Chemisorption

About: Chemisorption is a research topic. Over the lifetime, 16298 publications have been published within this topic receiving 554989 citations.

The Bond-Order Conservation Approach to Chemisorption and Heterogeneous Catalysis: Applications and Implications

Abstract: Publisher Summary For chemisorption phenomena on transition metal surfaces, including surface reactivity, the bond-order conservation-Morse potential (BOC-MP) model appears to provide such a framework in which the intricacies of real phenomena are coherently interrelated. The BOC-MP model is a simple, truly “back-of-the-envelope’’ model that can be directly used by practitioners in the field. It efficiently describes and interrelates a wide variety of chemisorption phenomena. Most important, the model maps out metal surface reactions providing insight into both regularities and details. In principle, any metal surface reaction can be treated this way. The only requirement is to retain the rigor and simplicity of the model projections. This analytic model proved to be efficient for treating energetics of atomic and diatomic adsorbates on transition metal surfaces, particularly, the heat of chemisorption and activation barriers for dissociation and recombination. Recently, the BOC-MP model has been extended to treat energetics of polyatomic adsorbates as well, which made it possible to analyze mechanisms of catalytic heterogeneous reactions of practical importance. The chapter surveys major applications and implications of BOC-MP modeling to chemisorption and heterogeneous catalysis.

Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the preparation method

Abstract: Three bimetallic PtSn/C catalysts have been prepared by successive impregnation of pregraphitized carbon black with an aqueous solutions of hexachloroplatinic acid and tin(II) chloride. One monometallic Pt/C sample was also prepared and studied for comparison. All catalysts were characterized by hydrogen and carbon monoxide chemisorption at room temperature and X-ray photoelectron spectroscopy and their behaviour in the gas phase hydrogenation of crotonaldehyde, at atmospheric pressure, determined. The amount of surface platinum is greatly reduced by the addition of tin, as deduced from chemisorption measurements and XPS. Both Pt0 and PtII are detected by XPS in the fresh bimetallic catalysts; after reduction in flowing hydrogen at 623 K platinum is completely reduced to the metallic state and, although a high proportion of tin remains in an oxidized state, a relatively important amount is reduced to Sn0, this allowing the possibility of PtSn alloys formation. The catalytic activity in the gas phase hydrogenation of crotonaldehyde is greatly improved by the presence of tin, in spite of the fact that the amount of surface platinum is reduced. Tin has also a very important effect on the selectivity towards the hydrogenation of the CO bond, increasing the production of crotyl alcohol in respect to the hydrogenation of the CC bond that would lead to the production of butyraldehyde. The observed results are explained on the basis of a promoting effect of oxidized tin species for the hydrogenation of the CO group, whereas the formation of a PtSn alloy or the dilution of surface platinum by metallic tin would hinder the hydrogenation of the olefinic CC bond.

Surface barrier for electrons in metals

Abstract: Density-functional calculations using the full-potential linearized augmented-plane-wave (FLAPW) film method have been used to compute the effective potential for electrons at different surfaces of Al, Ni, Cu, Ag, and W. In each case, the average of the potential parallel to the surface is reproduced well by a simple model barrier with three adjustable parameters, with relatively small variations between different metals and surfaces. FLAPW calculations have also been used to examine the effects of chemisorption on the surface barrier. The results of this work provide a basis for the analysis of low-energy-electron-diffraction fine-structure and inverse-photoemission spectra.