The identification of the active sites in heterogeneous catalysis requires a combination of surface sensitive methods and reactivity studies. We determined the active site for hydrogen evolution, a reaction catalyzed by precious metals, on nanoparticulate molybdenum disulfide (MoS2) by atomically resolving the surface of this catalyst before measuring electrochemical activity in solution. By preparing MoS2 nanoparticles of different sizes, we systematically varied the distribution of surface sites on MoS2 nanoparticles on Au(111), which we quantified with scanning tunneling microscopy. Electrocatalytic activity measurements for hydrogen evolution correlate linearly with the number of edge sites on the MoS2 catalyst.

http://science.sciencemag.org/content/sci/317/5834/100.full.pdf

Identification of active edge sites for electrochemical H2 evolution from MoS2 nanocatalysts.

Controlling surface structure at the atomic scale is paramount to developing effective catalysts. For example, the edge sites of MoS(2) are highly catalytically active and are thus preferred at the catalyst surface over MoS(2) basal planes, which are inert. However, thermodynamics favours the presence of the basal plane, limiting the number of active sites at the surface. Herein, we engineer the surface structure of MoS(2) to preferentially expose edge sites to effect improved catalysis by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS(2) bicontinuous network with nanoscaled pores. The high surface curvature of this catalyst mesostructure exposes a large fraction of edge sites, which, along with its high surface area, leads to excellent activity for electrocatalytic hydrogen evolution. This work elucidates how morphological control of materials at the nanoscale can significantly impact the surface structure at the atomic scale, enabling new opportunities for enhancing surface properties for catalysis and other important technological applications.

Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis

Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solutions, under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high density of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quantitative faradaic yield, while also affording stability in aqueous acidic media.

http://pubs.acs.org/doi/pdf/10.1021/ja403440e

Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution Reaction

Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels.

Layered materials consist of molecular layers stacked together by weak interlayer interactions. They often crystallize to form atomically smooth thin films, nanotubes, and platelet or fullerene-like nanoparticles due to the anisotropic bonding. Structures that predominately expose edges of the layers exhibit high surface energy and are often considered unstable. In this communication, we present a synthesis process to grow MoS2 and MoSe2 thin films with vertically aligned layers, thereby maximally exposing the edges on the film surface. Such edge-terminated films are metastable structures of MoS2 and MoSe2, which may find applications in diverse catalytic reactions. We have confirmed their catalytic activity in a hydrogen evolution reaction (HER), in which the exchange current density correlates directly with the density of the exposed edge sites.

Synthesis of MoS2 and MoSe2 Films with Vertically Aligned Layers

Etude de la structure d'un catalyseur utilise pour une hydrodesulfuration et plus particulierement etude de la localisation et de la structure des ions molybdene et cobalt a la surface de l'alumine. Discussion sur le role d'un promoteur modifiant un catalyseur, notamment determination du nombre de sites actifs

/pdf/structure-and-function-of-the-catalyst-and-the-promoter-in-4byxxp64yh.pdf

Structure and Function of the Catalyst and the Promoter in Co—Mo Hydrodesulfurization Catalysts

https://pure.tue.nl/ws/files/2007112/620387.pdf

Carbon-Supported Sulfide Catalysts

https://pure.tue.nl/ws/files/2325948/620870.pdf

Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

The X-ray absorption spectrum of the Rh K edge of a highly dispersed reduced 0.57 wt % Rh/ y-A1203 catalyst
shows EXAFS oscillations due to rhodium-rhodium nearest neighbors, which proves the existence of rhodium
metal crystallites. Adsorption of CO at room temperature on the reduced catalyst significantly decreases the
amplitude of these EXAFS oscillations. This implies that CO adsorption on very small rhodium crystallites
leads to a disruption of a significant number of the metal-metal bonds.

/pdf/an-extended-x-ray-absorption-fine-structure-spectroscopy-4zgfgt15dn.pdf

An Extended X-ray Absorption Fine Structure Spectroscopy Study of a Highly Dispersed Rhodium/Aluminum Oxide Catalyst: The Influence of Carbon Monoxide Chemisorption on the Topology of Rhodium

https://pure.tue.nl/ws/files/2063344/620401.pdf

R Roel Prins

Papers

Structure and Function of the Catalyst and the Promoter in Co—Mo Hydrodesulfurization Catalysts

Carbon-Supported Sulfide Catalysts

Determination of metal particle size of highly dispersed Rh, Ir, and Pt catalysts by hydrogen chemisorption and EXAFS

An Extended X-ray Absorption Fine Structure Spectroscopy Study of a Highly Dispersed Rhodium/Aluminum Oxide Catalyst: The Influence of Carbon Monoxide Chemisorption on the Topology of Rhodium

A temperature programmed reduction study of Pt on Al2O3 and TiO2