The simplest olefin, i.e. ethylene (C₂H₄), is an hydrocarbon utilized in polymerization reactions to produce commodities. In the petrochemical industry, C₂H₄ streams usually contain small amounts of acetylene (C₂H₂), which deactivate the catalysts used for C₂H₄ hydrogenation, limiting the applications in polymerization processes. An elegant strategy is to convert C₂H₂ selectively to C₂H₄, avoiding further C₂H₄ hydrogenation and enriching ethylene streams. Though Pd-based systems are utilized, these materials are expensive, limiting their use in the long term. Tungsten carbide (WC) is a cheap and easy available material which has a Pt-like catalytic behavior, particularly when used as support of a Pt monolater, i.e. Pt/WC, for H₂ dissociation reactions. Clean α-WC(0001)-C and α-WC(0001)-W were compared with Pt-supported 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 C₂H₂ selective hydrogenation, with a reaction energy of -0.44 eV. Moreover, surface poisoning is avoided on Pt/α-WC(0001)-W since ethylidyne species (CCH₃) are not formed over the surface, a behavior not seen on the other systems or even on Pt and Pd clean surfaces. The electronic analysis indicate that the Pt monolayer modulates the chemistry of the WC system. The calculated desorption rate of C₂H₄ from the Pt/α-WC(0001)-W system is reasonable in the temperature range 340 to 640 K, providing a theoretical basis for futher practical catalysis. The results of this work show that Pt/α-WC(0001)-W is a good candidate for acetylene selective hydrogenation, opening the doors for further experimental and/or theoretical works.

Carlos Jimenez-Orozco

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