Graphene-like ZnO (g-ZnO) nanostructures (NSs) and thin films were prepared on Au(111), and their reactivities toward CO and H 2 were compared with that of wurtzite ZnO (w-ZnO) (0001) single crystals. The interaction and reaction between CO/H 2 and the different types of ZnO surfaces were studied using near-ambient-pressure scanning tunneling microscopy (NAP-STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. The reactivity of the w-ZnO(0001) surface toward CO and H 2 was found to be more prominent than those on the surfaces of g-ZnO/Au(111). CO oxidation took place primarily at the edge sites of w-ZnO(0001) and the interface between g-ZnO NSs and Au(111), while g-ZnO thin films on Au(111) appeared to be inert below 600 K. Similarly, the w-ZnO(0001) surface could dissociate H 2 at 300 K, accompanied by a substantial surface reconstruction, while g-ZnO on Au(111) appeared inert for H 2 activation at 300 K. DFT calculations showed that the reactivities of ZnO surfaces toward CO could be related to the formation energy of oxygen vacancy (E Ovf ), which could be related to the charge transfer to lattice oxygen atoms or surface polarity.

Significant progress has been demonstrated in the development of bifunctional oxide-zeolite catalyst concept to tackle the selectivity challenge in syngas chemistry. Despite general recognition on the importance of defect sites of metal oxides for CO/H2 activation, the actual structure and catalytic roles are far from being well understood. We demonstrate here that syngas conversion can be steered along a highly active and selective pathway towards light olefins via ketene-acetate (acetyl) intermediates by the surface with coordination unsaturated metal species, oxygen vacancies and zinc vacancies over ZnGaOx spinel−SAPO-34 composites. It gives 75.6% light-olefins selectivity and 49.5% CO conversion. By contrast, spinel−SAPO-34 containing only a small amount of oxygen vacancies and zinc vacancies gives only 14.9% light olefins selectivity at 6.6% CO conversion under the same condition. These findings reveal the importance to tailor the structure of metal oxides with coordination unsaturated metal sites/oxygen vacancies in selectivity control within the oxide-zeolite framework for syngas conversion and being anticipated also for CO2 hydrogenation.

No abstract

Well-defined manganese oxide (MnO x ) overlayers with a controlled chemical state and coverage were deposited on Au(111), and CO activation at the model MnO x /Au­(111) surfaces was explored by combining treatments in high-pressure (up to 100 mbar) CO at elevated temperatures and in situ surface characterizations. We find that all MnO x nanostructures transformed into reduced MnO states (MnO1–y , 0 < y < 1) in the near-ambient pressure CO atmosphere, and dissociation of CO to carbon deposit occurs above 473 K. A volcano curve of the carbon deposit amount as a function of MnO coverage is clearly presented, indicating that MnO island edges are the active centers. Density functional theory calculations show that MnO/Au(111) interfaces provide edge Mn atoms coordinated with two oxygen atoms, where CO disproportionation occurs facilely through the CO dimer and further CCO* intermediates.

Interaction of hexagonal boron nitride (h-BN) with gases is of great importance for its properties and applications. In the present work, the structural changes of h-BN overlayers on Pt(111) in oxidative atmospheres including O2 and NO2 have been investigated by using low energy electron microscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy (XPS), and near ambient pressure XPS. We find that h-BN islands can be intercalated by oxygen in 10-6 Torr O2 at 200 °C, while oxygen intercalation of full layer h-BN around 200 °C requires near ambient pressure O2 (0.1 Torr) or such a strong oxidant as NO2 (10-6 Torr). h-BN overlayers can be etched away in the gases at much high temperatures, e.g. 800 °C. Upon mild oxidation in O2 or NO2 at temperatures of 400-450 °C, h-BN is transformed to boron oxide (BOx) overlayers, which can be converted back to h-BN by heating in NH3 at 800 °C.

No abstract

No abstract

No abstract