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Oxidic (photo-)catalysts have the potential to play an important role to efficiently implement sustainable feedstocks and green energy sources into future energy technologies. They may be used not only for solar energy harvesting, but also for hydrogen production or being essential for the fabrication of fine chemicals. Therefore, it is crucial to develop a detailed understanding of how the atomistic environment of the catalyst can be designed in order to promote distinct reaction pathways to influence the final product distribution of chemical reactions. In this perspective article, we survey the surface (photo-)chemistry of methanol on rutile TiO2 surfaces and hybrid catalysts based thereon. Especially the role of the surface bifunctionality by Lewis acidic and basic sites combined with the strong impact of point defects such as reduced titanium sites (mainly Ti3+ interstitials) shall be illuminated. It is shown how the selective activation of either O–H, C–H or C–O bonds in the methanol molecule can be used to tune not only the overall conversion, but to switch between oxidative and reductive routes in favor of either deoxygenation, partial oxidation or C–C coupling reactions. Especially the latter ones are of particular interest to introduce methanol from green sources such as biomass as a sustainable feedstock into already existing petrochemical technologies. [ABSTRACT FROM AUTHOR]

Systematic model investigations revealed that defects, particularly bulk Ti3+ interstitials, play a crucial role in directing reactions of alcohols and aldehydes at rutile Titania (TiO2), a cheap, nontoxic and earth abundant catalyst. Coadsorption with oxygen may enhance the population of certain reaction paths. As systematic studies on the reactivity of ketones are rare, we studied the interaction of acetone with slightly (∼5%) and highly (∼20%) reduced rutile TiO2(110) surfaces by Temperature Programmed Desorption (TPD) and polarised Fourier-Transform Infrared Reflexion Absorption Spectroscopy (FT-IRRAS) to elucidate surface intermediates and reaction products. For low defect densities the only reaction observed occurs at high temperatures resulting in the formation of propane and propene of less than 1%. At high Ti3+ defect densities a stabilisation of acetone on the surface by the formation of a diolate was observed. In the presence of oxygen, the partial formation of a tilted acetone species is apparent in FT-IRRAS. A concomitant activation of the CH-bond can be attributed to the interaction with Oad atoms and can relate to thermally induced low temperature decomposition to water and carbon dioxide. However, in contrast to alcohols and aldehydes, both intermediates do not react to other more valuable products. [ABSTRACT FROM AUTHOR]

The photochemical conversion of organic compounds on tailored transition metal oxide surfaces by UV irradiation has found wide applications ranging from the production of chemicals to the degradation of organic pollutants e.g. in waste water treatment. Here, we present a systematic surface science-based study of the UV photoconversion of methanol on a rutile TiO2(110) surface. Under the used conditions, the dominant photoreaction is the photo-oxidation forming formaldehyde, that is drastically boosted by the presence of adsorbed oxygen as well as (sub-)surface defects such as oxygen vacancies and Ti3+ interstitials. Moreover, a photostimulated and Ti3+ mediated C–C coupling was observed leading to the production of ethene. We have further deposited tungsten oxide clusters on the rutile surface and examined the impact on the methanol photochemistry. In this case, the C–C coupling can be suppressed. Surprisingly, especially for high Ti3+ contents the population of the photochemical pathway is quenched in favor of the population of the thermal reaction yielding more methane from the deoxygenation reaction. So, the common concept that long time charge separation is efficient by combining two photocatalysts with similar band gaps, but different work functions in order to enhance photochemical yields is apparently too naive for certain systems. We attribute the loss of photoproducts with tungsten oxide coadsorption to the "pinning" of Ti3+ centers and a related enhancement of electron density near the oxide clusters which makes a concomitant recombination of the photochemical relevant holes with the excess surface electrons more likely. [ABSTRACT FROM AUTHOR]

