Performance Study Of Loaded Polymetallic Nickel-Based Catalysts In Straw Pyrolysis For Syngas Production

During the pyrolysis process of biomass,bio-oil,biochar,and pyrolysis gas are generated.The high energy density gas produced by pyrolysis can be used for power generation and heating.However,the pyrolysis gas derived from biomass pyrolysis contains large amounts of CO₂ and tar,leading to equipment blockage and efficiency loss.The removal of tar is a critical issue that needs to be addressed in biomass pyrolysis.Nickel-based catalysts have been widely studied due to their low cost,easy accessibility,good catalytic activity,and excellent dispersion on carriers.Nevertheless,single nickel catalysts are prone to coking or nickel agglomeration,resulting in deactivation.Therefore,it is of great importance to develop and design new catalysts with higher product selectivity and catalytic activity through the combination of various metals.With this in mind,this paper aims to enhance the efficiency of syngas production from biomass pyrolysis by investigating the pyrolysis of several metal catalysts.Additionally,the study explores the promotional effects of non-metallic substances,analyzes the influence of different preparation and experimental conditions on catalytic efficiency,investigates the causes of catalyst deactivation,and examines the application of supported multi-metal nickel-based catalysts in biomass pyrolysis.A series of Ni-Co/Ca catalysts were synthesized via the sol-gel method.A fixed-bed pyrolysis reactor system was employed to investigate the effects of calcination temperature,Ni Co ratio,and residence time on catalytic performance.Moreover,the impact of the introduction of boron（B）on syngas production was specifically explored.The catalysts with and without B addition,as well as before and after use,were characterized by various techniques,including XRD,SEM,BET,and H₂-TPR,and the stability of the catalysts was tested.The results demonstrated that the presence of both Ni and Co led to a higher H₂ yield than when Ni or Co was present alone,resulting in a synergistic effect that increased the yield by at least 31.63%.According to the Scherrer formula,the addition of 4%B reduced the active metal particle size from 21.4 nm to 5.0 nm and prolonged the catalyst’s service life.Furthermore,under the conditions of a 2:1 biomass-to-catalyst mass ratio using rice straw,4%B addition,a 1:1 Ni Co ratio,a calcination temperature of 400℃,a pyrolysis temperature of 800℃,and a residence time of 20 minutes,the syngas production increased from 188.6 m L/g without a catalyst to 431.8 m L/g,representing an increase of 131.28%.Using Ni（NO₃）₂·6H₂O as the nickel source,a Ni/Ca Zn Al catalyst was prepared via the sol-gel method for catalyzing the production of syngas from rice straw pyrolysis.The performance of the catalyst was evaluated in terms of both H₂ and CO yield and concentration.Physicochemical changes of the catalyst were studied using various characterization techniques,such as XRD,BET,SEM,TGA,H₂-TPR,and XPS.The effects of different preparation and experimental conditions on the catalyst were investigated,with a particular focus on the influence of calcination temperature on catalytic performance.Experimental results revealed that,compared to the catalyst calcined at 400℃,the one calcined at 500℃possessed a larger surface area,a more abundant porous structure,greater stability,and stronger metal-support interaction,although its resistance to carbon deposition was slightly weaker.The 15%Ni/Ca Zn Al catalyst calcined at 500℃and pyrolyzed at 800℃for 20 minutes demonstrated the best performance for producing hydrogen-rich syngas.At this point,the syngas yield reached 424.8 m L/g,2.25 times higher than that without nickel（188.6 m L/g）.After six uses,the syngas yield remained at 247.6 m L/g,which was 31.28%higher than that without nickel.Ni/Zn Zr catalysts were synthesized via the sol-gel method using Zn and Zr as composite supports,and their catalytic performance in straw pyrolysis was systematically investigated.By continuously adjusting factors such as the support synthesis ratio,the loading of active metal Ni,calcination temperature,and pyrolysis temperature,optimal catalytic effects for syngas production were achieved.In addition,the changes of the catalyst during the pyrolysis process were characterized by XRD,SEM,BET,and H₂-TPR.The results indicated that Ni-loaded Zn Zr catalysts effectively formed porous structures,with metals present in the catalysts as oxides.After the catalyst’s usage,the surface showed evident carbon deposition and metal agglomeration,reducing the subsequent catalytic performance.Prolonged and repeated usage led to a decreased surface nickel content,severe metal agglomeration,and catalyst deactivation.Furthermore,a 5%Ni loading on the support with a Zn Zr ratio of 6:4 exhibited better catalytic performance,with a syngas yield of 507.3 m L/g.Even after the catalyst reached stability,the yield was still 340.0 m L/g,an increase of 80.28%compared to 188.6 m L/g without a catalyst.