Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Abstract

Catalytic hydrogenation of nitroaromatics is an environment‐benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)x deposition on Pt nanocrystals to give Fe(OH)x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the FeIII‐OH‐Pt interfaces. While H2 activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the FeIII‐OH‐Pt interfaces. In situ IR, X‐ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe3+/Fe2+ redox couple facilitates the hydrodeoxygenation of the ‐NO2 group during hydrogenation catalysis. Benefitting from FeIII‐OH‐Pt interfaces, the Fe(OH)x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.

Ultrathin Amorphous/Crystalline Heterophase Rh and Rh Alloy Nanosheets as Tandem Catalysts for Direct Indole Synthesis

“…First, the amorphous/crystalline heterophase can offer more abundant active sites. Compared with their crystalline counterparts (Figures S2c and S15c, Supporting Information), the a / c ‐Rh and a / c ‐RhCu NSs possess more abundant phase boundaries (Figures S3 and S18, Supporting Information) which could serve as active sites to boost the hydrogenation rate of the nitro group (NO 2 ) [ 42 ] and thus improve the catalytic activity. In addition, the undercoordinated Rh atoms in the amorphous domains, as confirmed by the fitted EXAFS data (Table S1, Supporting Information), could also serve as the active sites for the catalytic reactions, further improving their catalytic activity for hydrogenation process.…”

“…[ 43,44 ] The increased electron density of Rh could result in the weaker surface binding of H atoms on Rh atoms [ 23,45–47 ] further enhancing the hydrogenation activity. [ 42,48–50 ] Since H 2 only participated in the reduction of unsaturated bonds, when a / c ‐RhCu NSs instead of a / c ‐Rh NSs are used as the catalyst, the hydrogenation step (Figure 4a) 2‐NPA to (2‐aminophenyl)acetaldehyde) in the tandem reaction could be greatly promoted, and the decarbonylation rate of aldehyde group (Figure 4a) 2‐NPA to 2‐NT, non‐hydrogenation process) would be suppressed. As a result, the obtained amine intermediate, i.e., (2‐aminophenyl)acetaldehyde, can be rapidly condensed with the adjacent aldehyde group by the tandem process, leading to the more favored production of indole.…”

Surface Molecule Manipulated Pt/TiO2 Catalysts for Selective Hydrogenation of Cinnamaldehyde

“…Previous attempts to improve the chemoselectivity of metal nanocatalysts mainly focused on controlling the size, shape and composition of metal NPs, and, the interactions between metal and supports (1-6). More recent researches have seen an increased focus on understanding the interactions between adsorbates at nanoscale interfaces of heterogeneous catalysts (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). But, how these interactions can be precisely regulated to tune the chemical reactivity remains elusive.…”

Surface Electronic State Mediates Proton Transfer at Metal Nanoscale Interface for Catalytic Hydride Reduction of −NO2 to −NH2

“…It is generally believed that, the metal NPs is the active site of catalytic hydride reduction, which offers a dual role by providing its surface for the adsorption of reactants and mediating the transfer of electrons and protons to reduce the kinetic barrier for the −NO2 to −NH2 conversion (NaBH4 reducer is taken for granted as the source of hydrogen, Scheme 1a). However, the mass of solid evidences showed that, the efficiency of the catalytic 4-NP to 4-AP conversion is not only attributed to the metal NPs centers (14,15), but also to the microenvironment of the secondary coordination sphere of metal center, such as the pH and the type of solvent (16)(17)(18)(19)(20)(21)(22)(23), Very interestingly, the deuterium isotopic experiments recently confirmed that the interface water is prerequisite for catalytic reduction, and that, counter-intuitively, it is water rather than the NaBH4 reducer that provides the hydrogen for the formation of the 4-AP product (16,24), suggesting a completely new water-mediated proton transport mechanisms for the catalytic hydride reduction of −NO2 to −NH2 at metal NPs surface. In this report, with mesoporous silica nanosphere (MSNs) supported noble metal NPs as a model catalyst, we systematically study the effects of different reaction parameters on the reduction kinetics in the aqueous NaBH4 solution, mainly including the composition and valence of metals (Ag/Pd/Pt), isotopic solvent (D2O) or reducer (NaBD4), and concentration of sodium hydroxide (NaOH).…”