Preparation And Performance Study Of Sulfur-resistant (H₂S) Catalyst For Dry Reforming Of Methane

Dry reforming of methane（DRM）is a valuable utilization of resource with the following advantages:（1）Direct utilisation of two greenhouse gases,methane and carbon dioxide;and（2）The resulting syngas can be used in chemical processes such as Fischer-Tropsch reactions.Currently,the main problems for large-scale industrial applications of DRM are the deactivation of catalysts,including active phase sintering,carbon deposition and catalyst sulphur poisoning due to sulphur impurities（e.g.H₂S）in the feed gas.There are few studies about the effects of sulphur poisoning.DRM reactions require a fine desulphurisation process to ensure the sulphur content of the feed gas is below 0.05ppm,which causes the contradiction between desulfurization rate and cost.Therefore,it is of great value to improve the sulphur resistance of catalysts in DRM.The main factor of catalyst sulphur poisoning is the binding of sulphur to the surface active site,forming a metal-sulphur（Me-S）bond and limiting the subsequent utilisation of the active site.The Ni-based active centres commonly used in DRM are susceptible to sulphur poisoning by the incompletely desulphurised sulphur-containing impurities.The main principles for the design of sulphur-resistant catalysts are improving the interaction between Ni and the carrier,introducing auxiliary sulphur adsorption active sites and constructing catalyst systems in which the active sites are difficult to be poisoned by H₂S.The paper firstly prepared 2.5Ni/Al₂O₃ catalysts based on electrostatic adsorption strategy under alkaline conditions.The strong electrostatic adsorption coupled with the anchoring effect of unsaturated coordination Al₂O₃(Al³⁺_penta)changed the electronic environment of Ni to some extent and enhanced the interaction between Ni and support.In DRM tests at 550℃ without H₂S,the methane conversion rate of R_4-84))=160.87（L/h/g）was better than that of the Ni/Al₂O₃ catalyst prepared by conventional impregnation(R_4-84))=80.16（L/h/g）);the catalyst also showed a more excellent stability after the introduction of 100 ppmH₂S.The methane conversion in the 800℃ reaction was stable at around 15%for 10 h.On this basis,the Ni-Mo bifunctional catalysts were prepared by equal volume co-impregnation method to investigate the effect of Mo modulation on the sulphur resistance of the catalysts,and to investigate the sulphurisation process of the catalysts in the DRM reaction and to analyse the role of Mo in the catalysts as sulphur absorber or auxiliary.The results show 10Ni10Mo/Si O₂ exhibits the best sulphur resistance with an initial conversion of methane up to 90%and its activity and physicochemical properties remain almost unchanged even after 16 regeneration cycles.Subsequently,the paper synthesised a series of Ni-Mo alloy phase catalysts based on a deep reduction strategy that the Ni-Mo catalysts were prone to form Ni₃Mo and Ni₄Mo alloy phases during the treatment,which to reduced the oxygen-sulphur exchange capacity of the catalysts.The adsorption capacity of H₂S on the deep reduction treated catalysts was significantly enhanced,the sulphur poisoning process was slowed down and the reaction stability was improved.The Ni-Mo type catalysts were found to be 1.5 times more stable against sulphur for 400 ℃ deep reduction.The oxygen vacancy（defective）sites in CeO₂ catalysts have the ability to activate CH₄ and CO₂,while showing good sulphur resistance.In this study,we prepared CeO₂catalysts with different morphologies to effectively regulate the content of oxygen vacancies on the catalysts and construct sulphur-resistant DRM catalytic reaction system under the induction of oxygen vacancies.Among them,the nanosphere CeO₂catalysts maintained a methane conversion rate of about 22%within 30 h reaction at800℃.The results showed that there was no significant sulphur accumulation on the nanosphere CeO₂catalyst after 30 h of reaction and there was a positive correlation between the oxygen vacancy content on the catalyst and the methane conversion rate,which can be used as a reference for the subsequent design of sulphur-resistant DRM catalysts.