Theoretical Calculation Of Selective Oxidation Of Ethane On Isolated Molybdena Catalysts

In recent years,oil resources are increasingly scarce,and oil prices continue to rise.At the same time,low carbon alkanes in shale gas and natural gas are abundant,and their effective utilization rate needs to be improved.The selective oxidation of ethane in petrochemical industry is of great practical and potential economic benefits,and is a challenging task in catalytic research of carbon based energy.The key and difficult point of selective oxidation of ethane is to improve the activity of ethane and to keep the molecular stability of oxidation products to be selected.At present,highly dispersed and isolated active site catalysts can control the deep oxidation of products by providing proper amount of catalyst surface reactive oxygen,thus improving the selectivity of selective oxidation.In addition,this kind of catalyst is the most effective model compound to study the reaction mechanism of selective oxidation of hydrocarbons.The active mesoporous molecular sieve provides a good platform for the design of the catalyst.The framework of mesoporous molecular sieve is generally composed of Si and O.It is inert to most of the reactions,but its pore structure is clear.It can be used to introduce active sites with controllable structure and clear structure.First principles calculations study the reaction mechanism of C-H bond catalytic conversion.Generally speaking,oligomeric silica ring is used as a carrier as an alternative to amorphous silica model carrier.However,the mechanism of selective oxidation of ethane with high dispersion and isolated Mo based catalysts is rarely reported.Many problems in the process of reaction need to be solved urgently.For example,which structure of the isolated Mo based catalyst makes a better catalytic performance?What is the specific reactive potential?In this paper,the first principles calculation method of density functional theory is applied to study the reaction process and mechanism of selective oxidation of ethane on isolated Mo based catalysts,which lays a theoretical foundation for the design and development of efficient selective oxidation catalysts for low carbon alkanes.An isolated Mo based catalyst supported by a silicon oxygen ring is used as a catalyst to catalyze the reaction of ethane.This paper focuses on the reaction mechanism of selective oxidation of ethane on isolated Mo based catalysts.First,two silica based supported Mo based catalyst models were established,namely,a di-oxo based Mo cluster model containing one molybdenum oxygen double bond（mono-oxo）and two molybdenum oxygen double bonds.This is followed by the activation of different reactive sites of ethane first C-H bond,focuses on three kinds of reactive oxygen and Mo-O-Si Mo=O:end of the bridge oxygen and gaseous adsorption of molecular oxygen,the calculation results show that in the gaseous oxygen adsorption on the activation mechanism of the first C-H is inserted into the oxygen adsorption the formation of C-H bond and weak interactions of ethanol catalyst intermediates;mechanism of activation of the first C-H bond in the bridge and terminal oxygen on the catalyst surface is formed to H atoms ethane activity in the O Mo（OH）（OC₂H₅）intermediates.By comparing the energy barrier of the activated C-H bond,the gaseous oxygen adsorbed oxygen more easily to activate the C-H bond than the end oxygen and the bridge oxygen.Finally,the reaction path of ethylene and acetaldehyde by selective oxidation of ethane to ethylene and acetaldehyde was studied with the gaseous adsorption of oxygen sites as the reaction site.The results show that the isolated Mo based catalysts containing two molybdenum oxygen double bonds are more conducive to the selective oxidation of ethane.The reaction rate constant of the first C-H bond activation is three orders of magnitude higher than that of an isolated Mo based catalyst with a double bond of molybdenum and oxygen.In addition,the reaction process of selective oxidation of ethane catalyzed by Mo₃O₉ was also calculated.The results show that the isolated Mo based catalyst supported by the silicon oxygen ring is easier to make the reaction.