Catalysts in the form of dispersed platinum nanoparticles (Pt NPs) immobilized on carbon usually suffer from deactivation through sintering under reaction conditions. In this contribution, we report the enhanced stability of highly dispersed Pt NPs on surface-modified carbon nanotubes (CNTs) against thermal and electrochemical sintering by N heteroatoms in the N-doped carbon support. The improved antisintering property of Pt NPs under thermal condition is characterized by in situ transmission electron microscopy (TEM), while the stability in electrochemical methanol oxidation reaction (MOR) is further examined at identical location (IL) using an advanced IL-TEM technique. A correlation of the Pt NP growth with the electrochemical surface area (ECSA) and the mass activity in MOR has been inferred. Our results indicate that both the surface oxygen groups and nitrogen-doped species are responsible for the fine dispersion of Pt NPs on the surface-modified CNTs, while the Pt NPs can be effectively stabilized under thermal and electrochemical conditions through the strong metal–support interaction via N heteroatoms. We further reveal that the mass activity of Pt NP is closely associated with the ECSA rather than directly affected by N-doping to CNTs.

At present, the development of highly efficient electrocatalysts with more rational control of microstructures (e.g. particle size, morphology, surface structure, and electronic structure) and chemical composition is needed and remained great challenges. Transmission electron microscopy (TEM) can offer the information about the microstructures and chemical compositions of the electrocatalysts on nano and atomic scale, which enables us to establish the synthesis-structure-performance relationship and further direct the design of new electrocatalysts with high performance. In this minireview paper, a brief introduction on the basic characterization of electrocatalysts with TEM, followed by the studying of dynamic evolution of the electrocatalysts in electrochemical reactions with identical location-TEM, is discussed.The basic characterization of electrocatalysts with transmission electron microscopy (TEM) and the dynamic evolution study of the electrocatalysts with identical location-TEM are discussed in the review.Download high-res image (129KB)Download full-size image

The selective oxidation of hydrocarbons to the corresponding ketones with solvent-free and molecular oxygen as an oxidant is of great importance in academic and industrial fields in view of economy and environment. In this respect, we present the facile synthesis and characterization of excellent catalysts comprising cobalt nanoparticles encapsulated into graphitic nitrogen-doped carbon nanotubes (Co@GCNs) via one-pot pyrolysis of a chelate compound containing citric acid, melamine, and CoCl2·6H2O. The selective oxidation of ethylbenzene under molecular oxygen and solvent-free conditions is employed as a probe reaction to investigate the catalytic performance; the optimized catalyst shows the best conversion (68%) and selectivity for acetophenone (93%). Combination of the catalytic results of the control group and the different characterization methods demonstrates that high catalytic activity is due to the synergistic effect between metallic cobalt and nitrogen-doped carbon nanotubes. Moreover, the catalyst has high catalytic activity for the aerobic and solvent-free oxidation of other arylalkane substrates. The proposed mechanistic study illustrates that the reaction is a free radical reaction progressing through superoxide radical anions (˙O2−).

Developing highly selective and stable catalysts for acetylene hydrogenation is an imperative task in the chemical industry. Herein, core–shell Pd@carbon nanoparticles supported on carbon nanotubes (Pd@C/CNTs) were synthesized. During the hydrogenation of acetylene, the selectivity of Pd@C/CNTs to ethylene was distinctly improved. Moreover, Pd@C/CNTs showed excellent stability during the hydrogenation reaction.

Although nanosized Au clusters have been well developed for many applications, fundamental understanding of their adsorption/activation behaviors in catalytic applications is still lacking, especially when other elements provide promotion or hybridization functions. Au hybridized with Cu element is a highly investigated system; Cu is in the same element group as Au and thus displays similar physicochemical properties. However, their hybrids are not well understood in terms of their chemical states and adsorption/activation properties. In this work, typical γ-Al2O3-supported Au and CuO as well as Au–CuO nanoparticles were prepared and characterized to explore their adsorption/activation properties in depth using CO as a probe molecule using advanced techniques, such as XPS, HR-TEM, temperature programmed experiments and operando DRIFT combined with mass spectra. It was found that gold and copper can both act as active sites during CO adsorption and activation. The CO-TPD and operando DRIFT results also revealed that CO molecules were able to react with surface oxygenated species, resulting in the direct formation of CO2 over the three samples in the absence of gaseous O2. The gold step sites (Austep) participated more readily in the reaction, especially under gaseous O2-free conditions. During adsorption, CO molecules were more preferentially adsorbed on Au0 sites at lower temperature comparing with those on the Cu0 sites. However, competitive adsorption occurred between CO adsorbed on Au0 and Cu0 with increased reaction temperature, and the synergy between the Au and Cu compositions was too strong to suppress the adsorption and activation of the CO molecules. The dynamic adsorption equilibrium over 120 °C to 200 °C resulted in the appearance of a hysteresis performance platform.

Pearl necklace-like ZnO–ZnWO4 heterojunctions composites have been designed and synthesized. The photocatalytic activity of the ZnO–ZnWO4 heterojunctions depended on the calcination temperature and ZnO–ZnWO4 molar ratio. The ZnO–ZnWO4 composites showed higher degradation efficiency than that of ZnO or ZnWO4 individually. The photocatalytic reaction was enhanced due to the heterojunctions construction, which improved charge separation of the photogenerated electron–hole pairs.

