Study Of Ni/Biochar Catalysts For Catalytic Steam Reforming Of Biomass Tar

Biomass gasification technology can effectively convert low-grade biomass into high-quality gas,and tar has always been the most critical issue for gasification technology.Tar not only reduces the gasification efficiency,but also causes pipeline clogging and environmental pollution problems.Steam reforming can reduce the tar content and improve the gas production quality.It is generally considered as a tar treatment method with a good industrial application prospect.The key issue for steam reforming is development of high-performace catalyst.Considering the factor of cost,low-cost and disposable catalysts are more likely to be applied in practical gasification plants.Char with high specific surface area,low-cost,and can be prepared in-situ from biomass itself,is widely used in tar reforming.However,char,as a carbon material,can be consumed by steam during reforming at high temperatures and has poor catalytic activity at low temperatures,which is the key problem char as catalyst in tar steam reforming.However,the transition metal Ni shows an excellent activity on tar cracking and reforming.Therefore,this study develops biochar supported nickel?Ni/BC?catalysts,which can be realized efficient conversion in tar steam reforming under relatively low temperatures?600 ^oC?.In this paper,the formation process and regulation method of Ni nanoparticles in char matrix during carbothermal reduction were explored firstly.On this basis,a series of experimental were investigated using toluene as a biomass-derived tar model compound.The influence of preparation parameters?pyrolysis preparation temperature and Ni loading amount?on the Ni particle size and catalytic activity was examined and the initial activity?TOF?of different catalysts was explored comparatively.Then two conventional metal oxides supported Ni catalysts?Ni/ZrO₂ and Ni/?-Al₂O₃?were selected for comparison with high performance Ni/BC in100 hours long-term stability tests.Finally,high performance Ni/BC was further examined for its performance in steam reforming of real biomass tar.By studying the above studies,this work illustrates the formation process of Ni nanoparticles during carbothermal reduction,the regulation method for the dispersion of Ni nanoparticles and the preparation method of Ni/BC catalyst with high catalytic activity and stability.The main results and conclusions are as follows:1.Ni metal is the main active site of toluene steam reforming.When the Ni/BC catalyst pyrolysis preparation temperature is higher than 400 ^oC,the carbothermal reduction occurs on the char matrix,with generation of Ni nanoparticles.2.Lower pyrolysis preparation and Ni loading amount,which is benefit to the higher dispersion of Ni nanoparticles?i.e.lower particle size?.Ni/BC pyrolyzed at 600 ^oC with a Ni loading of 5%?5Ni-600/BC?catalyst displayed higher specific surface areas and higher Ni dispersion than other catalysts.Toluene steam reforming priority is carried out on small particles Ni with more steps and edge sites.Therefore,5Ni-600/BC catalyst showed superior catalytic performance in terms of initial activity?TOF?and stability than other catalysts.3.The 100h long-term stability tests showed that the spent 5Ni-600/BC catalyst experienced severe coke deposition and metal sintering resulted in the gradual deavtivation,but the 5Ni-600/BC catalyst has a larger specific surface area,which makes it have a higher carbon content ability.Therefore,the 5Ni-600/BC catalyst showed higher catalytic activity and better stability activity within 100 h.4.Compared with BC catalyst,5Ni-600/BC catalysts for real biomass tar steam reforming not only reduced the overall amount of tar,but also changed the composition of tar by cracking large molecules into smaller ones and usable gases.