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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]

Silica and three mixed silica oxides (silica-alumina, silica-niobia, and silica-zirconia) with nominally 5 wt% of the added element (Al, Nb and Zr) were prepared and used as supports for dispersing monometallic Pt-nanoparticles. The presence of the second oxide component on the silica surface influenced some properties of the final samples, like surface area and acidity. The samples acidity was measured in a recirculation adsorption line with 2-phenylethylamine probe, by performing the titrations both in cyclohexane and in methanol to gather the intrinsic and effective acidity, respectively. The acid site density of silica-alumina was the highest compared with the other oxides; in general, an important decrease of acid sites density was determined in methanol. The order of the effective acidity in methanol was different from that determined in cyclohexane only for silica-zirconia and silica-niobia, confirming the peculiar acidity of Nb-oxide compounds in polar liquids: Colloidal spherical platinum nanoparticles were synthesized and then deposited (1 wt%) on the oxide supports. The obtained metallic nanophases were studied in the reduction of 5-hydroxymethylfurfural (HMF) to valuable chemicals such as dimethylfuran, dimethyltetrahydro-furan, 2-hexanol. In particular, this study focused on the impact of the acidity of the oxide supports on reaction selectivity when 2-butanol is used as solvent. When Pt is not present, Nb-doped silica is the most effective catalyst to di-hydroxymethyl furan diether (DHMFDE) derived from Meerwein-Ponndorf-Verley reaction, maintaining its Lewis character also in protic medium. In the presence of Pt, Nb-doped silica, however, presents the higher selectivity to hydrogenolysis products, 5-methyl furan (5-MF). Graphical Abstract: [ABSTRACT FROM AUTHOR]

“…︁ Scientists need to be able to trust and rely on each other as a matter of care and responsibility towards our society.My further personal plea is that we have to give our students an awareness of good scientific practice and help them to find self‐confidence …︁” Read more in the Editorial by Katharina Al‐Shamery. [ABSTRACT FROM AUTHOR]

„…︁ Wir Wissenschaftler müssen uns gegenseitig vertrauen und uns aufeinander verlassen können aus Fürsorgepflicht und Verantwortung gegenüber unserer Gesellschaft. Mein persönliches Anliegen ist es, insbesondere dem wissenschaftlichen Nachwuchs dafür ein Bewusstsein zu vermitteln und ihm Selbstvertrauen zu geben …︁“ Lesen Sie mehr dazu im Editorial von Katharina Al ‐ Shamery. [ABSTRACT FROM AUTHOR]

Platinum nanocrystals in the size range of a few nanometers are especially interesting candidates for catalytic applications. We present an easy, low-temperature procedure, which allows for a precise size control of this material. Uniform platinum nanoparticles were obtained by reduction of platinum(IV)chloride with tetrabutylammonium borohydride in toluene solution at room temperature. Dodecylamine served as a ligand. The size of the resulting particles could be controlled in the range between 2 and 5 nm by slow addition of platinum monomers and the reducing agent to preformed 2 nm seeds. Furthermore, particles with a tetrapod shape could be synthesized. In contrast to the usual kinetic control leading to the formation of elongated structures, the analysis of the growth process of the tetrapods suggests a reactioncontrolled growth process. Their structure was investigated by powder X-ray diffraction and highresolution electron microscopy, which revealed that two branches of the tetrapods grow along the (111) direction, while the other two show growth in the (220) direction. This uncommon shape of the tetrapods is attributable to the presence of a twin defect parallel to the (220) direction. Thus, the method presented in the article allows for the formation of platinum particles with a single twin defect with a high yield. [ABSTRACT FROM AUTHOR]

The surface chemistry of oxygen and oxygenates on Rutile TiO2(110) is of great interest for various applications such as heterogeneous catalysis and photo catalysis. Though it is generally accepted that surface defects are active sites, the role of subsurface defects is under debate. We have therefore investigated the influence of the bulk defect density on the reductive coupling of benzaldehyde to stilbene as a model system. Using IRRAS we identify stilbene diolate as a reduction intermediate. The concentration of this intermediate is proportional to the bulk defect density, whereas adsorption of benzaldehyde at lower temperatures is not affected, which indicates a dominant role of Ti interstitials at temperatures above 400 K. [ABSTRACT FROM AUTHOR]

The ZrO:Er codoped with Yb phosphor powders have been prepared by the urea combustion route. Formation of the compounds ZrO:Er and ZrO:Er, Yb was confirmed by XRD. The frequency upconversion emissions in the green and red regions upon excitation with a CW diode laser at ∼978 nm are reported. Codoping with Yb enhances the emission intensities of the triply ionized erbium in the green and red spectral regions by about ∼130 and ∼820 times respectively. The emission properties of the ZrO:Er phosphor powders are discussed on the basis of excited state absorption, energy transfer, and cross-relaxation energy transfer mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Phosphor powders of Yb3+ co-doped BaZrO3:Er3+ have been prepared by the urea combustion route. The formation of single-phase BaZrO3:Er3+ and BaZrO3:Er3+,Yb3+ was confirmed by X-ray powder diffraction (XRD). Green and red luminescence along with a weaker blue emission is observed upon excitation at ∼978nm with a diode laser. These emissions are caused by frequency upconversion in the Er3+-doped BaZrO3 (BZO) phosphor. Both the green and red upconversion emissions of the Er3+ are enhanced by about ∼3 and ∼43 times respectively when triply ionized ytterbium is incorporated as a co-dopant. The frequency upconversion processes responsible for the blue, green and red emissions are discussed on the basis of the experimental data. [Copyright &y& Elsevier]

