Studies On Indium Oxide Supported Rhodium Catalysts For Selective Hydrogenation Of Carbon Dioxide

The consumption of fossil fuel contributes to the emission and accumulation of CO₂.The elevation of carbon dioxide level in the atmosphere,as we all know,leads to a series of problems such as global warming and extreme weather.The capture and utilization of CO₂ has received extensive attention due to its huge potential.CO₂hydrogenation to methanol is the emphasis owing to methanol’s broad applications.The In₂O₃ catalysts of different crystal phases were prepared by precipitation method using different precipitant,it was found that the In₂O₃-S catalyst prepared by Na₂CO₃ as precipitant has better performance than In₂O₃-U catalyst,which was prepared with urea as the precipitating agent.Further characterization found that In₂O₃-U catalyst is a cubic-hexagonal mixed structure and the crystal structure changes during the reaction.Furthermore,it was found that the surface of the In₂O₃-S catalyst is more likely to form oxygen vacancies,which can improve the adsorption and activation of CO₂.Consequently,significantly enhanced catalytic activity of CO₂ hydrogenation to methanol is achieved.In₂O₃ catalyst still faces the problems of low CO₂ conversion rate,low methanol yield,poor stability and so on.Therefore,further improvement of In₂O₃ is of great significance.As we all know,noble metal catalysts are widely used in the reaction of CO₂ hydrogenation due to their excellent hydrogen dissociation performance.Rh is one of the key research objects and has been widely used in the hydrogenation of CO₂ to methane and CO reactions,but its effects in the hydrogenation of CO₂ to methanol reaction has not been deeply explored.In this work,Rh was firstly combined with the In₂O₃,which has been widely used in hydrogenation of carbon dioxide to methanol reaction.Highly dispersed Rh/In₂O₃ catalyst was prepared by deposition precipitation method.The catalyst characterization demonstrated that the highly dispersed Rh species promotes the dissociative adsorption and spillover of hydrogen.On the one hand,these generated H can accelerate the formation of oxygen vacancies on the surface of In₂O₃,thus strengthening the adsorption and activation of CO₂.On the other hand,it can also be used for the subsequent hydrogenation of CO₂ to form methanol.Therefore,the enhanced activity and stability were achieved for selective hydrogenation of CO₂ to methanol.Rh was firstly used in the reaction of CO₂ hydrogenation to methanol,which broadened the application range of Rh-based catalysts.Zirconia has been uncovered as a carrier able to substantially boost the activity of In₂O₃ for CO₂ hydrogenation to methanol.Here,Zr O₂ was added to In₂O₃ to further enhance the catalytic performance.The In₂O₃-Zr O₂ carrier was prepared by the co-precipitation method,then Rh/In₂O₃-Zr O₂ catalyst was prepared by deposition precipitation method.Characterizations demonstrated that the addition of Zr O₂ can stabilize the structure of the In₂O₃ catalyst and mitigate the agglomeration,improving the stability of the catalyst,in addition,the concentration of the oxygen vacancy on the surface of the catalyst improves,which is believed to be the contributor to the higher CO₂ conversion rate and methanol yield.