Rational synthesis of sub-nanocatalysts with controllable electronic and atomic structures remains a challenge to break the limits of traditional catalysts for superior performance. Here we report the atomiclevel precise synthesis of Pt/graphene sub-nanocatalysts (from single atom, dimer, and to cluster) by atomic layer deposition, achieved by a novel high temperature pulsed ozone strategy to controllably precreate abundant in-plane epoxy groups on graphene as anchoring sites. The speci c in-plane epoxy structure endows the deposited Pt species with outstanding uniformity, controllability and stability. Their size-depended electronic and geometric effects have been observed for ammonia borane hydrolysis, revealing a volcano-type dependence of intrinsic activity on their sizes. Their active site structures have been identi ed based on extensive characterizations, dynamic compensation effect, kinetic isotope experiments and density function theory simulation. The Pt dimers show the highest catalytic activity and good durability than Pt single atoms and nanoparticles, ascribed to the unique C-Pt-Pt-O (C5Pt2O, metalmetal bond dimer) active site structure. Our work provides new insights into the precise tailoring and catalytic mechanism in sub-nanometer level.

Precise control of selectivity in hydrogenation reactions is a long-standing challenge. Surface decoration of nanocatalysts with transition-metal oxide nanoparticles (NPs) is an effective strategy to tailor the catalytic selectivity but generally at the expense of activity due to the blocking of active sites. Here, we report that constructing single-site metal oxide modifiers (NiO, CoO x , or FeO x ) on supported Au NPs by atomic layer deposition (ALD) can regulate their catalytic selectivity for nitroaromatic hydrogenation. The coverage of single-site metal oxide can be precisely tuned by altering the number of ALD cycles. The Au/TiO2 decorated with five cycles of NiO (Ni: 0.32 wt %) in the style of a single site can efficiently change the product selectivity from azo to azoxy compounds without significantly blocking the surface active sites. The density functional theory calculations indicate that the azoxybenzene bonded to the single-site NiO-decorated Au(111) with a larger adsorption energy, which inhibits the overhydrogenation of azoxybenzene and results in high azoxybenzene selectivity. Our work has demonstrated a general and efficient way to regulate the reaction selectivity of metal nanocatalysts by anchoring single-site metal oxide promoters.

Carbon−halogen reductive elimination is a conceptually novel elementary reaction. Its emergence broadens the horizons of transition-metal catalysis and provides new access to organohalides of versatile synthetic value. However, as the reverse process of facile oxidative addition of Pd(0) to organohalide, carbon−halogen reductive elimination remains elusive and practically difficult. Overcoming the thermodynamic disfavor inherent to such an elementary reaction is frustrated by the high reaction temperature and requirement of distinctive ligands. Here, we report a general strategy that employs [Et 3 NH] + [BF 4 ] − as an H-bond donor under a toluene/water/(CH 2 OH) 2 biphasic system to efficiently promote C(sp 3 )−halogen reductive elimination at low temperature. This enables a series of Pd(0)-catalyzed carbohalogenation reactions, including more challenging and unprecedented asymmetric carbobromination with a high level of efficiency and enantioselectivity by using readily available ligands. Mechanistic studies suggest that [Et 3 NH] + [BF 4 ] − can facilitate the heterolytic dissociation of halogen−Pd II C(sp 3 ) bonds via a potential H-bonding interaction to reduce the energy barrier of C(sp 3 )−halogen reductive elimination, thereby rendering it feasible in an S N 2 manner.

The selectivity of nitrile hydrogenation was turned by the concentration of hydrogen radicals on Pd surface.