Plasma-assisted Preparation Of Doped Ni/SiO₂ Catalyst For Application Of Methane Dry Reforming And Its Kinetic Study

Methane（CH₄）and carbon dioxide（CO₂）are not only considered as greenhouse gases,but also regarded as the main raw materials for value-added chemicals.Dry methane reforming（DRM）is recognized as an effective method to convert two abundant greenhouse gases into the required synthesis gas（CO and H₂）,which is the raw material of another chemical synthesis.Because nickel-based catalysts have the same activity as precious metals,coupled with abundant resources and low cost,it has been widely used in DRM.However,it is still a huge challenge to develop a stable catalyst with agood stability and activity under harsh reaction conditions.Rapid deactivation due to carbon deposition is the most serious threat to the nickel-based catalyst’s activity and stability and it also face the problem of sintering at high temperature.The cracking of CH₄and CO₂is the main source of inert coke deposition during the DRM reaction.In addition,due to the occurrence of the reverse water-gas shift reaction（RWGS）,the target product of H₂/CO ratio is usually less than 1.Therefore,in this paper,the preparation of Ni/SiO₂catalyst doped with La,Mg and Zr by plasma improved the activity and stability of conventional heat treatment Ni/SiO₂catalyst.In-situ diffuse reflectance infrared spectroscopy（DRIFTs）was used to preliminarily study the DRM mechanism.In the preparation of Ni/SiO₂catalyst,plasma and conventional calcination methods were used to prepare doped La,Mg and Zr as the second active metal catalyst.Compared with the conventional calcination catalyst,the doped catalyst prepared by plasma has a higher conversion rate of methane to carbon dioxide in the dry reforming of methane and carbon dioxide.Among them,the catalytic performance of doped La by plasma treatment was the best,and it is in the stability test.The conversion rates of methane and carbon dioxide were both stable at 82%and 88%,while the hydrogen-to-carbon ratio was closer to 1,and the unmodified catalyst was rapidly deactivated after 10 hours.After the activity and stability evaluation,it can be concluded that the introduction of DBD treatment in the preparation of the catalyst could improve the catalytic performance of the catalyst for methane dry reforming.The characterization results indicated that:compared with the catalyst that only undergoes calcination treatment,the doped Ni/SiO₂catalyst prepared by plasma had smaller catalyst particle size,higher metal dispersion on the support and stronger metal support interaction force.DBD treatment improved the interaction force between Ni-La,Ni-Mg and Ni-Zr,changed the surrounding environment of Ni,increased the number of Ni active sites on the catalyst surface,enhanced the adsorption capacity of CO₂on the catalyst surface and activation ability,encouraged the occurrence of CO₂activation reaction.At the same time,in the in-situ infrared diffuse reflectance characterization results,COOH^-intermediate species appeared on the catalyst prepared by DBD,that promoted the methane dry reforming reaction.Finally,this article chose the conventional roasting treatment 5Ni-5La/SiO₂-C and the plasma prepared 5Ni-5La/SiO₂-P catalyst to carry out the DRM reaction kinetics respectively.The kinetic experiment results showed that the plasma treated catalyst had lower activation energy and higher reaction rate of methane and carbon dioxide.