Study On Preparation And Performance Of Nickel-based Molecular Sieve Catalyst Enhanced By Plasma For CO₂ Reforming Of CH₄

The carbon dioxide reforming of methane is one of the research hotspots in energy,catalysis and environment.CO₂ reforming of CH₄ technology can not only produce syngas that is vital to industry,but also reduce the impact of greenhouse gases on the environment.Nickel-based catalysts are prone to sintering and carbon deposition due to high-temperature reactions in the CO₂ reforming of CH₄,which limits the application of nickel-based catalysts.Therefore,it is particularly important to prepare catalysts with highly dispersed active components and active components-support strong interaction.Based on the previous research work of the research group,this paper intends to use RF discharge plasma to treat the catalyst precursors to increase the dispersion of active component Ni and reduce the size of Ni particles,so as to improve the resistance to carbon deposition and stability of the catalyst.The main research contents of this paper are as follows:（1）The process conditions of the plasma treatment catalyst precursor were investigated.The Ni（NO₃）₂/MCM-41 catalyst precursors was processed by plasma with different treatment conditions to obtain Catal.-P.The catalytic performance results show that the plasma-treated catalyst can obviously improve the low temperature activity of the catalyst in CO₂ reforming of CH₄.After 30h stability test at 750℃,the CH₄ conversion retention rate of Catal.-C catalyst was 64.83%,and that of Catal.-P（2h/200w）catalyst was85.24%.XRD characterization showed that the catalysts treated with RF discharge plasma formed smaller Ni O species,which improved the dispersion of nickel.TPR characterization showed that Catal.-P（2h/200w）had a strong metal-support interaction,which was conducive to inhibiting the growth of Ni particles and stabilizing the active site of Ni at a smaller size during the pre-reduction process.TG-DTG characterization showed that the RF discharge plasma could decompose nickel salt effectively,and the catalyst prepared under the condition of long time and high power could significantly reduced the carbon deposition on the surface of the catalyst.Therefore,Catal.-P（2h/200w）had the best catalytic performance.（2）Research on the preparation of supported catalysts by plasma-modified support and loaded with active component nickel.The catalyst precursors were treated by calcination and plasma methods to investigate the influence of plasma-modified support on the catalytic performance of the catalyst,Sup.-P（2h/200w）-Catal.-P（2h/200w）showed the best catalytic performance.The results showed that the plasma-modified support enhanced the catalytic performance of the catalyst under the condition of long time and high power,whether by calcination or plasma method.XRD characterization showed that the Ni based catalyst supported by plasma-modified support could reduce the particle size of Ni O species and improve the dispersion of Ni.TPR characterization showed that the long time and high power plasma-modified support stabilized the Ni active site at a small size,which enhanced the interaction between the metal support.TG-DTG characterization showed that the plasma-modified support could enhance the carbon deposition resistance of the catalyst,thus improving the stability of the catalyst.（3）Investigation of plasma treatment parameters on catalytic reforming performance.The plasma parameters are as follows:atmosphere,time and power.The results of catalytic performance show that the catalyst treated with H₂ has better stability under the same time and power condition.TPR characterization showed that the metal-support interaction was stronger in the catalyst treated with H₂.TG-DTG characterization showed that the plasma treated catalyst with 60min had better reforming performance.The catalyst treated with 200w had excellent catalytic activity and stability,as well as strong resistance to carbon deposition.Therefore,the optimal parameters of plasma treatment were as follows:the treatment atmosphere was H₂,the treatment time was 60min,and the treatment power was 200w.（4）Optimization of the reduction process parameters of the nickel-based reforming catalyst.The effect of reduction time on reforming performance was investigated with catalyst Catal.-P（H₂-60min-200w）as the research object.The catalytic reforming performance results show that the reduction time of 60min was the best.TG-DTG characterization showed that the catalyst treated with H₂ reduction condition for 60 min had more active Ni⁰ species after the reaction.At the same reduction time,the 650℃reduction catalyst Catal.-P（H₂-60min-200w）had a CH₄ conversion retention rate of99.49%,which was better than the reduction conditions（700℃for 90min reduction）of the supported catalyst prepared by the traditional impregnation method.It not only shortened the reduction time,but also improved the catalytic performance.The unreduced catalyst was compared with the catalyst reduced with the best reduction parameters.The plasma treatment of（H₂-60min-200w）not only decomposed the catalyst precursors nickel nitrate into Ni O,but also reduced Ni O into highly dispersed active Ni⁰ species under the action of H₂ plasma with H atom as reducing agent.Therefore,plasma treatment parameters（H₂-60min-200w）can effectively replace reduction.