Theoretical Study Of Ordered Platinum/Palladium-based Alloys Catalyzing Hydrocarbon Small Molecule Reactions

In catalysis research,the ordered intermetallic compounds have several unique properties:electronic effect,geometric effect,steric effect,and ordering effect,which have important guiding significance for the design of directed catalysts.In order to study the effects of alloy geometry and electronic structure on catalytic activity and selectivity,first-principles calculations were used to systematically study the selective hydrogenation of acetylene on the surface of Pd-based alloys and dehydrogenation of formic acid on the ordered Pt-based alloys.First,the selective hydrogenation of acetylenes on ordered Cu-Pd intermetallic compounds（L1₀Cu Pd,L1₂Cu₃Pd,and L1₂Cu Pd₃）and Pd-modified Cu（111）surfaces was investigated.The results show that the activity and selectivity of Cu-Pd alloy catalysts are closely related to the crystal structure and surface composition of Cu-Pd intermetallic compounds and the size of Pd ensemble on the surface of Cu-based alloys.L1₂Cu₃Pd with isolated Pd atom on the surface is an efficient catalyst for the selective hydrogenation of acetylene reaction.On the Pd-modified Cu（111）surface,the catalytic activity of Pd dimers and trimers for C₂H₂+H→C₂H₃ and C₂H₃+H→C₂H₄ reactions is higher than that of single Pd atoms.However,the isolated Pd atoms on Cu（111）exhibit lower H₂ dissociation activity compared to the ordered Cu-Pd intermetallics.Secondly,the dehydrogenation of formic acid on L1₁-type Pt-based intermetallic compounds（X-Pt,X=Ag,Cu,Au,Pd,Ir,Rh,Tc,W,V）was studied.The results show that on L1₁-type Pt-based intermetallic compounds,the adsorption energies between carbon monoxide（CO）and carboxyl（COOH）and hydrogen atoms exhibit a linear scaling relationship with positive slope,but carbon monoxide（CO）is related to formate（HCOO）and hydroxyl groups（OH）.The adsorption energies between HCOO and OH showed a weak correlation with negative slope,so the unconventional d-band center model was used to describe the adsorption energies of HCOO and OH.Therefore,the selection of HCOOH dehydrogenation to HCOO（vs COOH）and COOH decomposition to CO₂（vs CO）on Pt-based ordered alloys can be adjusted by breaking the linear scaling relationship of the adsorption energies of HCOOH dehydrogenation intermediates.Finally,in order to further study the effect of linear scaling relationship on the selectivity of alloy catalysts,the complete reaction paths of HCOOH dehydrogenation on L1₁Cu Pt（0001）and L1₁WPt（0001）planes were calculated,It is found that the L1₁-type Cu Pt has high catalytic activity and selectivity,and the electronic effect plays an important role in regulating the catalytic activity and selectivity of the Pt atomic layer.The calculation results show that HCOOH has high selectivity when dissociated on the L1₁Cu Pt（0001）surface through the pathway of HCOOH→COOH+H→CO₂+2H to generate CO₂.HCOOH is also an excellent choice for electro-oxidation on this surface,which is consistent with the results of the linear scaling relationship between the adsorption energies of the intermediates described above.Therefore,the activity and selectivity of alloy catalysts can be regulated by changing the electronic structure of the alloy surfaces.The calculated results in this paper provide a crystal phase and composition control strategy for improving the catalytic activity and selectivity of Cu-Pd catalysts for the selective hydrogenation of acetylene and the dehydrogenation of formic acid on Pt-based alloys.Geometric and electronic structures can be used to tune catalytic activity and selectivity.And breaking the linear scaling relationship of adsorption energy between important intermediates in the formic acid dehydrogenation reaction can adjust the catalytic selectivity of the alloy,and suppressing the reaction path of carbon monoxide generation.This conclusion provides an effective strategy for designing bimetallic catalysts with tunable activity and selectivity for formic acid dehydrogenation.