Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLES16 Jun 2022Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts Qingyuan Wu†, Wenting Zhou†, Hui Shen, Ruixuan Qin, Qiming Hong, Xiaodong Yi and Nanfeng Zheng Qingyuan Wu† State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 †Q. Wu and W. Zhou contributed equally to this work.Google Scholar More articles by this author , Wenting Zhou† State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 †Q. Wu and W. Zhou contributed equally to this work.Google Scholar More articles by this author , Hui Shen State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 Google Scholar More articles by this author , Ruixuan Qin State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 Google Scholar More articles by this author , Qiming Hong State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 Google Scholar More articles by this author , Xiaodong Yi *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 Google Scholar More articles by this author and Nanfeng Zheng *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory for Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National & Local Joint Engineering Research Center for Preparation Technology of Nanomaterials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 Innovation Laboratory for Sciences and Technologies of Energy Materials of Fujian Province (IKKEM), Xiamen 361102 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.022.202202020 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Supported metal catalysts integrating advantages of catalytic hydrogenation and stoichiometric reduction are highly desirable for the green production of fine chemicals. Decoupling catalytic hydrogenation into H2 activation and selective reduction taking place at different locations is expected to provide an effective strategy to fabricate such catalyst systems. Herein, we report a decoupled hydrogenation system by modifying Pt catalysts supported on reducible In2O3 with ethylenediamine (EDA). The system exhibits good catalytic performance in oximes production from nitroalkanes, an industrially important reaction, by employing H2. Systematic studies demonstrate that the surface coordination of EDA on Pt is crucial to passivate the Pt surface from nitro hydrogenation without inhibiting H2 activation. The activated H2 species can then transfer and reduce the In2O3 support in situ to generate sustainable stoichiometric reducing agents for the chemoselective reduction of nitroalkanes. Based upon the mechanistic understanding, a sustainable strategy for the production of oximes has been successfully fabricated. Download figure Download PowerPoint Introduction Enhancing selectivity to minimize waste production is one of the core tasks of catalysis in the development of a sustainable society.1–4 Heterogeneous noble metal (e.g., Pt, Pd) catalysts usually exhibit high activity in hydrogenation catalysis, allowing the continuous activation of H2 for the rapid hydrogenation of unsaturated functional groups. However, besides the hydrogenation of targeted groups, other unsaturated groups are often hydrogenated as well, leading to poor selectivity.5,6 Such a situation is mainly due to the similar chemical adsorption capabilities of different unsaturated groups on unmodified noble metal surfaces, and thus easy reaction with activated hydrogen species occurs.7 To overcome the problem, several methods of regulating electronic or steric effects of noble metal catalysts have been developed, including but not limited to, controlling metal size and shape,8–12 adding organic or inorganic modifiers,13–17 and encapsulating metal species in porous materials.18–20 In contrast, it has been well documented that stoichiometric reducing agents such as Na2S2O4, Fe, SnCl2, or Zn are readily employed for the selective reduction of various unsaturated compounds.21 In spite of low cost and ease of use of these stoichiometric reductants, the formation of large amounts of solid waste makes the stoichiometric reduction process environmentally unsustainable and unfriendly.22 In rare cases, earth-abundant metal oxides can serve as effective catalysts for selective hydrogenation of unsaturated compounds. However, the hydrogenation process is typically conducted under harsh reaction conditions.23,24 As such, the development of heterogeneous catalysts integrating advantages of both catalytic hydrogenation and stoichiometric