Difference in reaction mechanism between ZnZrOx and InZrOx for CO2 hydrogenation.

Oxide solid-solution catalysts, such as Zn-doped ZrO2 (ZnZrOx) and In-doped ZrO2 (InZrOx), exhibit distinctive catalytic capabilities for CH3OH synthesis via CO2 hydrogenation. We investigated the active site structures of these catalysts and their associated reaction mechanisms using both experimental and computational approaches. Electron microscopy and X-ray absorption spectroscopy reveal that the primary active sites are isolated cations, such as Zn2+ and In3+, dissolved in tetragonal ZrO2. Notably, for Zn2+, decomposition of the methoxy group, which is an essential intermediate in CH4 synthesis, is partially suppressed because of the relatively high stability of the methoxy group. Conversely, the methyl group strongly adsorbs on In3+, facilitating the conversion of the methoxy species into methyl groups. The decomposition of CH3OH is also suggested to contribute to CH4 synthesis. These results highlight the generation of CH4 as a byproduct of the InZrOx catalyst. Understanding the active site structure and elucidating the reaction mechanism at the atomic level are anticipated to contribute significantly to the future development of oxide solid-solution catalysts.

Intermetallic Compound TiM (M=Co, Fe) with a Layered Structure Prepared by Deoxidizing Ilmenite-type Oxides in Molten LiCl-CaH2 Mixtures.

CsCl-type intermetallic compounds TiM (M=Co, Fe) were obtained by deoxidizing trigonal ilmenite-type MTiO3 with a reducing agent CaH2 in molten LiCl at 600 °C. X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and transmission electron microscopy with energy-dispersive X-ray, and X-ray photoelectron spectroscopy analyses revealed the formation of nanoscale layered structures, which enhanced specific surface areas (approximately 20 m2 /g) in the intermetallic compounds. In the initial deoxidation stage, Li2 TiO3 -like compounds were observed as an intermediate, suggesting the substitution of M in MTiO3 by Li from the molten LiCl. Compound MTiO3 has a layered structure perpendicular to the c axis of the trigonal structure, suggesting that the layered structures may originate from the crystal structure of the precursors. Formation of the Li2 TiO3 -like intermediate may help maintain the original layered structure during deoxidation and the subsequent alloying at temperatures as low as 600 °C.

Isolated Zr Surface Sites on Silica Promote Hydrogenation of CO2 to CH3OH in Supported Cu Catalysts.

Copper nanoparticles supported on zirconia (Cu/ZrO2) or related supported oxides (Cu/ZrO2/SiO2) show promising activity and selectivity for the hydrogenation of CO2 to CH3OH. However, the role of the support remains controversial because most spectroscopic techniques provide information dominated by the bulk, making interpretation and formulation of structure-activity relationships challenging. In order to understand the role of the support and in particular of the Zr surface species at a molecular level, a surface organometallic chemistry approach has been used to tailor a silica support containing isolated Zr(IV) surface sites, on which copper nanoparticles (∼3 nm) are generated. These supported Cu nanoparticles exhibit increased CH3OH activity and selectivity compared to those supported on SiO2, reaching catalytic performances comparable to those of the corresponding Cu/ZrO2. Ex situ and in situ X-ray absorption spectroscopy reveals that the Zr sites on silica remain isolated and in their +4 oxidation state, while ex situ solid-state nuclear magnetic resonance spectroscopy and catalytic performances show that similar mechanisms are involved with the single-site support and ZrO2. These observations imply that Zr(IV) surface sites at the periphery of Cu particles are responsible for promoting CH3OH formation on Cu-Zr-based catalysts and provide a guideline to develop selective CH3OH synthesis catalysts.

CO2 -to-Methanol Hydrogenation on Zirconia-Supported Copper Nanoparticles: Reaction Intermediates and the Role of the Metal-Support Interface.

Methanol synthesis by CO2 hydrogenation is a key process in a methanol-based economy. This reaction is catalyzed by supported copper nanoparticles and displays strong support or promoter effects. Zirconia is known to enhance both the methanol production rate and the selectivity. Nevertheless, the origin of this observation and the reaction mechanisms associated with the conversion of CO2 to methanol still remain unknown. A mechanistic study of the hydrogenation of CO2 on Cu/ZrO2 is presented. Using kinetics, in situ IR and NMR spectroscopies, and isotopic labeling strategies, surface intermediates evolved during CO2 hydrogenation were observed at different pressures. Combined with DFT calculations, it is shown that a formate species is the reaction intermediate and that the zirconia/copper interface is crucial for the conversion of this intermediate to methanol.

CO2 Hydrogenation: Supported Nanoparticles vs. Immobilized Catalysts.

The conversion of CO(2) to more valuable chemicals has been the focus of intense research over the past decades, and this field has become particularly important in view of the continuous increase of CO(2) levels in our atmosphere and the need to find alternative ways to store excess energy into fuels. In this review we will discuss different strategies for CO(2) conversion with heterogeneous and homogeneous catalysts. In addition, we will introduce some promising research concerning the immobilization of homogeneous catalysts on heterogeneous supports, as a hybrid of hetero- and homogeneous catalysts.

