Spectroscopic and catalytic characterization of extra large pore zeotype H-ITQ-33

Abstract

The ITQ-33 structure comprises 18-ring channels, and this material constitutes one of very few zeolites/zeotypes with extra large pores. Such materials are of interest due to their ability to catalyze reactions involving bulky species and the prospect of novel shape selective properties. In this work, the recently discovered and little studied H-ITQ-33 catalyst has been synthesized and characterized. Emphasis has been placed on characterization of the fundamental properties of this material and its catalytic properties in the industrially relevant conversion of methanol to hydrocarbons. An unusually harsh calcination procedure (5 h at 650 °C) is required to fully remove the structure directing agent. Using FTIR, it is shown that the Brønsted acid sites become available once persistent NH 3 / NH 4 + formed during the decomposition is removed. It is demonstrated that H-ITQ-33 is an active catalyst in the conversion of methanol to hydrocarbons. The catalyst is fully regenerable during three deactivation/regeneration cycles. The presence of extra large 18-ring channels is not reflected in the observed product shape selectivity, which is similar to that commonly observed for 12-ring zeolites. This indicates that the formation of bicyclic species as undesired byproducts (coke) is a slow reaction step relative to the reaction leading to arenes. Remarkably, the H-ITQ-33 catalyst contains unusually little carbonaceous deposits (coke) when fully deactivated and the mode of catalyst deactivation has been studied in detail using in situ FTIR, UV–Vis, thermogravimetry and a catalyst dissolution/coke extraction protocol.