Special Issue: Energy Conversion and Storage. Critical issues in current energy‐based societies are its generation through methods utilizing alternatives to fossil fuels as well as its storage. ...Considering the scope, it is not surprising that the research becomes more and more multidisciplinary. Therefore, it is important to keep focused. The ChemEner symposia, the last one being highlighted in this Special Issue, achieve this by focusing on the state of the art and the newest development of the Chemistry of hydrogen generation, carbon dioxide reduction, and other related topics, exploring new concepts for clean future energy.
The microstructure and electronic structure of environmentally relevant carbons such as Euro IV heavy duty diesel engine soot, soot from a black smoking diesel engine, spark discharge soot as model ...aerosol, commercial furnace soot and lamp black are investigated by transmission electron microscopy, electron energy-loss spectroscopy and X-ray photoelectron spectroscopy. The materials exhibit differences in the predominant bonding, which influences microstructure as well as surface functionalization. These chemical and physical properties depend on the formation history of the investigated carbonaceous materials. In this work, a correlation of the microstructure of the samples to the predominant bonding and incorporation of oxygen into the carbons is obtained. It is shown that a high amount of defects and the deviation of the carbons from a perfect graphitic structure results in a increased incorporation of oxygen and hydrogen. A correlation between the length and curvature of graphene layers with the bonding state of carbon atoms and incorporation of oxygen and hydrogen is established.
Carbon samples are being investigated with thermogravimetry, infrared spectroscopy and transmission electron microscopy. We focus on a spark discharge soot, soot from a heavy-duty diesel engine, soot ...from a diesel engine in black smoking conditions and a furnace carbon black from Degussa. The aim of this study is to correlate reactivity towards oxygen, functional groups and nanostructure. It is found that the amount of defects as well as the functionalisation plays an important role in the onset of combustion in the thermogravimetric experiments. Clear differences in reactivity towards oxidation are observed.
Spatial coupling during catalytic ignition of CO oxidation on μm-sized Pt(hkl) domains of a polycrystalline Pt foil has been studied in situ by PEEM (photoemission electron microscopy) in the ...10−5mbar pressure range. The same reaction has been examined under similar conditions by FIM (field ion microscopy) on nm-sized Pt(hkl) facets of a Pt nanotip. Proper orthogonal decomposition (POD) of the digitized FIM images has been employed to analyze spatiotemporal dynamics of catalytic ignition. The results show the essential role of the sample size and of the morphology of the domain (facet) boundary in the spatial coupling in CO oxidation.
•Catalytic ignition in CO oxidation was studied on μm-sized Pt(hkl) domains of a Pt foil and on nanofacets of a Pt tip.•Proper orthogonal decomposition of the FIM images has been employed to analyze dynamics of catalytic ignition.•The effect of the sample size and morphology in the spatial coupling in CO oxidation was observed.
The supply of free energy to our societies is today an intricate system comprising the regimes of technologies, regulatory frameworks, socio-economic impacts and techno-ecological interactions. As a ...consequence it is challenging to define clear directions or even device a master plan for the transformation of a single national energy system into a sustainable future. Even the term “sustainable” needs extensive discussion in this context that should not be defined solely in technological or ecological senses. The contribution illustrates some of the elements of the energy system and their interdependencies. It will become clear that multiple reasons exist to change the traditional generation and use of energy even when climate protection is not a sufficiently strong argument for a change.
The selective hydrogenation of propyne over a Pd-black model catalyst was investigated under
operando
conditions at 1 bar making use of advanced X-ray diffraction (bulk sensitive) and photo-electron ...spectroscopy (surface sensitive) techniques. It was found that the population of subsurface species controls the selective catalytic semi-hydrogenation of propyne to propylene due to the formation of surface and near-surface PdC
x
that inhibits the participation of more reactive bulk hydrogen in the hydrogenation reaction. However, increasing the partial pressure of hydrogen reduces the population of PdC
x
with the concomitant formation of a β-PdH
x
phase up to the surface, which is accompanied by a lattice expansion, allowing the participation of more active bulk hydrogen which is responsible for the unselective total alkyne hydrogenation. Therefore, controlling the surface and subsurface catalyst chemistry is crucial to control the selective alkyne semi-hydrogenation.