reduction while avoiding their disadvantages is highly desirable. One simple idea is to fabricate supported noble-metal catalysts on reducible oxides where the H2 activation takes place on the noble metal site while the stoichiometric reduction of substrates proceeds with the in situ generated reducing species on the supports. The key to such decoupled hydrogenation catalysis is to have activated hydrogen species migrate from the noble-metal surface to the reducible supports so that they can serve as stoichiometric reductants. A close examination of the literature reveals that ethylenediamine (EDA)-coated ultrathin Pt nanowires exhibit high selectivity in the hydrogenation of nitroaromatics, suggesting H2 can be activated on an EDA-passivated Pt surface.14 Moreover, strong metal-support interaction (SMSI) is present even at low reduction temperature.25,26 For example, the reduction of In2O3 surfaces can take place at the low temperature of 41 °C, indicating that In2O3 is a potential candidate for creating stoichiometric reducing species.27 Bringing these inspirations together, we now report a decoupled hydrogenation catalysis system using In2O3-supported Pt nanocatalysts in EDA solvent. The selective hydrogenation of nitrocyclohexane (NCH) to cyclohexanone oxime (CHO) is selected as a probe reaction because CHO is a highly demanded raw material for the production of ε-caprolactam, an important precursor for nylon-6, fibers, and resins.28–31 Conventional methods for CHO production from cyclohexanone (CHone) are typically limited by harsh reaction conditions, low yield,5,32 and generation of a significant amount of wastes.29,33 The selective hydrogenation of NCH to CHO represents an alternative strategy with many advantages (e.g., mild conditions, simple operation, and environmental friendliness).34–37 Nevertheless, selective production of CHO from NCH remains challenging because NCH can also be hydrogenated to cyclohexylamine (CHA) via competitive reaction pathways, CHO can be over-hydrogenated to CHA or hydrolyzed to CHone and then cyclohexanol, and condensation products are also detected ( Supporting Information Figure S1). It is worth noting that limited success on the synthesis of CHO via the selective hydrogenation of NCH has been reported.29,38–45 Despite good catalytic performances of reported catalysts in selective NCH hydrogenation, some drawbacks are still prominent, for example, unsatisfactory yields, harsh conditions, hazardous promoters, and unclear catalyst mechanisms. The catalyst demonstrated in this work exhibits high catalytic performance for the selective NCH hydrogenation to CHO under mild conditions. The use of EDA is demonstrated to be the key to the decoupled hydrogenation catalysis because the surface coordination of EDA on Pt inhibits the adsorption of NCH while still allowing H2 activation on Pt. More importantly, EDA does not coordinate to the In2O3 support so that the activated hydrogen species can migrate from Pt to reduce the In2O3 support in situ, thus affording a unique sustainable reducing species for the selective reduction. The as-reduced In2O3 surface can selectively reduce nitro but not oxime groups, resulting in the high selectivity for CHO. More importantly, our findings allow us to construct a family of catalysts for decoupled hydrogenation for the selective production of oximes from different nitro compounds. Experimental Methods Materials and measurements All chemicals were obtained from commercial sources and were used without further purification. Transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and energy dispersive spectroscopy (EDS) elemental mapping studies were performed on a TECNAI F30 transmission electron microscope (Philips-FEI, Amsterdam, Netherlands) operating at 300 kV. X-ray diffraction (XRD) experiments were conducted on a Rigaku Ultima IV diffractometer using Cu Kα radiation (Rigaku Corp., Tokyo, Japan). Gas chromatography mass spectrometry (GC-MS) tests were carried out on a gas chromatography mass spectrometer (GCMS-QP2010 SE W; Shimadzu Corp., Kyoto, Japan). Fourier transform infrared (FTIR) spectroscopy was carried out on a Nicolet iS50 Fourier Transform Infrared spectrometer equipped with a mercury cadmium telluride detector (Thermo Fisher Scientific Inc., Massachusetts, USA). X-ray photoelectron spectroscopy (XPS) measurements were carried out on a PHI Quantum-2000 photoelectron spectrometer (Al Kα