Takaharu Onishi

The mechanism of the reaction between NOx and NH3 on V2O5 in the presence of oxygen

In order to elucidate the mechanism of the reaction between nitric oxide and ammonia on a V2O5 catalyst, the elementary steps of the reaction were separately studied, and the reactivities of the adsorbates were examined by means of ir, XPS, mass spectrometry, and kinetic studies under reaction conditions. The role of oxygen, whose presence is essential for the reaction to occur, was examined. Nitric oxide was not adsorbed on the V2O5 surface in the absence of oxygen but was adsorbed as NO2(ad) in the presence of ambient oxygen. Ammonia was adsorbed on V2O5 in the form of NH4+(ad), which gives a band at 1413 cm−1 in the ir spectrum. These two adsorbates, NO2(ad) and NH4+(ad), reacted readily to form N2. Accordingly, a new mechanism was proposed for the role of oxygen in the reaction; namely, that the reaction proceeds via the two adsorbates, NO2(ad) and NH4+(ad), which react on the catalyst surface through a Langmuir-Hinshelwood mechanism to form N2 and H2O.

Photocatalytic decomposition of liquid water on a NiOSrTiO3 catalyst

Abstract The photocatalytic decomposition of liquid water on a NiOue5f8SrTiO3 catalyst was studied. The activity was increased considerably by an improvement of pretreatment conditions and using concentrated NaOH solution.

Assignments of the vibrational frequencies of glycine

Abstract Infra-red spectra of α-glycine, α-glycine-D3, glycine-hydrochloride, glycine-hydro-chloride-D3, Na-glycinate, and Na-monochloroacetate have been compared in the NaCl region. Infra-red spectra of α- and γ-glycine and α- and γ-glycine-D3 have been observed in the KBr region. A dichroic measurement has been made on the single crystal of γ-glycine, in which all the glycine molecules are arranged almost in the same direction. Based on the results a complete assignment has been made of the fundamental vibrational frequencies of glycine observed in the 1800–400 cm−1 region.

Molecular-Sieve Type Sorption on Alkali Graphite Intercalation Compounds

The sorption of H2, D2, N2, CH4 and rare gases was studied on alkali graphites C8M and C24M (M = K, Rb, Cs) at 196-63 K. The C24M compounds sorbed gases to various degrees, while all the C8M compounds were non-sorptive. The systematic study of the sorption isotherms for all the compound-gas systems revealed the dependence of the types of the isotherms and that of heats of sorption upon the size of the gas molecules and that of the intercalated alkali metals. Sorption from gas mixtures was also studied for several selected systems, to manifest the actual molecular-sieving action of C24K. The structural study for the system C24K-D2 by means of neutron diffraction technique confirmed that the sorption is due to the occlusion of the gas molecules between the intercalated carbon layers of graphite, and also suggested that the compounds swell up’ by sorption. Based on these results, the relation between the structure of the compounds and the sorption characteristics was discussed.

Normal vibrations of dimers of aluminum trichloride, trimethyl aluminum and dimethyl aluminum chloride

Abstract The calculation of normal vibrations of Al 2 Cl 6 , Al 2 Me 6 and Al 2 Me 4 Cl 2 has been made with a modified Urey—Bradley type potential. The force constants for Al 2 Cl 6 and Al 2 Me 6 have been calculated to agree with their observed frequencies. The frequencies of Al 2 Me 4 Cl 2 have been calculated with reference to the force constants transferred from those obtained for the two molecules. They are in satisfactory agreement with the observed values. The assigmnents of vibrational frequencies and the nature of ring modes are discussed on the basis of the calculations. The far infrared spectra of Al 2 Me 6 and Al 2 Et 6 in the region of 700-280 cm −1 were measured. The medium bands observed at 367 cm −1 for Al 2 Me 6 and at 338 cm −1 for Al 2 Et 6 have been assigned to one of the ring vibrations.

