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Formaldehyde is an important intermediate that affects the catalyst performance in the methanol-to-hydrocarbons (MTH) conversion. In this study, photoelectron photoion coincidence spectroscopy was applied to elucidate the formation of this species in empty quartz and stainless steel reactors as well as over zeolite catalysts (ZSM-5 and BETA) and commonly used bed diluents (silicon carbide and quartz). The yields of formaldehyde in an empty stainless steel reactor and over the crude silicon carbide particles were found to be higher or comparable to those over the zeolite catalysts under similar reaction conditions. In the former two systems, formaldehyde is formed via methanol dehydrogenation, which is catalyzed by transition metals and yields hydrogen and carbon monoxide as the main byproducts. Thus produced formaldehyde is readily consumed in the MTH reaction, wherein its conversion is higher for the more acidic zeolites. The formaldehyde generated by the transition metal sites causes a decrease of the catalyst stability as well as a reduction of the propeneto-ethene ratio, as corroborated by catalytic tests exploring different contacting patterns between the ZSM-5 catalyst and stainless steel chips or silicon carbide particles. These results uncover an important role of methanol dehydrogenation in the MTH conversion, which is relevant for the laboratory testing of the zeolite catalysts and the industrial implementation of this technology., ACS Catalysis, 12 (21), ISSN:2155-5435

Summary High saturation magnetization, hysteresis-less long linear response range, and resistance to device fabrication conditions are figures of merit for magnetic materials. Despite advances in materials research, many high-saturating micro- and nanomagnetic materials are hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in device inefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications. Holmium oxide is a promising material because of its high magnetic susceptibility, but synthetic options are limited, with low-temperature magnetism incompletely characterized. Here, we present physical vapor deposition synthesis and material characterization of polycrystalline holmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla, linear range (μ0H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistance to harsh processing conditions including oxygen plasma and concentrated hydrofluoric acid etching, making these thin films ideal for fabricating next-generation nanoscale magnetic devices in advanced scientific and engineering applications.

We report the promoting effect of graphitic carbon nitride in Cu-catalyzed N-arylation. The abundance of pyridinic coordination sites in this host permits the adsorption of copper iodide from the r...

The worldwide replacement of the toxic mercuric chloride catalyst in vinyl chloride manufacture via acetylene hydrochlorination is slowed by the limited durability of alternative catalytic systems at high space velocities. Here, we demonstrate that platinum single atoms on carbon carriers are substantially more stable (up to 1,073 K) than their gold counterparts (up to 473 K), enabling facile and scalable preparation and precise tuning of their coordination environment by simple temperature control. By combining kinetic analysis, advanced characterization, and density functional theory, we assess how the Pt species determines the catalytic performance and thereby identify Pt(ii)−Cl as the active site, being three times more active than Pt nanoparticles. We show that Pt single atoms exhibit outstanding stability in acetylene hydrochlorination and surpass the space–time yields of their gold-based analogues after 25 h time-on-stream, qualifying them as a candidate for sustainable vinyl chloride production. Platinum nanoparticles have been neglected as a catalyst for acetylene hydrochlorination due to their limited activity. Here, the authors show that nanostructuring to the single-atom level renders platinum on carbonaceous supports a superior catalyst for this important industrial process.

