Isomerization of citronellal to isopulegol using eclectically engineered sulfated zirconia-carbon molecular sieve composite catalysts, UDCaT-2

Sulfated zirconia (S-ZrO2) is a well-known solid superacid used as a cataly st in various reactions of commercial importance such as isomerization, Fri edel-Crafts alkylation and acylation, nitration, cracking, esterification, etc. S-ZrO2, per se, is not a shape-selective catalyst. The selectivity tow ard the formation of the desired product can be greatly enhanced by eclecti cally designing a shape-selective catalyst by a synergistic combination bet ween S-ZrO2 and carbon molecular Sieves (CMS). The paper presents the novel ty of the combination of S-ZrO2 and CMS, designated as UDCaT-2, as a shape- selective catalyst in the cyclization of citronellal to isopulegol which ha s industrial value. UDCaT-2 was found to be the best catalyst, among others , for the selective cyclization of citronellal to isopulegol wherein the sh ape selectivity can be tailored by proper pretreatment. The conversion and selectivity were found to be the maximum at 95 degrees C. The formation of isopulegol was found to be dependent on the average pore size of the carbon molecular sieve barrier encompassing S-ZrO2. A detailed kinetic study of t he reaction showed that it followed a Langmuir-Hinshelwood-Hougen-Watson ty pe of mechanism whereby citronellal was found to be weakly adsorbed on the catalytic surface sites. The reaction was found to follow first-order kinet ics for the disappearance of citronellal.