Fiber-glass supported catalysis: real-time, high-resolution visualization of active palladium catalytic centers during the reduction of nitro compounds

Abstract

The development of new flow-compatible high-performance catalysts requires the understanding of the activity of the material in the nanometric scale. Here we use a combination of fluorescence and electron microscopy, in-flow single molecule fluorescence, and bench chemistry, combined with a fluorogenic system, allowing an intimate understanding of the properties and performance of palladium on glass wool (Pd@GW) in the nitro-to-amine catalytic reduction. The process is monitored starting from the nitro-compounds' reversible association with catalytic centers, to the behavior, interaction, and departure of reduced amine products. The catalyst used, Pd@GW, is ideal for flow heterogeneous catalysis applications requiring a fixed bed catalyst. Using advanced microscopy techniques, we are able to fully characterize our catalyst in situ, providing deep insight into the catalytic abilities of the material. We also explore under flow conditions if Pd clusters could migrate and redeposit elsewhere on the surface of the heterogenous support. Overall Pd migration seems to be minimal over several hours, with the catalyst stability assisted by APTES anchoring. Further, some active Pd sites seem to have enhanced catalytic activity after reaction, as evidenced by in situ imaging of the catalyst. This deep understanding of the real activity of heterogeneous catalysts will help researchers to improve present catalysts and explore new catalysis systems.