Atomic Layer Deposition on Spray-Dried Supraparticles to Rationally Design Catalysts with Ultralow Noble Metal Loadings

The controlled assembly of supraparticles by using spray-drying enables the synthesis of nanoporous materials. Changing the size of the constituent nanoparticles or their agglomeration states provides access to a diverse range of pore frameworks. This turns supraparticles into ideal scaffolds in heterogeneous catalysis. The combination of supraparticles with atomic layer deposition (ALD) as a surface functionalization technique offers excellent control over the deposition of a functional material and its distribution over the scaffold on the nanoscale. This work reports the combination of SiO₂ supraparticles as tunable scaffolds and their loading with a platinum-based ALD catalyst. The deliberate adjustment of the scaffold pore framework via spray-drying and its effect on the catalyst deposition are highlighted. Furthermore, varying numbers of Pt ALD cycles are applied to explore the capability of the combination approach with respect to catalyst loading and Pt efficiency. High-resolution electron microscopy reveals ultrasmall Pt clusters deposited on the supraparticles after the very first ALD cycle. Using the hydrogenation of 4-nitrophenol as a demonstration, the impact of the pore framework and the Pt deposition variation in ALD on the catalytic functionality is investigated.