Synergistic Computational-Experimental Discovery of Highly Selective PtCu Nanocluster Catalysts for Acetylene Semihydrogenation

Abstract

<p>Semihydrogenation of acetylene (SHA) in an ethylene-rich stream is an important process for polymer industries. Presently, Pd-based catalysts have demonstrated good acetylene conversion (X<sub>C2H2</sub>), however, at the expense of ethylene selectivity (S<sub>C2H4</sub>). In this study, we have employed a systematic approach using density functional theory (DFT) to identify the best catalyst in a Cu-Pt system. The DFT results showed that with a 55 atom system at ∼1.1 Pt/Cu ratio for Pt<sub>28</sub>Cu<sub>27</sub>/Al<sub>2</sub>O<sub>3</sub>, the d-band center shifted -2.2 eV relative to the Fermi level leading to electron-saturated Pt, which allows only adsorption of ethylene via a π-bond, resulting in theoretical 99.7% S<sub>C2H4</sub> at nearly complete X<sub>C2H2</sub>. Based on the DFT results, Pt-Cu/Al<sub>2</sub>O<sub>3</sub> (PtCu) and Pt/Al<sub>2</sub>O<sub>3</sub> (Pt) nanocatalysts were synthesized via cluster beam deposition (CBD), and their properties and activities were correlated with the computational predictions. For bimetallic PtCu, the electron microscopy results show the formation of alloys. The bimetallic PtCu catalyst closely mimics the DFT predictions in terms of both electronic structure, as confirmed by X-ray photoelectron spectroscopy, and catalytic activity. The alloying of Pt with Cu was responsible for the high C<sub>2</sub>H<sub>4</sub> specific yield resulting from electron transfer between Cu and Pt, thus making PtCu a promising catalyst for SHA.</p>