DFT Study On Preparation Of1,3-Butadiene From Ethanol On MgO/SiO₂Catalyst

1,3-butadiene is an important organic chemical raw material. MgO/SiO2as asignificant catalyst is applied in the production of1,3-butadiene from ethanol. In thisthesis, the molecular simulation method was used to study the active surface structureand properties of MgO/SiO2catalyst. In addition, the adsorption properties of keyspecies and the reaction mechanism of reaction from ethanol to1,3-butadiene wereinvestigated in order to study the influence of structures and properties of catalyst onreaction performance.The structure and surface properties of MgO/SiO2catalyst were studied by bothexperimental characterization and simulation method. The results indicated that morefour-coordinate and three-coordinate O2-ions in MgO crystal were induced by SiO2,which would lead to increasing structural defects in MgO such as steps and kinks. Flat,stepped and kinked MgO surface models, and SiO2surface model were built in thisthesis. CO2was used as the probe to study the strength of Lewis base. On the basis ofthe order of adsrption energy of CO2, the strengh order of Lewis base was terrace site<step site <kink site. Thus, with the reduction of the coordination number of Mg2+and O2-species on the three kinds of MgO surfaces, the Lewis basicity increasedgradually.The adsorption properties of ethanol on SiO2surface and different MgOsurfaces were studied using density functional theory method. The electronicproperties of ethanol molecule before and after adsorption on the catalyst surfaceswere compared. Comparing the adsorption energy of ethanol on SiO2surface andthree kinds of MgO surfaces, ethanol molecule was preferentially adsorbed ondefective MgO surface. The order of adsorption energy of ethanol on three differentMgO surfaces was in accordance with the order of the surface basicity. With theincreasing of surface basicity, the adsorption strength of ethanol increased.The molecular simulation method was used to study the dehydrogenation ofethanol to acetaldehyde reaction, which is the initial step of ethanol dehydrogenationand dehydration to1,3-butadiene process. The influence of surface structures of MgOcatalyst on reaction performance was also analyzed. Ethanol dissociation to ethoxy onthe flat MgO surface is difficult. However, the reaction was preferable on defective MgO surfaces. The reaction of ethoxy dehydrogenation to acetaldehyde on steppedand kinked MgO surfaces was calculated. The results showed that the ethoxydissociation was more favorable on stepped MgO surface. Therefore, the steppedMgO surface is more active for the dehydrogenation of ethanol to acetaldehyde.In conclusion, the structural defects of MgO were increased by adding SiO2in thecatalyst, which is in favor of the dehydrogenation of ethanol to acetaldehyde. Thisstudy could provide theoretical information for the improvement of catalystperformance in order to enhance the conversion of ethanol to1,3-butadiene.