with 1486.6 eV operating at 15 kV, 35 W, and 200 μm spot size; Thermo Fisher Scientific Inc., Massachusetts, USA) and a Scienta Omicron Sphera II hemispherical electron energy analyzer (Monochromatic Al Kα with 1486.6 eV operating at 15 kV and 300 W; Thermo Fisher Scientific Inc., Massachusetts, USA). Temperature-programmed reduction by H2 (H2-TPR) was measured on an AutoChem II 2920 instrument (Micromeritics Instruments Corp., Georgia, USA). Synthesis of support and catalysts In2O3 support was synthesized by calcined In(NO3)3·xH2O at 400 °C for 2 h under air. The 1 wt % Pt/In2O3 catalyst was prepared by incipient wetness impregnation and reduction of K2PtCl6 on In2O3. The synthesis of Pt nanoparticles (NPs) was similar to the synthesis of Pt/In2O3, only the support was excluded. In a typical synthesis of In2O3-Pt/γ-Al2O3, first, 5 wt % Pt/γ-Al2O3 was prepared like the synthesis of Pt/In2O3. Next, In2O3-Pt/γ-Al2O3 (5 wt % In) was synthesized by incipient wetness impregnation of In(NO3)3·xH2O on Pt/γ-Al2O3, and then treated with NaOH solution. In a typical synthesis of Pt/Fe2O3, Pt/SnO2, Pt/Co3O4, Pd/In2O3, Pd/Fe2O3, Pd/SnO2, and Pd/Co3O4 catalysts, different supports and metal precursors were used. Catalytic reaction conditions For a typical catalytic experiment, a 48 mL glass pressure vessel equipped with a stirrer was employed as a reactor. Hydrogenation of NCH was carried out under 0.4 MPa H2 at 60 °C. For a reaction, 5 mL EDA, 50 mg (2.56 μmol Pt) catalyst (1 wt % Pt/In2O3), and 65 μL (531.9 μmol) NCH were added. After a given time, aliquots of 100 μL were periodically taken, diluted in 100 μL ethanol, and centrifuged for further analysis by gas chromatography spectrometry. For the hydrogenation of nitrocyclopentane and nitropropane, the same procedure was used except that NCH was replaced by 531.9 μmol nitrocyclopentane and nitropropane, respectively. Results and Discussion Synthesis, characterization and catalysis of Pt/In2O3 In the present study, the 1 wt % Pt/In2O3 catalyst was synthesized by incipient wetness impregnation of the In2O3 support with an aqueous solution of potassium hexachloroplatinate followed by chemical reduction by NaBH4. The obtained catalysts, as characterized by TEM and powder XRD, contained only small Pt NPs; no large Pt NPs were formed (Figure 1a and Supporting Information Figures S2 and S3). STEM and EDS elemental mapping measurements further demonstrated that the Pt NPs were well dispersed on the In2O3 support (Figure 1b–e).46 Figure 1 | (a) Representative TEM images of 1 wt % Pt/In2O3; typical Pt NPs marked by white dashed circles. (b) Representative STEM image of 1 wt % Pt/In2O3. Scale bar, 50 nm. (c–e) STEM-EDS elemental mapping of 1 wt % Pt/In2O3. (f) Selective NCH hydrogenation by 1 wt % Pt/In2O3 in EDA or EtOH. (g) The Ea of selective NCH hydrogenation catalyzed by 1 wt % Pt/In2O3 in EDA or EtOH. Download figure Download PowerPoint The catalysis performance of the as-prepared Pt/In2O3 catalyst was evaluated by using 50 mg catalyst (1 wt %, 2.56 μmol Pt) in a hydrogenation reaction containing 65 μL NCH (531.9 μmol) in 5 mL solvent in a 48 mL glass pressure vessel under 0.4 MPa H2 at 60 °C. The products were verified by GC-MS ( Supporting Information Figure S4a). As shown in Figure 1f, the catalysts exhibited high catalytic performance in EDA, as NCH was completely converted to CHO in 40 min with >99% selectivity. In sharp contrast, when the process was conducted in ethanol (EtOH), the selectivity was very poor although good activity was achieved. The major byproduct was determined by GC-MS to be CHA ( Supporting Information Figure S4b). The selectivity was also well maintained even with the use of a small amount of EDA in EtOH as the solvent ( Supporting Information Figure S5). The high selectivity can be rationalized by the poor activity of the catalyst in hydrogenating CHO in EDA ( Supporting Information Figure S6). Moreover, no activity decay was observed in five catalyst recycling tests in EDA, suggesting the excellent stability of the catalyst ( Supporting Information Figure S7). In addition, little effect of residue KCl on the catalytic performance was observed. As shown in Supporting Information Table S1, no obvious change in either conversion or selectivity of NCH hydrogenation in EDA was observed from the reactions upon the introduction of different amounts of KCl. Similar catalytic performance was observed when Pt(NH3)4(NO3)2 was