IR spectroscopic studies of adsorbate diffusion in porous catalysts

• Published in: Journal of physical chemistry (1952) 1989-09, Vol.93 (18), p.6758-6763
• Main Authors: Ballinger, Todd H, Basu, Pam, Yates, John T
• Format: Article
• Language: English
• Subjects: 360000 - Materials; 360603 - Materials- Properties; 400000 - Chemistry; 400201 - Chemical & Physicochemical Properties; ADSORPTION; ALUMINATES; ALUMINIUM COMPOUNDS; CATALYSTS; CHALCOGENIDES; Chemistry; DATA; DATA ANALYSIS; DIFFUSION; Exact sciences and technology; EXPERIMENTAL DATA; General and physical chemistry; INFORMATION; INFRARED SPECTRA; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MATERIALS SCIENCE; MEASURING INSTRUMENTS; MEASURING METHODS; MINERALS; NUMERICAL DATA; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; SILICA; SILICON COMPOUNDS; SILICON OXIDES; Solid-gas interface; SORPTION; SPECTRA; Surface physical chemistry; SURFACE PROPERTIES
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/j100355a037

Transmission infrared spectroscopy has been used to study xenon diffusion through high-area porous catalysts such as alumina and silica via xenon interactions with IR-active surface species. At low temperatures, xenon condenses on the external surface of silica. As the catalyst temperature is increased and the vapor pressure of Xe increases, diffusion occurs into the pores where Xe interacts with surface hydroxyl groups, a majority of which are contained within these pores. The dynamic dipole of OH induces a dynamic dipole image in the polarizable Xe, which is opposite in sign to the OH dipole. This interaction lowers the normal frequency of OH by 28 cm{sup {minus}1}. This effect is also observed for the chemisorbed Rh{sup I}(CO){sub 2} oscillator on Al{sub 2}O{sub 3}. Evidence is presented that cooling Xe-filled pores below {approx} 153 K causes Xe condensation on itself in the pores, reducing the Xe-HO interaction as monitored spectroscopically.