Preparation Of Sulfur-resistant Catalyst For Combined Steam And Dry Reforming Of Methane

The use of methane and carbon dioxide as feedstocks by using methane dry reforming（DRM）to produce syngas and chemicals plays an important role in reducing greenhouse gas emissions.However,in the actual reaction process,DRM is prone to coke deposition and lead to catalyst deactivation.Introducing water vapor during the DRM process is beneficial to avoid or delay catalyst deactivation due to carbon deposition.In addition,considering that in the actual production process,the presence of sulfur-containing substances such as H₂S in the feed gas will cause poisoning and deactivation of the reforming catalyst.Therefore,this paper focused on the combined steam and dry reforming of methane（CSDRM）process.Ni-based catalyst Ni/LDO-2CeO₂ was prepared with magnesium-aluminum hydrotalcite（LDO）as support and CeO₂ as auxiliary agent,and the deactivation and regeneration performance of Ni/LDO-2CeO₂ catalyst in CSDRM process under H₂S atmosphere was investigated.Based on the tolerance of CeO₂ to sulfides,the catalytic activity of CeO₂ prepared by different methods for CSDRM under H₂S atmosphere was explored,which can provide idea for the design of reforming catalysts suitable in H₂S atmosphere.The main research contents and results of the paper are as follows:（1）The effects of reaction temperature,space velocity and CeO₂ loading（x）on the CSDRM reaction performance of Ni/LDO-x CeO₂ under no H₂S atmosphere were investigated.Results showed that with the increase of reaction temperature,the conversion of CH₄ increases gradually,but the conversion of CO₂ increases first and then decreases,and the optimum reaction temperature is 750°C;With the increase of the reaction space velocity,the conversion of CH₄ decreases,and the conversion of CO₂ increases first and then decreases,and the optimum reaction space velocity was determined to be 24,000 m L·h^-1·g^-1_cat.Ni/LDO-2CeO₂catalyst has the largest specific surface area,the smallest Ni particle size and the least carbon deposition after the reaction,and shows the best activity.（2）The sulfur poisoning and regeneration behavior of Ni/LDO-2CeO₂ catalyst in CSDRM reaction under H₂S atmosphere were investigated.The effects of H₂S content and reaction temperature on reforming reaction,and the regeneration effects of H₂S-free atmosphere,high temperature water vapor/hydrogen and high temperature air/hydrogen treatment on catalyst were investigated.The results showed that the higher the H₂S content in the feed gas,the faster the deactivation of the catalyst.The higher the reaction temperature,the faster the deactivation of the catalyst,but the final activity of the deactivated catalyst at high temperature is higher than that of the deactivated catalyst at low temperature.After the catalyst is deactivated,the catalytic activity can be only partially recovered at 850°C by H₂S-free atmosphere.The catalyst activity can be recovered by steam/hydrogen treatment,but the stable catalytic activity cannot be maintained;Treatment for 3 h in 800°C air and reduction for 2 h in hydrogen atmosphere can completely recover the activity the poisoning catalyst.XRD and XPS analysis indicated that the catalyst deactivation was due to the transformation of Ni to Ni-S and Ni SO₄ species caused by the interaction of sulfur and Ni,and the degree of catalyst regeneration was related to the conversion of these species.High-temperature air oxidation and hydrogen reduction treatment is an effective regeneration method.（3）The sulfur poisoning tolerance of CeO₂ catalyst in CSDRM process was investigated.The resistance to sulfur poisoning of CeO₂ catalysts synthesized by hydrothermal and precipitation methods and commercial CeO₂ in CSDRM process was investigated based on CeO₂ catalysts’ability to activate methane and carbon dioxide.The results show that all three catalysts are active for CSDRM,but the CeO₂ synthesized by hydrothermal method has the highest activity,the conversion of methane and carbon dioxide is 17%and 25%,respectively.Three catalysts show strong stability in the presence of H₂S,and there was no significant decrease in activity within 10 h.There is a positive correlation between activity and oxygen vacancies in catalysts.