enhanced with the addition of appropriate amount of Na F,but the addition of excessive Na F would influence the polymerization of the nickel aluminosilicate,thus affecting the catalyt stability.