Surface alumina species on modified titanium dioxide: A solid-state 27Al MAS and 3QMAS NMR investigation of catalyst supports

Abstract

27Al MAS and 3QMAS NMR have been used to study Al 2O 3/TiO 2 catalyst supports synthesized via excess-solution impregnation and surface sol–gel methods. Temperature and alumina loading level strongly affect chemical states of aluminum oxide species observed. Surface cations, Al ( H 2 O ) 6 3 + , a surface alumina monolayer, and disordered transitional aluminas (multilayers) and α-alumina, coexist on the TiO 2 surface. Chemical shift and quadrupole coupling constants are reported for the major species identified in 3QMAS experiments. Gold particle catalysts prepared from supports calcined at 500 °C have optimum catalytic activity in CO oxidation, and smallest gold particle size for supports, which show maximum monolayer type octahedral alumina on the titania surface.