(583gd) Synthesis of a Non-Conventional Monolithic Catalyst by Immobilizing Mg/Al Layered Double Hydroxides within Microchannels of a Silica Monolith

Conventional monolithic catalysts allow fast mass/heat transfer, cause low pressure drops, and have been typically used for fast gas-phase reactions. These catalysts consist of parallel channels ≥100 μm in diameters and catalytically active species are coated on the channel walls. Because synthesis of such catalyst requires a mold, it is challenging to form a monolith that has parallel channels <100 μm in diameters. We aimed at the synthesis of a monolithic catalyst that has smaller parallel channels («100 μm in diameters) because it provides much higher geometrical surface area, potentially offers higher gas-liquid contact efficiency in multi-phase catalytic reactions and may function as a large assembly of microreactors. Previously, our group reported that directional freezing of a silica hydrogel under controlled conditions forms a monolith containing a large number of parallel microchannels of <100 μm in diameters. The resultant dried material (silica microhoneycomb, SMH) serves as a new catalyst support for continuous flow reaction systems. In this work, we show immobilization of Mg/Al layered double hydroxides (Mg/Al LDH) within the microchannels of a SMH by passing a formamide solution containing dispersed nanosheets of Mg/Al LDH through it. Because the SMH surface and dispersed Mg/Al LDH nanosheets were found to show opposite zeta potentials of -14 and 20 mV, respectively, Mg/Al LDH sheets were successfully immobilized on the microchannel walls. This work illustrates a new method of synthesizing non-conventional monolithic catalyst that is applicable to a continuous flow reaction system.