Heterogeneous catalysis of large biomolecules: insights from platinum particle size in NAD⁺ regeneration

Nicotinamide adenine dinucleotide (NAD⁺) cofactor regeneration is essential for enabling dehydrogenase-promoted biosynthesis for value-added chemicals. Heterogeneous catalytic cofactor regeneration, using supported metal catalysts, is an emerging approach and has shown great promise. However, mechanistic insight remains largely unexplored. In this work, a series of silica-supported platinum (Pt) catalysts have been prepared for NAD⁺ cofactor regeneration, to understand the roles of Pt particle size and structure. A turnover frequency (TOF) 'volcano plot' was obtained for Pt clusters in the range of 2.2-7.1 nm, with the maximum TOF (136 h^-1) observed at 5.6 nm. Selective Pt site blockage with polyvinyl pyrrolidone (PVP) revealed that the significant structure sensitivity originated from the synergistic effect of under- and well-coordinated sites in size-varied Pt clusters. In addition, a facet preference was also identified, where the cofactor regeneration favoured the Pt(100) surface more than Pt(111). These findings provide the first insight into NAD⁺ regeneration using heterogeneous Pt catalysts, which will be particularly useful for the rational design of supported metal catalysts.