The Oretical Study On Selective Catalytic Hydrogenation Of Crotonaldehyde Over In,Ir Modified Au(111) Surface

As a kind of important chemical raw material,α,β-unsaturated alcohol is widely used in medicine,pesticide and other industries.The selectively hydrogenation ofα,β-unsaturated aldehyde to the corresponding α,β-unsaturated alcohol attracted people,s widespread attention with its environmentally friendly and product easier purification.Among them,crotonaldehyde is a typical representative of the α,β-unsaturated aldehyde.Au,In-Au and Ir-Au are excellent hydrogenation catalyst.They are used in the selective hydrogenation of crotonaldehyde.In this paper,the adsorption and selective hydrogenation mechanism of crotonaldehyde on Au(111),In-Au(111)and Ir-Au(111)were investigated by Dmol3 program based on density functional theory.The main studies are as follows:(1)We investigate the adsorption and hydrogenation mechanism of E-(s)-transcrotonaldehyde on Au(111)surface.The results show that the adsorption at the Top site was most stable when the crotonaldehyde on the Au(111)surface with C=O.And the crotonaldehyde losed 0.045 electrons after adsorption on the Au(111)surface.In addition,comparing the reaction energy,activation energy and structure change of each elementary steps,we obtained that the crotonaldehyde was more likely to follow the2,1-addition mechanism to produce crotyl alcohol,and the lower temperature was helpful for the reaction to improve the conversion rate.(2)The stability of In-Au(111)and Ir-Au(111)plane model with three different configurations was compared.And the effect of In or Ir doped Au(111)for adsorption of crotonaldehyde was studied.The calculation show that the stability of In-Au(111)surface was increased as the increase of In atomic spacing;on the contrary,Ir-Au(111)surface was decreased.The adsorption at the TopIn,Ir site were most stable when the crotonaldehyde on the In,Ir-Au(111)surfaces with C=O.Comparison of In-Au(111)surface and Ir-Au(111)surface,we found that Ir-Au(111)surface not only had higher stability and activity,but also had stronger adsorption for crotonaldehyde.Compared with Au(111)surface,the stability and adsorption capacity of In,Ir-Au(111)surfaces were improved obviously with modified by In and Ir atom.(3)The effect of In or Ir doped Au(111)for selective hydrogenation of crotonaldehyde was studied.The calculations show that the crotonaldehyde was morelikely to follow the 2,1-addition mechanism to produce crotyl alcohol on In,Ir-Au(111)surfaces.In addition,the C hydrogenation is the rate-determining step,for which the highest activation energy barrier is required.The activation energy required for further hydrogenation of crotonol on In,Ir-Au(111)are much higher than that on Au(111).The introduction of In and Ir reduced the further conversion of crotonalanol,effectively improving the selectivity and yield of crotonaldehyde.And Ir exhibited better catalytic activity.