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Nano-structural and nano-analytical studies show that the dramatic difference in CO oxidation activity observed between two Au/Ce0.50Tb0.12Zr0.38O2−x samples prepared by deposition–precipitation with urea and further activated under oxidising or reducing conditions is due to the poisoning effect of a very thin layer of carbon grown on the pre-reduced catalyst. [ABSTRACT FROM AUTHOR]

Abstract: The effect of palladium–gallia interaction in Pd(1wt.%)/β-Ga2O3 during selective methanol synthesis by CO2 hydrogenation was studied. A detailed quasi-in situ transmission electron microscopy analysis of the as-prepared H2-reduced catalyst, without exposing it to air, showed that Ga–Pd bimetallic (nano)particles were formed under a reductive atmosphere at or above 523K. However, these particles were unstable; upon air exposure, a dramatic and extensive encapsulation of the metallic crystallites by Ga2O3 occurred. In addition, the function of the bimetallic particles in the mechanism of methanol synthesis was investigated by in situ infrared spectroscopy at 0.7MPa. The results confirmed those of previous studies in which the stepwise hydrogenation of (bi)carbonate to formate and then to methoxy groups on the Ga2O3 surface took place via a bifunctional pathway. In this pathway, the role of the Ga–Pd bimetallic crystallites was to provide atomic hydrogen, via spillover, to the oxidic surface and to hamper both CH3OH decomposition and CO production. [Copyright &y& Elsevier]

Abstract: A well-controlled homemade Pt–BaO/Al2O3 monolith catalyst has been used for tuning the operational conditions at which the NO x storage and reduction (NSR) of the lean-burn engine exhaust gases is achieved more efficiently. The following operational conditions have been analyzed: the duration of the lean (storage) period, and the reductant (H2) concentration and duration of the regeneration (rich) period. The storage pattern during the lean period is evaluated by the percentage of NO x stored or NO x trapping efficiency (η T ), and the performance during the rich period is evaluated by the NO x reduction conversion (X R ) and the selectivity to nitrogen (). These three response variables have been integrated into the single parameter that we have named integral NSR efficiency (ɛ NSR) of the whole NSR process, which represents the percentage of N2 produced at the reactor exit relative to the NO x fed to the reactor. The proposed graphical map consists of a series of ɛ NSR-isocurves and allows predicting the NSR efficiency for any combination of the three studied operational conditions . Such operational map shall also be useful to compare the global NSR behavior of commercial catalysts under real operating conditions. [Copyright &y& Elsevier]

Abstract: The redox behaviour under flowing 5%CO/He and 5%H2/Ar of two Ce0.62Zr0.38O2 mixed oxides is investigated. The samples, hereafter referred to as CZ-MO and CZ-SO, were obtained by application to the same starting material two well established thermal ageing routines. These routines ensured the preparation of oxide samples with significantly different chemical and structural properties. To evaluate their redox behaviour, ultimate oxygen storage capacity (OSC) data were determined from stepwise thermo-gravimetric experiments at temperatures ranging from 473K to 1173K. In good agreement with earlier studies from the literature, both CO-OSC and H2-OSC data show that CZ-MO exhibits a superior reducibility throughout the whole range of temperatures. If CO-OSC and H2-OSC data are compared, we may notice that, in qualitative agreement with the thermodynamic predictions, CO-OSC values are significantly larger than those of H2-OSC at T ≤773K. Above this reference temperature CO-OSC and H2-OSC show much closer values. Though ultimate OSC data are generally assumed to be determined by the thermodynamics of the oxide-reductant system, it is shown that the CO-OSC values recorded at the lowest temperatures are not consistent with this assumption. As in the case of H2-OSC, the low-temperature CO-OSC data are actually determined by kinetic factors. [Copyright &y& Elsevier]

The gram-scale synthesis, stabilization, and characterization of well-defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X-ray snapshots of Pt 0 2 clusters, homogenously distributed and densely packaged within the channels of a metal-organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO 2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less-dangerous industrial reactions., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Nano-structural and nano-analytical studies show that the dramatic difference in CO oxidation activity observed between two Au/Ce0.50Tb0.12Zr0.38O2-x samples prepared by deposition-precipitation with urea and further activated under oxidising or reducing conditions is due to the poisoning effect of a very thin layer of carbon grown on the pre-reduced catalyst.

A variety of advanced (scanning) transmission electron microscopy experiments, carried out in aberration-corrected equipment, provide direct evidence about subtle structural changes taking place at nanometer-sized Au||ceria oxide interfaces, which agrees with the occurrence of charge transfer effects between the reduced support and supported gold nanoparticles suggested by macroscopic techniques. Tighter binding of the gold nanoparticles onto the ceria oxide support when this is reduced is revealed by the structural analysis. This structural modification is accompanied by parallel deactivation of the CO chemisorption capacity of the gold nanoparticles, which is interpreted in exact quantitative terms as due to deactivation of the gold atoms at the perimeter of the Au||cerium oxide interface.