A dual system comprising two catalytic reactors connected in series was developed for the direct conversion of ethene to vinyl chloride monomer (VCM). The first reactor uses ZrO2-supported ceria (CeO2/ZrO2) to perform ethene oxychlorination to 1,2-dichloroethene (EDC) that is dehydrochlorinated to VCM in the second reactor over calcium-promoted γ-Al2O3. The choice of carrier for ceria is of critical importance to maximize the EDC production by reducing combustion products. While MgO, SiO2, SiC, TiO2, ZSM-5, and γ-Al2O3 carriers induced higher overoxidation compared to bulk ceria, ZrO2 was the only carrier that suppressed COx formation. Moreover, the latter carrier led to the highest oxychlorination activity. The unique performance of the CeO2/ZrO2 catalyst was rationalized by its ability to promote chlorine evolution and to suppress the combustion of chlorinated products, as inferred from the activity evaluation in HCl and VCM oxidation, respectively. The outstanding redox properties, enabling operation at low temperature and thus high selectivity, are associated with the formation of defective CeO2 nanoparticles, contrasting the low activity over Ce–Zr mixed oxide. In order to subsequently form VCM, an efficient EDC dehydrochlorination catalyst was designed by moderating the acidity of γ-Al2O3via calcium doping and used in a reactor after CeO2/ZrO2. This dual catalyst system displayed 100% selectivity to VCM at 25% ethene conversion, surpassing the space time yield of the best ethene-to-VCM catalyst EuOCl by a factor of four, where the first step is operated at an elevated temperature of about 100–150 K with respect to cupric chloride benchmarks. In addition, the catalytic dehydrochlorination, operated at a lower temperature of 100 K than the current non-catalytic process, showed minimized coke formation. This developed system rendered stable after slight initial deactivation, offering promising potential to intensify VCM production.

Monoclinic zirconia has been uncovered as a carrier able to substantially boost the activity of indium oxide for CO2 hydrogenation to methanol. Here, electronic, geometric, and interfacial phenomen...

Monolithic, nitrogen-doped carbon sorbents were prepared from resorcinol-urea-formaldehyde resins and physically activated with CO2 for different activation times. The effect of the activation time on the water sorption behavior and the physicochemical properties were investigated. Longer activation times lead to a steeper slope of the water sorption isotherm and, due to a higher specific surface area and micropore volume, an increased water sorption capacity. It was found that, after physical activation for 3 h at 800 °C, the physically activated, nitrogen-doped carbon has a high surface area (>1000 m2/g) and a high water sorption capacity (50 wt%). In a miniaturized adsorption heat pump test stand, the best candidate material was assessed alongside commercial silica gel for reference. At a temperature swing from 90 °C → 50 °C, the CO2-activated carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison with the reference silica gel (429 W/kg versus 255 W/kg). At a more applicable temperature swing, 60 °C → 30 °C, the CO2-activated carbon yields a specific cooling power 3.8 times higher than that of the silica gel reference (932 W/kg versus 240 W/kg).

Suspended carbon nanotube field-effect transistors fabricated with a dry transfer technique demonstrate strong promise as ultra-low-power, hysteresis-free gas sensors. However, the difficulty of establishing a good electrical contact between a nanotube and the electrode surface often limits the yield of low-resistance devices that can operate as low-power gas sensors. In this work, the contact resistance at the nanotube-metal interface and the distribution thereof are reduced significantly by removing the top layer of electrode surface with Ar-ion etching directly before nanotube placement. Combined with post-transfer annealing, this pre-transfer electrode surface cleaning reduces the median ON-resistance of transistors by an order of magnitude--from 1.56 MOhm to 143 kOhm--and the interquartile range by more than two orders of magnitude--from 9.38 MOhm to 59 kOhm. The ability to consistently improve nanotube-metal contact demonstrated in this work is a significant advance in the fabrication of ultraclean nanotube transistors and carbon nanotube gas sensors., Sensors and Actuators B: Chemical, 331

In this study, the possibilities of noise tailoring in filamentary resistive switching memory devices are investigated. To this end, the resistance and frequency scaling of the low-frequency 1/f-type noise properties are studied in representative mainstream material systems. It is shown that the overall noise floor is tailorable by the proper material choice, as demonstrated by the order-of-magnitude smaller noise levels in Ta2O5 and Nb2O5 transition-metal oxide memristors compared to Ag-based devices. Furthermore, the variation of the resistance states allows orders-of-magnitude tuning of the relative noise level in all of these material systems. This behavior is analyzed in the framework of a point-contact noise model highlighting the possibility for the disorder-induced suppression of the noise contribution arising from remote fluctuators. These findings promote the design of multipurpose resistive switching units, which can simultaneously serve as analog-tunable memory elements and tunable noise sources in probabilistic computing machines., ACS Applied Materials & Interfaces, 13 (6), ISSN:1944-8244, ISSN:1944-8252

