The Regulation Of Pd_xIn,Pd_xCu(x=1,3)and Pd Modified Cu Based Catalysts On The Dissociation Reaction Activity And Selectivity Of Formic Acid

H₂ is the most clean and efficient energy carrier,which is widely used as the energy sources,and the products are water with non-pollution for the environment.However,searching for efficient and safe hydrogen storage materials is one of the biggest challenges for large-scale utilization of hydrogen.Formic acid has been attracted extensive attention due to its stable properties,high hydrogen storage energy density and non-toxic properties.As a high active hydrogen storage medium,the preparation of high purity hydrogen by catalytic decomposition of formic acid is one of the potential technologies to solve the problem of hydrogen storage and transportation in hydrogen and oxygen fuel cells.In recent years,the progress in the catalytic decomposition of polyphase catalysts by formic acid has been developed rapidly.The catalysts with high catalytic activity and selectivity have been obtained,but the problems of short service life,high cost and intolerance of high concentration formic acid still exist.Therefore,the development of new catalysts with high efficiency and stability is the key for the development and practical application of formic acid.In this paper,aiming at improving the selectivity of formic acid decomposition and inhibit the production of CO,the effects of the single atom effect of Pd sites,the metal doping ratio in the bulk alloy,the metal doping ratio in the surface alloy with different Pd ratio on the selectivity of formic acid decomposition are investigated using density functional theory calculations.By studying the decomposition of formic acid on Pd_xIn,Pd_xCu?x=1,3?intermetallic compound and Pd-doped Cu-based catalysts,the type of catalysts for inhibiting CO formation in formic acid decomposition were obtained,the results provided the valuable theoretical guidance for the development of excellent catalysts for resistance toward CO poisoning.The conclusions are presented as follows:1.PdIn catalyst with the single atom Pd active site had high selectivity for the direct dissociation of formic acid,the yield of formic acid dissociation was increased,and the formation of CO was inhibited;moreover,CO is weakly adsorbed on PdIn catalysts,which inhibited the production and accumulation of CO,therefore,PdIn catalysts had good resistance toward CO poisoning.The analysis of electronic structure for PdIn?110?surface with the single atom Pd showed that the In atom of Pd In?110?completely surrounded and separated by Pd atoms,and limited the activity of a single Pd atom within a certain range to form a mono-atomic Pd active site,which can be used to dissociate formic acid and make PdIn?110?exhibit the best resistance toward CO poisoning;Pd₃In catalyst cannot suppress the production and accumulation of CO,and had poor resistance toward CO poisoning.2.For Pd_xCu?x=1,3?bulk alloy catalysts,the selectivity of formic acid direct dissociation on Pd₃Cu?111?was the best when the ratio of Pd:Cu was 3:1,and the yield of hydrogen production by formic acid dissociation was the highest.DFT calculations showed that the Pd trimer on Pd₃Cu?111?surface was the reaction region for formic acid dissociation,and the surrounding Cu atoms acted as electron donors to modify the Pd trimer.The synergistic effect between Pd and Cu improved the selectivity of formic acid direct dissociation and inhibited the production and accumulation of CO.When the ratio of Pd:Cu was1:1,there was a competitive relationship between the direct dissociation path of formic acid and CO formation path,which would not inhibit the production of CO,the ability of resistance toward CO poisoning was poor and the yield of formic acid dissociation to CO₂ and H₂ was low.3.When the ratios of surface alloys Pd:Cu were 1:8 and 3:6,the path of formic acid was through CO,the yield of hydrogen produced by formic acid dissociation was low;when the ratios of surface alloys Pd:Cu were 6:3 and 9:0,formic acid goes through direct dissociation,and the production of CO was inhibited,moreover,the yield of hydrogen produced by formic acid dissociation was high.Above results showed that the difference of Pd and Cu atoms ratio in the surface alloy on Pd-modified Cu-based catalysts leads to the different arrangement of Pd atoms,which results in the different selectivity of formic acid direct dissociation.On the Pd₁Cu₈ and Pd₃Cu₆ surfaces,the surface Pd atoms were not connected with each other;on the Pd₆Cu₃ and Pd₉Cu₀ surfaces,the surface Pd atoms were connected with each other,the formation of polymer Pd made the selectivity of formic acid direct dissociation high.