Isothermal Chemisorption upon Oxide-Supported Platinum

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Abstract
The extent of isothermal chemisorption (q in μmol g−1) of gaseous carbon monoxide, oxygen, and hydrogen on the surfaces of platinum crystallites supported upon silica, alumina, titania, molybdena, tungsta and sodium-tungsten bronzes has been investigated at 77–523 K and 0–5 kPa. The extent of adsorption under these conditions rarely reaches a saturation value (qmax) and in general the gradient dq/dp is not zero. Platinum dispersion and surface area, the nature of the support and the adsorbate, pressure and temperature all affect the value of dq/dp, which is interpreted in terms of the effects of weak secondary chemisorption on the platinum, physical adsorption, and spillover onto the support. The optimum conditions for differentiating chemisorption are described and methods of estimating monolayer adsorption capacity and specific surface areas of supported platinum from adsorption data measured at optimum temperatures and pressures are considered in detail. The accuracy of the derived surface areas are found to depend upon the conditions of pretreatment and adsorption chosen, the method of interpretation of the monolayer adsorption capacity qm and the variable stoichiometry of adsorption n.

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