Adsorption and catalytic studies on model mono- and bimetallic catalysts

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1993

OSTI ID:6930968

Szanyi, J

The adsorption and oxidation of carbon monoxide were studied on model mono- and bimetallic catalysts of Pd(111), Pd(100), Cu(100), Rh(100) and Cu/Rh(100), using combined elevated pressure reactor/IR cell-UHV surface analysis systems. Adsorption studies were carried out in wide pressure and temperature ranges of 10[sup [minus]7]-10[sup 1] Torr and 90-1000 K, respectively, employing techniques of RAIRS and TPD. The adsorption of CO on Pd(111) was found to be very sensitive for the preparation conditions of the adsorbed CO layer. Isosteric heats of adsorption were determined for Pd(111) an equilibrium phase diagram was constructed which shows the continuity of CO molecules in different adsorption positions. For Pd(111) an equilibrium phase diagram was constructed which shows the continuity of CO adsorption phases with increasing CO pressure and surface temperature. Excellent agreement was found between IR spectra of equilibrated CO layers on Pd(111) and Pd(100) single crystals and a Pd/SiO[sub 2] catalyst. Results of elevated pressure kinetic and IR measurements for the oxidation of CO on Pd(111) and Pd(100) strongly support the generally accepted correspondence between the heat of CO adsorption and the activation energy. Deposition of Cu on the Rh(100) surface results in an increase in catalytic activity for CO oxidation. Maximum activity is seen at [theta][sub Cu] = 1.3ML and the activity of Cu/Rh(100) catalysts are higher than that of Rh(100) even at [theta][sub Cu] > 3ML. The Cu overlayer is not stable under the oxidizing reaction conditions employed and by interacting with oxygen present in the reactant gas mixture it forms 3D Cu[sub x]O agglomerates. The kinetics of CO oxidation on Cu/Rh(100) catalysts are similar to those on Rh(100), the largest deviation is seen for catalysts with [theta][sub Cu] < 0.5ML. The role of Cu in the Cu/Rh(100) bimetallic catalysts is to increase the local oxygen concentration at the Cu-Rh peripheries.

• Research Organization: Texas A and M Univ., College Station, TX (United States)
• OSTI ID: 6930968
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
ADSORPTION
BIMETALS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CATALYTIC EFFECTS
CHALCOGENIDES
COPPER
ELEMENTS
METALS
OXIDES
OXYGEN COMPOUNDS
PALLADIUM
PLATINUM METALS
PRESSURE DEPENDENCE
RHODIUM
SORPTION
SORPTIVE PROPERTIES
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENTS