Oxidative Addition of Methane and Reductive Elimination of Ethane and Hydrogen on Surfaces: From Pure Metals to Single Atom Alloys

Abstract

Oxidative addition of CH4 to the catalyst surface produces CH3 and H. If the CH3 species generated on the surface couple with each other, reductive elimination of C2H6 may be achieved. Similarly, H’s could couple to form H2. This is the outline of nonoxidative coupling of methane (NOCM). It is difficult to achieve this reaction on a typical Pt catalyst surface. This is because methane is overoxidized and coking occurs. In this study, the authors approach this problem from a molecular aspect, relying on organometallic or complex chemistry concepts. Diagrams obtained by extending the concepts of the Walsh diagram to surface reactions are used extensively. C–H bond activation, i.e., oxidative addition, and C–C and H–H bond formation, i.e., reductive elimination, on metal catalyst surfaces are thoroughly discussed from the point of view of orbital theory. The density functional theory method for structural optimization and accurate energy calculations and the extended Hückel method for detailed analysis of crystal orbital changes and interactions play complementary roles. Limitations of monometallic catalysts are noted. Therefore, a rational design of single atom alloy (SAA) catalysts is attempted. As a result, the effectiveness of the Pt1/Au­(111) SAA catalyst for NOCM is theoretically proposed. On such an SAA surface, one would expect to find a single Pt monatomic site in a sea of inert Au atoms. This is desirable for both inhibiting overoxidation and promoting reductive elimination.

Exploring Metal Nanocluster Catalysts for Ammonia Synthesis Using Informatics Methods: A Concerted Effort of Bayesian Optimization, Swarm Intelligence, and First-Principles Computation

“…The distance between the nanocluster and the periodic images in the vicinity was set longer than 15 Å. The need for a distance greater than 15 Å is based on the literature. − The results of the literature survey, − which shows that a vacuum layer thicker than 15 Å is generally introduced when building a slab model, also support the validity of setting this distance. We refer to previous studies for the calculation of clusters using such a method. − ,− In the VASP calculation, the Perdew–Burke–Ernzerhof (PBE) functional, a generalized gradient approximation (GGA), was used.…”

Concepts of Computational Approach to Explore Heterogeneous Catalysts for Direct Methane Conversion

“…The concept we have elaborated should not yet be abandoned. In some cases, a good catalyst can be designed through logic, [46] whereas in some cases it cannot. We emphasize two important points when interpreting the conclusions drawn in the previous section: the data of Toyao et al [48] were obtained for Cu-based alloys, and not all of the data points in Figure 3 are located on the regression lines represented by Equations ( 1)-( 4).…”

“…Such a system might enable the direct conversion of CH 4 to useful compounds without the steam reforming process. We have worked toward establishing such a concept, [43,44,45,46] but in a piecemeal fashion, past studies have also argued for such a concept. For example, Matsumura et al [47] .…”

“…The concept we have elaborated should not yet be abandoned. In some cases, a good catalyst can be designed through logic, [46] whereas in some cases it cannot. We emphasize two important points when interpreting the conclusions drawn in the previous section: the data of Toyao et al [48] .…”

Electronic and Structural Engineering of Atomically Dispersed Isolated Single‐Atom and Alloy Architectures

“…These alloys exhibit excellent electronic properties, such as alternate lattice structure, atomic migration, d-band close to Fermi level, and resistant to dopant atom aggregation (Figure 1c,d). [10,[7][8][9] Alloying of Pt nanocrystals (NCs) with Ni single-atoms (SAs) is an example of single-atom alloying on inter atom surface, in which in situ anchoring followed by metal atom alloying in Ni-Pt-SAA system via electrochemical deposition results in a lattice distortion of Pt NCs (Figure 1e). [10] The geometric and electrical structures of metal centers in SACs can be controlled by adjusting the number and type of adjacent coordination species in the anchoring sites (i.e., the first coordination shell).…”