Encapsulation of Laccase/TEMPO in Nanoreactors with Different Microenvironments for Aerobic Diol Lactonization

The aerobic dehydrogenation of 1,4-butanediol (BDO) to γ-butyrolactone (GBL) is of great importance but remains challenging in terms of catalytic efficiency and selectivity. Laccase (multicopper oxidase)/2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), a highly efficient homogeneous catalyst, could promote the lactonization of BDO at room temperature and atmospheric pressure. Encapsulating laccase/TEMPO to construct nanoreactors for heterogeneous applications is desirable for the low-cost industrial production of GBL. Using SBA-15 as the support, TEMPO was immobilized by different reagents, 3-aminopropyltrimethoxysilane, trimethoxysilane, and 1,4-diisocyanatobutane, which also enabled the regulation of the microenvironment of the nanoreactor. Laccase was subsequently impregnated into the SBA-15 channels, and different cycles of TiO₂ deposited via low-temperature atomic layer deposition (ALD) were employed to adjust the pore entrance size, and the obtained encapsulated catalysts were denoted as mTiO₂/laccase/SBA-15-TEMPO-x. The encapsulated laccase within the nanoreactor demonstrated a significant synergistic effect, and the turnover frequency (TOF) of 130TiO₂/laccase/SBA-15-TEMPO-3 can reach 9.48 × 10³ h^-1, much higher than that of homogeneous laccase/TEMPO with a TOF of 0.74 × 10³ h^-1. Kinetic experiments indicated that the aerobic lactonization of BDO follows a pseudo-first-order reaction, and a hydrophilic microenvironment facilitated the adsorption of BDO within the nanoreactor, thereby greatly promoting the reaction. This encapsulated catalyst also exhibited excellent performance in the lactonization of various diols.