Infra-red study of hydrogen chloride adsorption on rutile surfaces

The adsorption of hydrogen chloride on outgassed, deuterated, and reduced rutile surfaces has been studied by infra-red spectroscopy. Surface Ti4+O2–Ti4+ groups react with hydrogen chloride to form hydroxide ions and chloride ions on adjacent titanium ion sites. The reaction of hydrogen chloride with surface hydroxide ions leads to water coordinately bound to Ti4+ and associated with a chloride ion. Rearrangement to Ti4+Cl– species occurs and leads to the formation of adsorbed water which can react with hydrogen chloride to form H3O+Cl– on the surface. The adsorption of hydrogen chloride leads to surface species which act as Bronsted acid sites in the presence of adsorbed ammonia or pyridine.