Paper Title
Tuning Acidity in Metal-Organic Frameworks-Based Catalysts for Enhanced Production of Butyl Butyrate as a Biofuel Additive

Abstract
In an attempt to optimize the production of biofuel additives from biomass-derived components, different structures of Zr-based metal-organic frameworks (MOFs) were synthesized to serve as catalysts for the esterification reaction of butyric acid with butanol to produce a green fuel additive, butyl butyrate. The thrust of this study is to understand at a fundamental level the relations between the structure, properties and catalytic performance of champion materials that confer upon them the capacity to function as efficient esterification catalysts. For this purpose, UiO-66(COOH)2 and UiO-66(OH)2 were synthesized and fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) measurements, and thermogravimetric analysis (TGA). All prepared MOFs were efficiently used as catalysts of the liquid-phase esterification reaction for the production of butyl butyrate. The number of missing linkers per cluster in each structure was calculated based on TGA results. Interestingly, 92% conversion was achieved by employing UiO-66(OH)2 as a heterogeneous catalyst,which is very close to the 96% conversion obtained by the conventional homogeneous liquid catalyst H2SO4. This exceptional rate was attributed to the combination of a variety of factors such as its higher surface area, lower particle size, and less bulky organic linker. All MOFs were easily separated from the reaction medium, and their heterogeneity was confirmed by hot filtration method. With this knowledge, catalytic conversion rates and efficiencies of MOFs can be engineered from a laboratory prototype and optimized by tuning the functional groups of the organic linkers to serve as effective catalysts for the production of fine chemicals such as biofuels. Keywords - Heterogeneous Catalysts, Metal Organic Frameworks (MOFs), MOFs Defects, Esterification, Biofuel, Acid Density.