title: Adsorption of small hydrocarbons on the three-fold PdGa surfaces: the road to selective hydrogenation.
abstract: Intermetallic compounds are a promising class of materials as stable and selective heterogeneous catalysts. Here, the (111) and (-1-1-1) single crystal surfaces of the PdGa intermetallic compound were studied as model catalysts with regard to the selective hydrogenation of acetylene (C2H2) to ethylene (C2H4). The distinct atomic surface structures exhibit isolated active centers of single atomic and three atomic Pd ensembles, respectively. For the two prototypal model catalyst surfaces, the adsorption sites and configurations for hydrogen (H2), acetylene, and ethylene were investigated by combining scanning tunneling microscopy, temperature-programmed desorption, and ab initio modeling. The topmost Pd surface atoms provide the preferred adsorption sites for all studied molecules. The structural difference of the Pd ensembles has a significant influence on the adsorption energy and configuration of C2H2, while the influence of the ensemble structure is weak for C2H4 and H2 adsorption. To approach the question of catalytic performance, we simulated the reaction pathways for the heterogeneous catalytic hydrogenation of acetylene on the two surfaces by means of density functional theory. Due to the geometrical separation of the Pd sites on the surfaces, the steric approach of the reactants (H and C2Hx) was found to be of importance to the energetics of the reaction. The presented study gives a direct comparison of binding properties of catalytic Pd on-top sites vs three-fold Pd hollow sites and is therefore of major relevance to the knowledge-based design of highly selective hydrogenation catalysts.
authors: Nanotech@surfaces Laboratory and †Nanoscale Materials Science, Empa. Swiss Federal Laboratories for Materials Science and Technology , Ueberlandstrasse 129, 8600 Dübendorf, Switzerland.
authors: Jan
authors: J
authors: Prinz
authors: Carlo A
authors: CA
authors: Pignedoli
authors: Quirin S
authors: QS
authors: Stöckl
authors: Marc
authors: M
authors: Armbrüster
authors: Harald
authors: H
authors: Brune
authors: Oliver
authors: O
authors: Gröning
authors: Roland
authors: R
authors: Widmer
authors: Daniele
authors: D
authors: Passerone
mesh_terms: D000114:Acetylene / Q000737:chemistry*; D000327:Adsorption; D000497:Alloys / Q000737:chemistry*; D002384:Catalysis; D005030:Ethylenes / Q000138:chemical synthesis* / Q000737:chemistry; D005708:Gallium / Q000737:chemistry; D006865:Hydrogenation; D010165:Palladium / Q000737:chemistry; D010316:Particle Size; D011789:Quantum Theory; D013499:Surface Properties
chemical_list: D000497:Alloys; D005030:Ethylenes; D010165:Palladium; C036216:ethylene; D005708:Gallium; D000114:Acetylene