Highly active small Pd nanocatalysts obtained by visible-light-induced photoreduction with citrate and oxalate salts under batch and flow approaches

A fast, economical and straightforward photochemical method was developed to produce small Pd-PVP NPs in aqueous media at room temperature. The photochemical approach involved the use of a combination of citrate and oxalate salts as photoinitiators (PIs) under visible light. In addition, the protocol was successfully performed in a photo-flow reactor and after only 150 s, it was possible to obtain Pd-PVP NPs with a small size and narrow size distribution. We also investigated the effects of the ratio of citrate : oxalate as the PIs on the size distribution and stability of the nanoparticles. The results indicated that the optimum conditions to achieve efficient production of Pd-PVP NPs with short-time irradiation comprise a citrate : oxalate combination in ratios between 4 : 6 and 9 : 1 to yield optimum Pd nanocatalysts in terms of stability, narrow size distribution and high catalytic activity. The catalytic activity of the photochemically prepared Pd-PVP NPs was evaluated in Suzuki-Miyaura coupling reaction and reduction of nitroaromatic compounds. Depending on the reaction under study, the ratio of PIs was found to have a remarkable effect on the catalysis, which can be associated to the optimal balance between the stabilization and surface activation of nanoparticles.