Tungsten oxide clusters deposited on rutile TiO2 (110) single crystals were used as a model system for heterogenous oxide-oxide bifunctional catalysts. The population of different thermal reaction routes in methanol conversion in the presence of preadsorbed oxygen was probed under UHV conditions. By temperature programmed reaction spectroscopy, we have identified three thermal reaction channels, namely the deoxygenation under formation of methane, the partial oxidation forming formaldehyde and the condensation route under desorption of ethane and dimethyl ether. The specific local reaction environment at the oxidic surface was found to be key for the population of the different reaction channels as exhibited by the introduction of Lewis acidic and basic sites (especially (WO3)n clusters) and available charge carriers such as Ti3+. Especially the amount of bulk Ti3+ interstitials, that can partially transfer charge towards the tungsten oxide clusters at the TiO2 surface, was found to be a key parameter that enables a relatively high methanol conversion in thermal reactions. It turned out that the deoxygenation is by far the most dominant reaction followed by the partial oxidation. The condensation is observed only in low amounts under special conditions, but is an interesting example for reactivity at defect sites. [ABSTRACT FROM AUTHOR]

Rutile TiO2 is an important model system for understanding the adsorption and conversion of molecules on transition metal oxide catalysts. In the last decades, point defects, such as oxygen vacancies and Ti3+ interstitials, exhibited an important influence on the reaction of oxygen and oxygen-containing molecules on titania surfaces. In brief, partially reduced TiO2 containing a significant amount of Ti3+ is often more active for the conversion of such molecules. In this study, we investigate an even higher reduced surface prepared by argon ion bombardment of a rutile TiO2 (110) single crystal. By X-ray photoelectron spectroscopy we show that, besides Ti4+, this surface is almost equally dominated by Ti3+ and Ti2+. To probe the reactivity of these highly reduced surfaces, we have adsorbed two different classes of oxygen-containing molecules and utilized temperature programmed reaction spectroscopy to investigate the conversion. While alcohols (in this case methanol) already show a defect-dependent partial conversion in a deoxygenation reaction on the (stochiometric or slightly reduced) rutile TiO2 (110) surface, ketones (e.g. acetone) are usually not converted on the rutile TiO2 (110) surface independent on the bulk defect density. Here, we present a nearly full conversion for both molecules via deoxygenation reactions and reductive C–C coupling, forming different hydrocarbons at different temperatures between 375 K and 640 K on the sputtered Ti2+ rich surface. [ABSTRACT FROM AUTHOR]

The slow solvent evaporation technique has been employed for the synthesis of l-arginine perchlorate (LAPCl) single crystals. The grown crystals are doped with 1, 2 and 3 mol% of MnCl2. The Powder X-ray Diffraction (PXRD) analysis confirmed that the pure and doped crystals belong to the orthorhombic crystal system with non-centrosymmetric space group P212121. The incorporation of dopants has been confirmed by Laser-Induced Breakdown Spectroscopy (LIBS) and Energy Dispersive X-ray Analysis (EDX). The modification in the linear optical properties has been analyzed by measuring the cut off wavelength, band gap, Urbach energy and the refractive index of the pure and doped crystals. The changes in the nonlinearity of the LAPCl have been studied by open aperture Z-scan technique and found that two-photon absorption (2PA) coefficient increased with increasing the dopant concentration. The dielectric properties, electronic polarizability and thermal properties of the pure and doped crystals are also studied. [ABSTRACT FROM AUTHOR]

