Activation of tungsten oxide for propane dehydrogenation and its high catalytic activity and selectivity

Dehydrogenation of propane to propene is one of the important reactions for the production of higher-value chemical intermediates. In the commercial processes, platinum- or chromium oxide-based catalysts have been used for catalytic propane dehydrogenation. Herein, we first report that bulk tungsten oxide can serve as the catalyst for propane dehydrogenation. Tungsten oxide is activated by hydrogen pretreatment and/or co-feeding of hydrogen. Its catalytic activity strongly depends on hydrogen pretreatment time and partial pressure of hydrogen in the feed gas. The activation of tungsten oxide by hydrogen is attributed to reduction of the metal oxide and presence of multivalent oxidation states. Comparison of the catalytic performance of partially reduced WO3-x to other highly active metal oxides shows that WO3-x exhibits superior catalytic activity and selectivity than Cr2O3 and Ga2O3. The findings of this work provide the possibility for activation of metal oxides for catalytic reactions and the opportunity for the development of new type of catalytic systems utilizing partially reduced metal oxides. [GRAPHICS] .1152Nsciescopu

Revealing lattice disorder, oxygen incorporation and pore formation in laser induced two-photon oxidized graphene

Laser induced two-photon oxidation has proven to be a reliable method to pattern and control the level of oxidation of single layer graphene, which in turn allows the development of graphene-based electronic and optoelectronic devices with an all-optical method. Here we provide a full structural and chemical description of modifications of air-suspended graphene during the oxidation process. By using different laser irradiation doses, we were able to show via transmission electron microscopy, electron energy loss spectroscopy, electron diffraction and Raman spectroscopy how graphene develops from its pristine form up to a completely oxidized, porous and amorphous carbon layer. Furthermore, the gradual control of the oxidation process is used to correlate lattice disorder, oxygen incorporation and pores formation in graphene oxide. This study provides a model system that will benefit research on graphene and other two-dimensional materials.peerReviewe

Dilute GaAs1−xBix epilayers with different bismuth concentrations grown by Molecular Beam Epitaxy: A promising candidate for gamma radiation sensor applications

Radiation interaction studies are very important for exploring the technological applications of new materials in radiation environments. This work reports the effect of gamma radiation dose on the structural and optical properties of dilute GaAs1−xBix epitaxial layers grown with different Bismuth contents by MBE on (1 0 0) GaAs substrates. The influence of radiation has been studied by X-Ray Diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) measurements. The samples were also characterized by Scanning Transmission Electron Microscopy (STEM) and Scanning Electron Microscopy (SEM. Gamma radiation (γ-) was found to influence the optical properties of GaAs1−xBix epitaxial layers. From Raman measurements it was found that the concentration of holes increased when the samples were irradiated. This result is in good agreement with photoluminescence results, which showed that the intensity of the main peak increases after irradiation, indicating that the optical properties have improved for all samples. Furthermore, the XRD data revealed that for irradiated GaAs1−xBix samples, the crystallographic quality of the samples was slightly changed after irradiation. This result is consistent with the results of photoluminescence measurements, which demonstrated that the GaAs1−xBix samples exposed to 50 kGy dose showed an increase in photoluminescence and full width at half maximum for all irradiated samples

Copper Nanocrystals Encapsulated in Zr-based Metal–Organic Frameworks for Highly Selective CO₂ Hydrogenation to Methanol

We show that the activity and selectivity of Cu catalyst can be promoted by a Zr-based metal–organic framework (MOF), Zr₆O₄(OH)₄(BDC)₆ (BDC = 1,4-benzenedicarboxylate), UiO-66, to have a strong interaction with Zr oxide [Zr₆O₄(OH)₄(−CO₂)₁₂] secondary building units (SBUs) of the MOF for CO₂ hydrogenation to methanol. These interesting features are achieved by a catalyst composed of 18 nm single Cu nanocrystal (NC) encapsulated within single crystal UiO-66 (Cu⊂UiO-66). The performance of this catalyst construct exceeds the benchmark Cu/ZnO/Al₂O₃ catalyst and gives a steady 8-fold enhanced yield and 100% selectivity for methanol. The X-ray photoelectron spectroscopy data obtained on the surface of the catalyst show that Zr 3d binding energy is shifted toward lower oxidation state in the presence of Cu NC, suggesting that there is a strong interaction between Cu NC and Zr oxide SBUs of the MOF to make a highly active Cu catalyst

All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing

The fabrication of an all-diamond microprobe is demonstrated for the first time. This ME (microelectrode) assembly consists of an inner boron doped diamond (BDD) layer and an outer undoped diamond layer. Both layers were grown on a sharp tungsten tip by chemical vapor deposition (CVD) in a stepwise manner within a single deposition run. BDD is a material with proven potential as an electrochemical sensor. Undoped CVD diamond is an insulating material with superior chemical stability in comparison to conventional insulators. Focused ion beam (FIB) cutting of the apex of the ME was used to expose an electroactive BDD disk. By cyclic voltammetry, the redox reaction of ferrocenemethanol was shown to take place at the BDD microdisk surface. In order to ensure that the outer layer was nonelectrically conductive, a diffusion barrier for boron atoms was established seeking the formation of boron hydrogen complexes at the interface between the doped and the undoped diamond layers. The applicability of the microelectrodes in localized corrosion was demonstrated by scanning amperometric measurements of oxygen distribution above an Al-Cu-CFRP (Carbon Fiber Reinforced Polymer) galvanic corrosion cell

All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing

The fabrication of an all-diamond microprobe is demonstrated for the first time. This ME (microelectrode) assembly consists of an inner boron doped diamond (BDD) layer and an outer undoped diamond layer. Both layers were grown on a sharp tungsten tip by chemical vapor deposition (CVD) in a stepwise manner within a single deposition run. BDD is a material with proven potential as an electrochemical sensor. Undoped CVD diamond is an insulating material with superior chemical stability in comparison to conventional insulators. Focused ion beam (FIB) cutting of the apex of the ME was used to expose an electroactive BDD disk. By cyclic voltammetry, the redox reaction of ferrocenemethanol was shown to take place at the BDD microdisk surface. In order to ensure that the outer layer was nonelectrically conductive, a diffusion barrier for boron atoms was established seeking the formation of boron–hydrogen complexes at the interface between the doped and the undoped diamond layers. The applicability of the microelectrodes in localized corrosion was demonstrated by scanning amperometric measurements of oxygen distribution above an Al–Cu–CFRP (Carbon Fiber Reinforced Polymer) galvanic corrosion cell

Biochar built soil carbon over a decade by stabilizing rhizodeposits

Biochar can increase the stable C content of soil. However, studies on the longer-term role of plant–soil–biochar interactions and the consequent changes to native soil organic carbon (SOC) are lacking. Periodic 13CO2 pulse labelling of ryegrass was used to monitor belowground C allocation, SOC priming, and stabilization of root-derived C for a 15-month period—commencing 8.2 years after biochar (Eucalyptus saligna, 550 °C) was amended into a subtropical ferralsol. We found that field-aged biochar enhanced the belowground recovery of new root-derived C (13C) by 20%, and facilitated negative rhizosphere priming (it slowed SOC mineralization by 5.5%, that is, 46 g CO2-C m−2 yr−1). Retention of root-derived 13C in the stable organo-mineral fraction (\u3c53 \u3eμm) was also increased (6%, P \u3c 0.05). Through synchrotron-based spectroscopic analysis of bulk soil, field-aged biochar and microaggregates