In this work, the oxidative dehydrogenation (ODH) of ethylbenzene to styrene reaction over an activated carbon felt was studied by experiments of mass spectrometry coupled to a quasi in situ XPS ...system. These experiments permit to deepen into the mechanism of the aforementioned reaction. The results obtained allow us to conclude that carbonyl-quinone and hydroxyl groups are involved in the ODH. The amount of both types of oxygen groups increases when the ethylbenzene conversion to styrene increases. Therefore, the reaction seems to take place through the carbonyl-quinone/hydroxyl and styrene/ethylbenzene redox couples, confirming that carbonyl-quinone are the active phase in this oxidative dehydrogenation.
The aim of the PROX reaction is to reduce the CO content of hydrogen feed to proton-exchange membrane fuel cells (PEMFCs) by selective oxidation of CO in the presence of excess hydrogen. Both Pt and ...Pd on ceria are active in CO oxidation (without hydrogen), whereas Pd is poorly active in the presence of hydrogen. In this paper we explore the reasons for such behavior, using the same techniques for Pd/CeO 2 as used for Pt/CeO2 in Part I: catalytic tests, in situ DRIFTS, high-pressure XPS, HRTEM, and TDS. We also examine the reaction mechanism of CO oxidation (without hydrogen), which does not occur via exactly the same mechanism on Pt and Pd/CeO2 catalysts. In the presence of hydrogen (PROX) at low temperature (T = 350-380K), the formation of Pd β-hydride was confirmed by high-pressure in situ XPS. Its formation greatly suppressed the possibility of CO oxidation, because oxygen both from gas-phase and support sites reacted rapidly with hydride H to form water, which readily desorbed from Pd. Nevertheless, CO adsorption was not hampered here. These entities transformed mainly to surface formate and formyl (single bondCHO) species instead of oxidation as observed by DRIFTS. The participation of a low-temperature water-gas shift type reaction proposed for the platinum system (see Part I) was hindered. Increasing temperature led to decomposition of the hydride phase and a parallel increase in the selectivity toward CO oxidation. This still remained lower on Pd/CeO 2 than on Pt/CeO2 , however.
Our recent surface characterization studies of extended and nanosized PtCo alloys under hydrogen and oxygen atmospheres, indicated significant and reversible surface segregation in response to the ...gas phase environment J. Phys. Chem. Lett. 2011, 2, 900 . In the present communication, an insight into the effect of the support on the PtCo alloy stability is attempted. A model PtCo/TiO2 interface is investigated under reducing, oxidizing, and catalytic reaction conditions using ambient pressure X-ray photoelectron and absorption spectroscopies (APPES and NEXAFS respectively). Encapsulation of PtCo by the TiO2 support was observed upon vacuum annealing. Upon oxidation/reduction conditions, a mixture of CoO y (1 ≤ y < 1.33), TiO2, and mixed Co x Ti y O z phases with Pt located in the subsurface was formed. TiO2 was found to be remarkably stable under the temperature and pressure conditions used here (up to 620 K, 0.2 mbar), with titanium remaining always in the Ti4+ state. The interplay between the gas atmosphere and the surface is limited to modifications of the cobalt oxidation state. However, in contrast to the observations on the unsupported PtCo alloy, neither oxidation of CoO to Co3O4 in O2 nor full reduction to metallic Co under various reducing agents (H2, CH3OH), occurred. Synchronized changes of the binding energy position of core level photoelectron peaks in response to the gas phase are related to the band-bending development at the gas/solid interface. This documents the direct coupling of the electronic properties and the gas phase chemical potential of a chemically functional material useful as catalyst or gas sensing device.
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