Preparation Of High-dispersion Ni/C Catalyst And Its Catalytic Performance For Cracking Of Corncob Tar

The removal of tar is the key issue for low temperature gasification of biomass.In this work,a series of highly dispersed Ni/C catalysts were prepared using lignite as a carbon precursor.The catalytic cracking of biomass tar was performed in a falling quartz tube reactor.This work provides important theoretical basis and technical support for development of biomass gasification technology for syngas production.In this paper,Shengli lignite?SL?was modified using HCl and HF treatment,and then the acid washed SL?AWSL?and demineralized SL?DMSL?were obtained.The oxidized AWSL?OXAWSL?and oxidized DMSL?OXDMSL?were prepared by H₂O₂oxidation.The Ni/C catalysts were prepared with modified lignite via ion exchange method,and were used for catalytic cracking of corncob tar.The effects of pH of solution and carbonization temperature?CT?on the physical-chemical properties of the catalyst were investigated.In addition,the effects of reaction atmosphere and space velocity?SV?on gas yield and carbon distribution resulting from tar cracking were also investigated in detail.The results show that the Ni/C catalyst prepared under the optimum CT and pH of 650 ^oC and 11 has the best nickel dispersity,the smallest metal nickel particle size,and the strongest cracking activity.Demineralization caused the corrosion of the pore structure of SL and gave a Ni/C with a low specific surface.Oxidation with DMSL further destroyed the structure and provided a lowest specific surface of 141.11 m²/g.Ni/AWSL has a large specific surface area?266.2 m²/g?,high dispersity of Ni,and small crystallite size?NCS?.The yield was maintained at 47.9 mmol/g after 5 times test when Ni/AWSL was used,which is 3.4 times higher than non-catalytic experiment and 1.1 times higher than Ni/SL catalyst under the same conditions.The Ni/C catalyst prepared with OXAWSL,which have the highest carboxyl content?3.8 mmol/g?,the largest specific surface area,the smallest NCS,and the highest Ni loading.The gas yield reached 41.14mmol/g when Ni/OXAWSL was used under 650 ^oC and SV of 3600 h^-1.Steam promotes corncob tar cracking,gas formation and coke elimination.Ni/AWSL has an excellent layered delocalized electronic structure and carrier structure,which provides a platform for electronic exchange and exhibits potential catalytic activity and stability for tar cracking.To improve the anti-coke ability of Ni/AWSL,a dual-functional Ni/C catalyst was synthesized by rare-earth metal Ce doping.The optimum doping ratio of Ni/Ce was determined to be 50:1 by XRD,physical adsorption and other characterization.The Ce-doped catalyst with a Ni/Ce weight ratio of 50:1 showed the most stable gas yield?69.1%?after 5 times.From the SEM images before and after the reforming test,it can be seen that the addition of Ce significantly suppresses the carbon deposition.