Abstract: Using the combustion synthesis, CaYAl3O7:Er3+ phosphor powders co-doped with Yb3+ have been prepared at low temperatures (550°C) in a few minutes. Formation of the compound was confirmed by X-ray powder diffraction. Near-infrared to visible upconversion fluorescence emission in the Er3+ doped CaYAl3O7 phosphor powder has been observed. The effect of co-doping with triply ionized ytterbium in the CaYAl3O7:Er3+ phosphor has been studied and the process involved is discussed. [Copyright &y& Elsevier]

Abstract: The activity of supported Ni catalysts can easily be affected by high temperatures and oxidative atmosphere. In order to study the origin of this behaviour, we performed systematic LEED and XPS investigations on a model system prepared by physical vapour deposition of Ni on a thin epitaxial alumina film on NiAl(110). Annealing experiments showed that deposited Ni is thermally stable up to ∼370K. Further annealing seems to lead first to changes in the island structure and then, at temperatures above ∼480K, to diffusion of Ni through the alumina film. Analysis of the complex oxidation behaviour revealed that there is a competition between oxidation of the Ni deposit and of the NiAl support. The latter process is probably enabled by a solid state reaction at the interface which means that Ni catalyses the further oxidation of the support. While the surface of the deposited Ni clusters is easily oxidised, the further oxidation processes of the Ni particles and the support were found to be diffusion-controlled. [Copyright &y& Elsevier]

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 catalytic performance of ligand-capped monometallic Pt and bimetallic PtSn nanoparticles supported on SiO2 toward the selective hydrogenation of acetylene to ethylene in ethylene-rich streams was investigated. To evaluate the effect of organic ligands on the hydrogenation performance, dodecylamine (DDA)-capped monometallic and bimetallic nanoparticles were compared with ligand-free nanoparticles. Both ligands and Sn promote the selectivity of the catalysts. The most selective catalyst was found to be the DDA-capped PtSn catalyst, with a nominal metal atom ratio of 1:1. An increase in Pt content resulted in a decrease in the selectivity, whereas an increase in Sn content caused a decrease in the activity. [ABSTRACT FROM AUTHOR]

Abstract: Tb3+ doped CaZrO3 has been prepared by an easy solution combustion synthesis method. The combustion derived powder was investigated by X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscopy techniques. A room temperature photoluminescence study showed that the phosphors can be efficiently excited by 251nm light with a weak emission in the blue and orange region and a strong emission in green light region. CaZrO3:Tb3+ exhibits three thermoluminescence (TL) glow peaks at 126°C, 200°C and 480°C. Electron Spin Resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the centres responsible for the TL peaks. The room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0233 is identified as an O− ion. Centre II with an axial symmetric g-tensor with principal values g =1.9986 and g ˔=2.0023 is assigned to an F+ centre (singly ionised oxygen vacancy). An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F+ centre) seems to originate from an F centre (oxygen vacancy with two electrons). The F centre and also the F+ centre appear to correlate with the observed high temperature TL peak in CaZrO3:Tb3+ phosphor. [Copyright &y& Elsevier]

Abstract: The adsorption of CO on well-defined Co–Pt alloy surfaces prepared by physical vapour deposition in ultra-high vacuum was studied by Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) and temperature-programmed desorption (TPD) spectroscopy. The adsorption behaviour was found to depend strongly on the composition of the surface and the first subsurface atomic layer. In the case of low Co concentrations at the surface CO adsorbs preferentially on Pt sites, however with an enthalpy of adsorption which is substantially lowered when compared to CO adsorption on Pt single crystals. TPD shifts of ∼60K were found. When Co dominates the surface composition, CO adsorbs preferentially on Co sites, however with an enthalpy of adsorption leading to a TPD shift by ∼80K to higher temperatures with respect to monometallic single crystals. This behaviour can be explained by ligand effects, i.e., by an electronic influence of the presence of a second metal in the chemical environment of a given adsorption center. The experimental findings were compared with theoretical calculations. [Copyright &y& Elsevier]

Abstract: Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO2(110) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C2H2, C2H4, H2, and hydrogen atoms. Although, C2H4 and H2 did not show any indications of reduction of oxidized gold clusters, CO, C2H2, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters. [Copyright &y& Elsevier]

Abstract: Deposition and fabrication of films of Au nanoclusters protected by alkanethiolate ligands are attempted on a TiO2(110) surface and the structures of films are observed by a scanning tunneling microscope (STM). Effects of oxygen and hydrogen-plasma etching in addition to UV irradiation on the structure and chemical composition of the films are also investigated by using STM and X-ray photoelectron spectroscopy. Alkanethiolate Au nanoclusters are produced using a modified Brust synthesis method and their LB films are dip-coated on TiO2(110). Alkanethiolate Au nanoclusters are weakly bound to the substrate and can be manipulated with an STM tip. Net-like structures of alkanethiolate Au nanoclusters are formed by a strong blast of air. Oxygen-plasma etching removes alkanethiolate ligands and simultaneously oxidizes Au clusters. At room temperature, prolonged oxygen-plasma etching causes agglomeration of Au nanoclusters. UV irradiation removes ligands partly, which makes Au nanoclusters less mobile. The net-like structure of alkanethiolate Au clusters produced by a blast of air is retained after oxygen and hydrogen-plasma etching. [Copyright &y& Elsevier]

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]

Triclinic Ag6Mo10O33 nanorods are prepared by hydrothermal reaction of an aqueous solution of AgNO3 and (NH4)6Mo7O24 (pH 2 adjusted with HNO3, autoclave, 140 °C, 12 h). [ABSTRACT FROM AUTHOR]