Ultrasmall-sized platinum nanoparticles (Pt NPs) (∼1 nm) supported on carbon nanotubes (CNTs) with nitrogen doping and oxygen functional groups were synthesized and applied in the catalytic hydrogenation of nitroarenes. The advanced identical location transmission electron microscopy (IL-TEM) method was applied to probe the structure evolution of the Pt/CNT catalysts in the reaction. The results indicate that Pt NPs supported on CNTs with a high amount of nitrogen doping (Pt/H-NCNTs) afford 2-fold activity to that of Pt NPs supported on CNTs with oxygen functional groups (Pt/oCNTs) and 4-fold to that of the commercial Pt NPs supported on active carbon (Pt/C) catalyst toward nitrobenzene. The catalytic performance of Pt/H-NCNTs remained constant during four cycles, whereas the activity of the Pt/oCNTs was halved at the second cycle. Compared with Pt/oCNTs, Pt/H-NCNTs exhibited a higher selectivity (>99%) in chemoselective hydrogenation of halonitrobenzenes to haloanilines due to the electron-rich chemical state of Pt NPs. The strong metal–support interaction along with the electron-donor capacity of nitrogen sites on H-NCNTs are capable of stabilizing the Pt NPs and achieving related catalytic recyclability as well as approximately 100% selectivity. The catalyst also delivers exclusively selective hydrogenation toward nitro groups for a wide scope of substituent nitroarenes into their corresponding anilines.Keywords: chemoselective hydrogenation; IL-TEM; metal−support interaction; nitrogen doping; platinum nanoparticles

The completely C2-selective arylation of N-methylindole was achieved by using a reusable solid Pd catalyst and water as a solvent without any other ligands or additives or exclusion of air. The catalysts possess well-dispersed Pd nanoparticles (∼1.5 nm), N-containing functional groups (∼11 wt %), and uniform mesopores (∼5 nm). The turnover frequency (TOF) is calculated to be 82 h–1.Arylations of both N-H indoles and N-protected indoles with diaryliodonium salts were achieved to give the desired products in high to excellent isolated yields in water. Mercapto-functionalized silica as a selective trapping agent, together with hot filtration, confirms the undetected leaching of Pd. The catalyst samples can be reused at least eight times without any additional activation treatment. The catalytic performance of the Pd catalyst is also compared with the performance of other mesoporous Pd catalysts on silica, carbon, and resins. The catalytic activity and stability of the present catalyst may be related to the well-dispersed Pd nanoparticles, the electron-rich environment stabilized by the N-containing functional groups, and the large, uniform mesopores.Keywords: C2 arylation; hybrid mesoporous polymer; Pd cluster; reusability; water-mediated

The structures of PtNix nanoalloy particles were modified through thermal annealing in different atmospheres. The evolution of surface structures was uncovered by advanced transmission electron microscopy, and the structure–function correlation in methanol electro-oxidation was probed. It provided new insights into the design and synthesis of highly efficient electrocatalysts.

As an emerging catalyst based on earth-abundant metals, Co3O4 supported on carbon materials, derived from the pyrolysis of metal salts and nitrogen-containing ligands, shows excellent performance in hydrogenation, hydrogenated coupling, oxidative esterification and oxidation of amines. Herein, we unravel the real active sites of this catalyst through a combination of XRD, XPS, HRTEM, EELS and poisoning experiments with sulfur-containing compounds. The oxidative esterification of benzyl alcohol, hydrogenation of nitrobenzene and hydrogenated coupling of nitrobenzene with benzaldehyde were used as probe reactions. By comparing the catalytic performance before and after HCl washing, it was demonstrated that particulate Co3O4 has a marginal effect on the catalysis, and the highly dispersed CoNx on carbon nanotubes created during the pyrolysis is responsible for the activity. It was proposed that cobalt chelate complexes bonded to 2 to 3 nitrogens in the graphene lattice, probably like the pyridinic vacancy, might be responsible for the activity.

As an emerging catalyst based on earth-abundant metals, Co3O4 supported on carbon materials, derived from the pyrolysis of metal salts and nitrogen-containing ligands, shows excellent performance in hydrogenation, hydrogenated coupling, oxidative esterification and oxidation of amines. Herein, we unravel the real active sites of this catalyst through a combination of XRD, XPS, HRTEM, EELS and poisoning experiments with sulfur-containing compounds. The oxidative esterification of benzyl alcohol, hydrogenation of nitrobenzene and hydrogenated coupling of nitrobenzene with benzaldehyde were used as probe reactions. By comparing the catalytic performance before and after HCl washing, it was demonstrated that particulate Co3O4 has a marginal effect on the catalysis, and the highly dispersed CoNx on carbon nanotubes created during the pyrolysis is responsible for the activity. It was proposed that cobalt chelate complexes bonded to 2 to 3 nitrogens in the graphene lattice, probably like the pyridinic vacancy, might be responsible for the activity.

The structures of PtNix nanoalloy particles were modified through thermal annealing in different atmospheres. The evolution of surface structures was uncovered by advanced transmission electron microscopy, and the structure–function correlation in methanol electro-oxidation was probed. It provided new insights into the design and synthesis of highly efficient electrocatalysts.