Acidic properties of molybdenum oxide highly dispersed on titania

Abstract

The adsorption of ammonia and pyridine on Mo–Ti oxide (2.0 and 5.0 wt%) has been studied by i.r. spectroscopy. Mo–Ti oxide exhibits both Brønsted- and Lewis-acidic sites. The Lewis-acidic sites are converted into Brønsted sites on the introduction of water vapour. The Brønsted sites determined from pyridine adsorption are smaller in number than those from ammonia adsorption. It is found that ammonia is adsorbed in three forms: on Lewis sites, on surface OH groups as NH₄⁺ and as NH₂ species, resulting in the increase in Brønsted sites.