Selective hydrogenation of acetylene to ethylene: Performance of a Pt monolayer over an α-WC(0001) surface for binding and hydroconversion of acetylene

Ethylene (C₂H₄) is a useful hydrocarbon in polymerization reactions and as a probe system to understand hydrogenation reactions of complex unsaturated hydrocarbons and olefins. However, C₂H₄ streams usually contain small amounts of acetylene (C₂H₂), which deactivates the catalyst used for ethylene hydroconversions. This issue is overcome by hydrogenating C₂H₂ selectively into C₂H₄, avoiding further ethylene hydrogenation reactions. For this process, expensive palladium-based catalysts have shown good performance. Here, based on the results of density functional calculations, we propose the use of cheap and easily available tungsten carbide (WC) as a support of Pt, being an alternative material to Pt-group metals. Clean α-WC(0001)-C and α-WC(0001)-W were compared with Pt-supported on them, i.e. Pt/α-WC(0001)-C and Pt/α-WC(0001)-W. The theoretical results indicate that among the evaluated systems, the Pt/α-WC(0001)-W surface has a remarkable capacity to achieve selective hydrogenation of C₂H₂ into C₂H₄, with a reaction energy of -0.44 eV, avoiding further hydrogenation into ethyl (C₂H₅, +0.29 eV) and ethane (C₂H₆, +0.33 eV). In Pt/α-WC(0001)-W, the surface poisoning is avoided since ethylidyne (CCH₃), a species responsible of catalyst deactivation is not formed. In contrast, the selective acetylene hydrogenation is not feasible on Pt/α-WC(0001)-C, α-WC(0001)-C, and α-WC(0001)-W; these surfaces are all poisoned due to the formation and deposition of CCH₃ and C₂H₂ on them. The atomic charges indicate that the electron density flux from the Pt/α-WC(0001)-W surface to the C₂H₂ and C₂H₄ molecules is higher as compared to bare α-WC(0001)-W, since the Pt monolayer modulates electron density migration, as verified by a Projected Density of States (PDOS) analysis. The C₂H₄ desorption rate from Pt/α-WC(0001)-W is reasonable in the temperature range from 340 to 640 K, providing a theoretical basis for further practical catalysis. The results of this work show that Pt/α-WC(0001)-W is a good candidate for acetylene selective hydrogenation, opening a new window for further experimental and/or theoretical works.