A combinatorial screening approach has been designed for identification of Hf-Ta anodic memristors with enhanced properties. Three distinct compositional zones with similar characteristics have been identified, two of which are relevant for memristive applications. In a Hf-poor zone, (

Nanocrystalline Ba0.5Sr0.5Co0.8Fe0.2O3-? powders were prepared by a cost-effective solvent-deficient method using metal nitrates and ammonium bicarbonate as precursors. X-ray diffraction (XRD), specific surface determination (BET), thermal analyses (TG-DTA-DSC), dynamic light scattering (DLS) and scanning electron microscopy (SEM) were used to examine the effects of the calcination temperature on the Ba0.5Sr0.5Co0.8Fe0.2O3-? (BSCF) formation. XRD analysis showed that a cubic Ba0.5Sr0.5Co0.8Fe0.2O3-? was obtained after heating for 1 h at 1000?C. BSCF nanocrystals with a diameter of about 25 nm were obtained. On the other hand, the sample mass was stabilized at 915?C as recorded by thermogravimetric analysis (TG), indicating a formation of the complex BSCF oxide already at this temperature. The phase transformations during the synthesis of BSCF oxide are defined and confirmed with the note on the instability of the cubic phase. Using the four-point DC measurements between ?73?C and 127?C, the band gap of 0.84 eV was determined. The solvent-deficient method used in this study to synthesize Ba0.5Sr0.5Co0.8Fe0.2O3-? showed distinct advantages in comparison with other synthesis techniques considering simplicity, rapid synthesis, and quality of the produced nanocrystals.

An improved understanding of the nature and distribution of boron and cesium species in BCsX zeolites is a prerequisite to guide future developments in the environmentally attractive, yet challenging, production of styrene through the side-chain alkylation of toluene with methanol. Herein, standard characterization and catalytic tests are complemented by integrated visualization through time-of-flight secondary-ion mass spectrometry and energy-dispersive X-ray spectroscopy and detailed assessment by 133 Cs and 11 B NMR spectroscopy, to correlate the properties and performance during successive ion-exchange and impregnation steps in the preparation of both powders and millimeter-sized granules. The results highlight a significant impact of catalyst scaleup on the effective introduction of boron species, which originates chemical heterogeneity that is linked to selectivity losses. They also illustrate the complexity of elucidating the role of this promotor, which interacts with cesium cations and exhibits different coordination states and chemical environments, depending on the pretreatment.

The electroreduction of CO2 to fuels and chemicals is an attractive strategy for the valorization of CO2 emissions. In this study, a Cu2 O electrocatalyst prepared by a simple and potentially scalable solvothermal route effectively targeted CO evolution at low-to-moderate overpotentials [with a current efficiency for CO (CECO ) of ca. 60 % after 12 h at -0.6 V vs. reversible hydrogen electrode, RHE], and its selectivity was tuned by the introduction of p-block elements (In, Sn, Ga, Al) into the catalyst. SEM, HRTEM, and voltammetric analyses revealed that the Cu2 O catalyst undergoes extensive surface restructuring (favorable for CO evolution) under the reaction conditions. The modification of Cu2 O with Sn and In further enhanced the current efficiency (CE) for CO (ca. 75 % after 12 h at -0.6 V). In contrast, the introduction of Al altered the selectivity profile of the catalyst significantly, decreasing the selectivity toward CO but promoting the reduction of CO2 to ethylene (CE≈7 %), n-propanol, and ethanol (CE≈2 % each) at -0.8 V vs. RHE. This result is related to a decreased reducibility of Al-doped Cu2 O that might preserve Cu+ species (favorable for C2 H4 production) under the reaction conditions, which is supported by XRD, X-ray photoelectron spectroscopy, and H2 temperature-programmed reduction observations.

