Hirofumi Aritani

Decomposition of methanol on Pt-loaded ceria

Abstract Methanol was decomposed to carbon monoxide and hydrogen on supported precious metals. Among the precious metals examined the performance of Pt was found to be the best, and ceria was the best support. Pt/CeO2 decomposed methanol completely at 230°C with 99.2% and 94.6% of selectivities to H2 and CO, respectively. TEM, ESCA, and XAFS analyses showed that Pt interacted very strongly with ceria, indicating the possibility of the formation of Pt–O–Ce bond and the penetration of Pt into the bulk ceria. The reaction mechanism was discussed on the basis of the kinetic analysis.

Zirconia-supported copper catalysts for NO[ndash ]CO reactions Surface copper species on zirconia

Cu/ZrO2 catalysts show high activity for the NO–CO reaction, even at low temperature (100–200°C). The structure and reduction behaviour of ZrO2-supported Cu species have been characterized by means of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), FTIR and temperature-programmed reduction (TPR). It was found that highly dispersed Cu2+ species in an octahedral symmetry dominated at a Cu content lower than 1 wt.% and that the amount of the Cu2+ species was saturated at 1 wt.% Cu. On the other hand, Cu oxide clusters were exclusively formed upon additional Cu incorporation after 1 wt.%. The highly dispersed Cu2+ species were produced by reaction with the terminal OH groups of the ZrO2 surface. The highly dispersed Cu2+ species were reduced by CO at a much lower temperature than Cu oxide clusters and produced highly dispersed Cu+ species at 100°C, which subsequently formed C species at 170–180°C. It is concluded that the high catalytic activity of Cu/ZrO2 for NO–CO reactions at low temperature is brought about by the formation of highly active C species on low-temperature reduction of the Cu2+ species interacting with the ZrO2 surface, and that the activity of the C species is lost by agglomeration into Cu metal particles.

XAFS STUDY OF ZIRCONIA-SUPPORTED COPPER CATALYSTS FOR THE NO-CO REACTION :DEACTIVATION, REJUVENATION AND STABILIZATION OF CU SPECIES

A Cu/ZrO2 (1 wt.% Cu) catalyst shows high activity for the NO–CO reaction, even at low temperature (100–200 °C). However, the low-temperature activity is easily lost during prolonged reaction at 250 °C. The activity of the deactivated Cu/ZrO2 catalyst is completely restored by NO treatment (1% in He) at >250 °C or O2 treatment (5% in He) at 500 °C. The addition of iron (2 wt.%) to Cu/ZrO2 causes not only a dramatic increase in the low-temperature activity but also high stability against deactivation. An X-ray absorption fine structure (XAFS) study has been conducted to reveal the local structure and chemical state of the Cu species in Cu/ZrO2 and Cu–Fe/ZrO2 during the reaction and rejuvenation. X-ray absorption near-edge structure (XANES) spectra and, in particular, their first derivatives are shown to be very effective for characterization of the Cu species. It is revealed that the deactivation of Cu/ZrO2 is a consequence of reduction and sintering of highly dispersed Cu+ species, derived from Cu2+(Oct) species in an octahedral symmetry, to Cu metal particles. The Cu metal particles in a deactivated Cu/ZrO2 catalyst are transformed into the original Cu2+(Oct) species by the NO treatment at 250 °C via highly dispersed Cu+ species. On the other hand, O2 treatments bring about successive formation of Cu2O at 150 °C and CuO at 250 °C. The Cu2+(Oct) species are reformed at >400 °C. The XAFS study of Cu–Fe/ZrO2 suggests that the high stability of highly dispersed Cu+ species is a consequence of direct interaction of Cu species with iron oxide clusters. On the basis of kinetics and XAFS results, the catalytic synergies between Cu and Fe are inferred to be two-fold: stabilization of highly dispersed and catalytically active Cu+ species during the reaction and simultaneous participation of both Cu and Fe in the reaction.

XAFS study of niobium oxide on alumina

Abstract The structure of the niobium oxide on alumina surface was investigated for low loading (5 wt.-%) and high loading (19 wt.-%) samples. The TPD profile of water molecules showed the appearance of water adsorption sites other than those on alumina. The XANES and EXAFS spectra clearly showed that niobic acid-like species are formed on the surface of 19 wt.-% NbO x /Al 2 O 3 . The XANES spectra of 5 wt.-% NbO x /Al 2 O 3 suggests that NbO 4 tetrahedra with two NbO bonds are present and one or two water molecules are adsorbed onto the species. On 5 wt.-% NbO x /Al 2 O 3 , the presence of a mixture of the monomer NbO 4 and the dimer Nb 2 O 7 are concluded from the EXAFS analysis.

