Koichi Yuzaki

Catalytic decomposition of N2O over supported Rh catalysts: effects of supports and Rh dispersion

The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al2O3, ZrO2, FSM-16, CeO2, La2O3) showed that the activities of Rh/Al2O3 and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N2O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. A pulsed N2O experiment over a Rh/USY catalyst suggested that the catalytic N2O decomposition occurs on oxygen-covered surface and that O2 may be freed on collision of N2O molecules with the adsorbed oxygen atoms.

Strong rhodium–niobia interaction in Rh/Nb2O5, Nb2O5–Rh/SiO2 and RhNbO4/SiO2 catalysts: Application to selective CO oxidation and CO hydrogenation

Abstract The extent of Rh–niobia interaction in niobia-supported Rh (Rh/Nb 2 O 5 ), niobia-promoted Rh/SiO 2 (Nb 2 O 5 –Rh/SiO 2 ) and RhNbO 4 /SiO 2 catalyst after H 2 reduction has been investigated by H 2 and CO chemisorption measurements. These catalysts have been applied to selective CO oxidation in H 2 (CO+H 2 +O 2 ) and CO hydrogenation (CO+H 2 ), and the results are compared with those of unpromoted Rh/SiO 2 catalysts. It has been found that niobia (NbO x ) increases the activity and selectivity for both the reactions.

Catalytic decomposition of N2O over supported rhodium catalysts: high activities of Rh/USY and Rh/Al2O3 and the effect of Rh precursors

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over Al2O3-supported and zeolite-supported Rh catalysts. The activities of Rh/Al2O3 and Rh/USY (ultrastable Y zeolite) catalysts prepared from Rh(NO3)3 were higher than those of Rh/ZSM-5 and Rh/ZnO reported in the literature, while the activity of a Rh/Al2O3 catalyst prepared from RhCl3 was suppressed severely in spite of the high H/Rh and CO/Rh values. The catalytic activity of N2O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used.

Simultaneous removal of N2O and CH4 as the strong greenhouse‐effect gases over Fe‐BEA zeolite in the presence of excess O2

Simultaneous catalytic removal of N2O and CH4 as the strong greenhouse‐effect gases was found to be possible over an Fe‐ion‐exchanged BEA zeolite (Fe‐BEA) by the selective catalytic reduction (SCR) of N2O with CH4. The direct decomposition of N2O (2N2O → 2N2 + O2) and the oxidation of CH4 (CH4 + 2O2 → CO2 + 2H2O) over Fe‐BEA zeolite required high temperature above 400 and 450 °C, respectively. Nevertheless, the catalytic reduction of N2O by adding CH4 over Fe‐BEA zeolite readily occurred at much lower temperatures (ca. 250–350 °C) whether in the presence of O2 or not. No oxidation of CH4 by O2 took place at these temperatures. On the basis of these results and the kinetic studies, it was concluded that CH4 reacted selectively with N2O to produce N2, CO2 and H2O over Fe‐BEA zeolite even in the presence of excess O2. Overall stoichiometry of the SCR of N2O with CH4 was determined as follows: 4N2O + CH4 → 4N2 + CO2 + 2H2O.

Mechanism of N2O decomposition over a Rh black catalyst studied by a tracer method the reaction of N2O with 18O(a)

Abstract N2O decomposition on an unsupported Rh catalyst has been studied using tracer technique in order to reveal the reaction mechanism. N216O was pulsed onto 18O/oxidized Rh catalyst at 220°C and desorbed O2 molecules (m/e=32,34,36) were monitored by means of mass spectrometer. The 18O fraction in the desorbed dioxygen was the same value as that on the surface oxygen. The result shows that the O2 molecules desorb via Langmuir–Hinshelwood mechanism, i.e., the desorption of dioxygen through the recombination of adsorbed oxygen. On the other hand, TPD measurements in He showed that desorption of oxygen from the Rh black catalyst occurred at the higher temperatures. Therefore, reaction-assisted desorption of oxygen during N2O decomposition reaction at the low temperature was proposed.

Selective catalytic reduction of N2O with C3H6 over Fe-ZSM5 catalyst in the presence of excess O2: The correlation between the induction period and the surface species produced

The catalytic activity of N2O reduction over Fe-ZSM5 prepared by an ion exchange method was significantly increased by adding C3H6, even in the presence of excess O2, i.e., selective catalytic reduction (SCR) of N2O occurred with C3H6. We found that there was an induction period for the increase in activity after adding C3H6 to the N2O–O2 flow. Another induction period was also observed for the decrease in activity after removing C3H6 or O2–C3H6 from the N2O–O2–C3H6 mixture. The length of the induction period was influenced by the partial pressure of C3H6, the composition of the reaction gases and the reaction temperature. During the latter induction period, CO2, H2O and N2 were detected as products. These results suggest that adsorbed surface species such as CxHy(a) and/or CxHyOz(a), produced by the reaction in the N2O–O2–C3H6 mixture, reacted with N2O or N2O–O2 to produce CO2, H2O and N2. In situ DRIFT studies showed the formation of CxHy(a) and/or CxHyOz(a) species during the N2O–O2–C3H6 reaction, the behavior of which (formation and reactivity) correlated well with the induction period phenomenon.

Isotopic study of nitrous oxide decomposition on an oxidized Rh catalyst: mechanism of oxygen desorption

N2O decomposition on an oxidized Rh catalyst (unsupported) has been studied using a tracer technique in order to reveal the reaction mechanism. N216O was pulsed onto an 18O/oxidized Rh catalyst at 493 K and desorbed O2 molecules were monitored. The 18O fraction in the desorbed oxygen had the same value as that on the surface oxygen. The result shows that the oxygen molecules do not desorb via the Eley–Rideal mechanism, but via the Langmuir–Hinshelwood mechanism. On the other hand, desorption of oxygen from Rh surfaces (in vacuum or in He) occurs at higher temperatures, which suggests reaction-assisted desorption of oxygen during the N2O decomposition reaction at low temperature.

Metal-oxide interactions and catalytic behaviors of La2O3- and V2O5-promoted Rh/NaY catalysts

A higher activity of N 2 O decomposition on a La 2 O 3 -Rh/NaY catalyst and a higher selectivity of cyclohexane dehydrogenation on a V 2 O 5 -Rh/NaY catalyst were observed, compared with unpromoted Rh/NaY catalysts. The ethane hydrogenolysis, H 2 chemisorption and TPR studies revealed that the nature of metal-oxide interactions is quite different between La 2 O 3 -promoted and V 2 O 5 -promoted catalyst systems.

Selective catalytic reduction of N2O with methane in the presence of excess oxygen over Fe-BEA zeolite

An Fe ion-exchanged BEA zeolite (Fe-BEA), which effectively performs selective catalytic reduction of N2O with methane in the presence of excess oxygen, is much more active than Fe-MFI zeolite reported in the literature.