Catalytic Performance Regulation Of Noble Metal And Noble Metal-Like Catalysts For C₂H₂ Semi-Hydrogenation

The trace C₂H₂ in C₂H₄ not only reduces the properties of C₂H₄ polymers but also cause irreversible deactivation of C₂H₄ polymerization catalysts.Therefore,it is necessary to efficiently remove trace C₂H₂ in C₂H₄ feedstock.C₂H₂ semi-hydrogenation is an efficient method to remove C₂H₂;Intermetallic compounds and noble metal-like catalysts,such as metal phosphide（M_xP_y）,have attracted extensive attention in C₂H₂ semi-hydrogenation due to their unique atomic arrangement and electronic properties.In this paper,C₂H₂ semi-hydrogenation has been systematic studied over a series of PtM intermetallic compounds and M_xP_y catalysts using density functional theory calculations.Meanwhile,the microscopic essence of the influence of catalyst composition,composition ratio and surface structure on catalytic performance has been clarified at the electron-molecular level.Furthermore,the target structure of different types of catalysts with the excellent catalytic performance has been given out.The research results can provide theoretical guidance for designing efficient catalysts in C₂H₂ semi-hydrogenation.The main conclusions obtained are as follows:（1）C₂H₂ semi-hydrogenation over the four kinds of surface structures catalysts existing during prepare PtM IMCs,including Pt_xM_y IMCs（x:y=1:1,1:3,3:1）,shell@core Pt_{n L}@Pt_xM_y and Pt_{n L}@M（n=1-3）,as well as the subsurface structure Pt_1L-M,have been investigated to illustrate the influence of surface structure and composition modulation on catalytic performance in C₂H₂ semi-hydrogenation.a)Surface structure and composition affect catalytic performance in C₂H₂semi-hydrogenation.Among Pt Au,Pt Ag and PtCu catalysts with four kinds of different surface structures,the analysis of electronic properties indicated that the d-band center of surface Pt atoms shows a volcano-type relationship with catalytic activity,the d-band center located in a moderate range,the catalyst would achieve a higher catalytic activity.Furthermore,PtCu₃ IMC with the isolate Pt atoms as the active site not only exhibits better C₂H₄ selectivity and formation activity,but also can effectively inhibit green oil formation.b)The adsorption energy of C₂H₂ can be used as a good descriptor to efficiently evaluate catalytic activity for PtM catalysts.C₂H₂ adsorption energy shows a good linear relationship with catalytic activity over the PtM catalysts.The Pt_1L-Cu and PtCu₃ IMC exhibit excellent C₂H₄ formation activity due to their weaker C₂H₂ adsorption ability;However,the Pt Au,Pt₃Au,Pt Ag,Pt₃Ag IMCs,the shell@core Pt_1L@Pt Au₃,Pt_1L@Pt Au,Pt_2L@Pt Au,Pt_1L@Au,Pt_1L@Pt Ag₃,Pt_1L@Ag,Pt_2L@Ag,Pt_3L@Ag,and subsurface Pt_1L-Ag present lower activity due to their stronger C₂H₂ adsorption ability.c)PtCu₃ IMC could substitute industrial Pd Ag/Al₂O₃ catalyst.Among a series of PtM catalysts,PtCu₃ IMC was screened out due to the Pt atoms are fully efficiently utilized,and the introduction of Cu reduces economic costs;Meanwhile,the catalyst not only exhibits high C₂H₄ selectivity and better activity,but also can reduce green oil formation to keep better stability in C₂H₂ semi-hydrogenation,therefore,its economic cost and catalytic performance are superior to the current industrial Pd Ag/Al₂O₃ catalysts.2)C₂H₂ semi-hydrogenation over a series of M_xP_y（M=Mo,W,Fe,Co,Ni and Pd）with different crystal facet,exposed termination,M type and M:P ratio is fully examined to illustrate the influence of surface structure and composition modulation on catalytic performance in C₂H₂ semi-hydrogenation.a)Surface structure and composition affect catalytic performance in C₂H₂semi-hydrogenation.Among these M_xP_y catalysts,electronic properties analysis indicated that the charge transfer number between the M and P atoms within a smaller value,the catalyst can simultaneously achieve high C₂H₄ selectivity and activity.Furthermore,FeP（101）-I,whose metal site is completely dispersed by P atoms,not only exhibits better C₂H₄ selectivity and Pd-like activity,but also can effectively inhibit green oil formation to maintain better stability.b)C₂H₂ adsorption energy can be used as a good descriptor to efficiently evaluate catalytic activity for M_xP_y catalysts.C₂H₂ adsorption energy shows a volcano-type relationship with catalytic activity.The Mo P（110）,Mo P（101）,WP（101）-I and WP（101）-II with stronger C₂H₂adsorption ability resulted in lower C₂H₄ activity;Both Ni₁₂P₅（001）and Pd₃P（010）with weaker C₂H₂adsorption ability exhibit lower C₂H₄ activity.However,FeP（101）-I and Ni₂P（002）exhibit excellent activity due to moderate C₂H₂ adsorption ability.c)The essence of FeP（101）-I exhibits Pd-like activity attributes to three reasons:Firstly,FeP presents metallic properties.Secondly,compared to the metallic Fe,the presence of P atoms in FeP results in the d-orbital density of state of Fe in FeP nearly resemble Pd rather than that of Fe near Fermi level;Thirdly,the d-band center of FeP（101）-I is very close to Pd（111）.d)FeP（101）-I exhibits the best catalytic performance.Among a series of M_xP_y catalysts,FeP（101）-I exhibits better C₂H₄ selectivity,Pd-like activity and excellent stability in C₂H₂ semi-hydrogenation,its catalytic performance is superior to the current industrial Pd Ag/Al₂O₃ catalyst.e)The PtCu₃ IMC and FeP（101）-I are obtained attribute to their catalytic performance are better than that of the industrial Pd Ag/Al₂O₃ catalyst.PtCu₃ IMC with higher utilization of noble metal Pt atoms exhibits superior C₂H₄ selectivity but inferior activity under lower temperature;However,the low-cost noble metal-like FeP（101）-I exhibits superior activity but inferior C₂H₄ selectivity under higher temperature.