Engineering UiO-66 Metal Organic Framework for Heterogeneous Catalysis

Metal organic frameworks (MOFs) are currently attracting considerable attention as heterogeneous catalysts at moderate temperatures, mainly for liquid-phase reactions. Since structural stability is one of the major concerns for the use of MOFs in catalysis, particularly considering that frequently some of the reported MOF materials are very unstable, the interest in this area has been focused on those MOFs exhibiting the highest structural robustness, UiO-66 being among the most widely used. Two introductory sections deal with the synthesis, structure and main properties of UiO-66, including its remarkable thermal (up to 350 degrees C) and chemical (aqueous solution in a wide pH range) stability. The main body of the review summarizes those examples of using UiO-66 in catalysis grouped according to the nature of the active sites, starting with the use of UiO-66 as Lewis acids. In this section, emphasis has been made in the recent strategies to create structural defects in a controlled way that generate Lewis acidity. Other sections cover examples illustrating substituted terephthalate as active sites and the evidence that there is a synergy between acid and basic sites in close proximity that make some of these UiO-66 with substituents at the linker to act as dual acid-base catalysts. Other sections are focused on the use of UiO-66 as hosts of metal nanoparticles, metal oxides and other host, remarking the influence that the nature of UiO-66 and the possible presence of substituents in the framework play on the activity of the incorporated guest. The last section summarizes the current state of the art in the use of UiO-66 in catalysis and provides our views on future developments regarding the application of UiO-66 in industrial processes.