Effect of binders on the physicochemical and catalytic properties of extrudate-shaped beta zeolite catalysts for cyclization of citronellal

Citronellal cyclization was carried out in a continuous mode over H-beta-25 zeolite-based extrudates in a trickle-bed reactor at 35 °C and 10 bar of Ar. The physicochemical properties of zeolitic catalysts in the form of extrudates with a different diameter (1.4–3 mm) containing 30 wt % of a binder were correlated with the catalytic results. Alumina, aluminosilicate clay, and colloidal silica were used as binders. For extrudates with 1.4 mm in diameter, a significant decrease in the surface area, pore volume, and the total number of acid sites was observed in comparison to the values expected from a simple mechanical mixture of constituents. The specific surface area was similar, while the pore volume and mechanical strength decreased with increasing extrudate diameter. For all catalysts, conversion of citronellal and the yield of the desired pulegols decreased because of lower acidity and more prominent mass transfer with a size increase, while the selectivity ratio for different pulegols was similar. Overall, the effect of mass transfer on catalytic results in citronellal cyclization was larger than the effect of acidity. The yield of pulegols and the ratio of isopulegol ethers were correlated with strong Brønsted and strong Lewis acid sites, respectively. A proper selection of the binder and diameter of the extrudates plays a crucial role in the cyclization of citronellal.