Abstract
The isomerization of citronellal to isopulegol is an important step in the synthesis of menthol. Several solid acid catalysts were evaluated for this reaction. However, to maintain economic viability, a suitable heterogeneous system which exhibit better activity and selectivity comparable or superior to the existing catalytic methods is needed. Among solid acids, larger pore zeolites have been found to exhibit superior property for isomerization of citronellal to isopulegol. However, the active sites inside the ZSM-5 micropores imposes severe mass transfer constrains. Hierarchical porous zeolite contains micro, meso and macro pores in the same material to overcome the mass transfer constrains. The present paper is aimed at an investigation of the catalytic activity of hierarchical porous nanocrystalline ZSM-5 towards the isomerization of citronellal to isopulegol. The catalyst was characterized by DLS, XRD, FT-IR, SEM, and ASAP analyses. The effects of various parameters such as, catalyst weight, reaction temperature, citronellal concentration and reusability of catalyst were studied. The results show that the hierarchical porous nanocrystalline ZSM-5 catalysts are highly efficient, selective, reusable and environmentally benign system for the isomerization of citronellal to isopulegol.