Study On Catalytic Performance Of Ni/AC Catalyst For CH₄-CO₂ Reforming To Syngas

The content of CH₄ and CO₂ in the atmosphere is increasing,and the impact of the greenhouse effect has attracted the attention of researchers all over the world.It is very critical to find a method to alleviate the pollution of CH₄ and CO₂ greenhouse gases.The CH₄-CO₂reforming reaction is a potential technology that can convert two greenhouse gases,CH₄ and CO₂,into syngas with a H₂/CO molar ratio close to 1.Since CH₄ and CO₂ have stable structures,the splitting decomposition of CH₄ and CO₂ molecules requires a lot of energy in the reforming reaction.In order to improve the conversion efficiency,the development of highly active catalysts is particularly important.Before the experiment,the relationship betweenΔG and temperature of each reaction in the reforming system was investigated by using the Gibbs free energy minimization method in thermodynamic software HSC.The effects of reaction pressure and temperature on reforming reaction components and conversion were stuieded.The results show that the CH₄-CO₂ reforming reaction needs to be achieved under high temperature or catalytic conditions.The core of the reforming reaction is to develop a new catalyst with high activity and high stability.Carbon materials have the advantages of wide sources,good thermal stability,easily changed surface chemical properties,so they are often used as catalysts or carriers.Using bamboo（ZZ）,walnut shell（HT）,and Ordos coal（ED）as experimental raw materials,activated carbon catalysts/supports were prepared by carbonization and chemical activation methods.It was found that the catalytic activity of carbon materials alone was low.In order to improve the performance of carbon-based catalysts,Ni/AC catalysts were prepared by impregnation method（AC is the activated carbon prepared when the mass ratio of KOH and ZZ semi-coke is 3）.Thermogravimetric（TG-DTG）analysis of the experimental raw materials showed that the carbonization temperatures of biomass（ZZ,HT）and coal（ED）were 550℃ and 650℃,respectively.The performance of the activated carbon catalyst prepared by activating ZZ semi-coke with three activators,KOH,NaOH and K₂CO₃,was investigated in the CH₄-CO₂reforming reaction.The results showed that the carbon-based catalyst（AC-KOH）prepared with KOH activation has the best performance.The characterization by using nitrogen adsorption-desorption showed that AC-KOH had abundant pore structure and the total specific surface area reached 1780 m²/g.The performance of activated carbons prepared from ZZ semi-coke and different proportions of KOH in the reforming reaction were investigated.The results showed that when the mass ratio of KOH and ZZ semi-coke is 3,the prepared AC has the best performance.The characterization of SEM and nitrogen adsorption-desorption showed that the AC activated carbon had abundant pore structure.The performance of activated carbon（AC,AC-HT,AC-ED）prepared when the mass ratio of KOH and ZZ,HT,ED semi-coke is 3 in the refor ming reaction were investigated,the results show that the performance of AC is the best.The characterization of nitrogen adsorption and desorption,Raman,ICP-OES,FTIR systems showed that AC has the largest specific surface area and the lowest degree of graphitization;AC contains a small amounts of alkali metals（K）,alkaline earth metals（Ca and Mg）;The-OH,C=O,C-O oxygen-containing functional groups in AC will participate in the refor ming reaction.The performance of the catalysts prepared from Fe,Co and Ni（with a loading of 10 wt%）in the CH₄-CO₂ refor ming reaction was investigated with AC as the carrier.The results show that the best performance of Ni-based catalyst.Ni（NO₃）₂,Ni（CH₃COO）₂ and NiCl₂ aqueous solutions were used as active metal impregnation solutions to prepare Ni-based catalysts（all loadings were 10wt%）for CH₄-CO₂ reforming reaction.The results show that the Ni-based catalyst prepared by Ninitrate has the best performance.Ni(NO₃2) aqueous solution was used as the active metal impregnation solution to prepare 5 wt%,7 wt%,10 wt%and 13 wt%Ni/AC catalysts（represented as 5Ni/AC,7Ni/AC,10Ni/AC,13Ni/AC,respectively）,and the effect of Nicontent on the CH₄-CO₂ reforming reaction was investigated.The results show that the10Ni/AC catalyst has the best performance.It was found that the catalyst contained a small amount of NiO diffraction peaks,and the NiO diffraction peaks disappeared after the reaction,by XRD characterization shows that the carbon material has a certain reducing ability.Through nitrogen adsorption and desorption test,TG-DTG,SEM,and Raman system characterization,it was found that the specific surface area of 10Ni/AC catalyst decreased significantly after the reaction;After the reaction,the weight loss peak of the catalyst moved to the high temperature region,which proved that carbon deposition occurred in the catalyst;and the degree of graphitization of the catalyst increased after the reaction.The performance of Ni-based catalysts prepared on activated carbon supports（AC,AC-HT,AC-ED）was investigated（the loadings were all 10 wt%）.The experimental results combined with ICP-OES analysis showed that,10Ni/AC-ED had the best performance,and the 10Ni/AC-ED catalyst had the highest content of alkali metals（K）and alkaline earth metals（Ca,Mg）.Finally,the performance of the Ni-based catalysts prepared by AC,Al₂O₃,and Mg O supports were investigated（the loadings were all 10 wt%）.Combined with nitrogen adsorption and desorption analysis,it was shows that the mesoporous structure was beneficial to improve the activity and stability of the catalyst.