Search

The oxidation of carbon monoxide has been studied on a series of Cu/Rh(100) model bimetallic catalysts using a combined elevated pressure reactor-ultrahigh vacuum surface analysis system. The effects of temperature and oxygen/carbon monoxide partial pressures on the rates of CO₂ formation and surface composition/morphology were determined. Although the addition of copper to Rh(100) altered the rate of CO oxidation, the kinetic behavior of the Cu/Rh(100) catalysts was essentially the same as that for Rh(100) with modifications within the low Cu coverage region, i.e., at θ_Cu < 0.5 ML. The altered kinetics are attributed to two types of reaction sites at these low Cu coverages. The primary role of copper in the Cu/Rh(100) bimetallic catalyst is to increase the surface oxygen coverage. The presence of Cu and Rh carbonate-like surface species was evident in postreaction TPD analysis.Copyright 1994, 1999 Academic Press

Ordered bimetallic Sn/Pt(111) surface alloys have been prepared in an ultrahigh vacuum system and used in model moderate pressure (1-200 Torr) batch catalytic reactions. Hydrogenolysis of n-butane (H₂/n-C₄ = 100) was conducted on these surfaces to characterize the effects of ordered bimetallic ensembles relative to those available at the Pt(111) surface over the temperature range 525-625 K. For these conditions, specific n-butane hydrogenolysis reaction rates were determined for the p(2 × 2) Sn/Pt(111) surface alloy, the (√3 × √3)R30° Sn/Pt(111) surface alloy, and Pt(111) as a function of temperature. The order of relative activities is p(2 × 2) Sn/Pt(111) surface alloy > Pt(111) > (√3 × √3)R30° Sn/Pt(111) surface alloy with specific activation energies of 29 ± 2 kcal mol−1 for all three surfaces below 575 K. A leveling in activity is seen for all three surfaces at temperatures above 575 K. The hydrogenolysis activity of the p(2 × 2) Sn/Pt(111) surface alloy is approximately 5-6 times greater than that seen over Pt(111) and the (√3 × √3)R30° Sn/Pt(111) surface alloy is approximately an order of magnitude less active. Product distributions and catalytic deactivation were found to be substantially different for these three surfaces. These results are discussed in terms of the ensemble requirement differences inherent to the hydrogenolysis pathways available at each of the base metals under these conditions of temperature, pressure, and hydrogen/hydrocarbon ratio.Copyright 1994, 1999 Academic Press, Inc.

Pyridine (py) and acetic acid (Ac) adsorption on dealuminated HY zeolites with Al content in the range of 3.9–58 per unit cell (U.C.) was studied at 553 K by a flow-gravimetric technique. The ratio of the number of adsorbed py and Ac molecules to the number of Al atoms was plotted as a function of the Al content. The plot passes through a maximum for py and a minimum for Ac. The extrema are at about 30 Al/U.C.

The adsorption of acetone and its co-adsorption with CO were studied on a solid state ion exchanged Cu-ZSM-5 catalyst using in situ Fourier transform infrared (FTIR) spectroscopy. The C-O stretching vibrational band of adsorbed acetone at Cu1+is centered at 1671 cm-1, red-shifted by 48 cm-1in comparison to that in the gas phase. Adsorbed acetone at the Cu1+site does not eliminate the adsorption of CO onto the same cationic center (and vice-versa); however, the strength of the CO binding is suggested to be weaker to the {Cu[(CH3)2CO]}+center than to the adsorbate free Cu1+site and is manifested by a 28 cm-1red-shift in the C-O stretching frequency of adsorbed CO in the former complex in comparison to the latter complex. The position of the C-O stretching vibrational band of adsorbed acetone blue-shifts by about 20 cm-1as a result of the presence of CO on the cationic center. The changes in the C-O stretching vibrational frequencies of the absorption features of the two adsorbate molecules can be rationalized by the changes in the electronic environment at the Cu1+adsorption center.

The catalytic alkylation is studied at atmospheric pressure, 698 K, and toluene/MeOH = 5 mol/mol in a fixed bed reactor.