H₂ Activation and Spillover on Catalytically Relevant Pt–Cu Single Atom Alloys

Abstract

Platinum is a key component in many heterogeneous hydrogenation catalysts. Because of its high price, fairly strong interaction with intermediates, and susceptibility to CO poisoning, it is often mixed with other elements. These bimetallic alloys have complex surface structures, and the atomic structure of their active sites is not well understood. In this study, we examine the effect of the geometric arrangement of dilute Pt−Cu alloys on H 2 activation, spillover, and release. Using scanning tunneling microscopy, we directly visualize the atomic arrangement of Pt−Cu alloys and show that small amounts of Pt (∼1%) exists as isolated atoms in the Cu surface. These Pt monomers are capable of facile H 2 dissociation and spillover to Cu at temperatures as low as 85 K. Additionally, the low-temperature desorption of H 2 (230 K) suggests a reduced desorption barrier compared to monometallic Pt or Cu. We find these single atom alloy surfaces are robust to multiple adsorption/desorption and heating cycles to 450 K. Larger Pt ensembles in Cu exhibit higher temperature desorption profiles due to the stronger binding of H to extended Pt ensembles, demonstrating how the geometric arrangement of Pt atoms in Cu impacts the binding of H to catalytic surface sites. Overall, dilute Pt−Cu alloys containing only isolated Pt atoms are most favorable for H 2 activation, spillover, and release and hence should be capable of catalyzing hydrogenation reactions with a greatly reduced concentration of the precious metal.

Intermetallic Compounds as an Alternative to Single‐atom Alloy Catalysts: Geometric and Electronic Structures from Advanced X‐ray Spectroscopies and Computational Studies

“…Chemical bonding between the constituents in alloys alters the valence electronic states that are responsible for the catalytic behavior of the metals. Experimental and theoretical works have shown that the unique isolated geometries of metals in SAA's can lead to electronic perturbations, which can in turn lead to changes in adsorption enthalpies and reaction barriers . To determine the effect of atomic ordering on the valence states of Pt, in situ RIXS measurements and DFT calculations were performed.…”

“…Experimental and theoretical works have shown that the unique isolated geometries of metals in SAA's can lead to electronic perturbations, which can in turn lead to changes in adsorption enthalpies and reaction barriers. [12,27,[37][38][39] To determine the effect of atomic ordering on the valence states of Pt, in situ RIXS measurements and DFT calculations were performed. The 2-D RIXS planes show the incident photon energy (x-axis) and energy loss (y-axis) versus the intensity of emitted photons ( Figure 5).…”

The Chemical Properties of Hydrogen Atoms Adsorbed on M0‐Nanoparticles Suspended in Aqueous Solutions: The Case of Ag0‐NPs and Au0‐NPs Reduced by BD4−

“…Hydrogen atoms bound to metal surfaces are involved in avariety of important chemical processes.T his study focuses on M 0 -nanoparticles (M 0 -NPs). These processes include,f or example,e lectrochemical processes, [1][2][3][4][5][6][7] photochemical processes, [8][9][10] catalytic reduction processes [11] including reductions by BH 4 À , [12][13][14][15][16][17][18][19][20][21] hydrogen atom transfer processes, [22,23] water reduction by radicals, [24,25] hydrogen splitting reactions, [26,27] hydrogen spillover processes, [28][29][30][31][32][33][34][35] hydrogen storage, [36][37][38] etc.Ina queous media, the equilibrium reaction: is expected to occur, although k 2 is usually unknown. When M = Pt, k À2 is very fast, [39] whereas when M = Au, k À2 is very slow.…”

Single‐Atom Catalysts of Precious Metals for Electrochemical Reactions

“…As ingle-atom alloy (SAA) typicallyh as ab imetallic structure in which single-atom metalsa re dispersed on another single-crystalline metal surfaceo rn anoparticles. The characteristics of active single atoms in the alloys can be modulated by controlling the electronic, [26] geometric, [27] and ensemble structures. [28] Various single-atom alloy structures have been reported, such as Pd-Au, [28,29] Pd-Cu, [17j, 27, 30] Pd-Ag, [31] Pt-Cu, [26,32] Pt-Au, [33] and Au-Ni, [34] for selectived ehydrogenation or hydrogenation, Ullmann coupling reactions, CO oxidation, etc.…”

“…The characteristics of active single atoms in the alloys can be modulated by controlling the electronic, [26] geometric, [27] and ensemble structures. [28] Various single-atom alloy structures have been reported, such as Pd-Au, [28,29] Pd-Cu, [17j, 27, 30] Pd-Ag, [31] Pt-Cu, [26,32] Pt-Au, [33] and Au-Ni, [34] for selectived ehydrogenation or hydrogenation, Ullmann coupling reactions, CO oxidation, etc. Although many bimetallicn anoparticle catalysts have been used for electrochemicalr eactions, the importance of the single-atom alloy structure hasn ot been recognized in the electrocatalysis field.…”