used as the metal precursor. The large catalytic performance difference in different solvents motivated us to gain insight into the reaction mechanism. At first, the apparent activation energy (Ea) was calculated, in which the Ea of NCH to CHO hydrogenation in EDA (∼31.2 kJ·mol−1) was much lower than that in EtOH (Ea ≈ 70 kJ·mol−1) (Figure 1g). The difference in Ea suggests different catalytic sites and reaction pathways of the two situations.47,48 Important roles of In2O3 and ethylenediamine It should be noted that the use of In2O3 as the support is crucial to achieve the high catalytic performance. We compared the catalytic performances of Pt/In2O3, Pt NPs, a mixture of Pt NPs and In2O3, as well as Pt/Al2O3. As shown in Figure 2a, In2O3 of the same weight showed no catalytic activity due to the lack of active sites for activating H2. With the presence of EDA, Pt NPs and a mixture of Pt NPs and In2O3 also displayed no activity, indicating that EDA coordinated Pt metal surfaces were not active sites of NCH hydrogenation. The In2O3-supported Pt catalyst exhibited high activity in the hydrogenation, suggesting that the interfaces between Pt metal and In2O3 support or the reduced surfaces of In2O3 support were reactive sites for NCH hydrogenation. When Pt/Al2O3 catalysts having similar Pt–O–M (In or Al) interfaces but irreducible cations on support were employed, negligible hydrogenation activity was observed. The comparison suggests that the activity was not simply related to the presence of the non-zero Pt species at the Pt–O–M interface. Together with the importance of introducing EDA in catalysis, we propose that the hydrogenation of NCH was proceeded on the In2O3 support whose surface was reduced by the spillover hydrogen atoms from Pt. In other words, the chemical modification of EDA on Pt helped to prevent the adsorption of NCH while still allowing the activation of H2. The activated hydrogen species could then migrate and reduce In2O3 to generate reductive species for the stoichiometric reduction of NCH to CHO. To verify the proposal, the adsorption behaviors of EDA on In2O3 and Pt/In2O3 were first studied by measuring there in situ FTIR spectra by introducing EDA (Figure 2b). Whereas strong chemisorption of EDA on Pt/In2O3 was observed, no EDA adsorption on In2O3 was detected.14,49 Furthermore, in situ CO adsorption FTIR spectra illustrated the strong adsorption of CO on Pt NPs surface but negligible adsorption on EDA-Pt/In2O3 (Figure 2c). These results clearly indicate that the coordination of EDA took place on the Pt surface and readily altered the adsorption behaviors of small molecules such as CO. Thus, it is not surprising that the EDA-modified Pt/In2O3 treated with 0.1 MPa CO also showed good activity and selectivity ( Supporting Information Figure S8). More importantly, when trace CO (0.1%) was introduced into the reactor,50 Pt/In2O3 catalyst exhibited much better CO resistance in EDA than in EtOH. While NCH was completely converted to CHO with high selectivity in 120 min by Pt/In2O3 in EDA, Pt/In2O3 was almost completely poisoned by CO in EtOH (Figure 2d). Our studies also revealed that other weakly coordinated molecules, such as targeted product (NCH), were less likely to get adsorbed on the EDA-Pt/In2O3 catalyst ( Supporting Information Figure S9), suggesting that the Pt sites were not the active sites for NCH hydrogenation. Figure 2 | (a) Selective hydrogenation of NCH to cyclohexanone oxime catalyzed by Pt/In2O3, Pt NPs, mixture of Pt NPs, and In2O3, as well as Pt/Al2O3 in EDA. (b) FTIR spectra of EDA, in situ FTIR spectra of EDA adsorption on In2O3 and Pt/In2O3. (c) In situ FTIR spectra of CO adsorption on Pt/In2O3 and EDA-Pt/In2O3. (d) Selective hydrogenation of NCH catalyzed by Pt/In2O3 in EDA and EtOH with 0.1% CO in reactor. Reaction time, 120 min. Download figure Download PowerPoint Mechanism of the selective hydrogenation To understand reaction mechanism, we performed isotope trace experiments. D2 was used for the FTIR detection of activated hydrogen species (e.g., O–D stretching vibration at ∼2500 cm−1) to distinguish them from the background H species on the catalyst.51,52 When D2 was introduced to In2O3 and EDA-Pt/In2O3, respectively, an obvious O–D signal was detected only in EDA-Pt/In2O3, suggesting that In2O3 itself was inactive for H2 activation. The result was also a strong indication that the coordination of EDA did not poison the Pt surface for