Graphene cover-promoted metal-catalyzed reactions

Abstract

Graphitic overlayers on metals have commonly been considered as inhibitors for surface reactions due to their chemical inertness and physical blockage of surface active sites. In this work, however, we find that surface reactions, for instance, CO adsorption/desorption and CO oxidation, can take place on Pt(111) surface covered by monolayer graphene sheets. Surface science measurements combined with density functional calculations show that the graphene overlayer weakens the strong interaction between CO and Pt and, consequently, facilitates the CO oxidation with lower apparent activation energy. These results suggest that interfaces between graphitic overlayers and metal surfaces act as 2D confined nanoreactors, in which catalytic reactions are promoted. The finding contrasts with the conventional knowledge that graphitic carbon poisons a catalyst surface but opens up an avenue to enhance catalytic performance through coating of metal catalysts with controlled graphitic covers.arbonaceous deposits such as carbidic carbon and graphitic carbon often form on transition metal (TM) surfaces in catalytic processes involving carbon-containing reactants (1). It has been shown that carbidic species can be involved in some hydrogenation reactions, which are attributed to the observed high reaction activity (2-5). In contrast, graphitic carbon deposited on TM is conventionally considered as catalyst poison due to its chemical inertness and physical blockage of surface active sites (6-8). It has been generally assumed that formation of graphitic carbon on metal catalysts should be avoided before and during catalytic reactions (9, 10). Nevertheless, for decades, extensive research efforts have been made to use surface carbon layers formed on TMs and to understand their role in catalytic reactions (11)(12)(13)(14), which, however, have been impeded by complexity of the ill-defined carbon structures. Graphene, as a simple form of graphitic deposit, has been grown on many late TM surfaces via catalytic cracking of carbon-containing gases (15)(16)(17)(18)(19)(20). Surface science studies on the well-defined graphene/metal surfaces have shown that gaseous molecules such as CO, O 2 , and H 2 O can be readily intercalated under the graphene overlayers (21-27). Defects in graphene including island edges (22,23,(28)(29)(30), domain boundaries (26,31,32), and wrinkles (33) provide channels for molecule diffusion into the graphene/metal interfaces. These new results raise the intriguing possibility that the space between graphene overlayers and metal substrates can act as a 2D container for reactions. The distance between the graphene overlayers and the metal surfaces typically falls in the subnanometer range (19,20), and molecules trapped inside interact directly with both the graphene cover and the metal substrate. Catalytic reactions, if occurring, are strongly confined in the 2D space, and extraordinary catalytic performance may be expected due to the confinement effect. In the present work, graphene/Pt(111) [Gr/Pt(111)] was used ...

Confined catalysis under two-dimensional materials

“…25). Surface science experiments confirm that molecule adsorption in the 2D confined space has been significantly weakened (22,26,28,29,52), which is consistent with the theoretical prediction in the present work.…”

“…More interestingly, the Gr or h-BN covers can promote reactions underneath the 2D overlayers. For example, CO oxidation on Pt(111) has been enhanced by covering the Pt surface with Gr and h-BN layers (22,28), and metal corrosion has been accelerated in the presence of Gr overlayers (53,54). Our calculation results for the feasible modulation of reactions under 2D covers can be solidified by recent reaction data.…”

“…1). The planar microenvironment walls can be appropriately modeled in theoretical calculations (20,21) and investigated well by advanced characterization techniques, particularly surface science methods (22)(23)(24)(25)(26). The newly emerging 2D materials such as graphene (Gr) and hexagonal boron nitride (h-BN) have been facilely supported on solid surfaces via surface deposition or transfer methods (27).…”

“…The newly emerging 2D materials such as graphene (Gr) and hexagonal boron nitride (h-BN) have been facilely supported on solid surfaces via surface deposition or transfer methods (27). Many experiments provide solid evidence that 2D spaces under the 2D material overlayers can act as stable nanoreactors for molecule adsorption and chemical reactions, which provide intriguing confined spaces for catalysis (22,25,(28)(29)(30)(31). A few sophisticated theoretical studies have been conducted to understand reactions under graphene covers in a quantitative way (32,33).…”

Transition-metal-decorated germanene as promising catalyst for removing CO contamination in H2

“…In H 2 feed gas of fuel cell, CO contaminant causes the deactivation of Pt catalysts. To solve this problem, people have focused on searching for anti-CO catalysts or effective techniques to transform CO into other molecules [1][2][3][4][5][6][7][8]. In recent studies, single-atom transition metal (TM) catalysts anchored to substrate exhibit more superior catalytic activity than conventional TM nanoparticles in many important chemical reactions [9][10][11][12].…”