Kyoko K. Bando

In-situ FT-IR study on CO2 hydrogenation over Cu catalysts supported on SiO2, Al2O3, and TiO2

Abstract For methanol synthesis from CO2 hydrogenation, TiO2-supported Cu catalyst (Cu/TiO2) showed the highest turnover frequency (specific rate per one active site) among three catalysts (Cu/Al2O3, Cu/SiO2, and Cu/TiO2). According to in-situ FT-IR observations, the peaks of adsorbed formate species observed during the reaction were suppressed for Cu/TiO2, although they were dominant for both Cu/Al2O3 and Cu/SiO2. In order to understand the relationship between IR spectra and the activity, as well as to find out the essential factors that control the activity, we investigated the reactivity of intermediate species mainly by in-situ FT-IR spectroscopy. Each Cu site itself had little ability to adsorb CO2; however, Al2O3 and TiO2 readily adsorbed CO2 by weak bondings on them. CO2 species adsorbed on Cu sites were rapidly converted to formate species under reaction conditions. Formate species generated on Cu sites of Cu/SiO2 remained under H2 at 473 K. On Cu/Al2O3 the formate species adsorbed on the support firmly, so it was difficult to distinguish the formate on Cu from that on the support (Al2O3), and they were stable under H2 at 473 K. On Cu/TiO2, hydrogenation of formate species occurred at 423 K. The behavior of IR spectra during reaction over Cu/TiO2 could be explained by the promotion of formate hydrogenation by the synergetic effect between Cu and TiO2.

Enhancement of cyclic ether formation from polyalcohol compounds in high temperature liquid water by high pressure carbon dioxide

Cyclic ethers were produced by a dehydration reaction of polyalcohol compounds in high temperature liquid water, which was accelerated by the presence of carbon dioxide dissolved in the water. 3-hydroxytetrahydrofuran was produced by the dehydration of 1,2,4-butanetriol. Both tetrahydrofurfuryl alcohol and 3-hydroxytetrahydropyran were produced by the dehydration of 1,2,5-pentanetriol. Five-membered cyclic ethers were formed faster than six-membered cyclic ethers and the formation rates of the cyclic ethers depended strongly on the structure of the polyalcohol compounds. The position of the hydroxyl groups is crucial for the efficient intramolecular dehydration.

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

The dynamic behavior and kinetics of the structural transformation of supported bimetallic nanoparticle catalysts with synergistic functions in the oxidation process are fundamental issues to understand their unique catalytic properties as well as to regulate the catalytic capability of alloy nanoparticles. The phase separation and structural transformation of Pt(3)Sn/C and PtSn/C catalysts during the oxidation process were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques, which are element-selective spectroscopies, at the Pt L(III)-edge and the Sn K-edge. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticles on carbon surfaces. The kinetic parameters and mechanisms for the oxidation of the Pt(3)Sn/C and PtSn/C catalysts were determined by time-resolved XAFS techniques. The oxidation of Pt to PtO in Pt(3)Sn/C proceeded via two successive processes, while the oxidation of Sn to SnO(2) in Pt(3)Sn/C proceeded as a one step process. The rate constant for the fast Pt oxidation, which was completed in 3 s at 573 K, was the same as that for the Sn oxidation, and the following slow Pt oxidation rate was one fifth of that for the first Pt oxidation process. The rate constant and activation energy for the Sn oxidation in PtSn/C were similar to those for the Sn oxidation in Pt(3)Sn/C. In the PtSn/C, however, it was hard for Pt oxidation to PtO to proceed at 573 K, where Pt oxidation was strongly affected by the quantity of Sn in the alloy nanoparticles due to swift segregation of SnO(2) nanoparticles/layers on the Pt nanoparticles. The mechanisms for the phase separation and structure transformation in the Pt(3)Sn/C and PtSn/C catalysts are also discussed on the basis of the structural kinetics of the catalysts themselves determined by the in situ time-resolved DXAFS and QXAFS.

CO2 hydrogenation reactivity and structure of Rh/SiO2 catalysts prepared from acetate, chloride and nitrate precursors

Abstract Silica-supported Rh catalysts (Rh/SiO 2 ) were prepared from acetate, chloride and nitrate precursors by an impregnation method and were applied to CO 2 hydrogenation reaction. CO 2 conversion over the catalyst prepared from chloride precursor was lower than that over acetate or nitrate one, because of fewer active sites on catalysts, as estimated by H 2 chemisorption. The main product was CO over the catalysts prepared from acetate and nitrate, but it was CH 4 over the catalyst prepared from chloride precursor. Characterization of catalysts by TEM, FT-IR and XPS was carried out in order to elucidate the effect of metal precursor on the CO 2 hydrogenation reactivity. The results of XPS showed that the O atomic ratio to Rh on surface hydroxyl groups increased in the order: chloride 2 surface was expected to have a significant influence on the reactivity.

