Direct Synthesis Of Ethanol And Acetic Acid From CH₄-CO₂ By A Step-wise Conversion Technology

The reaction process in which CH₄-CO₂ co-activates and converts directly into acetic acid is an atomic,economical and environmentally friendly reaction process,and it is one of the most challenging research topics in the field of catalysis.In order to actively respond to the national environmental protection policies and energy efficiency policy,the research group has proposed that the huge reserves of CH₄ resources combine with the largest pollutant CO₂ of the release of fossil fuel combustion.Finally,a new CH₄-CO₂ synthesis and conversion route is explored.The key point of this conversion pathway is to divide the reaction process into two steps,which can effectively bypass the thermodynamic limitations of the direct conversion of synthetic acetic acid,achieve efficient use of atomic economy.Previously,based on the theoretical simulation calculations and experimental results analysis,the research group have defined the reaction mechanism,process technology,the entire catalytic system for the direct conversion of CH₄-CO₂ to ethanol and acetic acid,laid a good foundation for further research.Based on the research results of our group's predecessors,this paper continues to modify the catalyst to study the factors that affect the activity of the catalyst.The Co-Pd/TiO₂ catalyst prepared in this paper is supported by TiO₂ and the active metals are Co-Pd bimetallic.The preparation methods are sol-gel method and impregnation method.The activity evaluation device is a dual-tube fixed-bed step reactor independently designed and developed by the research group.This article focuses on investigating the effect of mixed palladium source,alkali metal and heteropolyacids modification on the catalytic activity.The catalyst is analyzed using XRD,NH₃-TPD-MS,N₂-adsorption,FT-IR and XPS.The relationship between the performance of the catalyst and its structure is thoroughly studied.The following conclusions are drawn:1.Pd?NO₃?₂·2H₂O as a Pd source is not conducive to the stability of the crystal structure for Anatase TiO₂ and it is not conducive to the high dispersion of metal Pd.2.The active components of Co and Pd in the electron-withdrawing state are favorable for improving the activity of the catalyst.3.The presence of Ti-O-Ti chemical bonds in the catalyst system favors the formation of acetic acid.4.In the mixed palladium catalyst,the more Pd?NO₃?₂·2H₂O doped,the more the amount of medium-strong acid on the surface of the catalyst.5.Selecting KNO₃ as alkali metal salt,the alkali metal modified catalyst prepared by stepwise impregnation method has the best catalytic activity.6.Highly dispersed Co species and Pd species contribute to the improvement of the space-time yield of the product.7.The order and type of alkali metal salt will affect the physical and chemical properties of the catalyst.8.Ethanol in the catalytic system modified by phosphotungstic acid is mainly synthesized by CH₄ oxidative coupling reaction.In other catalytic systems,ethanol is mainly synthesized by the hydrogenation of acetic acid.9.The pore structure of the catalyst is the key factor affecting the synthesis of ethanol by hydrogenation of acetic acid.10.The specific surface area of the catalyst and the amount of medium acidity on the surface affect the synthesis of acetic acid together.11.The TiO₂ modified with the appropriate concentration ofphosphotungstic acid and phosphotungstic acid in the catalyst have generated a certain chemical bond,which will promote oxidative coupling of CH₄ andincrease ethanol selectivity.