Preparation Of Composite Nickel-based Catalyst And Its Research On Improving The Quality Of Straw Pyrolysis Gas

The energy utilization of biomass is one of the important ways to solve the current energy supply and demand problem.Converting biomass into high-quality gas through pyrolysis technology is an efficient and promising technology,and it is also a high-quality way to achieve carbon-neutral recycling and reuse.The research of catalyst is the key in catalytic pyrolysis technology,in order to continuously improve the catalyst so that it can exert its catalytic effect efficiently and stably.In this paper,based on the widely studied nickel-based catalysts,nickel-based composite catalysts were prepared by improving supports and adding active metals,and their properties were discussed.（1）Rice straw was selected as the raw material for pyrolysis in this experiment.First,a separate pyrolysis experiment was carried out.The results showed that the continuous increase of temperature greatly promoted the generation of CO and H₂.At900°C,the yields of CO and H₂were 130.4 m L/g and 120.6 m L/g,respectively.（2）The composite support ZrO₂-dolomite（ZrO₂-Dol）was obtained by sol-gel method and the active component nickel was loaded on it.The characterization methods of XRF,XRD,BET and SEM were used to analyze the composition and structure of the support and catalyst.The results showed that Ni O was formed by calcination of the nickel component and successfully supported on the composite support.The effects of calcination temperature,Ni loading,reaction temperature and catalytic residence time on synthesis gas were studied in catalytic pyrolysis experiments.It was found that the catalyst calcined at high temperature would destroy the surface phase structure,resulting in a decrease in its performance.The catalytic hydrogen production efficiency of rice straw catalytic pyrolysis was the highest when the calcination temperature was 400℃and the Ni loading was 10 wt%.Under this premise,the optimal hydrogen yield of 206.2 m L/g could be obtained through the pyrolysis experiment at 800°C for 20 min,and the catalyst could still significantly improve the hydrogen yield in other types of biomass pyrolysis experiments.（3）Three catalysts Ni/C,Ni-Co/C and Ni-Co-La/C were obtained by loading Ni,Co and La by uniform precipitation method using biomass carbon obtained by calcining coconut shells at high temperature as a support.Catalysts were analyzed by XRF,XRD,SEM,BET and thermogravimetric test methods.The results showed that the active components were well combined with the carbon support,and the surface morphology of the catalyst varied with the increase of active components,the specific surface areas of Ni-Co/C and Ni-Co-La/C were both lower than that of Ni/C,the three samples are all in line with the characteristics of mesoporous materials and the types of N₂adsorption/desorption isotherms are also corresponding to the corresponding materials.The thermogravimetric results of Ni-Co-La/C showed good thermal stability.In the straw catalytic pyrolysis experiment,the effects of three catalysts on CO and H₂production under different calcination temperature,reaction temperature and different residence time were discussed,and it was found that the catalytic effect of Ni/C and Ni-Co/C was inferior to that of Ni-Co-La/C.Using Ni-Co-La/C as catalyst,the optimal catalytic effect was obtained under the conditions of calcination at 400℃and pyrolysis at 800℃for 20 min,in which the yields of H₂and CO were163 m L/g and 176 m L/g,respectively.The volume concentrations were 39.76 vol%and 40.16 vol%.After six cycles of recycling,although the catalyst was deactivated partially,it still maintained catalytic activity.The volume concentrations of H₂and CO changed to 36.79 vol%and 32.58 vol%,respectively,and the decrease of H₂did not exceed 3 vol%.（4）A composite support（Al₂O₃-WSC）was obtained by co-precipitation of walnut shell carbon（WSC）and Al₂O₃,and Ni-M（M=Fe,Co,Ce）/Al₂O₃-WSC catalyst was prepared by co-precipitation.Through thermogravimetric,XRF,XRD,SEM and BET characterizations,it was found that the obtained composite support has extremely strong thermal stability and large specific surface area;there were interactions between various metals of the catalyst;The dispersity of the loaded active components was good.In the catalytic pyrolysis experiment,the effects of reaction temperature,catalyst type and straw moisture content on the pyrolysis gas yield were investigated.The results show that when there were catalysts involved in the reaction,the increase of temperature had the best promotion effect on improving CO production;Compared without catalyst,all three catalysts could effectively improve the production of CO and H₂at the same temperature.Increasing the moisture content of the straw is equivalent to introducing hydrogen into the pyrolysis system.Using Ni-Co/Al₂O₃-WSC,the H₂and CO production reached up to 231.6 m L/g and 201m L/g under the optimal conditions,which greatly improved the yields of H₂and CO.The stability experiments showed that Ni-Co/Al₂O₃-WSC also had the best cycling stability.In the seven cycle experiments,the concentration of CO varied from 37.18vol%to 30.29 vol%,and the concentration of H₂varied from 42.84 vol%to 35.14vol%.