Catalysts in this category are more environmentally benign and
sustainable than their homogeneous counterparts and have so far
shown very limited corrosion and recycling problems. However, high
porosity systems are required to obtain better performance. The
porosity allows appropriate adsorption-desorption and diffusion of
the reactants and products. Thus, acidic zeolites (see Table 2)would be
preferable here than the metal oxides or carbonates. Their structural
and acidity properties can always be modified to address diffusional
limitations and thus enhance the production of larger biodiesel yields
[44e47]. However, a challenging issue with zeolites is selecting the
most appropriate silicaealumina ratio as well as the modifier