Investigating size-dependent selectivity in benzaldehyde reductive amination via Ni nanoparticles

Selectivity control is a fundamental focus in catalysis chemistry, as it directly reflects the efficiency and efficacy of catalytic processes. While catalysis often involves intricate and cascade reaction steps using nanoparticle (NP) catalysts, the mechanism behind the size effect of nanoparticles on product selectivity has not been fully explored. We herein prepared a series of Ni-containing zeolitic catalysts in which the Ni NPs are uniformly supported on the mesopores and outer surfaces of H-ZSM-5 zeolites. The dynamic formation of Ni NPs from highly dispersed Ni precursors was monitored using transmission electron microscopy, in-situ X-ray pair distribution function, and in-situ X-ray absorption fine structure analysis. The metal nanoparticle size was carefully controlled between 3.72(5) nm and 11.91(7) by controlling the reduction temperature. We evaluated the catalytic performance of Ni NPs using the reductive amination of benzaldehyde in batch reactors at low temperatures. This reaction inherently favors the formation of a series of products, suffering highly from selectivity issues. Our results revealed a size-dependent behavior in reaction efficiency, with the catalyst achieving the highest catalytic activity (93 % selectivity in primary amine) at a particle size of 5.62(3) nm. This optimal performance is attributed to a balanced interplay between hydrogenation and amination capabilities. These findings highlight the intricate relationship between nanoparticle size and catalytic performance, emphasizing the necessity for precise optimization in catalyst design to enhance selectivity and sustainability in industrial applications.