Switching from weak to strong cortical attachment of microtubules accounts for the transition from nuclear centration to spindle elongation in metazoans.

The centrosome is a major microtubule organizing center in animal cells. The position of the centrosomes inside the cell is important for cell functions such as cell cycle, and thus should be tightly regulated. Theoretical models based on the forces generated along the microtubules have been proposed to account for the dynamic movements of the centrosomes during the cell cycle. These models, however, often adopted inconsistent assumptions to explain distinct but successive movements, thus preventing a unified model for centrosome positioning. For the centration of the centrosomes, weak attachment of the astral microtubules to the cell cortex was assumed. In contrast, for the separation of the centrosomes during spindle elongation, strong attachment was assumed. Here, we mathematically analyzed these processes at steady state and found that the different assumptions are proper for each process. We experimentally validated our conclusion using nematode and sea urchin embryos by manipulating their shapes. Our results suggest the existence of a molecular mechanism that converts the cortical attachment from weak to strong during the transition from centrosome centration to spindle elongation.

An in situ DRIFTS study on nitrogen electrochemical reduction over an Fe/BaZr0.8Y0.2O3-δ -Ru catalyst at 220 °C in an electrolysis cell using a CsH2PO4/SiP2O7 electrolyte.

In situ DRIFTS measurements of an Fe/BZY-Ru cathode catalyst in an electrolysis cell using a CsH2PO4/SiP2O7 electrolyte were carried out in a mixed N2-H2 gas flow under polarization. The formation of N2H x species was confirmed under polarization, and an associative mechanism in the electrochemical NRR process was verified.

Direct conversion of carbon dioxide and steam into hydrocarbons and oxygenates using solid acid electrolysis cells.

Electrolysis at intermediate temperatures (100-600°C) is promising because high reaction rates and high product selectivity can be achieved simultaneously during CO2 reduction. However, intermediate temperature electrolysis has rarely been reported owing to electrolyte limitations. Here, solid acid electrolysis cells (SAECs) were adopted for electrochemically reducing CO2. Carbon monoxide, methane, methanol, ethane, ethylene, ethanol, acetaldehyde and propylene were produced from CO2 and steam, using Cu-containing composite cathodes at 220°C and atmospheric pressure. The results demonstrate the potential of SAECs for producing valuable chemical feedstocks. At the SAEC cathode, CO2 was electrochemically reduced by protons and electrons. The product selectivity and reaction rate were considerably different from those of thermochemical reactions with gaseous hydrogen. Based on the differences, plausible reaction pathways were proposed.

Superior catalytic performance of intermetallic CaPt2 nanoparticles supported on titanium group oxides in hydrogenation of ketones to alcohols.

Intermetallic CaPt2 nanoparticles, supported on titanium group oxides, were prepared using a molten salt method with CaH2 as both the reducing agent and the calcium source. The nanoparticles exhibited superior catalytic activity compared to a commercial Pt/C catalyst in the hydrogenation of ketones to alcohols, which could be promoted by electron-rich Pt sites in CaPt2.

Porous intermetallic Ni2XAl (X = Ti or Zr) nanoparticles prepared from oxide precursors.

Porous intermetallic Ni2XAl (X = Ti or Zr) nanoparticles with small crystallite sizes (24-34 nm) and high Brunauer-Emmett-Teller (BET) surface areas (10-71 m2 g-1) were prepared from oxide precursors by a chemical route. CaH2 acted as a template to form the porous morphologies and assisted the reduction.

Chemical route to prepare nickel supported on intermetallic Ti6Si7Ni16 nanoparticles catalyzing CO methanation.

In this study, ternary intermetallic nickel silicide, Ti6Si7Ni16, nanoparticles with a high surface area of 37.5 m2 g-1 were chemically prepared from SiO2-impregnated oxide precursors, which were reduced at as low as 600 °C by a CaH2 reducing agent in molten LiCl, resulting in the formation of single-phase Ti6Si7Ni16 with a nanosized morphology. The intermetallic Ti6Si7Ni16 phase in the nanoparticles was stabilized in air by surface passive oxide layers of TiOx-SiOy, which facilitated the handling of the nanoparticles. Considering our previous successful work of preparing single-phase LaNi2Si2 (39.3 m2 g-1) and YNi2Si2 (27.0 m2 g-1) nanoparticles in a similar manner, the proposed chemical method showed to be a versatile approach in preparing ternary silicide nanoparticles. In this study, we applied the obtained Ti6Si7Ni16 nanoparticles as catalyst supports in CO methanation. The supported nickel catalyst showed an activation energy of 56 kJ mol-1, which is half as low as that of common TiO2-supported nickel catalysts. Also, Ni/Ti6Si7Ni16 provided the lower activation energy more than any previous Ni-based catalyst. Since the measured work function of Ti6Si7Ni16 (4.5 eV) was lower than that of nickel (5.15 eV), it was suggested that the Ti6Si7Ni16 support can accelerate the rate-determining step of C-O bond dissociation in CO methanation due to its good electron donation capacity.