Journal of Materials Chemistry A, 5 (31), ISSN:2050-7488, ISSN:2050-7496

ISSN:1867-3880 ISSN:1867-3899

Recent progress in the on-surface synthesis of graphene nanoribbons (GNRs) has given access to atomically precise narrow GNRs with tunable electronic band gaps that makes them excellent candidates for room-temperature switching devices such as field-effect transistors (FET). However, in spite of their exceptional properties, significant challenges remain for GNR processing and characterization. This contribution addresses some of the most important challenges, including GNR fabrication scalability, substrate transfer, long-term stability under ambient conditions and ex situ characterization. We focus on 7- and 9-atom wide armchair graphene nanoribbons (i.e, 7-AGNR; and 9-AGNR) grown on 200 nm Au(111)/mica substrates using a high throughput system. Transfer of both, 7- and 9-AGNRs from their Au growth sub-strate onto various target substrates for additional characterization is accomplished utilizing a polymer-free method that avoids residual contamination. This results in a homogeneous GNR film morphology with very few tears and wrinkles, as examined by atomic force microscopy. Raman spectroscopy indicates no significant degradation of GNR quality upon substrate transfer, and reveals that GNRs have remarkable stability under ambient conditions over a 24-month period. The transferred GNRs are analyzed using multi-wavelength Raman spectroscopy, which provides detailed insight into the wavelength dependence of the width-specific vibrational modes. Finally, we characterize the optical properties of 7- and 9-AGNRs via ultra-violet-visible (UV-Vis) spectroscopy

Carbon nitrides are promising hosts for single-atom catalysts (SACs) based on small amounts of precious metals dispersed as isolated atoms, presenting tantalizing opportunities to reduce the cost a...

Chemical Science, 10 (2), ISSN:2041-6520, ISSN:2041-6539

Controlling the structure sensitivity of catalyzed reactions over metals is central to developing atom-efficient chemical processes. Approaching the minimum ensemble size, the properties enter a non-scalable regime in which each atom counts. Almost all trends in this ultra-small frontier derive from surface science approaches using model systems, because of both synthetic and analytical challenges. Exploiting the unique coordination chemistry of carbon nitride, we discriminate through experiments and simulations the interplay between the geometry, electronic structure, and reactivity of palladium atoms, dimers, and trimers. Catalytic tests evidence applicationdependent requirements of the active ensemble. In the semihydrogenation of alkynes, the nuclearity primarily impacts activity, whereas the selectivity and stability are affected in Suzuki coupling. This powerful approach will provide practical insights into the design of heterogeneous catalysts comprising well-defined numbers of atoms.

Ceramic composite materials are increasingly used in dental restoration procedures, but current ceramic surface designs do not yet achieve the osseointegration potential of state-of-the-art titanium implants. Rapid bone tissue integration of an implant is greatly dependent on its surface characteristics, but the material properties of ceramic composite materials interfere with classical surface modification techniques. Here, ultra-short pulsed laser machining, which offers a defined energy input mitigating a heat-affected zone, is explored for surface modification of ceramic composites. Inspired by surface textures of clinically relevant titanium implants, dual roughness surfaces are laser patterned. Raman mapping reveals a negligible effect of ultra-short pulsed laser ablation on material properties, but a laser-induced change in the wetting state is revealed by static contact angle measurements. Laser patterning of surfaces also influences blood coagulation, but not the attachment and spreading of osteoblastic cells. The presented laser machining approach thus allows the introduction of a rational surface design on ceramic composites, holding great promise for the manufacturing of ceramic implants., Applied Surface Science, 545, ISSN:0169-4332, ISSN:1873-5584

