Catalytic surfaces, ESCA study

However, when the reductions were carried out with lithium and a catalytic amount of naphthalene as an electron carrier, far different results were obtained(36-39, 43-48). Using this approach a highly reactive form of finely divided nickel resulted. It should be pointed out that with the electron carrier approach the reductions can be conveniently monitored, for when the reductions are complete the solutions turn green from the buildup of lithium naphthalide. It was determined that 2.2 to 2.3 equivalents of lithium were required to reach complete reduction of Ni(+2) salts. It is also significant to point out that ESCA studies on the nickel powders produced from reductions using 2.0 equivalents of potassium showed considerable amounts of Ni(+2) on the metal surface. In contrast, little Ni(+2) was observed on the surface of the nickel powders generated by reductions using 2.3 equivalents of lithium. While it is only speculation, our interpretation of these results is that the absorption of the Ni(+2) ions on the nickel surface in effect raised the work function of the nickel and rendered it ineffective towards oxidative addition reactions. An alternative explanation is that the Ni(+2) ions were simply adsorbed on the active sites of the nickel surface. 

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

The acronym ESCA refers to the technique of bombarding the surface with X-ray photons, which produce the emission of characteristic electrons measured as a function of electron energy. Because of the low energy of the characteristic electrons, the depth to which the analysis is made is only 20 A. The composition of this thin layer as a function of depth can be determined by sputtering away layers of the surface and analyzing the underlying surfaces. A number of important catalytic properties have been studied by this technique, including oxidation state of the active species, interaction of a metal with an... 

The ability of the poison to block the active catalytic sites can be studied by determining a decrease in the catalytically active component on the surface. Selective chemisorption changes may be employed53 to detect changes in the accessible metal. Alternately, the covering of active species may be inferred from its decrease in detection from surface-sensitive techniques such as ESCA O. The approach is that the ESCA or Auger spectra for the active component decreases as it becomes covered with the poison. The escape depth for the emission from the active elements is limited and... 

The dissociative chemisrapdon of MeOH on a Pd(l 11) surface to give methyl groups was found to be coverage-dependent. Decomposition of diazirine on a Pd(110) surface proceeds by cleavage of C-N and N-N bonds.38l The oxidative addition of CH4 and C2H5 to Pd and Pt has been examined by theoretical methods.268.382.383 Various catalytically important Pd(0) and Pd(II) cmnplexes have been studied by ESCA photoelectron specoosct y. ... 

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