Isamu Toyoshima

Formation of carbidic and graphite carbon from CO on polycrystalline cobalt

Abstract Deposition of carbon by the dissociation of adsorbed CO and by the Boudouard reaction was studied on cobalt with XPS. A limited amount of adsorbed CO undergoes dissociation at a temperature higher than 333 K, which results in a fixed amount of carbidic carbon (θC = 0.4), but the Boudouard reaction yielded a larger amount of carbidic carbon as well as graphitic carbon at 500 and 700 K. Carbidic carbon formed by the Boudouard reaction at 500 K undergoes decomposition to graphitic carbon at 700 K, but a limited part of the carbidic carbon (θC = 0.4) remains at this high temperature of 700 K. The cobalt surface covered with the stable carbidic carbon (θC=0.4) is no longer active for the dissociation of C(a) but the Boudouard reaction can proceed on it.

Study of methanol electrooxidation on RhSn oxide, PtSn oxide, and IrSn oxide in comparison with that on the Pt metals

Abstract Catalytic activities of RhSn oxide, IrSn oxide, and PtSn oxide were studied with respect to their tin oxide effect in comparison with those of the Pt metals and each other. Surface chemical states were observed using XPS for the RhSn and PtSn oxides. Electrochemical and XPS results were compared to each other. Tin oxide showed a pronounced enhancement of the catalytic activity toward methanol electrooxidation on PtSn oxide with respect to Pt itself in acidic solutions, but not in alkaline solutions. In the case of RhSn oxide, tin oxide had a negative catalytic activity effect, with respect to Rh, and had no effect in the case of IrSn oxide, with respect to Ir. This difference was considered to be correlated to the presence or the absence of redox coupling of the respective Pt group metal species. Formaldehyde electrooxidation was also studied on PtSn oxide in acidic solution. In alkaline solution, PtSn oxide was also used for not only formaldehyde, but also formate electrooxidation and its catalytic activity was discussed in comparison with Pt itself.

Friedel-Crafts reaction in the heterogeneous system: V. Friedel-Crafts benzylation and benzoylation of toluene catalyzed by calcined iron sulfates

The Friedel-Crafts benzylation of toluene with benzyl chloride was carried out at 45 °C over ferrous and ferric sulfates calcined in air at 700, 800, and 900 °C. The benzoylation of toluene with benzoyl chloride was also performed at 110 °C over both iron sulfates heat-treated at 500, 700, 900 °C. The catalysts prepared by calcining both sulfates at 700 °C showed the maximum activity in both reactions. The products were 41% ortho-, 7% meta-, and 52% para-benzyltoluene for the benzylation and 18–22% ortho-, 2–4% meta-, and 74–78% para-methylbenzo-phenone for the benzoylation in all the analyzed runs. The ratio of rate of the benzoylation in toluene and benzene, kTkB, was 7.4 and 6.3 for FeSO4 and Fe2(SO4)3 calcined at 700 °C, respectively, which are surprisingly small compared with that for AlCl3 (ktkb = 110–115). From the former values, the positional selectivities of toluene, of, mf, pf, were obtained as 3–5, 4–9, and 32, respectively. The specific surface areas of calcined sulfates were 49–71 m2/g, indicating no relationship between them and the catalytic activities. The analysis of Fe and S contents of the catalysts showed that both ferrous and ferric sulfates are mainly remained as sulfate forms at 500 °C of calcination and decomposed to form iron oxides containing 0.15% S at 700 °C. Mossbauer spectra showed that ferrous sulfate calcined in air consists of 73% Fe2+ and 27% Fe3+ at 300 °C and 100% Fe3+ above 500 °C. On the basis of the observed results, the nature of active sites of catalyst was discussed.

Formation of a linear LiOH compound on Cu(001): reaction of H2O with Li adatoms at low coverages

The reaction of H2O with Li adatoms at low coverages on Cu(001) has been studied at room temperature by using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and work-function measurement. The coverage (θ) of Li was 0.125 except for the experiment of the work function (θ = 0.25). The O 1s XPS spectra from the H2O exposed Li/Cu(001) surface showed a single peak at 531.5 eV. It was found by comparing the area of the O 1s peaks of H2O/Li/Cu(001) with that of (√2 × 2√2) R45°OCu(001) that the stoichiometry of oxygen to Li is 1:1. HREELS spectra showed a strong peak at 600 cm−1 and small peaks at 3600, 1300 and 1100 cm−1. The work function increased with increasing H2O exposure. These observations and the results of previous studies lead to the conclusion that the reaction product as a result of interaction of H2O with Li adatoms on Cu(001) is a linear triatomic molecule of LiOH which sits on the surface upright with Li down. The reaction scheme is expressed as Li(a) + H2O(a) → LiOH(a) + H(a), where (a) denotes adspecies. The strong 600 cm−1 peak in HREELS spectra is assigned to the Li-OH stretching mode. The intense loss-peak indicates the LiOH molecule formed on Cu(001) has an ionic-bond character. In fact the effective dynamic charge of the Li-OH stretching vibration is estimated to be ∼ 0.5e, and this is larger than that of the Li stretching vibration in the Li/Cu(001) system, ∼ 0.3e. Force constants of the LiOH admolecule are estimated. A transition state for the reaction is proposed.