Colloidal deposition of noble metal nanoparticles on oxidic supports is a recent approach for the fabrication of heterogeneous catalyst materials. We present studies on the interaction of different amine ligands with gold nanoparticles before and after deposition on several oxidic supports (titania, silica, alumina, magnesia or zinc oxide), using X-ray photoelectron and Auger spectroscopy, and high-resolution transmission electron microscopy. The adsorption of amines on thin gold films as well as on nanoparticles leads to a decrease in metal photoelectron binding energies. Usually, this is explained by donor-acceptor interactions via the amine group. By additional analysis of Auger signals, which are more sensitive to changes in the oxidation state than photoelectron spectra, we demonstrate that these shifts are due to a final state effect, namely, the increased photoelectron hole screening in presence of amine adsorbates. It will be shown, that this effect is not sensitive neither to the nanoparticle size nor the sterical properties of the capping amine. After deposition on oxide supports, the photoelectron binding energies are even further decreased. The presented findings exhibit that care has to be taken to interpret binding energy shifts simply with charging, which has impact on understanding the local electronic situation on the surface of metal-loaded oxides, crucial for heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Sodium ion batteries (SIBs) are promising alternatives to lithium ion batteries with advantages of cost effectiveness. Metal sulfides as emerging SIB anodes have relatively high electronic conductivity and high theoretical capacity, however, large volume change during electrochemical testing often leads to unsatisfactory electrochemical performance. Herein bimetallic sulfide Cu2MoS4 (CMS) with layered crystal structures are prepared with glucose addition (CMS1), resulting in the formation of hollow nanospheres that endow large interlayer spacing, benefitting the rate performance and cycling stability. The electrochemical mechanisms of CMS1 are investigated using ex situ X‐ray photoelectron spectroscopy and in situ X‐ray absorption spectroscopy, revealing the conversion‐based mechanism in carbonate electrolyte and intercalation‐based mechanism in ether‐electrolyte, thus allowing fast and reversible Na+ storage. With further introduction of reduced graphene oxide (rGO), CMS1–rGO composites are obtained, maintaining the hollow structure of CMS1. CMS1–rGO delivers excellent rate performance (258 mAh g−1 at 50 mA g−1 and 131.9 mAh g−1 at 5000 mA g−1) and notably enhanced cycling stability (95.6% after 2000 cycles). A full cell SIB is assembled by coupling CMS1–rGO with Na3V2(PO4)3‐based cathode, delivering excellent cycling stability (75.5% after 500 cycles). The excellent rate performance and cycling stability emphasize the advantage of CMS1–rGO toward advanced SIB full cells assembly. Bimetallic Cu2MoS4 (CMS) hollow nanospheres (CMS1) are obtained by modified solvothermal reactions. CMS1 delivers notably improved rate performance than CMS in ether‐electrolyte, in which an intercalation‐dominant electrochemical reaction mechanism is revealed. With further incorporation of reduced graphene oxide (rGO), the CMS1–rGO composites deliver excellent cycling stability, allowing fast and stable Na+ storage in full cell by coupling with an optimized Na3V2(PO4)3 cathode. [ABSTRACT FROM AUTHOR]

The photochemical conversion of organic compounds on tailored transition metal oxide surfaces by UV irradiation has found wide applications ranging from the production of chemicals to the degradation of organic pollutants e.g. in waste water treatment. Here, we present a systematic surface science-based study of the UV photoconversion of methanol on a rutile TiO2(110) surface. Under the used conditions, the dominant photoreaction is the photo-oxidation forming formaldehyde, that is drastically boosted by the presence of adsorbed oxygen as well as (sub-)surface defects such as oxygen vacancies and Ti3+ interstitials. Moreover, a photostimulated and Ti3+ mediated C-C coupling was observed leading to the production of ethene. We have further deposited tungsten oxide clusters on the rutile surface and examined the impact on the methanol photochemistry. In this case, the C-C coupling can be suppressed. Surprisingly, especially for high Ti3+ contents the population of the photochemical pathway is quenched in favor of the population of the thermal reaction yielding more methane from the deoxygenation reaction. So, the common concept that long time charge separation is efficient by combining two photocatalysts with similar band gaps, but different work functions in order to enhance photochemical yields is apparently too naive for certain systems. We attribute the loss of photoproducts with tungsten oxide coadsorption to the "pinning" of Ti3+ centers and a related enhancement of electron density near the oxide clusters which makes a concomitant recombination of the photochemical relevant holes with the excess surface electrons more likely.

Tungsten oxide clusters deposited on rutile TiO2 (110) single crystals were used as a model system for heterogenous oxide-oxide bifunctional catalysts. The population of different thermal reaction routes in methanol conversion in the presence of preadsorbed oxygen was probed under UHV conditions. By temperature programmed reaction spectroscopy, we have identified three thermal reaction channels, namely the deoxygenation under formation of methane, the partial oxidation forming formaldehyde and the condensation route under desorption of ethane and dimethyl ether. The specific local reaction environment at the oxidic surface was found to be key for the population of the different reaction channels as exhibited by the introduction of Lewis acidic and basic sites (especially (WO3)n clusters) and available charge carriers such as Ti3+. Especially the amount of bulk Ti3+ interstitials, that can partially transfer charge towards the tungsten oxide clusters at the TiO2 surface, was found to be a key parameter that enables a relatively high methanol conversion in thermal reactions. It turned out that the deoxygenation is by far the most dominant reaction followed by the partial oxidation. The condensation is observed only in low amounts under special conditions, but is an interesting example for reactivity at defect sites.