Confined catalysis under two-dimensional materials

Abstract

Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. The microenvironment created by coating a catalyst surface with 2D material overlayer can be used to modulate surface reactivity, which has been illustrated by optimizing oxygen reduction reaction activity on Pt(111) covered by various 2D materials. We demonstrate a concept of confined catalysis under 2D cover based on a weak van der Waals interaction between 2D material overlayers and underlying catalyst surfaces.confined catalysis | two-dimensional materials | density functional theory | oxygen reduction reaction | graphene I n heterogeneous catalysis, active sites have long been regarded as one of the most important concepts (1-3), and, recently, the heterogeneous catalysis community has started to recognize that microenvironment around the active site is equally important (4-9). The confined microenvironment on a heterogeneous catalyst can help to stabilize active sites and modulate chemistry at the sites, which has a significant effect on catalytic performance, similar to the role of spheroproteins in an enzyme (10). Hence, understanding fundamentals of confined catalysis has become an important topic in heterogeneous catalysis (11,12).Reactions in zero-dimensional (0D) nanocavities of microporous and mesoporous materials such as zeolites and metal−organic frameworks (MOFs) have shown enhanced catalytic performance (6,9,(13)(14)(15). Theoretical investigations reveal that the spatially confined environment increases the molecular orbital energy and changes activity of the confined molecules, which have been recognized as the nest effect and quantum confinement effect (15, 16). In past decades, some experimental studies have demonstrated that carbon nanotubes (CNTs) strongly affect catalytic reactions occurring inside the nanotubes (7,17,18), and confined catalysis in 1D nanocavities has been theoretically addressed by studying molecule adsorption on metal clusters encapsulated in CNTs (19). As illustrated in Fig. 1, both 0D nanocavities in zeolites and 1D nanocavities in CNTs are spatially confined in three dimensions and two dimensions, respectively, in which simple and well-defined model systems are not feasible for both theoretical and experimental studies. Moreover, structural and composit...

Single Graphene Layer on Pt(111) Creates Confined Electrochemical Environment via Selective Ion Transport

“…[2] Among various nanoreactors,t he two-dimensional (2D) confined space between a2 Dm aterial and as olid surface emerges as an important model system. [3] This research topic largely benefits from the discoveries of new classes of 2D materials, [4] among which graphene stands out. It is often considered an almost perfect material due to its advantageous properties of as ingle-atom-thin 2D structure yet with chemical stability and mechanical strength that allows ultrafast and selective mass transport of reactants from the bulk into aconfined 2D space.…”

“…[5] So far, chemical studies using a2 Dc onfined space are mostly carried out under gas phase or ultrahigh vacuum conditions in the context of intercalation of atomic/molecular species and their heterogeneous surface-catalyzed reactions. [3] In contrast, the knowledge of electrochemical processes occurring in such confined 2D space is scarce.E xperimental efforts have been mostly devoted to the non-destructive method for graphene exfoliation by hydrogen evolution [6] and the inhibited [7] /promoted [8] corrosion of metals by graphene coatings.L ittle is known of electrochemical processes in confined 2D environments such as ion/molecule adsorption, hydrogen/metal underpotential deposition (UPD), which are of fundamental importance for electrochemical energy conversion and storage. [9] Here,w eu se the 2D space between as ingle layer of graphene and an atomically flat Pt(111) single-crystal surface as am odel system to study interfacial electrochemical processes in confined spaces.A2D confined space is constructed by chemical vapor deposition (CVD) of af ull monolayer of single-layer graphene on aPt(111) surface.The electrochemical behavior of ab are Pt(111) electrode is well documented, [10] displaying well-defined fingerprint voltammetric characteristics for many interfacial processes such as: hydrogen and metal UPD,a dsorption of anions,o rder/ disorder phase transitions and surface oxidation.…”

Effect of Confined Spaces in the Catalytic Activity of 1D and 2D Heterogeneous Carbon‐Based Catalysts for Synthesis of 1,3,5‐Triarylbenzenes: RGO‐SO3H vs. MWCNTs‐SO3H

“…Interestingly, the functionalized graphene sheets have an open double side surface, and in principle, all functional groups are accessible by reactants in organic reactions ,. Therefore, the 2D nanoreactor formed under 2D graphene sheets and can provide a well‐defined cavity to perform organic reactions in addition to the double side surface of graphene sheets . The interlayer spacing increases from 0.34 nm in graphite layers to more than 1.5 nm in some functionalized graphene .…”

Electrochemical CO 2 reduction in confined space: Enhanced activity of metal catalysts by graphene overlayer

“…Compared with bare metal surfaces, ΔG (CO 2 + H + + e − ! 32,36 Indeed, the confinement effect tends to enhance G (CO 2 *) (CO 2 adsorbed on metal surface) and G (COOH*). CHO*) (shown by arrows in Figure A1 in Appendix S1) on graphene-covered metal surfaces become even lower.…”

“…2D materials have open double-sided surfaces with all atoms subject to surface reactions. [31][32][33][34][35][36] Graphene and hexagonal boron nitride overlayers on transition metal surfaces are able to facilitate reactions involving small molecules, 31,32 with the interface between graphene and metal surface playing a role of confined "nano reactor." [17][18][19][20][21] Over the last decade, possible applications of 2D materials in catalysis have been attracting considerable interest.…”