Controlling the pyrolysis conditions of microporous/mesoporous MIL-125 to synthesize porous, carbon-supported Ti catalysts with targeted Ti phases for the oxidation of dibenzothiophene

Abstract

Metal-organic frameworks (MOFs) have been used as templates to synthesize a variety of functional materials. Pyrolysis of Zn-MOFs typically yields materials that retain the high surface area of the parent MOF while imparting mesoporosity due to carbothermal reduction and Zn evaporation. When non-Zn containing MOFs are used, significant loss in surface area and porosity after pyrolysis is observed. To overcome these limitations, a hierarchical microporous/mesoporous analogue of microporous MIL-125 (Ti) was synthesized and subjected to pyrolysis at various temperatures. By varying the pyrolysis temperature, both Ti content and phase in the final materials could be altered. The resulting materials exhibited enhanced mesoporosity and activity as catalysts in the oxidation of dibenzothiophene when compared to pyrolyzed microporous MIL-125. This increased activity was attributed to the greater mesoporosity of the hierarchical materials. This work demonstrated that the properties of MOF-templated materials can be tuned by altering the morphology of the precursor MOF.