Although amorphous silica-alumina catalysts (ASA) are a promising candidate for the replacement of HCl in the production of methylenedianiline (MDA) and higher homologues, their industrial implementation has been hampered by the lack of systematic studies targeting their design. The complexity of both, the materials as well as the reaction, necessitates the development of synthesis-structure-performance relationships to indicate if, and how, the stringent specifications in terms of activity, selectivity, and stability can be met. Herein, we investigate a large set of ASA obtained by coprecipitation, deposition-precipitation, grafting, and from commercial sources. A detailed analysis of their porosity, composition, Al speciation, acidity, and morphology reveals that every synthesis method leads to a unique combination of material properties. Through high-throughput batch experiments we investigate the importance of each of these parameters for the catalytic performance. The properties that determine the activity relate to the specific surface area, which should be as large as possible while featuring tetrahedrally-coordinated aluminum atoms in the silica matrix. In contrast, the selectivity is determined by the employed reaction conditions, namely the reaction temperature and the aniline content of the feed. Continuous tests under industrial conditions reveal that ASA deactivate via fouling during the initial restructuring of aminal. Pore-mouth blockage by fouling was minimized and optimal lifetimes ensured by employing mesopore networks consisting primarily of pyramidal or cylindrical pores. Based on these insights, we demonstrate that ASA can outperform hierarchical zeolites in terms of activity, while approaching industrially attractive oligomer contents and keeping the concentration of byproducts low at a high catalyst lifetime, advertising their potential for large-scale implementation.

The emergence of synergistic effects in multicomponent systems opens new opportunities to design improved catalysts for the electrochemical CO 2 reduction reaction (eCO 2 RR). Targeting the selective formation of CO, we have evaluated a comprehensive set of silver–indium electrocatalysts with different architectures, ranging from bulk intermetallic compounds to Ag nanoparticles supported on In 2 O 3 and In(OH) 3 . This approach allowed the design of a supported electrocatalyst with maximized performance. Despite very different bulk compositions, XPS analyses on Ag–In alloy electrodes revealed a near-surface indium enrichment, leading to a comparatively poor electrocatalytic performance. In contrast, the presence of oxidized indium deposits on the surface of bulk silver had a positive effect on the selectivity for CO at moderate overpotential. Based on these findings, we studied the interactions between silver and oxidic indium phases by preparing sets of In 2 O 3 - and In(OH) 3 -supported Ag catalysts, which were characterized with XRD, N 2 sorption, H 2 -TPR, CO 2 -TPD, STEM and EDX. With respect to the pristine supports and to similarly prepared Ag catalysts on carbon black, these nanostructured systems exhibited an enhanced current efficiency for CO at moderate overpotential, evidencing a synergistic effect between the metal nanoparticles and the supports. This effect was particularly marked at higher Ag loadings and with In(OH) 3 as support which, unlike In 2 O 3 , was stable against reduction under eCO 2 RR conditions. As a final step, the selectivity enhancement achieved in Ag/In(OH) 3 was combined with the known activity-promoting role of P25 TiO 2 by depositing Ag on a composite support. The Ag/In(OH) 3 –TiO 2 catalyst showed concurrent gains in selectivity and activity for CO. The findings highlight the potential of stable metal (hydr)oxide supports to act as promoters in the eCO 2 RR and the importance of the structural configuration in multicomponent electrocatalysts.

Copper–indium catalysts have recently shown promising performance for the selective electrochemical reduction of CO2 to CO. In this work, we prepared Cu–In nanoalloys by the in situ reduction of CuInO2 and In2O3-supported Cu nanoparticles and found that the structure of these nanoalloys evolves substantially over several electrocatalytic cycles, in parallel with an increase in the activity and selectivity for CO evolution. By combining electrochemical measurements with ex situ characterization techniques, such as XRD, STEM, elemental mapping, and XPS, we show that this behavior is caused by the segregation of copper and indium in these materials, resulting in the formation of a heterogeneous nanostructure of Cu-rich cores embedded within an In(OH)3 shell-like matrix. The evolved catalysts show high electrocatalytic performance at moderate overpotential (i.e., jCO > 1.5 mA cm–2 at −0.6 V vs RHE). We found that the removal of In(OH)3 from these heterogeneous nanostructures decreases the performance of the e...

Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.

In this work, nitrogen doped resorcinol–melamine–formaldehyde (RMF) resins were synthesized, pyrolyzed and physically activated with CO2. The influence of the activation time on the physicochemical properties and the water sorption behavior produced in this way was investigated. Furthermore, a comparison between physical activation with CO2 and chemical activation with KOH is presented. Materials performance was validated in an adsorption chiller test setup with a temperature step from 90 °C → 50 °C. The CO2 activated RMF carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison to a commonly used, commercial silica gel reference material (430 W kg−1 compared to 255 W kg−1). This is surprising considering that the hydrophilicity of the CO2 activated carbon is rather low. The superior performance of carbon based sorbents is attributed to originate from the superior thermal transport properties of monolithic carbons over commercial silica gels. At a more feasible temperature swing 60 °C → 30 °C, the RMF derived carbon yields a specific cooling power 3.2 times greater than that of the silica gel reference.

In the present study, we report on the development of carbon adsorbents for water adsorption heat pumps. Resorcinol-melamine-formaldehyde (RMF) resins were synthesized and molded into monolithic shapes before pyrolysis and chemical activation with KOH. The influence of the carbonization and activation treatments on the physicochemical properties and the water sorption behavior of the final adsorbent materials were investigated. Activated carbons with a one-to-one (C to KOH) impregnation mass ratio, an activation temperature of 800 °C and an activation time of one hour exhibited the highest water cycling ability. For isobaric adsorption at 23 mbar, the peak specific cooling power of the best monolithic activated carbon produced in this way was 192 W kg−1 for a temperature step from 90 °C to 50 °C compared to 255 W kg−1 for silica gel for a finned tube heat exchanger of comparable fin spacing. For a temperature step from 60 °C to 30 °C, the monolithic activated carbon exhibited a higher peak specific cooling power (389 W kg−1) compared to silica gel (240 W kg−1). In situ infrared thermography revealed superior thermal transport properties of the monolithic carbons compared to commercial silica gel.

The dynamical aspects of bipolar resistive switchings have been investigated in Nb/Nb

Cellulose, 18 (6), ISSN:1572-882X, ISSN:0969-0239

ACS Catalysis, 8 (2), ISSN:2155-5435

ACS Catalysis, 8 (1), ISSN:2155-5435

The dynamical aspects of bipolar resistive switchings have been investigated in Nb/Nb2O5/PtIr nanojunctions. We found that the widely tuneable ON and OFF state resistances are well separated at low bias. On the other hand, the high-bias regime of the resistive switchings coincides with the onset of a high nonlinearity in the current–voltage characteristics, where the impedance of both states rapidly decreases and becomes equivalent around 50 Ω. This phenomenon enables the overriding of the RC limitations of fast switchings between higher resistance ON and OFF states. Consequently, nanosecond switching times between multiple resistance states due to subnanosecond voltage pulses are demonstrated. Moreover, this finding provides the possibility of impedance engineering by the appropriate choice of voltage signals, which facilitates that both the set and reset transitions take place in an impedance matched manner to the surrounding circuit, demonstrating the merits of ultra-fast operation of Nb2O5 based neuromorphic networks., Nanoscale, 10 (41), ISSN:2040-3364, ISSN:2040-3372

