Exploring the Stability of Single-Atom Catalysts Using the Density Functional Theory-Based Global Optimization Method: H2 Formation on VOx/γ-Al2O3(100)

Abstract

Single-atom catalysis is indisputably one of the most trending topics in heterogeneous catalysis with distinctive performances in many important chemical reactions. However, surface reconstruction during loading of single-atom targets and its impact on vital reaction steps have rarely been studied. Herein, taking H2 formation, a key step of alkane dehydrogenation, as an example, with genetic algorithm structure search, we reveal the structure–reactivity relationship in the H2 formation on VOx/γ-Al2O3(100). We explore a large number of VOx/γ-Al2O3(100) (x = 0, 1, 2, 3) structures and discover a few reconstructed structures with low formation energies. Since the pristine γ-Al2O3(100) support is highly stable, the production of such structures was completely induced by VOx loading. One VO3/γ-Al2O3(100) structure generates a stable VO4 motif by reconstructing the support surface. Its distinct local chemical environment of vanadium can not only resist the oxygen removal under reductive conditions but can also offer a low-barrier surface reaction channel to H2 formation. Moreover, the hydrogen atom prefers to diffuse into the vanadium site and then couple with another hydrogen instead of direct coupling if the initial state involves two hydrogen atoms both on oxygen sites. Therefore, the H2 formation prefers a surface process that occurs on the vanadium–oxygen pair.