Ultrafine Pd Nanoparticles Encapsulated in Mesoporous TiO2 Region Selectively Confined in Bamboo Microchannels: An Ultrastable Continuous-Flow Catalytic Hydrogenation Microreactor

Plant-based flow microreactors with natural channel structures, renewable properties, and environmental friendliness have increasingly gained popularity in heterogeneous catalysis. However, firmly immobilizing the catalysts simultaneously with ease and adaptability, maintaining great effectivity and long-term stability, is still a fundamental challenge. Herein, a highly efficient and ultrastable bamboo-based catalytic microreactor (CMR) containing mesoporous TiO2 (M-TiO2)-encapsulating ultrafine Pd nanoparticles (NPs) is constructed for the continuous-flow hydrogenation of nitroaromatics. The fabrication of the Pd-TiO2 catalysts in required bamboo microchannels (Pd-TiO2/B CMR) mainly involves a two-step region-selective synthetic strategy with ultra-low chemical usage, fast preparation, and low catalyst loading (0.007 wt%). The M-TiO2 films: 1) provide abundant oxygen vacancies and enough open cavities to facilitate the growth of Pd NPs; 2) improve Pd dispersion and reduce particle size; 3) allow diffusion of reactants, and 4) induce strong metal-support interactions for enhanced catalytic activity and stability. The optimized Pd-TiO2/B CMR demonstrates high efficiency (>97%) and excellent stability (1,000 h) for the continuous-flow hydrogenation of nitroaniline, even under intermittent operation (12 h on/12 h off for five cycles) or in a real aqueous matrix (>200 h), making it a promising candidate for Pd-catalyzed hydrogenation.

Automated summary

Plant-based flow microreactors with bamboo microchannels containing mesoporous TiO2-encapsulating ultrafine Pd nanoparticles were synthesized for continuous-flow hydrogenation. The design of the reactor enables high efficiency (>97%) and excellent stability (1,000 h) due to the abundant oxygen vacancies and open cavities provided by the TiO2 films, which facilitate the growth of Pd nanoparticles and improve their dispersion and catalytic activity. The optimized reactor shows promising potential for Pd-catalyzed hydrogenation in various conditions.