Infrared studies of the adsorption of probe molecules onto the surface of haematite

Abstract

Infrared spectra have been recorded of haematite in contact with ammonia, pyridine, nitric oxide, carbon dioxide, acetic acid and trimethylchlorosilane. Ammonia and pyridine were adsorbed onto weak Lewis acidic surface sites on haematite which had been heated in oxygen at 713 K. No detectable Lewis acidic sites existed on haematite which had been heated at 973 K. No evidence was observed for the adsorption of nitric oxide on haematite and carbon dioxide only gave a single weak band in spectra at 1320 cm^–1. Acetic acid was chemisorbed to give surface acetato species possibly in three distinct configurations. Surface hydroxyl groups on haematite reacted with trimethylchlorosilane vapour to give hydrogen chloride, which was in part adsorbed, and surface trimethylsiloxyl groups. The relative reactivities of different types of surface hydroxyl group could be distinguished.