Design of a high-temperature and high-pressure liquid flow cell for x-ray absorption fine structure measurements under catalytic reaction conditions

The design and performance of a new high-pressure and high-temperature cell for measurement of x-ray absorption fine structure (XAFS) spectra of solid catalysts working in a flowing liquid are presented. The cell has flat, high-purity sintered cubic boron nitride (c-BN) windows which can tolerate high temperature (900 K) and high pressure (10 MPa). The c-BN is a new material which has the highest tensile strength, second only to diamond, and is also chemically and thermally stable. The use of the cell is demonstrated for measurements of PtPdAl(2)O(3) and Ni(2)PSiO(2) hydrodesulfurization catalysts at reaction conditions. A technique called delta chi (Deltachi), involving determining the difference between XAFS spectra of the sample at reaction conditions and the bare sample, is introduced.

In situ fluorescence XAFS study for hydrodesulfurization catalysts

The chemical state analysis of Co and Ni in Co–W and Ni–W sulfide catalysts are studied by means of an in situ fluorescence XAFS technique. The structural changes of Co and Ni with the reaction atmosphere and temperature and the effects of the addition of a chelating agent on the sulfidability of Co and Ni are discussed. In the absence of a chelating agent, sulfidation of Co and Ni rapidly proceeds with increasing temperature and is almost completed at 473 K. On the other hand, the Co and Ni species of Co–W/Al2O3 and Ni–W/Al2O3 catalysts having nitrilotriacetic acid (NTA) were scarcely sulfided at room temperature. Furthermore, XANES analysis revealed that the rate of sulfidation is significantly suppressed in the presence of NTA even at a higher temperature. It is also found that the catalytic activity of Co–W/Al2O3 for thiophene hydrodesulfurization is improved more significantly by the addition of NTA than that of Ni–W/Al2O3. It is demonstrated by means of the XANES analysis that the formation of bulk Co sulfide species is considerably suppressed in the NTA-added Co–W catalyst.

Surface treatment- and calcination temperature-dependent adsorption of methyl orange molecules in wastewater on self-standing alumina nanofiber films

A novel form of alumina, free-standing and transparent alumina nanofiber thin films has been synthesized and utilized as highly efficient adsorbents for organic dye removal and decoloration, and their adsorption capacities are sensitively dependent on surface treatment and calcination temperature. Compared with commercial alumina powders, the films exhibited totally different adsorption behaviors and enhanced adsorption capacities, which may originate from their different pore sizes in the two forms. The as-prepared dye-adsorbed alumina nanofiber films may open up new possibilities for some potential applications, e.g., pH indicator paper for pH testing derived from the dye-adsorbed alumina films was enabled based on different dye-desorption characteristics in different solutions.

In situ XAFS analysis system for high-pressure catalytic reactions and its application to CO2 hydrogenation over a Rh/Y-zeolite catalyst

An in-situ XAFS cell was developed and used for the structural analysis of a Rh ion-exchanged zeolite catalyst during high-pressure hydrogenation of carbon dioxide. The in-situ cell enabled analyses of the catalyst structures that changed with the reaction atmosphere and elapsed time; the peak assigned to Rh-O scattering changed to that assigned to Rh-Rh scattering at 404 K during the pretreatment by hydrogen. After 30 min. of the carbon dioxide hydrogenation reaction, the peak intensity assigned to Rh-Rh scattering increased corresponding to the increase in the catalytic activity.

Gaseous fuel production from nonrecyclable paper wastes by using supported metal catalysts in high-temperature liquid water.

Paper wastes are used for the production of gaseous fuels over supported metal catalysts. The gasification of the nonrecyclable paper wastes, such as shredded documents and paper sludge, is carried out in high-temperature liquid water. The order of the catalytic activity for the gasification is found to be ruthenium>rhodium>>platinum>>palladium. A charcoal-supported ruthenium catalyst (Ru/C) is the most effective for the gasification of paper and cellulose. Paper wastes are gasified to a limited degree (32.6 carbon %) for 30 min in water at 523 K to produce methane and carbon dioxide, with a small amount of hydrogen. At 573 K, more complete gasification with almost 100 carbon % is achieved within 10 min in water. At 523 K, the gas yield of paper gasification over Ru/C is higher than that of cellulose powder. The gas yields are increased by ball-milling treatment of the recycled paper and cellulose powder. Printed paper wastes are also gasified at 523 K in water.

Operando QEXAFS studies of Ni2P during thiophene hydrodesulfurization: direct observation of Ni-S bond formation under reaction conditions

Structural changes in Ni(2)P/MCM-41 were followed by quick extended X-ray absorption fine structure (QEXAFS) and were directly related to changes in X-ray absorption near-edge structure (XANES) which had been used earlier for the study of the active catalyst phase. An equation is proposed to correct the transient QEXAFS spectra up to second-order in time to remove spectral distortions induced by structural changes occurring during measurements. A good correlation between the corrected QEXAFS and the XANES spectral changes was found, giving support to the conclusions derived from the XANES in the previous work, namely that the formation of a Ni-S bond in a surface NiPS phase is involved in the active site for the hydrodesulfurization reaction.