Scalable Synthesis of Selective Hydrodeoxygenation Core-Shell Pd@TiO2 Nanocatalysts

Catalytic materials have the potential to reduce our dependence on petroleum provided that new designs can enable the selective conversion of biomass to produce value-added products. Specifically, bifunctional materials with metal-metal oxide interfaces have been demonstrated for important reactions such as hydrodeoxygenation (HDO) of furanic compounds. With growing interest in renewable energy, the key challenge is to produce these materials in a scalable manner. Recently, inverted systems consisting of palladium nanoparticles (Pd NPs) encapsulated in a porous titania shell (Pd@TiO₂) have shown high selectivity for HDO. The catalytic selectivity for HDO is associated with the extent of microporosity in the titania shell. These catalysts are synthesized in low-throughput batch processes that are difficult to scale up because of poor mixing at large scales. These problems can be circumvented by using microreactors that provide a small mixing time. Further, high throughput can be obtained by increasing reactor run-time. We have developed a simple, inexpensive continuous jet-mixing reactor that has been successfully tested for silver nanoparticle (Ag NP) synthesis. In this work, the jet-mixing reactor is adapted to synthesize Pd@TiO₂ nanocatalysts in a continuous manner. The microporosity of the material obtained via jet-mixing is compared with that obtained from a batch process as a control. It is observed that jet-mixing leads to higher microporosity in the titania shell as compared to its batch counterpart. This is attributed to the fast rate of hydrolysis of the titanium precursor in the jet-mixing synthesized materials. Further, both materials are tested as catalysts for the HDO of furfuryl alcohol. It is observed that the selectivity for the HDO product, 2-methyl furan, obtained using the jet-mixing-synthesized material is comparable to that obtained by batch synthesis. Overall, these results suggest that jet-mixing may be an attractive technology for bulk synthesis of these catalysts.