Enthalpy changes during O2 adsorption and H sub 2 titration of adsorbed oxygen on platinum

Journal Article · Wed May 01 00:00:00 EDT 1991 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(91)90006-P· OSTI ID:5619466

Sen, B; Vannice, M A ^[1]

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1. The Pennsylvania State Univ., University Park (USA)

Integral, isothermal heats of adsorption were measured for O{sub 2} on UHP Pt powder and SiO{sub 2{minus}} supported Pt, with the latter providing an average crystallite size range of 1.3-22.3nm. The energy changes that occur during the titration of this chemisorbed oxygen by dihydrogen were also measured. The average Q{sub ad} value of 67.9{plus minus}8.9 kcal/mol for well-dispersed Pt on Davison 57 silica compared to that of 52.6{plus minus}6.1 kcal/mol for the Pt powder indicates that a small increase may occur on very small Pt crystallites. The enthalpy of titration was relatively constant, with a value of{Delta}H{sub titr} = {minus}26.7{plus minus}4.2 kcal/mol H{sub 2} obtained for all the Pt/SiO{sub 2} samples compared to {minus}24.5{plus minus}3.5 kcal/mol H{sub 2} for the Pt powder. The use of a thermodynamic cycle not only gave an approximate value of 11 kcal/mol for the heat of adsorption of water on SiO{sub 2}, but also indicated that all the water desorbed from the Pt surface at 300 K thus allowing a complete monolayer of hydrogen to form.

• DOE Contract Number: FG02-84ER13276
• OSTI ID: 5619466
• Journal Information: Journal of Catalysis; (USA), Vol. 129:1; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDROGEN
DIFFUSION
OXYGEN
ADSORPTION
PLATINUM
PERMEABILITY
SURFACE PROPERTIES
ADSORPTION HEAT
ALUMINIUM OXIDES
CATALYST SUPPORTS
CATALYSTS
CHEMISORPTION
CRYSTAL STRUCTURE
DESORPTION
ENTHALPY
SILICA
THERMODYNAMIC CYCLES
WATER
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
HYDROGEN COMPOUNDS
METALS
MINERALS
NONMETALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PLATINUM METALS
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SORPTION
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties