Materials engineering of Zr-metal-organic frameworks catalysts for the optimized production of biofuel additives

Abstract

The development of novel fuel additives from sustainable biomass feedstock is one of the common paths in the global transportation sector to mitigate the environmental drawbacks of the excessive dependence on fossil fuels. In order to boost the competitiveness of these green fuel additives, the use of an efficient catalyst becomes critical to obtain a satisfactory overall conversion to the product of interest in a short time. Metal-Organic frameworks (MOFs) have recently emerged as an important candidate to become the next generation of catalysts for biofuel production. The reason behind this interest in MOF catalysts originates from different features such as their permanent porosities, very high surface areas, and, most importantly, the flexibility by which their characteristics could be altered for a specific application. MOFs have thus opened a vast door to materials engineering in the catalysis field. In our study, we focus on the optimization of Zr-based MOFs’ characteristics by selectively engrafting active functional groups onto their organic linkers, by the intentional introduction of structural defects on their metal cluster, and by using a mixed-linker approach. The obtained samples are fully characterized and subsequently serve as acid catalysts in the esterification reaction of butyric acid in the presence of butanol for the efficient production of butyl butyrate, a novel green biofuel. We investigate the effect of the different characteristics of the MOFs catalysts such as their surface area, particle size, linker deficiency, acidity, and porosity on the mechanism and conversion in the catalytic reaction. Based on all the data obtained, a linear regression model is developed to determine the relative significance of each characteristic of the MOF structure in dictating its catalytic activity and to predict the final yield to butyl butyrate based on these characteristics. With the knowledge obtained, the catalytic activity of MOFs can be engineered from a laboratory prototype and optimized to serve as effective catalysts for the production of fine chemicals such as biofuels.