Theoretical Study On Synthesis Of Syngas And Acetic Acid From Methane And Carbon Dioxide Over Ni And Pd Catalysts

There has been an increase in energy consumption,mainly due to continuous development in society.Natural gas is one of the three main fossil fuels,and the reserves of nature gas are more than of coal and oil.Under the dual pressure of oil shortage and huge energy consumption,the rational and effective use of natural gas can alleviate China's energy crisis to some extent.Carbon dioxideis the main cause of global warming.Therefore,emission reduction and chemical utilization ofcarbon dioxide are very important.Conversion of methane and carbon dioxide to high value-added syngas or other chemical products not only achieve comprehensive utilization of methane and carbon dioxide,but also has great significance for environmental protection,energy conservation,and emission reduction.In this paper,density functional theory?DFT?method was used to explore the reaction mechanism about dry reforming of methane on Ni₄/?-MoC?111?and acetic acid synthesis from methane and carbon dioxide on Pd?111?surface.The main results are as follows:1.On Ni₄/?-MoC?111?,the optimal route for syngas from dry reforming of methane is that CH₄ continuous cracks to form CH and CO₂ directly decomposes to CO and O,then CH is oxidized by O atom to form CHO,finally,CO and H are formation from CHO dehydrogenation.The detail pathway is as follow:CH₄+CO₂?CH₃+H+CO₂?CH₂+2H+CO₂?CH+3H+CO₂?CH+3H+CO+O?CHO+3H+CO?2CO+4H?2CO+2H₂,the rate-determining step is formation of CHO from CH oxygenation.2.On Ni₄/?-MoC?111?,there are three possible pathways for carbon elimination,the first is that C is oxidized by O atoms to form CO;the second is that C reacts with OH to produce COH intermediate;and the third is reverse Bouduard reaction?C+CO₂?2CO?.According to the DFT results,the oxidation of C by O atoms to CO is the best way to eliminate carbon.3.On Pd?111?surface,the optimal route for synthesis of acetic acid from methane and carbon dioxide is that continous cleavage of CH₄ to C,and CO₂ is directly inserted into C to form CCOO intermediate,CCOO is hydrogenated to form CCOOH,subsequently,CCOOH is further hydrogenated to produce acetic acid.The detail pathway is as follow:CH₄+CO₂?CH₃+H+CO₂?CH₂+2H+CO₂?CH+3H+CO₂?C+4H+CO₂?CCOO+4H?CCOOH+3H?CHCOOH+2H?CH₂COOH+H?CH₃COOH,the rate-determining step is formation of C from CH cracking.