Recent advances in waste-based and natural zeolitic catalytic materials for biodiesel production

Considering the current world crisis and definite future energy challenges, biomass-to-fuel transformation is increasingly becoming important both to the policy makers and to the industry. In this perspective, the valorisation of oils and fats via transesterification/esteri-fication reaction is an attractive method for producing biodiesel with qualities suitable for diesel engines. The recent interest indicated a significant shift to industrial waste valorisation as another approach for achieving process eco-efficiency. In this respect, the use of zeolite-based catalysts for the production of biofuels is reviewed here, with a special emphasis on the utilization of waste raw materials following the principles of green chemistry and sustainable development. Zeolites are interesting due to their outstanding catalytic properties, including the presence of intrinsic acid sites, simple loading of base sites, shape-selectivity, and high thermal stability. Neat zeolites or modified by the loading of active species are classified into several groups following their origin. For each group, the most relevant recent results reported in the literature are reviewed together with some critical considerations on the catalyst effectiveness, stability, reusability, and economy of synthesis. As an important part required for understanding and optimization of the biodiesel production process, the mechanisms of the reaction were discussed in detail. Finally, key perspective directions for further research studies were carefully identified and elaborated.