An Alloy Strategy To Construct Metal/Oxide Interfacial Catalysts

Metal/oxide catalyst is an important part of heterogeneous catalysis and has a wide range of applications in chemical production.The metal oxide as supports can not only disperse the loaded metal particles,but also interact strongly with the metal to affect the catalytic performance.Recent studies have proved that the metal/oxide interface is the active center of the metal/oxide catalysts for many reactions,which suggests the key role of the oxide support in the catalytic reaction.However,the traditional metal/oxide catalyst is limited by the structure and specific surface area of the oxide,so the few metal/oxide interface sites would affect the performance in the catalytic reaction.There-fore,in order to improve the activity of the catalysts,the researchers proposed to support oxide nanostructures on the metal to construct a large number of metal/oxide interface sites.Scientists have developed several preparation methods such as deposition,hy-drolysis of precusors and alloy oxidation to synthesize the metal/oxide interfacial cat-alysts.Among them,the alloy oxidation method has gradually become a hot spot for researchers due to its simple and easy preparation process.In the preparation process of alloy oxidation,with use of the difference in the oxygen binding ability of different metals in the alloy,annealing in the air induces the metal segregation to the surface to form oxides.However,so far the alloy method are still limited to the oxides of late transition metal elements such as Fe,Co and Ni,while the metal/oxide interfaces which consist of early metal oxides which are commonly used supports such as TiO2 and ZrO2 are rarely reported.Here,we proposes a high-temperature alloy method for preparing a series of Pt/early transition metal oxide interface catalysts.We further explored the application of Pt/metal oxide interface catalysts in diverse catalytic reactions and found that they have excellent catalytic activity for hydrogenation of a variety of groups.The increased activity comes from the heterolytic dissociation of H2 at the Pt/oxide interface.The main results achieved are as follows:1.An alloy strategy was devoloped to prepare of a variety of Pt/metal oxide inter-face catalysts.We prepared S-doped carbon(SC)using the method of transition metal-assisted carbonization of small organic molecules developed by our research group.Using sulfur-doped carbon as support and impregnation method,6 kinds of sulfur-doped carbon supported Pt-based alloy catalysts(denoted as PtM/SC,M=Ti,Zr,Sc,Fe,Co,Ni)were successfully prepared by the high-temperature hydrogen reduction.We used X-ray diffraction(XRD)and energy scattering spectroscopy(EDS-mapping)characterization to prove that a uniform PtM alloy phase was successfully obtained in PtM/SC.Then the obtained PtM/SC catalysts were annealed in air at a certain tempera-ture to obtain sulfur-doped carbon supported Pt/metal oxide interface catalysts(denoted as Pt-MOx/SC).Through the XRD and high-angle annular dark field-scanning transmis-sion electron microscope(HAADF-STEM)characterization of the Pt-MOx/SC catalyst proved that the transition metal segregated to the surface after annealing process.X-ray photoelectron spectroscopy(XPS)and X-ray absorption fine structure(XAFS)charac-terization of the Pt-MOx/SC catalyst showed that the oxidation state of transition metals increased and metals formed metal oxides after annealing process.2.The catalytic activity of the prepared Pt/oxide interface catalysts in the hydro-genation reactions was explored,and a series of experiments proved that the increase in catalytic activity comes from the constructed Pt/metal oxide interface sites.Taking sulfur-doped carbon supported Pt/titanium oxide catalyst(Pt-TiOx/SC)as an example,it has excellent catalytic activity for the hydrogenation of benzaldehyde,and the turnover frequency(TOF)can reach 7564 h-1,which is increased by 2.5 times compared with commercial Pt/C catalyst.In addition,other sulfur-doped carbon supported Pt/metal oxide catalysts(Pt-MOx/SC,M=Sc,Zr)also exhibit excellent catalytic activity for the hydrogenation of benzaldehyde,which have better activity compared with fresh PtM/SC catalysts.In addition,Pt-TiOx/SC catalyst showed excellent stability in cycle experi-ments.We also explored activity of Pt-TiOx/SC catalyst in hydrogenate of nitrobenzene and styrene,and the conversion is 3.5 times and 1.4 times higher than that of Pt3Ti/SC catalyst.Moreover,in the hydrogenation reaction of furfural with Pt-TiOx/SC catalyst,not only the activity is increased by 4.3 times,but the selectivity is also increased from 95%to 99%.The catalytic experiment results prove that the constructed Pt-TiOx cat-alyst can be applied to the catalytic hydrogenation of various groups and molecules.In addition,the kinetic isotope effect(KIE)was also used to explore the catalytic hy-drogenation process of Pt-TiOx/SC.The KIE result of Pt-TiOx catalyst has a significant change from the commercial Pt/C catalyst,which proves that the reaction process of Pt-TiOx catalyst is different from the commercial Pt/C catalyst.We infer that H2 can be split at the Pt-TiOx interface to generate Hδ+ and Hδ-,so that the Pt-TiOx/SC catalyst has excellent catalytic activity.