Dealuminated BEA zeolite for selective synthesis of five-membered cyclic acetal from glycerol under ambient conditions

Abstract

BEA zeolite was treated with phenoldisulfonic acid (PDSA) of different concentrations from 0.1 M to 1.0 M to obtain dealuminated zeolites. The treated BEA samples were characterized by XRD, ²⁷Al-MAS NMR, SEM-EDX, TPD NH₃, pyridine-FTIR and BET measurements. Modified zeolites showed an increase in surface area and pore volume and a decrease in acid amount with an increase in PDSA concentration. An untreated BEA sample catalyzed the reaction between glycerol and acetone to form glycerol acteals to yield two products, five-membered dioxalane and six-membered dioxane. Under optimized reaction conditions, the untreated BEA sample showed 83% dioxalane and 17% dioxane while the modified samples showed an increase in dioxalane selectivity with an increase in the acid concentration used for the treatment. The 1 M PDSA treated sample exhibited 100% selectivity for dioxalane. This is attributed to an increase in pore volume and decrease in acid amount of the modified BEA samples with an increase in PDSA concentration. The combined effect of pore volume and acidity in determining dioxalane selectivity is discussed.