Effect Of Microwave Field On The Properties Of Modified Alumina

γ-Al₂O₃ is often used as a support for hydrodesulfurization catalysts due to its excellent properties.During the catalytic reaction,the strong surface acidity ofγ-Al₂O₃causes the strong interaction between the active phase and the carrier.When changes the way the active phase exists on the surface of the carrier,can affect the reactivity of the catalyst.Molecular simulation methods can observe the structure of the active sites adsorbed on the alumina surface more clearly and intuitively.Therefore,using density functional theory（DFT）,taking theγ-Al₂O₃（110）crystal plane as the research object,the surface of alumina was modified with boron and phosphorus respectively,so as to achieve the purpose of moderately reducing the surface adsorption energy.The effect of microwave electric field conditions on surface adsorption performance was investigated as well in detail..Results indicate that Lewis acid centers exists on theγ-Al₂O₃（110）crystal plane,which are coordination unsaturated aluminum atoms,and three kinds of structures:two-coordination,four-coordination and five-coordination are found within the structure.Both boron and phosphorus are successfully substituted into the aluminum atomic sites of three different coordination structures on the alumina surface,and boron element is found to be easier to substitute on the alumina surface than phosphorus element.Through the calculation of surface adsorption energy,it is found that the boron-modified surface can effectively and moderately reduce the adsorption capacity of the alumina surface,while the surface modified by phosphorus can enhance the adsorption capacity at the adsorption site of the four-coordinate structure,in addition,the adsorption capacity of the other two sites was significantly weakened.Therefore,the boron modification scheme is effective than the phosphorus scheme.Through the comparison of Mulliken charge and adsorption energy,it is found that the amount of charge transferred during adsorption has no positive correlation with the adsorption capacity of the adsorption site,and the adsorption capacity is related to the number of positive charges at the adsorption site.Hydroxyl groups are easily adsorbed on the alumina surface,and the boron-modified surface can effectively weaken the adsorption of hydroxyl groups on the surface,while the phosphorus-modified surface deepens the degree of hydroxylation on the alumina surface,which is not conductive to surface adsorption.In the presence of hydroxyl groups on the surface,steric hindrance is the main factor affecting the surface adsorption,and the number of charges at the adsorption site has less effect.The boron-modified surface still shows a good weakening ability to the surface acidity.The alumina model is very sensitive to the vertical electric field,and a very small field strength will cause obvious deformation of the surface.Under the action of the horizontal electric field in the negative X direction of the maximum field strength of0.02 a.u.and the positive direction of Y the maximum field strength of 0.015 a.u.,with the increase of the field strength,the site adsorption capacity of the four-coordinate structure on the original surface gradually decreases,making the adsorption capacity of the sites over five-coordinate structure and two-coordinate structure gradually increases.However,for the boron-modified surface,the addition of the electric field in both directions can reduce the adsorption capacity of all sites,and there are regular changes.The adsorption performance of alumina surface further decreases with the increase of the field strength.