Abstract
An adsorption microcalorimeter with two Tian–Calvet thermopiles has been used for the determination at 77.4 K of differential energies of adsorption of argon and nitrogen as a function of surface coverage on a sample of pure rutile (surface area, 22 m2 g–1) and on the rutile coated with 2.55 wt.% silica (surface area, 23 m2 g–1). With each adsorbent, the adsorption measurements were made in stages; after outgassing at 150°C, after outgassing at 250°C and after outgassing at 400°C.All the plots of the differential energy of adsorption, ΔaU, against surface coverage, θ, reveal energetic heterogeneity; the greatest variation of ΔaU is given by N2 on rutile (400°C) and the least variation of ΔaU by argon on the silica-coated sample (150 and 250°C). The remarkably high initial adsorption energies (ΔaU > 25 kJ mol–1 at θ 20 kJ mol–1), whilst at higher coverage the N2—OH group interaction becomes the predominant specific contribution to the adsorption energy. Rutile (250°C) behaves in a similar manner to rutile (400°C), but cationic sites are not exposed to any significant extent on the surface of rutile (150°C) and its interaction with N2 is therefore very similar to that given by hydroxylated silica (150 and 250°C).
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Schedule a callMore From: Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
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