Selective Catalytic Conversion Of Ethanol Into 1,3-butadiene Over Multifunctional Composite Oxides

Butadiene is an important building block of the chemical intermadiates,especially a synthetic rubber used in the production of car tires.With climate change,environmental pollution and the increasing depletion of petroleum resources,it is important and worthy to the exploration of alternative resources for energy and chemical production.Over the last few decades,the synthesis of ethanol technology got rapid development,it is valuable to produce butadiene from ethanol.In this work,the MgO-SiO₂ catalysts were prepared for the one-pot ethanol transformation into butadiene process.A series of magnesia-silica binary composite catalysts with different molar ratios were prepared using various preparation methods,operation conditions and evaluated for the one-step production of 1,3-butadiene（BD）from bio-ethanol.The main results were as follows:（1）The MgO-SiO₂ catalysts with varying molar ratios were prepared,while the morphology,structure and acid-base properties of the catalysts were characterized by XRD,SEM,BET,FTIR,UV-vis,NH₃-TPD,CO₂-TPD.The results illustrated that the flower-like MgO prepared by hydrothermal method shows the highest surface area and pore volume.Overall,the enhanced large specific surface area and unique mesoporous structure would be more favorable for adsorption and mass transport,which is beneficial for high catalytic performance,compared with commercial MgO.The catalyst using the hydrothermal-derived MgO,which possesses more active sites than the commercial MgO,and consequently higher catalytic activity,is more favorable for BD production.The catalytic test results revealed that the conversion of the ethanol over MgO-SiO₂（MgO:SiO₂=65:35）reaches the ethanol conversion of 95%and the yield of butadiene is 77%at 450^oC and a high WHSV of 4.1 h^-1.（2）The MgO-SiO₂ catalysts prepared by four different preparation methods（physical mixture,sol-gel method,incipient wetness impregnation and wet-kneading）,while the morphology,structure and acid-base properties of the catalysts were characterized by XRD,BET,FTIR,UV-vis,NH₃-TPD,CO₂-TPD.The catalysts prepared by wek-knesding performed better,indicating that a proper balance in acid-base sites formed on this MgO-SiO₂ catalyst surface.In conclusion,the catalytic activity is associated with the balanced surface acid/base sites in relation to the interfacial Si-O-Mg link caused by the strong interaction between MgO and SiO₂,which due to the preparation methods and catalyst compositions.（3）The study on the formation process of butadiene was studied by ethanol-TPD with an on-line mass spectroscopy and operating conditions.The results indicate that the firstly consists in the dehydrogenation of ethanol to acetaldehyde,then gose through the aldol condensation and dehydration,a final to form butadiene.In addition,with the addition of a little oxygen,it facilitates the dehydrogenation of ethanol to acetaldehyde and consequently higher catalytic performance.