Immobilization of β-glucosidase over structured cordierite monoliths washcoated with wrinkled silica nanoparticles

The enzymatic conversion of biomass-derived compounds represents a key step in the biorefinery flowsheet, allowing low-temperature high-efficiency reactions. β-Glucosidases are able to hydrolyze cellobiose into glucose. Wrinkled silica nanoparticles (WSNs) were demonstrated to be a good support for the immobilization of β-glucosidases, showing better performance than free enzymes in batch reaction; on the other hand, immobilized enzyme microreactors (IEMs) are receiving significant attention, because small quantities of reagents can be used, and favorable heat and mass transfer can be achieved with respect to conventional batch systems. In this work, we prepared, characterized, and tested structured enzymatic reactor compounds by a honeycomb monolith, a WSN washcoat, and β-glucosidases as the active phase. Powder and structured materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 physisorption, thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR). Structured catalysts were tested under both batch and continuous flow reaction conditions and compared to powder catalysts (batch reaction). The WSN washcoat was attached well onto the monolith walls, as suggested by the negligible weight loss after ultrasound treatment; the WSNs preserved their shape, porosity, and individual nature when deposited onto the monolith walls. The immobilized enzyme microreactors proved to be very efficient in hydrolysis of cellobiose to glucose, showing a complete conversion under continuous flow reaction at a batch-equivalent contact time equal to 120 min vs. 24 h obtained in the batch experiments. The apparent KM value showed a 20-fold decrease with respect to the batch process, due to the absence of external diffusive transport limitations.