Hydrogen Production by Steam Electrolysis in Solid Acid Electrolysis Cells.

Hydrogen production by steam electrolysis at intermediate temperatures has potential for both the high energy conversion efficiency and the flexible operability suitable for the utilization of renewable energy resources. Employment of proton-conducting solid acid electrolytes at around 200 °C is considered promising but has rarely been investigated. Here, steam electrolysis was performed at 160-220 °C using a solid acid electrolysis cell (SAEC) composed of a CsH2 PO4 /SiP2 O7 composite electrolyte and Pt/C electrodes. Hydrogen production was successfully demonstrated with Faraday efficiencies around 80 %. Key factors affecting the SAEC stability were investigated in detail for the first time. It was revealed that a certain part of the electrolyte migrated into the porous anode structure during the operation. The migrated electrolyte prevented the gas diffusion and flooded the Pt/C catalyst layer. It was also found that carbonaceous materials in the anode was oxidized, leading to the decrease in the number of electrochemically active sites. Based on the findings, Pt mesh was employed as an alternative anode. The SAEC with the Pt mesh anode showed superior stability, demonstrating the importance of the anode design. The present work provides a comprehensive view of the stability issues, which is essential for the development of durable and practical SAECs.

Direct electrochemical synthesis of oxygenates from ethane using phosphate-based electrolysis cells.

Ethane was converted directly to acetaldehyde and ethanol by partial oxidation at 220 °C and ambient pressure using an electrolysis cell with a proton-conducting electrolyte, CsH2PO4/SiP2O7, and Pt/C electrodes. The ethane conversion and the selectivity to the products increased with the voltage applied to the cell. It was found that O species generated by water electrolysis functioned as a favorable oxidant for partial oxidation of ethane on the Pt/C anode at intermediate temperatures. The production rates of acetaldehyde and ethanol recorded in this study were significantly higher than those in preceding reports.

Biosynthetic Pathway and Genes of Chitin/Chitosan-Like Bioflocculant in the Genus Citrobacter.

Chitin/chitosan, one of the most abundant polysaccharides in nature, is industrially produced as a powder or flake form from the exoskeletons of crustaceans such as crabs and shrimps. Intriguingly, many bacterial strains in the genus Citrobacter secrete a soluble chitin/chitosan-like polysaccharide into the culture medium during growth in acetate. Because this polysaccharide shows strong flocculation activity for suspended solids in water, it can be used as a bioflocculant (BF). The BF synthetic pathway of C. freundii IFO 13545 is expected from known bacterial metabolic pathways to be as follows: acetate is metabolized in the TCA cycle and the glyoxylate shunt via acetyl-CoA. Next, fructose 6-phosphate is generated from the intermediates of the TCA cycle through gluconeogenesis and enters into the hexosamine synthetic pathway to form UDP-N-acetylglucosamine, which is used as a direct precursor to extend the BF polysaccharide chain. We conducted the draft genome sequencing of IFO 13545 and identified all of the candidate genes corresponding to the enzymes in this pathway in the 5420-kb genome sequence. Disruption of the genes encoding acetyl-CoA synthetase and isocitrate lyase by homologous recombination resulted in little or no growth on acetate, indicating that the cell growth depends on acetate assimilation via the glyoxylate shunt. Disruption of the gene encoding glucosamine 6-phosphate synthase, a key enzyme for the hexosamine synthetic pathway, caused a significant decrease in flocculation activity, demonstrating that this pathway is primarily used for the BF biosynthesis. A gene cluster necessary for the polymerization and secretion of BF, named bfpABCD, was also identified for the first time. In addition, quantitative RT-PCR analysis of several key genes in the expected pathway was conducted to know their expression in acetate assimilation and BF biosynthesis. Based on the data obtained in this study, an overview of the BF synthetic pathway is discussed.

Surface Sites in Cu-Nanoparticles: Chemical Reactivity or Microscopy?

Copper nanoparticles are widely used in catalysis and electrocatalysis, and the fundamental understanding of their activity requires reliable methods to assess the number of potentially reactive atoms exposed on the surface. Herein, we provide a molecular understanding of the difference observed in addressing surface site titration using prototypical methods: transmission electron micrscopy (TEM), H2 chemisorption, and N2O titration by a combination of experimental and theoretical study. We show in particular that microscopy does not allow assessing the amount of reactive surface sites, while H2 and N2O chemisorptions can, albeit with slightly different stoichiometries (1 O/2CuS and 1 H2/2.2CuS), which can be rationalized by density functional theory calculations. High-resolution TEM shows that the origin of the observed difference between microscopy and titration methods is due to the strong metal support interaction experienced by small copper nanoparticles with the silica surface.