Spectroscopic Investigation of Grafting Sites in Oxide Supports of Heterogeneous Catalysts

Amorphous and crystalline aluminosilicate metal oxides have a wide range of industrial applications and are important materials in the field of heterogeneous catalysis as supports, cracking catalysts, shape selective materials, and molecular sieves. Extra catalytic functionality is imparted to these materials by grafting metals onto their surface and into their pores through silanol (≡SiOH), aluminol (≡AlOH), and Brønsted ≡SiO(H)Al≡ sites. The distribution of grafting sites in amorphous and crystalline metal oxide supports is often assumed to be statistically controlled and when the concentration of grafting sites on the supports is low, metals grafted onto these supports are assumed to be isolated. A combination of mass balancing, DFT calculations, IR, MAS NMR, and X-ray absorbance spectroscopy has been used in this dissertation to show that in many types of silicas and ZSM-5, grafting sites are, in fact, oriented in pairs or clusters even when it is highly unlikely given a random distribution of sites