Activity modulation of core and shell in nanozeolite@enzyme bi-functional catalyst for dynamic kinetic resolution

A core-shell nanozeolite@enzyme bi-functional catalyst is prepared by using nanozeolite β as acidic core and immobilized Candida antarctica lipase B (CALB) as enzyme shell for the purpose of dynamic kinetic resolution (DKR), and polydiallyldimethylammonium chloride (PDDA) is used as interlayer to compart core and shell. The activities of core and shell in bi-functional catalyst are modulated to achieve the matching between racemization and kinetic resolution (KR) rates in DKR, i.e., a slow racemization rate on core while a fast KR rate on shell. Nanozeolite β with intermediate SiO2/Al2O3 ratio provides proper acid amount for racemization step. A relatively thick layer of PDDA not only improves the activity of CALB by its coverage for surface acidic sites but also limits the accessibility and diffusion of substrate towards the acidic core. The CALB shell with larger immobilized amount and higher enzyme activity offers enhanced driving force of DKR process, leading to higher conversion, selectivity and yield. The preparation and activity modulation of core-shell catalyst provide an ideal method to improve the catalytic performance of bi-functional catalyst.