Regulation of Remote Sites to Enhance Pt Activity in the Hydrogenation of Sulfur-Containing Nitroarenes

Abstract Outer-sphere catalysis, commonly associated with enzyme catalysis and homogeneous catalysis, utilizes remote sites to drive reactions and is particularly effective for reactants that are toxic to the catalyst. However, this approach has been rarely explored in heterogeneous catalysis. In this study, we demonstrate the use of remote sites to enhance the activity of Pt nanoparticles (NPs) in the hydrogenation of sulfur-containing nitroarenes. Catalysts with Pt and MoO3 co-deposited on TiO2 efficiently catalyze the hydrogenation of 5-nitrobenzothiazole (NBZ) under mild conditions, achieving a conversion rate of 5448 molNBZ · molPt⁻¹ · h⁻¹, the highest reported to date, even with ppm levels of Pt. The optimized Pt density (~ 3 NPs per 1×104 nm2) on the catalyst was found to favor HxMoO3 mediated sequential H transfer from Pt to Mo and subsequently to the substrate. Higher Pt density may enhance H transfer to Mo, but the hydrogenation process becomes limited by the availability of HxMoO3 for further H transfer to the substrate, revealing the intrinsic reason for the high activity of catalysts with ppm Pt. A direct H transfer pathway via HxMoO3 to the substrate, rather than solvent-mediated proton-coupled electron transfer, was observed and confirmed through solvent isotope kinetic effects and solvent studies. Tuning remote sites on solid catalysts offers a promising strategy for developing catalysts with the minim use of precious metals in the hydrogenation of strongly coordinating reactants.