US EPA

1198180 

Journal Article 

ADSORPTION AND CATALYTIC PROPERTIES OF PD/SIO2, CU/SIO2, AND PD-CU/SIO2 SYSTEMS .1. HYDROGEN, CARBON-MONOXIDE AND OXYGEN-ADSORPTION ON PD/SIO2 AND CU/SIO2 

Leon, C; Vannice, MA 

1991 

Yes 

Applied Catalysis
ISSN: 0166-9834 

69 

2 

269-290 

WOS:A1991FB18500010 

Uptakes of hydrogen, carbon monoxide, and oxygen on 1.23% Pd/SiO2 and 2.48% Pd/SiO2 catalysts prepared by ion exchange were affected little by the pretreatment. However, the initial carbon monoxide exposure significantly reduced all subsequent chemisorption capacities. Isobars were measured at 27 kPa for hydrogen and oxygen on well dispersed 2.48% Pd/SiO2 and on poorly dispersed 4.32% Cu/SiO2. On palladium, hydrogen monolayer coverages at 300 K were slightly above unity, but the irreversibly adsorbed hydrogen remaining after evacuation at 300 K was slightly less than a complete monolayer. The hydrogen adsorption stoichiometry, H(irr)/Pd(s), decreased smoothly from 1.45 at 77 K to 0.05 at 673 K. Irreversible oxygen adsorption varied little between 140 and 273 K on palladium, but it then increased continuously until bulk palladium oxide formed at 473 K. On copper, saturation hydrogen coverages near unity were achieved only at 77 K and this irreversibly adsorbed hydrogen decreased continuously as the temperature increased to 553 K, where coverages become very low (THETA-H < 0.02). The total oxygen uptake passed through a minimum near 200 K, but irreversibly adsorbed oxygen increased from near zero at 77 K to that corresponding to bulk copper(I)oxide formation at 473 K. Oxygen adsorption at 140 K and low pressure (approximately 1 kPa) appears to be a satisfactory method to measure copper surface area. 

PALLADIUM SILICA; COPPER SILICA; PALLADIUM-COPPER SILICA; ADSORPTION OF (HYDROGEN; OXYGEN AND CARBON DIOXIDE); CATALYST PREPARATION (ION EXCHANGE)