activating H2 or D2. The activated D species were then transferred to support as Dδ+ (Figure 3a). The in situ H2 FTIR spectra revealed the appearance of O–Hδ+ and In–Hδ− ( Supporting Information Figure S10) in H2-treated EDA-Pt/In2O3.53,54 To test that O–Hδ+ was involved in NCH hydrogenation, we explored the kinetic isotope effect (KIE) with the use of H2 or D2. A primary KIE (KH/KD = 2.4, the change of reaction rate due to isotopic substitution at the site of bond breaking) was observed for the reaction in EDA (Figure 3b), suggesting the bond cleavage of O–D rather than Pt–D in the rate-determining step.51 In contrast, a secondary KIE (KH/KD = 1.2, the change of reaction rate due to the zero-point energy difference between isotopic isomers) was observed for the reaction in EtOH ( Supporting Information Figure S11).55 The appearance of In–Hδ− indicated the existence of low valent indium, which was also confirmed by in situ XPS.56 As displayed in Figure 3c, the binding energy of surface indium species were shifted to a smaller value when Pt/In2O3 was subjected to the H2 treatment at 60 °C for 30 min.57 The binding energy of the C 1s peak at 285.5 eV served as the reference ( Supporting Information Figure S12). Furthermore, the temperature programmed reduction coupled with a thermal conductivity detector using H2 (H2-TPR) showed that reduction of the indium species of Pt/In2O3 began at 30 °C and the reduction degree increased with the increase of temperature. In comparison, indium species of In2O3 were reduced at temperatures >130 °C. No hydrogen-consuming species were found on Pt/Al2O3 (Figure 3d).27 In addition, the classical SMSI was proved to widely exist when platinum-group metals were supported on reducible oxides after reduction treatment. The migration of reduced oxides onto metal surfaces would strongly suppress or entirely disrupt the chemisorption of CO on metals.26,58 So it was not surprising that a weaker CO adsorption on the Pt/In2O3 catalyst was revealed by the FTIR experiments at the higher reduction temperature. No CO signal was observed even at 100 °C reduction, indicating facile reduction of indium species ( Supporting Information Figure S13).27,59 Figure 3 | (a) In situ FTIR spectra of D2 treated In2O3 and EDA-Pt/In2O3. (b) The kinetic isotope effect of selective NCH hydrogenation in EDA. Reaction conditions: 0.4 MPa H2 or D2, 30 °C, 5 mL EDA, 50 mg (2.56 μmol Pt) Pt/In2O3, 65 μL (531.9 μmol) NCH. (c) In situ XPS spectra of Pt/In2O3 and H2 treated Pt/In2O3. (d) H2-TPR of In2O3, Pt/Al2O3, and Pt/In2O3 (the downward signal means the decrease in hydrogen concentration in flowing gas over the catalyst). Download figure Download PowerPoint All these results suggest the generation of reductive indium species on the EDA-modified Pt/In2O3 upon introducing H2. These low-valent indium species were ready to reduce NCH to CHO. As shown in Supporting Information Figure S14, when NCH vapor carried by Ar was charged to H2-treated EDA-Pt/In2O3, the characteristic signal of adsorptive CHO was detected. In contrast, no signal of CHO on EDA-Pt/In2O3 was found without the introduction of H2. To further verify the importance of In2O3, we constructed an In2O3-modified Pt/Al2O3 catalyst by depositing In2O3 onto the Pt/Al2O3 surface.1,7,60,61 The high dispersion of In2O3 on Pt/Al2O3 was confirmed by XRD, STEM, and EDS elemental mapping measurements ( Supporting Information Figures S15 and S16). As expected, the catalyst exhibited much better catalytic performance than Pt/Al2O3 ( Supporting Information Figure S17). Applying the understanding to prepare diverse Pt or Pd catalysts for selective production of oximes With the deep understanding of how the copresence of In2O3 and EDA regulates the catalytic selectivity toward oximes, we explored the potential of the Pt/In2O3 catalyst in selective hydrogenation of more substrates, for example, nitrocyclopentane, and nitropropane. As shown in Figure 4a,b and Supporting Information Figures S18 and S19, the Pt/In2O3 catalyst exhibited both high activity and high selectivity in production of cyclopentanone oxime and 2-propanone oxime. Both nitrocyclopentane and nitropropane were completely converted to target products in 60 min with >99% selectivity. The selectivity toward oximes was perfectly maintained even if the reaction time was doubled. Figure 4 | (a) Selective hydrogenation of nitrocyclopentane by Pt/In2O3 in EDA. (b) Selective hydrogenation