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.
Lang et al. (Mon,) studied this question.