Local contact damage as well as cohesive and adhesive failure can limit the lifetime and applicability of hydrogenated diamond-like carbon (DLC) films on metallic substrates. DLC on titanium (Ti) is very interesting for industrial applications (e.g. biomedical applications), while also an excellent model system for the general understanding of hard and brittle films on ductile metallic substrates. Interlayers deposited between the DLC film and the Ti substrate have been shown to affect failure of such DLC coated Ti substrates. In this study, the effect of interlayer structure on contact damage and cohesive and adhesive failure is studied with tantalum (Ta) in its α- and β-phase. In all investigated cases the more ductile α-Ta provides improved results over the hard and brittle β-Ta interlayer. Due to plastic deformation effects, the resistance to contact damage is significantly increased with an α-Ta interlayer. Delamination occurs at the interface between the Ti substrate and the Ta interlayer. Compared to DLC on Ti without a Ta interlayer no enhancement in onset strain of fragmentation and delamination was achieved. A finite-element analysis shows that stress concentrations can be distributed over both interfaces if the Young's modulus of the interlayer material is of the order of the Young's modulus of the DLC.

In this study, we gathered further understanding of the function of the components in the Cu-ZnO-Al2O3 catalyst for methanol synthesis from mixed syngas feeds (CO/CO2/H2) to rationally develop systems displaying superior performance. In order to unravel the role of ZnO in the hydrogenation of the preferred methanol source, CO2, and in the (reverse) water–gas shift ((R)WGS) reaction, we tested coprecipitated materials with variable surface zinc content under industrially relevant conditions (5.0 MPa, 503–543 K). We found that a surface enrichment in zinc leads to higher activity and selectivity due to (i) the enhancement of the unique synergistic Cu-ZnO interactions boosting CO2 hydrogenation, (ii) the inhibition of the RWGS reaction which produces the undesired CO, and (iii) the electronic stabilization of the Cu sites against reoxidation by CO2 or H2O. Thus, a catalyst with a surface Zn/(Cu + Zn) ratio of 0.8 displayed superior catalytic properties than a commercial benchmark sample, which featured only ...

After base treatment of ZSM-5 crystals below 100 nm in size, TEM shows hollow single crystals with a 10 nm shell. SEM images confirm that the shell is well- preserved even after prolonged treatment. Determination of the Si/Al ratios with AAS and XPS in combination with argon sputtering reveals aluminum zoning of the parent zeolite, and the total pore volume increases in the first two hours of base treatment. In corresponding TEM images, the amount of hollow crystals are observed to increase during the first two hours of base treatment, and intact crystals are visible even after 10 h of leaching; these observations indicate different dissolution rates between individual crystals. TEM of large, commercially available ZSM-5 crystals shows inhomogeneous distribution of mesopores among different crystals, which points to the existence of structural differences between individual crystals. Only tetrahedrally coordinated aluminum is detected with (27) Al MAS NMR after the base leaching of nano-sized ZSM-5.

Friction and wear minimizing coatings are crucial for applications in combustion engines and medical implants. Their performance is typically limited by mechanical failure especially due to local overload. In this work, the contact damage creation, evolution, and final morphology of hydrogenated diamond-like carbon (DLC)-coated titanium (Ti) substrates are investigated. The influence of the DLC film thickness and the elastic–plastic deformation of the Ti on the contact damage are studied by microindentation and static finite-element analysis. Film thickness, indenter radius, and applied load as well as the elastic–plastic deformation of the Ti are shown to significantly affect contact damage. A failure plot is presented with the location of first failure in the DLC and compared to the experimental observation. In addition, a case study with variable fracture toughness of the DLC and its influence on the failure plot is shown. The stress distribution in the DLC follows a transition from a membrane-like to a plate-like deformation behavior upon increasing the DLC film thickness. Thin DLC films reveal increased cracking in the inner zone of the indent, while thicker DLC films reveal pronounced edge cracking. These edge cracks were correlated to pop-ins in force–displacement curves upon microindentation. Finally, a film thickness optimization process is presented for hard and brittle films on soft and ductile metallic substrates.

