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Molybdenum phosphide (MoP) and supported molybdenum phosphide (MoP/gamma-Al2O3) are prepared and characterized by the temperature-programmed reduction method. Co that is observed to get adsorbed on the surface of MoP/Al2O3 shows a characteristic band at ~2037 per cm because of the linearly adsorbed CO on Mo(super delta+) sites.

The surface nature of fresh Mo2C/AI2O3 and reduced passivated Mo2C/AI2O3 are studied by using in situ IR spectroscopy using CO as the probe molecule. Adsorbed CO on the reduced passivated Mo2C/AI2O3 catalyst gives a main band at 2180 cm-1, which can be assigned to linearly adsorbed CO on Mo4+ sites and the results show that the surface of reduced passivated sample is dominated by molybdenum oxycarbide.

The surface species derived from the adsorption of 1,3-butadiene and 1-butene on Mo2N/gama-Al2O3 catalyst are characterized by in situ FT-IR spectroscopy with an attempt to get insight into the selective hydrogenation of 1,3-butadiene on transition metal nitride catalysts. The high selectivity of 1,3-butadiene hydrogenation to 1-butene is mainly because of the competitive adsorption of the surface species; namely, the pi (sub d) -adsorbed butadiene strongly prevents 1-butene from its adsorption and further hydrogenation.

The adsorption and reaction of 1-butene on Mo2N/gamma-Al2O3 catalyst are studied by in situ FT-IR spectroscopy at low temperatures. The result of coadsorption of 1-butene with CO indicates that 1-butene is mainly adsorbed on the surface Mo sites of the nitrided catalyst.

Investigation of atomically precise Au nanoclusters provides a route to understand the roles of coordination, size, and ligand effects on Au catalysis. Herein, we explored the catalytic behavior of a newly synthesized Au22(L8)6 nanocluster (L = 1,8-bis(diphenylphosphino) octane) with in situ uncoordinated Au sites supported on TiO2, CeO2, and Al2O3. Stability of the supported Au22 nanoclusters was probed structurally by in situ extended X-ray absorption fine structure (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and their ability to adsorb and oxidize CO was investigated by IR absorption spectroscopy and a temperature-programmed flow reaction. Low-temperature CO oxidation activity was observed for the supported pristine Au22(L8)6 nanoclusters without ligand removal. Density functional theory (DFT) calculations confirmed that the eight uncoordinated Au sites in the intact Au22(L8)6 nanoclusters can chemisorb both CO and O2. Use of isotopically labeled O2 demonstrated that the reaction pathway occurs mainly through a redox mechanism, consistent with the observed support-dependent activity trend of CeO2 < TiO2 < Al2O3. We conclude that the uncoordinated Au sites in the intact Au22(L8)6 nanoclusters are capable of adsorbing CO, activating O2, and catalyzing CO oxidation reaction. This work is the first clear demonstration of a ligand-protected intact Au nanocluster that is active for gas-phase catalysis without the need of ligand removal. [ABSTRACT FROM AUTHOR]

In this communication, we report a facile approach to constructing catalytic active hierarchical interfaces in one-dimensional (ID) nanostructure, exemplified by the synthesis of TiO2-supported PtFe-FeOx nanowires (NWs). The hierarchical interface, constituting atomic level interactions between PtFe and FeOx within each NW and the interactions between NWs and support (TiO2), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeOx and TiO2 participate in the initial CO oxidation, facilitating the reaction through a redox pathway. Moreover, the intact ID structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe--FeOx/TiO2 catalyst exhibits no activity decay. Our results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis. [ABSTRACT FROM AUTHOR]

Wereport an aberration-corrected electron microscopy analysis of theadhesion and atomic structures of gold nanoparticle catalysts supportedon ceria nanocubes and nanorods. Under oxidative conditions, the as-preparedgold nanoparticles on the ceria nanocubes have extended atom layersat the metal–support interface. In contrast, regular gold nanoparticlesand rafts are present on the ceria nanorod supports. Under the reducingconditions of water–gas shift reaction, the extended gold atomlayers and rafts vanish. In addition, the gold particles on the nanocubeschange in morphology and increase in size while those on the nanorodsare almost unchanged. The size, morphology, and atomic interface structuresof gold strongly depend on the surface structures of ceria supports((100) surface versus (111) surface) and the reaction environment(reductive versus oxidative). These findings provide insights intothe deactivation mechanisms and the shape-dependent catalysis of oxidesupported metal catalysts. [ABSTRACT FROM AUTHOR]

The effect of thiolate ligands was explored on the catalysis of CeO2 rod supported Au25(SR)18 (SR = -SCH2CH2Ph) by using CO oxidation as a probe reaction. Reaction kinetic tests, in situ IR and X-ray absorption spectroscopy, and density functional theory (DFT) were employed to understand how the thiolate ligands affect the nature of active sites, activation of CO and 02, and reaction mechanism and kinetics. The intact Au2S(SR)18 on the CeO2 rod is found not able to adsorb CO. Only when the thiolate ligands are partially removed, starting from the interface between Au25(SR)18 and CeO2 at temperatures of 423 K and above, can the adsorption of CO be observed by IR DFT calculations suggest that CO adsorbs favorably on the exposed gold atoms. Accordingly, the CO oxidation light-off temperature shifts to lower temperature. Several types of Au sites are probed by IR of CO adsorption during the ligand removal process. The cationic Au sites (charged between 0 and +l) are found to play the major role for low-temperature CO oxidation. Similar activation energies and reaction rates are found for CO oxidation on differently treated Au25(SR)18/CeO2 rod catalysts, suggesting a simple site-blocking effect of the thiolate ligands in Au nanocluster catalysis. Isotopic labeling experiments clearly indicate that CO oxidation on the Au25(SR)18/ CeO2 rod catalyst proceeds predominantly via the redox mechanism where CeO2 activates O2 while CO is activated on the dethiolated gold sites. These results point to a double-edged sword role played by the thiolate ligands on Au25 nanoclusters for CO oxidation. [ABSTRACT FROM AUTHOR]

Lithium-ion-conducting solid electrolytes hold promise for enabling high-energy battery chemistries and circumventing safety issues of conventional lithium batteries. Achieving the combination of high ionic conductivity and a broad electrochemical window in solid electrolytes is a grand challenge for the synthesis of battery materials. Herein we show an enhancement of the room-temperature lithium-ion conductivity by 3 orders of magnitude through the creation of nanostructured Li3PS4. This material has a wide electrochemical window (5 V) and superior chemical stability against lithium metal. The nanoporous structure of Li3PS4 reconciles two vital effects that enhance the ionic conductivity: (1) the reduction of the dimensions to a nanometer-sized framework stabilizes the high-conduction β phase that occurs at elevated temperatures, and (2) the high surface-to-bulk ratio of nanoporous β-Li3PS4 promotes surface conduction. Manipulating the ionic conductivity of solid electrolytes has far-reaching implications for materials design and synthesis in a broad range of applications, including batteries, fuel cells, sensors, photovoltaic systems, and so forth. [ABSTRACT FROM AUTHOR]