Theoretical Study On Acetylation Of Acetylene Catalyzed By Low-dimensional Carbon Nitrogen And Boron-nitrogen Materials

Vinyl acetate（VAc）is an important chemical intermediate,which is often used to synthesize other high value-added chemical products.The preparation methods of vinyl acetate mainly include calcium carbide acetylene method and petroleum ethylene method.Because China is rich in coal resources and has a large amount of acetylene resources,the acetylene method has gradually become the main way to prepare vinyl acetate in China.At present,the acetylene process is mainly based on zinc-based catalysts,of which zinc acetate catalyst almost monopolizes the whole industrial field of acetylene process.Therefore,the research and development of a new type of catalyst for acetylene acetylation reaction is conducive to changing the current situation of the single type of catalyst,thus promoting the healthy development of China’s vinyl acetate industry.Based on the density functional theory,using the B3LYP functional and 6-31G（d,p）group under the Gaussian software package,this paper studied the adsorption performance,catalytic activity,and reaction mechanism of two-dimensional carbon nitrogen catalysts with different carbon to nitrogen ratios,boron nitrogen catalysts with different geometric structures（2D,1D,and 0D）,and 0-dimensional C₂₄N₂₄nano-cage catalysts modified with different elements in acetylene acetylation reaction.The properties of the catalysts were further analyzed through wave functions,The main research results show that:The order of adsorption capacity of boron nitrogen materials with three different dimensions for reactants is:C₃N>C₂N>C₄N>C₅N,and the order of the energy barrier of the speed control step in the catalytic process is:C₂N<C₅N-p1<C₃N-p1<C₃N-p2<C₄N<C₅N-p2.When the reaction conditions reach220℃,only C₃N adsorption of the reaction components is thermodynamically advantageous.In a word,C₃N not only has the strongest adsorption capacity for the reaction components,but also has a lower reaction energy barrier among the four two-dimensional carbon-nitrogen materials.It is likely to be one of the potential new catalysts for the preparation of vinyl acetate by acetylene gas phase method.However,its weak physical adsorption may still be the main factor affecting the reaction,which needs to be solved through further research.The order of adsorption capacity of boron nitrogen materials with three different dimensions for reactants is:B₁₂N₁₂nanocage>BN nanosheet>BN nanotube.The order of the energy barrier of the reaction rate control step in the catalytic process is:B₁₂N₁₂nanocage<BN nanotube<BN nanotube.Compared with 2D BN nano-sheet and 1D BN nanotube,the 0D B₁₂N₁₂nanocage breaks the inherent reaction inertia of BN materials,and shows good adsorption and catalytic effect for acetylene acetylation reaction.It is likely to be an excellent catalyst for acetylene acetylation reaction.Based on the excellent adsorption performance of 0D nanocages,12 different elements were further selected to modify the 0-dimensional C₂₄N₂₄nanocage.The catalyst selection was performed by calculating the binding energy of different elements on C₂₄N₂₄,the adsorption energy of reaction components,and the size of reaction rate controlled step barrier.The order of adsorption performance of the four catalysts for reactants obtained through screening is:Al-C₂₄N₂₄>Ga-C₂₄N₂₄>Zn-C₂₄N₂₄>Cu-C₂₄N₂₄.The order of energy barrier of reaction rate control step in the catalytic process is:Cu-C₂₄N₂₄<Al-C₂₄N₂₄<Zn-C₂₄N₂₄<Ga-C₂₄N₂₄.Due to the high price of metal Ga and its lack of competitiveness compared to zinc acetate catalysts,Cu-C₂₄N₂₄,Al-C₂₄N₂₄,and Zn-C₂₄N₂₄may be ideal monoatomic metal catalysts for the acetic acid reaction of acetylene.