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

• Pt/WC-W is a good candidate for acetylene selective hydrogenation • The surface poisoning is avoided on Pt/WC-W, but the other systems are poisoned • C 2 H 4 desorption rate from Pt/WC-W is reasonable in the temperature range 340 – 640 K • Pt/WC and Pt share similarities to adsorb C 2 H 2 , C 2 H 4 , C 2 H 5 , and CCH 3 • Ethane binding is the weakest among all the evaluated systems. Ethylene (C 2 H 4) is a useful hydrocarbon in polymerization reactions and as a probe system to understand hydrogenation reactions of complex unsaturated hydrocarbons and olefins. However, C 2 H 4 streams usually contain small amounts of acetylene (C 2 H 2), which deactivates the catalyst used for ethylene hydroconversions. This issue is overcome by hydrogenating C 2 H 2 selectively into C 2 H 4 , 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 C 2 H 2 into C 2 H 4 , with a reaction energy of -0.44 eV, avoiding further hydrogenation into ethyl (C 2 H 5 , +0.29 eV) and ethane (C 2 H 6 , +0.33 eV). In Pt/α-WC(0001)-W, the surface poisoning is avoided since ethylidyne (CCH 3), 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 CCH 3 and C 2 H 2 on them. The atomic charges indicate that the electron density flux from the Pt/α-WC(0001)-W surface to the C 2 H 2 and C 2 H 4 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 C 2 H 4 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. [Display omitted] [ABSTRACT FROM AUTHOR]