A photoelectron spectroscopic study of the effect of particle size on the adsorbed state of carbon monoxide over supported palladium catalysts

Abstract UPS experiments on the adsorbed state of carbon monoxide over Pd/graphite model catalysts at 77–653 K have been performed. The CO-derived levels, (5σ + 1π) and 4σ, shift to higher with binding energy with decrease in the palladium particle size. Upon warming, the included levels on smaller Pd particles disappeared at much lower temperature than those on larger palladium particles.

Catalysis and coordinative unsaturation of active sites on sulfurated nickel catalyst: I. Reversible formation of active sites for partial hydrogenation of acetylene

Abstract Active sites are generated on sulfurated nickel surface by contacting with acetylene, on which the hydrogenation of acetylene and ethylene as well as the H 2 -D 2 equilibration reaction proceed. These sites are wiped up by exhaustion of acetylene, and such reversible formation and vanishment of the active sites controls the partial hydrogenation of acetylene to ethylene on the sulfurated nickel catalyst. A nickel sulfide having an atomic ratio of S Ni = 0.62 had the activity for the partial hydrogenation of acetylene, while a nickel sulfide of S Ni = 0.96 had no catalytic activity. The surface composition of the sulfurated nickel estimated by Auger electron spectroscopy was a value of the ratio S Ni = 0.69 . From these results it is concluded that partial hydrogenation is enabled by reversible formation of active sites on sulfide with appropriate coordinative unsaturation of nickel atoms.

On the kinetics and mechanism of the CO oxidation over polycrystalline iridium

Abstract The kinetics of the CO oxidation was studied over polycrystalline iridium under ultrahigh vacuum conditions. The reaction was first-order in CO and zero-order in O2 for low CO pressures, while it was inhibited by CO above a certain critical CO pressure. Above that pressure the reaction was first-order in O2 and negative-order in CO. The amount of adsorbed CO and oxygen during the catalyzed reaction was determined with flash-desorption, AES, and UPS. Above the critical CO pressure the amount of adsorbed CO was equal to that in the CO/Ir equilibrium (nonworking) system. It decreased sharply around the CO pressure and was very small at lower pressures. The amount of adsorbed oxygen decreased smoothly as the CO pressure increased and became very small around the critical CO pressure. This kinetic behavior can be explained in terms of a Langmuir-Hinshelwood mechanism and a change in the rate-limiting process.

Reactivity of deposited carbon on CoAl2O3 catalyst

Reactivity and characteristics of the carbon deposited on Co-Al2O3 by disproportionation of CO (the Boudouard reaction) were studied by pulse experiments using 13C or D isotopes. Three types of deposited carbon were identified by the reaction with hydrogen: highly reactive CH and/or CH2 species, reactive carbidic carbon, and less reactive graphitic carbon. The existence of CH and CH2 species was proved by the reaction with D2 pulse at 80 °C, but the predominant species was carbidic carbon when the disproportionation of CO was performed on cobalt catalyst at 230 °C. Carbidic carbon was decomposed to graphitic carbon by raising the temperature. However, a certain amount of carbidic carbon was found to remain on the surface even at 430 °C. This phenomenon may suggest reversible formation of carbidic carbon from graphitic carbon on the catalyst.

Adsorption of nitrous oxide on metallic copper catalysts

With the help of UPS spectroscopy, it has been shown that N2O decomposes into N2 and surface Cu2O over copper catalysts in the temperature range −150, −100°C. The surface oxide oxygen dissolved into the bulk above 100°C to some extent.AbstractС помошвю фотоэлектронной спектроскопии было показзно, что N2O разлагается на медных катализатоах в интервале темперттур −150° −100°C, давая N2 и поверхностный Cu2O. Кислород поверхностноло окисла растворяется в некоторой степени в массе при температуре выше 100°C.

Temperature-programmed desorption on the unstable lattice oxygen of praseodymium oxide

Abstract A TPD (temperature-programmed desorption) study on the unstable lattice oxygen from praseodymium oxide has been made with a view to know catalytic behaviors of such an unstable lattice oxygen to the oxidation reactions. Five different oxygen peaks [α (340 °C), α′ (380 °C), β (400 °C), γ (440 °C), and δ (500 °C)] were observed on the TPD spectra from the oxide between 25 and 600 °C, and the thermal behaviors of the β, γ, δ peak oxygens were investigated as functions of oxygen absorption temperature, pressure, and time. The total amount of oxygen desorbed (evolved) between 25 and 600 °C from Pr 6 O 11 , which is one of the oxides having a stable composition, corresponded to 7.5% of total oxygen in the oxide. The absorption rates of oxygens for each peaks were very fast, and the activation energies for desorption were rather high ranging from 34 to 43 kcal/mol. Among these three peaks, only the β peak oxygen reacted with nitric oxide at 300 °C.