Mechanism of catalytic reduction of NO by H2 or CO on a Pd foil; Role of chemisorbed nitrogen on Pd

Abstract The adsorption of NO and its reaction with H 2 over polycrystalline Pd were investigated using flash desorption technique and ultraviolet photoelectron spectroscopy under 10 −5 Pa pressure range of reactants and surface temperatures between 300 and 900 K. NO was adsorbed dissociatively onto the Pd surface above 500 K, and the heat of dissociative adsorption was ca. 126 kJ/mol. Atomic nitrogen was observed to accumulate on the Pd surface during the NO-H 2 reaction, whose desorption rate exhibited second order kinetics and is expressed as follows: V d = 10 −9.8 ± 0.3 exp (−67( kJ / mol )/ RT ) (cm 2 /atom·s). Hydrogenation of the adsorbed nitrogen proceeded rapidly at 485 K. It was confirmed from these results that formation of N 2 and NH 3 in the NO-H 2 reaction proceeds through this atomically adsorbed nitrogen. Pd-N bond energy and enthalpies of some intermediate states of the NO-H 2 reaction were estimated.

Segregation of sulphur on a molybdenum surface studied by auger electron spectroscopy

The kinetic behaviour of sulphur segregation was studied during heat treatment of a molybdenum ribbon between 750°C and 1350°C by using an Auger electron spectroscopic technique. When the specimen is heated to high temperatures, the sulphur present as an impurity in the polycrystalline molybdenum diffuses on to the surface along grain boundaries. The intensity changes of Auger electron signals of sulphur and molybdenum showed that the rate of the diffusion remained constant until the surface was covered with a first sulphide layer in the temperature range studied. The activation energy in the initial stage of the diffusion was 26kcal/mol. High resolution Auger spectra of the sulphur were measured and explained from the density of states of MoS2.

XPS and UPS study on the chemisorptive bond of formic acid, pyridine and water over metal-phthalocyanines

Abstract X-ray photoelectron (XPS) and ultraviolet photoelectron (UPS) spectroscopic techniques have been employed to study the chemisorption of various molecules over metal-phthalocyanines (MePc). It was revealed that pyridine is adsorbed on the Fe atom in FePc which is accompanied by a change in the spin state without transfer of net electron charge, while HCOOH is heterolytically dissociated, the formate ion staying on the central metal atom and the proton on the bridge N atom of the porphyrin ring. H 2 O on MgPc behaved like HCOOH, with a proton being adsorbed at a bridge N atom. On the basis of these results, the catalytic decomposition of HCOOH and adsorption of pyridine on MePc are discussed.

Oxidation of CO on a Pd surface: application of IR-RAS to the study of the steady state surface reaction

The catalytic oxidation of CO and O2 to form CO2 has been studied on a polycrystalline palladium foil in a pressure range from 10-4 to 1 Pa. The concentrations of both reactants and products were analyzed by a quadrupole mass spectrometer, while the coverage and binding states of the adsorbed species were determined by infrared reflection-absorption spectroscopy (IR-RAS), using an FT-IR spectrometer. This reaction was found to proceed via the Langmuir- Hinshelwood mechanism on the basis of the finding that the rate of steady state reaction of CO2 formation was associated not with the gaseous pressures, but with the amounts of adsorbates. A reaction intermediate, adsorbed CO, was bridge-bonded on the Pd surface. It was also shown that the density of adsorbed CO depended only on the ratio of the gaseous pressure of CO to O2 and not on the partial pressure of CO.

Mechanism of NOH2 reaction over Rh foil and the role of chemisorbed nitrogen atoms

Abstract The behaviour of adsorbed nitrogen and the overall catalytic reaction between NO and H 2 on Rh foil were investigated in a pressure region around 10 −5 –10 −4 Pa and a temperature range between 400 and 1200 K, using the flash desorption technique and ultraviolet photoelectron spectroscopy. In a reducing condition, the NOue5f8H 2 reaction proceeded rapidly in the temperature range between 500 and 1000 K, and the reaction probability of NO was almost unity in the temperature region studied. The major product was N 2 , but NH 3 was also formed around 500 K. Chemisorbed nitrogen was accumulated during the NO-H 2 reaction and also during the NH 3 decomposition reaction. In both cases, the dependence of the rate of N 2 formation upon the amount of N(ad) estimated during the reaction was similar to that in the case of N(ad) flash desorption, which indicates that N 2 is formed by recombination of N(ad) in both the NO-H 2 reaction and the NH 3 decomposition reaction. The rate constant for the second order desorption of N(ad) was estimated to be 10 −6.8 ± 0.3 exp(−97 ± 5( kJ mol ) RT) ( cm 2 atom·s) . The overall reaction of NO-H 2 on Rh proceeds in a similar manner to Pd previously reported, but the dissociation of NO takes place more easily over Rh and O(ad) is more stable, being liable to cause an inhibition of the NO-H 2 reaction, especially at lower temperature.