of nitropropane by Pt/In2O3 in EDA. (c) Considerable catalytic performance was observed for various catalysts. Reaction conditions: 50 mg catalyst, 65 μL NCH, 60 °C, 0.4 MPa H2, 5 mL EDA. Download figure Download PowerPoint Following the insight into reaction mechanism and identification of active sites of Pt/In2O3 catalyst, the developed heterogeneous system should be applicable to a wide variety of supported Pt or Pd catalysts on reducible oxides (In2O3, Fe2O3, SnO2, and Co3O4). Synthetically, the catalysts with a metal loading of 1 wt % were prepared by incipient wetness impregnation and reduction of potassium hexachloroplatinate(IV) or sodium tetrachloropalladate(II) on different reducible oxides. Before catalytic testing, the obtained catalysts, Pt/Fe2O3, Pt/SnO2, Pt/Co3O4, Pd/In2O3, Pd/Fe2O3, Pd/SnO2, and Pd/Co3O4 were characterized by XRD to confirm their composition and geometrical structures. As displayed in Supporting Information Figure S20, the XRD patterns of all the as-prepared catalysts show that no obvious metal NPs were found, indicating the metal species were well dispersed on oxides. Considerable catalytic performance was observed for the as-prepared catalysts of Pt/Fe2O3, Pt/SnO2, Pt/Co3O4, Pd/In2O3, Pd/Fe2O3, Pd/SnO2, and Pd/Co3O4 (Figure 4c and Supporting Information Figure S21). Overall, supported Pt catalysts showed better catalytic performance than their Pd counterparts. When Fe2O3 was used as the support, the catalyst exhibited the best performance. A 100% conversion of NCH to CHO with >99% selectivity was readily accomplished in 10 min by the Pt/Fe2O3 catalyst. It should be noted that the high catalytic performance was not observed on supported Pt or Pd catalysts on irreducible oxides. Moreover, the above studies demonstrated that the coordination of EDA on metals controlled the catalytic performance of decoupled hydrogenation catalysis. Such a coordination modification is not limited to EDA only. The use of bidentate amines (e.g., 1,3-diaminopropane, 1,6-hexanediamine) was revealed to be a more effective modifier or solvent than monodentate amines (e.g., ethanolamine and n-propylamine) to enhance the decoupled hydrogenation catalysis demonstrated in this work ( Supporting Information Figure S22). The introduction of different bidentate amines all offered good selectivity toward CHO. With the full conversion of NCH, the selectivities of >99%, >99%, and >97% toward CHO were observed in EDA, 1,3-diaminopropane, and 1,6-hexanediamine, respectively. In contrast, the use of monodentate amines not only reduced the reaction rate but also failed to achieve good selectivity. For example, in ethanolamine, the 84% conversion of NCH already led to a CHO selectivity of <85%. The use of n-propylamine gave 90% selectivity with 53% conversion. The downward trend of CHO selectivity continued with the increasing conversion of NCH. Conclusion A decoupled hydrogenation catalysis using fine Pt NPs supported on reducible oxides has been successfully developed for the selective hydrogenation of NCH to CHO. Comprehensive studies reveal the crucial roles of both the EDA solvent and the reducible support for the catalytic system. With the surface coordination of EDA on Pt, while H2 activation is still possible on Pt, the hydrogenation of nitro groups on Pt is inhibited so that the activated H2 species would instead reduce In2O3 to generate sustainable and reductive indium species for the selective reduction of nitro groups into oximes. The C=N bonds on oximes cannot be further reduced by reductive In2O3-x, leading to an unexpectedly high chemoselectivity toward oximes. With understanding the mechanism, a class of promising Pt or Pd catalysts supported on reducible oxides for the selective hydrogenation of nitro compounds to oximes are discovered. The work provides a simple and sustainable strategy for stoichiometric NCH hydrogenation, which we believe, will stimulate much interest for hydrogenation of functional nitro compounds. Supporting Information Supporting information is available and includes more detailed materials, synthesis processes, measurement methods, and supported figures. Conflict of Interest The authors declare that they have no conflict of interest. Funding Information This work was supported by the National Key R&D Program of China (grant no. 2017YFA0207302) and the National Natural Science Foundation of China (grant nos. 21890752, 21731005, and 21721001).