The rates of reduction of NO by IIs and of Hz-D2 equilibration were measured in a flow system on Au supported on SiOr, AliOa, and MgO. For the NO reduction the temperature was 350°C partial pressures were 1.52 < pNo < 12.16 Torr, 6.08 6 pn? < 9.12 Torr, 0.5 < ~NO/PXQ < 5, and total pressure was 1 atm. For the HZ-DA equilibration the temperature was 150 to 300°C 10 6 pn$ 6 100 Torr, and p!+/pHa = 1. The Au preparations were characterized by wide-angle X-ray scattering and transmission electron microscopy. No characteristic effect on the rate of reaction was observed by varying the Au precursor salt or the preparative method. There was an effect of the support on the reaction selectivity to Nt, $02~supported preparations showing the lowest and AllOo-supported preparations the highest value of the selectivity. The rate of the IIs-1~2 equilibration was fastest on Au supported on SiO,. It is argued that the different tendency of the supports employed to act as electron donor-acceptor with supported Au influences t,he electron density at the surface Au site. The interpretation is consistent with the relative acid-base ranking of the supports and of the precursor Au salt. An increased electron density at the Au site increases electron back donation from metal to adsorbed NO, weakening the NO bond and facilitating the formation of Nz over that of NHS. This interpretation of the role of the support in modifying the electronic conditions at the Au site is empIoyed to suggest that the higher HZ-D, equilibration rate on Au-SiOe results from a more ionic hydrogen chemisarption bond. Suggestions on the morphoIo~ca1 and chemical nature of the Au which interacts with the support are advanced in the context of the highly heterogeneous morphology of the supported Au, as revealed by the characterization methods employed. The meaning of these findings in the framework of present ideas for high Nz selectivity in the NO reduction as well as the impact of the conclusions from the present study on other important reactions (CO + HZ, NZ + HZ) are pointed out.

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The rate of redistribution of isotopic carbon between CO and COZ has been studied on An supported on MgO in the temperature range 300 to 4OO"C, Pw,/Pco ratios 9.1 to 1.2 and total pressure of 50 Torr. A few experiments were also carried out on supported Rn and Pt. The effect of Au concentration, temperature, and catalyst preparation method have been selected for investigation. In addition, determinations of the particle size of Au have been carried out by X-ray to illustrate the effect of the temperature of reduction and decomposition of the Au salt upon the particle size of the metal in the supported catalyst. Chemicai reduction of the Au salt at low temperature (

Preparations of Au supported on Si02 and A1203 were characterized by small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), extended X-ray absorption fine structure spectroscopy (EXAFS), and transmission electron microscopy (TEM). The Lm X-ray absorption coefficient was used in the EXAFS analysis and the radial structure function was calculated. The interatomic distances and coordination numbers of Au preparations were obtained. EXAFS data indicated an interaction between Au and A1203, while no evidence of interaction between gold and Si02 could be detected. The average Au-Au coordination number was also determined on the basis of particle diameters measured by SAXS and WAXS. Percentages of total Au present in the metallic phase, directly determined by EXAFS, were compared with the ones computed on the basis of SAXS and WAXS particle size measurements. By SAXS measurements normal-logarithmic particle size distribution curves and metal surface area were obtained. From the particle size and Au concentrations so determined the percentage of Au exposed was calculated. The catalytic activity of the three catalysts examined was studied for the isotopic equilibration reaction H2(g) + D2(g) -»• 2HD(g), and for the reduction of NO by H2. Moreover, selectivity measurements are reported for the reduction of NO to N2. An interpretation of possible relationships among catalytic activity, selectivity, degree of dispersion of metal, and interaction between gold and support material is discussed.