Reduction of NO over TiO2-supported Cu catalysts

TiO2-supported Cu catalyst pretreated with H2 at 473 K exhibits higher activity for the conversion of NO at low temperatures than Cu on other supports. The NO is converted to N2via N2O as an intermediate. In the reaction at 303 K, NO is reduced to N2O. For the reaction above 323 K, the conversion of N2O to N2 is accelerated.The samples were characterized by X-ray absorption near-edge structure (XANES), UV–VIS and EPR spectroscopies. Treatment of the sample with hydrogen at 473 K leads to formation of Cu metal particles and promotes the reduction of Ti ions. The extent of the reduction of TiO2 supporting Cu is much higher than that of TiO2 itself. NO has a role in the oxidation of both Cu and Ti ion, even at room temperature and H2 reduces both ions. The active Cu-species is a CuO particle with a Cu metal core.

XANES study of Li-MgO and Li-La2O3-MgO catalysts for oxidative coupling of methane.

To characterize the defect sites in the near-surface and bulk phase of Li-MgO and Li-La2O3-MgO, XANES at Mg K-edge and La L3-edge was applied. For Li-MgO, it can be suggested that Li doping at a low content (2.5 wt%) brings about the formation of defect species only in the near-surface. This is due to the localization of doped Li ions in the surface, and thus the catalytically active species containing [Li+ O-] type center exist in the surface region. After OCM reaction, the detect species are formed in the near-surface over MgO and Li-MgO. By addition of La2O3 to Li-MgO (La/(Mg+La)=0.25), the structural change during the reaction is almost suppressed in the surface. In addition, the Li-La2O3-MgO shows higher C2 selectivity than Li-MgO.

Surface copper-TiO2 interaction species for NOCO reactions

Abstract The catalytic properties of Cu TiO 2 have been studied for an NOCO reaction as a function of the calcination temperature, Cu content, and orgin of TiO2. It was found that CuTiO2 interaction species were responsible for catalytic activity at low temperature (140°C). It is suggested by means of XAFS and TPR that a rutile phase of TiO2 is very effective for the formation of the catalytically active CuTiO2 interaction species in an octahedral symmetry.

Structures and catalytic behavior of some niobium oxides

Abstract On niobium oxide catalysts, induction period was observed during 1-butene isomerizatlon, because surface strong adsorption sites for 1-butene existed. With sodium-loading on Nb 2 O 5 /Al 2 O 3 , new and weak basic sites such as Nb-O-Na-OH were formed. Nb 2 O 5 supported on TlO 2 functioned as a sensor for oxygen and nitrogen monoxide.

Performance of the YB66 soft X-ray monochromator crystal at the wiggler beamline of the UVSOR facility

Soft X-ray spectra have been measured using a pair of YB(66)(400) monochromator crystals at the double-crystal monochromator beamline BL7A of the UVSOR facility, where the wiggler radiation has a magnetic field of 4 T. Deformation of the YB(66) crystal due to heat load from the synchrotron radiation is almost negligible. The photon flux is about 10(8) photons s(-1) (100 mA)(-1) in the energy region 1.2-2 keV and the energy resolution is 0.7 +/- 0.1 eV around hnu = 1.5 keV. These results show that the YB(66) crystal is suitable for use as a monochromator crystal. Its application to soft X-ray spectroscopy is discussed.

Synthesis of Fe-substituted Al-mordenites by hydrothermal method

Al-mordenite and Fe-mordenite were synthesized with the tetraethylammonium as atemplate by hydrothermal method at 150°C in the Na2O–Al2O3–SiO2–H2O and Na2O–Fe2O3–SiO2–H2O system, respectively. Synthesis of several Al-mordenites substituted with Fe, Al/Fe ratio = 75/25, 50/50, 25/75, were also attempted in the Na2O–Al2O3–Fe2O3–SiO2–H2O system under the same conditions by the hydrothermal method. The continuous solid solution of Fe in Al-mordenite was successfully obtained in mordenites with various Al-Fe molar ratios. Al-mordenite crystal was tablet-like with approximately 20–30 μm in diameter and 5–10 μm in thickness. Fiber-like Fe-mordenite grew up to 20–30 μm in length and 5 μm in diameter. The morphology of Fe-substituted Al-mordenite was cubic-like with 5–10 μm in size. The size of Fe-substituted Al-mordenite decreased with the increase of Fe-content.