Study On Catalytic Performance Of Ni/Al₂O₃-Y₂O₃ Catalysts Doped By Nd₂O₃ In Dry Reforming Of Methane

Based on the dual difficulties of energy shortage and global warming caused by the huge consumption of fossil energy,it is an ideal approach to convert greenhouse gases carbon dioxide and methane into syngas.Dry reforming of methane（DRM）technology has attracted extensive attention.But it absorbs large amounts of heat at high temperature,and the catalyst is easily deactivated due to the carbon deposition and sintering.Therefore,the research challenge of DRM is to improve the anti-coking ability and stability of the catalyst.Compared with noble metal catalysts,Ni-based catalysts are cheap and rich in resources,and have high catalytic activity for methane reforming,so it has become one of the main research hotspots.In this paper,to enhance the basicity of the support and the oxygen vacancies of the samples based on traditional Ni-based catalysts,a sol-gel method was used to synthesize dual-support catalysts Ni/Al₂O₃-x%Y₂O₃（x=0,5,10,15）,and the influence of the Y₂O₃addition amount on the performance for the mixed oxides catalyst was studied,and the effects of reaction temperature,reaction space velocity and reactant feed ratio on the catalytic activity were further investigated.Based on this research,a new Ni/Al₂O₃-Y₂O₃-x%Nd₂O₃（x=0,2,2.5,3,3.5,4）catalyst was obtained by doping different proportions of rare earth oxide Nd₂O₃,and the impact of the Nd₂O₃doping amount on the performance of the dual-support Ni/Al₂O₃-Y₂O₃catalyst was researched.Moreover,the effects of reaction temperature,reaction space velocity and reactant feed ratio on the catalytic activity also were discussed.At the same time,combined with various sample characterization methods including X-ray photoelectron spectroscopy（XPS）and thermogravimetric（TG）,the structure and properties of the catalysts were analyzed.The main research contents are concluded as follows:（1）A new dual-support Ni/Al₂O₃-x%Y₂O₃（x=0,5,10,15）catalyst was prepared by one-pot sol-gel method,and the effect of yttrium addition on the reaction was investigated by DRM activity test.The results presented that the addition of Y₂O₃had a positive effect on the reaction activity.The conversions of CH₄and CO₂were improved after the addition of Y₂O₃,and the Ni/Al₂O₃-10%Y₂O₃catalyst behaved the best reaction performance and the lowest deactivation rate,the deactivation rate was the lowest in the 30 h stability test.（2）The results of N₂adsorption and desorption experiments exhibited that the Y₂O₃promoted samples had mesoporous structure with uniform pore size distribution,and the pore volume and pore size of the catalyst could be effectively increased.SEM and XRD results showed the lattice size of metallic Ni particles was small,and CO₂-TPD spectra confirmed that the Y₂O₃promoted catalysts may facilitate forming more alkaline sites in dual-support.The TG results proved that the introduction of Y₂O₃reduced the amount of carbon deposits on the catalyst.Therefore,the performance of the dual-support catalyst after the addition of Y₂O₃is better than Ni/Al₂O₃.（3）Ni/Al₂O₃-Y₂O₃-x%Nd₂O₃（x=0,2,2.5,3,3.5,4）catalysts were obtained by introducing the rare earth oxide Nd₂O₃based on Ni/Al₂O₃-10%Y₂O₃,and the reaction performance of the catalyst was investigated in a fixed-bed tubular reactor.The experimental results showed that the Nd-doped catalyst exhibited the prominent reactivity at 800°C.Meanwhile the reactivity and stability of Ni/Al₂O₃-Y₂O₃-3%Nd₂O₃reached the peak,and the conversions of CH₄and CO₂could achieve 88.5%and 92.2%,respectively.Additionally,after 30 h of stability test,the activity still has no obvious decrease in DRM process.（4）TEM images and XRD calculation results confirmed that the Nd₂O₃addition in Ni/Al₂O₃-Y₂O₃catalysts processed small and high dispersion of Ni.XPS results revealed that the Nd-doped catalyst owned abundant oxygen vacancies,which can facilitate the activation and dissociation of CO₂,and create more O*species at the initial stage of the reaction.After the carbon accumulated over the catalyst surface,O*species can realize its value and gasify the filamentous carbon,suppressing the coke formation for the catalysts eventually.As a result,the Nd₂O₃doping catalysts displayed the superior reaction activity and stability even after 30 h perpetuating experiment.