Using the model system hydrogenated diamond-like carbon (a-C:H) on titanium (Ti) substrates the effect of a changing film thickness on the cohesive and adhesive failure of hard and brittle films on ductile metallic substrates is analyzed by uniaxial loading. A film thickness size effect has been observed for the fracture strength and the onset strain of delamination. For a a-C:H film thickness 1 μm, whereas for film thicknesses of 200 and 500 nm the effect of the strain is only secondary. Upon uniaxial loading the Ti substrate exhibits an anisotropic deformation which affects the cohesive and adhesive failure of thin a-C:H films. The energy release rates for cohesive and adhesive failure and the fracture toughness of a-C:H are all independent of film thickness. The corresponding values have been determined to be 63.5 ± 2.6 J m −2 , 579 ± 20 J m −2 and 3.2 ± 0.1 MPa m 1/2 , respectively. Finally, a schematic is presented to determine qualitatively the adhesion of ductile and moderately brittle films on any kind of substrate.

Angewandte Chemie. International Edition, 56 (33), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Advanced Functional Materials, 27 (8), ISSN:1616-3028, ISSN:1616-301X

The electronic transport properties of perovskite-type oxides with promising thermoelectric properties can be tuned by cationic substitutions as well as by creating oxygen vacancies. Here, two series of SrxEu1–xTiO3-δ (x = 0.00, 0.03, 0.25, 0.75, 0.97) samples with different oxygen stoichiometries are synthesized using various reductive atmospheres. Oxygen deficiencies in the series produced in highly reducing atmosphere are confirmed by thermogravimetric analysis. Electrical resistivity (ρ) and Seebeck coefficient (S) data reflect the strong influence of the oxygen nonstoichiometry on the transport properties. Samples from the strongly reduced series possess up to 5 orders of magnitude lower electrical resistivities than samples from the less reduced series, confirming that oxygen vacancies act as electron donors in the former. Their Seebeck coefficients strongly decrease with the increase of the charge carrier concentration (lower ρ). Pronounced S(T) peaks are observed, and are attributed to strong hybr...

Alkaline treatment of hydrothermally synthesised Sn-MFI and alkaline-assisted stannation of silicalite-1 were investigated as industrially amenable post-synthetic strategies to generate hierarchical Lewis-acidic MFI zeolites for the isomerisation of mono- and disaccharides. The mesoporosity introduced upon both treatments produced materials that are able to convert glucose, xylose, and lactose, which suffer from access or diffusion limitations to the active sites of the purely microporous Sn-MFI. The stannation of silicalite-1 rendered more active catalysts than the base leaching of Sn-MFI. This is due to a better utilisation of Sn, which is mainly incorporated at the crystals' external surface in the former case but mostly remains in the inaccessible micropores in the latter. The amount of Sn introduced via stannation could also be controlled by varying the strength of the alkaline solution and the molarity of the tin salt added. A Sn loading of 0.25 wt.% already ensures remarkable activity and selectivity.

Tantalum (Ta) and tantalum nitride thin films are highly important as diffusion barriers and adhesion layers in microelectronics and hard coatings for cutting tools. In this study, the effect of the underlying substrate on the phase formation of Ta and the influence of a changing N 2 /Ar flow ratio on hardness, phase and composition of reactively formed tantalum nitride have been investigated. Ta is DC sputter deposited and forms β-Ta on amorphous diamond-like carbon and on the amorphous natural oxide layers of Ti and Si(100) while a 15 nm TaN seed layer results in the formation of α-Ta. The chemical composition of the topmost layers of a substrate influences the formation of α- and β-Ta. With increasing N 2 /Ar flow ratios a transition from amorphous Ta-rich tantalum nitride over face-centered cubic tantalum nitride (fcc-TaN) to (100) textured fcc-TaN at flow ratios above 45% is observed. The hardness of the tantalum nitride thin film reaches a maximum at a flow ratio of 45%, followed by a decrease in hardness for higher N 2 /Ar flow ratios. The increase in hardness is associated with a decrease in grain size and shows a stronger correlation for a Meyers and Ashworth relationship than for a Hall–Petch relationship.