Robust continuous synthesis and in situ deposition of catalytically active nanoparticles on colloidal support materials in a triphasic flow millireactor

Abstract Ultra-small noble metal nanoparticles, such as palladium, platinum and rhodium, are invaluable catalysts for the synthesis of a plethora of materials, ranging from pharmaceutical drugs to polymers and fertilizers due to their high catalytic activities and large surface area-to-volume ratios. In practice, these particles are typically deposited on larger-sized support materials to stabilize them against agglomeration, whilst maintaining catalytic activity. We choose colloidal deposition as the process to synthesize supported nanoparticles, as it enables the deposition of nanoparticles with complex compositions and shapes on the support material, since the physical properties of the colloid nanoparticles are not affected by the deposition process. In this paper, we demonstrate a robust triphasic flow millireactor for catalytic nanoparticle synthesis and their facile in situ deposition onto colloidal support materials with tunable metal loading from 5% to 23% and a high degree of control over the spatial distribution on the support material. We highlight the consistency and quality of the supported nanoparticles produced by the flow synthesis compared to their batch-synthesized counterparts. We also demonstrate the versatility of our method for different nanoparticles types, including bi-/tri-metallics (Pd5Pt5, Rh5Pt5, Ru5Pt5 and Rh3Pd4Pt5) and three different support materials - titania, alumina and ceria.