This Perspective illustrates how the presence of internal and external electric fields can affect catalytic activity and selectivity, with a focus on heterogeneous catalysts. Specifically, experimental investigations of the electric field influence on catalyst selectivity in pulsed field mass desorption microscopes, scanning tunneling microscopes, probe–bed–probe reactors, continuous-circuit reactors, and capacitor reactors are described. Through these examples, we show how the electric field, whether externally applied or intrinsically present, can affect the behavior of a wide number of materials relevant to catalysis. We review some of the theoretical methods that have been used to elucidate the influence of external electric fields on catalytic reactions, as well as the application of such methods to selective methane activation. In doing so, we illustrate the breadth of possibilities in field-assisted catalysis.

X-ray photoelectron spectroscopy (XPS) was employed to study the surface composition and electronic structure of Au/TiO 2 catalysts in comparison with TiO 2 (anatase) and to reveal time-dependent X-ray irradiation damage of the samples. The occurrence of Au nano-sized particles on a TiO 2 support was found to result in a slight shift of Ti 2p core-level spectrum and in changes of the valence band and X-ray induced Auger spectra, compared to TiO 2 -only. It was shown that for different means of energy referencing the charge-corrected Au 4f 7/2 binding energy in Au/TiO 2 catalysts was 0.15-0.45 eV lower than that in pure bulk Au. Exposure to X-rays of Au/TiO 2 catalysts and pure TiO 2 caused a reduction of Ti 4+ oxidation state and desorption of oxygen from the surface. As a result, the surface chemical composition and electronic structure of the samples changed with time. The X-ray irradiation affected charge transfer processes in Au/TiO 2 so that the pattern of X-ray induced damage in the Au-based catalyst turned out to be quite different from that in TiO 2 , with some characteristics displaying the very opposite features. Decreasing of the Au 4f 7/2 binding energy and concurrent increasing of the fraction of Ti 3+ species observed in the beginning of X-ray irradiation of Au/TiO 2 may be taken as direct evidence for charge transfer from oxygen vacancies created by irradiation to Au particles.

Model cobalt catalysts for CO 2 hydrogenation were prepared using colloidal chemistry. The turnover frequency at 6 bar and at 200−300°C increased with cobalt nanoparticle size from 3 to 10 nm. It was demonstrated that near monodisperse nanoparticles in the size range of 3−10 nm could be generated without using trioctylphosphine oxide, a capping ligand that we demonstrate results in phosphorus being present on the metal surface and poisoning catalyst activity in our application.KEYWORDS: Cobalt nanoparticles, CO 2 hydrogenation, heterogeneous catalysis, catalytic poisoning C obalt-catalyzed processes and specifically the conversion of synthesis gas to hydrocarbons using cobalt (Co), Fischer−Tropsch synthesis, although long established, 1 have recently become a topic of renewed interest. This results from increased demand and declining fossil fuel reserves making both gas-to-liquid and biomass-to-liquid attractive routes to transportation fuels. 2 Especially when derived from biomass, the synthesis gas typically contains a significant fraction of CO 2 , however studies on CO 2 hydrogenation and its catalytic mechanism on Co are much less well developed than the analogous reaction with CO. 3,4 Because of its environmental impact through the greenhouse effect, fixation of CO 2 by reaction (rather than simply capture and storage) also makes studying the possibility of Co-catalyzed CO 2 hydrogenation a topic of considerable interest. 4 Additionally, there is an important technical precedent in terms of producing desirable oxygenated products by incorporation of CO 2 in such reactions (important in producing synthetic fuels). In the case of classical Cu/ZnO catalyzed methanol production, Chinchen et al. demonstrated using isotopic labeling studies that it is CO 2 , rather than CO, that is incorporated in the methanol produced. 5 Few kinetic studies of the chemistry of Co-catalyzed CO 2 hydrogenation exist. In our laboratory the conversion of CO 2 to CH 4 was explored at atmospheric pressure in a batch reactor over high-purity Co foil, 6 subsequently Welder and co-workers also studied the hydrogenation of CO 2 over Co foils in a flow reactor. 7,8 Wetherbee and Bartholomew however have reported on the use of a Co/SiO 2 catalyst prepared by incipient wetness impregnation to obtain various kinetic parameters, 9 although this does not contain information at the atomic scale about the nature of the Co catalyst particles, and it is this problem that we now address.In our laboratory size-and morphology-controlled nanoparticles, which are synthesized using colloidal techniques, have allowed the production of model catalysts via deposition within mesoporous silica supports. This is important because selectivity in multipath reactions has been found to vary with catalyst particle size and shape. In combination with powerful characterization techniques that provide atomic-and molecularlevel information, these model nanoparticle catalysts have been employed in studying fundamental mechanistic questions in many key chemica...

The catalytic CO hydrogenation is one of the most versatile large-scale chemical syntheses leading to variable chemical feedstock. While traditionally mainly methanol and long-chain hydrocarbons are produced by CO hydrogenation, here we show that the same reaction can be tuned to produce long-chain n-aldehydes, 1-alcohols and olefins, as well as n-paraffins over potassium-promoted CoMn catalysts. The sum selectivity of aldehydes and alcohols is usually >50 wt% whereof up to ∼97% can be n-aldehydes. While the product slate contains ∼60% n-aldehydes at /pCO=0.5, a 65/35% slate of paraffins/alcohols is obtained at a ratio of 9. A linear Anderson–Schulz–Flory behaviour, independent of the /pCO ratio, is found for the sum of C4+ products. We advocate a synergistic interaction between a Mn5O8 oxide and a bulk Co2C phase, promoted by the presence of potassium, to be responsible for the unique product spectra in our studies.