Study On Synthesis Of Dimethyl Carbonate From Carbon Dioxide And Methanol Over Cerium Based Catalysts

Dimethyl carbonate(DMC)is a poison free and pollution free environmentally benign chemical raw material and can be used as an organic intermediate in many chemical industries.DMC has a wide range of applications,such as gasoline additives and organic solvents.Among the environmentally friendly synthesis methods of DMC,the direct synthesis of DMC from methanol and carbon dioxide is an attractive route.The reaction use carbon dioxide,which is a kind of greenhouse gas,as the carbon source,and only produce water as the by-product.This environmentally friendly reaction has a good atomic economy and meets the requirements of green chemical industry.In this paper,ceria was used as the catalyst in direct synthesis of DMC from carbon dioxide and methanol.The effect of the hollow sphere morphology of catalyst and the hydrophilicity of carbon nanotubes carrier on the catalytic performance was studied.A series of hollow sphere cerium oxide catalysts with the different size and shell number were prepared via a sacrifice template method.Modifying the size of carbon sphere template and the condition of hydrothermal treatment,the cavity structure of ceria hollow spheres was precisely controlled.Results show that the hollow sphere cerium oxide had a larger specific surface area,more exposed active crystal plane and more moderate basic sites than the solid particle cerium oxide,with the enrichment ability of carbon dioxide,the hollow sphere cerium oxide showed better catalytic performance.Multi-shelled spheres and small spheres had better catalytic activity due to their stronger enrichment ability.The smallest multi-shelled hollow sphere ceria with a diameter of about 120 nm had the best catalytic activity(5.1mmol DMC/g-cat),which was about three times as much as the activity of solid particles.In order to explore the general rule of influence of enrichment ability of cavity structure on catalytic activity,a hollow sphere model was established.As a result,the surface area per unit cavity volume(S/V)could affect catalytic performance,and the catalytic activity increased with the increase of S/V value.Different ceria based supported catalysts were prepared using carbon nanotubes modified with different functional groups as carriers to study the effect of hydrophilicity of carriers on catalytic activity.The Ce/N-CNT with the N-doped CNT(N-CNT)as carriers showed a better catalytic activity of 6.0 mmol DMC/g-cat.The carbon nanotubes can bound water molecules due to the internal hollow structure.The N-CNT could bind more water molecules with better hydrophilicity,remove more byproduct and improve the reaction conversion.In the reaction of direct synthesis of DMC,the better the hydrophilicity of catalyst carrier,the higher the catalytic activity.