Assessing the surface sites of the large pore 3-dimensional microporous material H-ITQ-7 using FT-IR spectroscopy and molecular probes

Abstract

H-ITQ-7 ((Si + Ge)/Al = 103) has been synthesized and submitted to thorough characterization, in particular with respect to the acidic properties. The H-ITQ-7 material, being one of very few known zeolite or zeotype materials with a three dimensional large pore channel structure, is of particular interest due to its structural similarities with the well studied and industrially relevant H-beta zeolite. By using a variety of molecular probes (H 2O, CH 3OH, CO, and pyridine) in combination with FT-IR spectroscopy, detailed insights regarding the acidic character of the various surface sites have been obtained. The use of several probes is required, as complementary knowledge is gained. Al containing H-ITQ-7 possesses strong Brønsted acid sites of at least two families that are clearly seen to interact differently with both CH 3OH and CO. The spectral features observed upon adsorption of H 2O and CH 3OH indicate that the Brønsted acid sites of H-ITQ-7 are of strength comparable to those of H-beta. However, the spectra recorded upon adsorption of the more sensitive CO probe suggest that the acid strength of the Brønsted sites of H-ITQ-7 is slightly lower than those of several other acidic zeolites. H-ITQ-7 is an active catalyst in the conversion of methanol to hydrocarbons at 400 °C, a reaction that requires strong Brønsted acidity, and the product shape selectivity observed indicates that the pores of H-ITQ-7 are slightly more restricted than those of H-beta.