Satoshi Kameoka

In situ diffuse reflectance infrared Fourier transform spectroscopy study of surface species involved in NOx reduction by ethanol over alumina-supported silver catalyst

Abstract In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been used to investigate the surface species involved in NOx reduction by ethanol over alumina-supported silver catalyst. The experiments were carried out in dynamic conditions (under reaction mixture flow and reaction temperature) at atmospheric pressure. The DRIFT measurements were combined with gas chromatography (GC) analysis to monitor the N2 formation under reaction mixture and when the reaction mixture flow was switched to He followed by heating the catalyst under He flow (mixture, 250°C→He, 250°C→heating under He). A parallelism has been observed between the isocyanate band change and N2 formation during the step change experiment using an initial C2H5OH/NO/O2/He reaction mixture. Furthermore, the isocyanate species (NCO) were found to be generated from the decomposition of adsorbed organic nitro compounds formed under both ethanol/NO/O2/He and ethanol/NO/He and reaction mixtures. The role of oxygen in NOx reduction process was determined by comparing the result of different step-change experiment using an initial reaction mixture containing oxygen and without oxygen.

Catalytic performance of K-promoted Rh/USY catalysts in preferential oxidation of CO in rich hydrogen

Abstract K-promoted Rh/USY (molar ratio: K/Rh=3) catalyst was found to exhibit high performance in preferential oxidation of CO in rich hydrogen. Such high performance was maintained in the presence of steam and CO 2 . The CO oxidation activity of the K-Rh/USY catalyst was independent of the partial pressure of H 2 , while the activity of the unpromoted Rh/USY catalyst was decreased significantly in hydrogen-rich stream. The effect of potassium addition on the catalyst structure was investigated and is discussed in terms of the differences in the catalytic performance.

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.

Rh-based catalysts for catalytic dechlorination of aromatic chloride at ambient temperature

Abstract Catalytic dechlorination of chlorotoluene to toluene was carried out using several supported Rh-based catalysts in a 2-propanol solution of NaOH at ambient temperature (27°C). A carbon-supported Rh catalyst (Rh/C) showed high catalytic activity, although an induction period was involved in the reaction and the activity of the catalyst reduced during storage in air. The existence of Pt on the Rh catalyst was effective in overcoming the activity reduction by exposure to air and gave the reaction without any induction period. The composite Rh–Pt catalyst supported on TiO2 as well as on carbon was much more active for the reaction than the catalysts supported on SiO2, MgO and Al2O3.

Reaction between N2O and CH4 over Fe ion-exchanged BEA zeolite catalyst: A possible role of nascent oxygen transients from N2O

The reaction between N2O and CH4 over an Fe ion-exchanged BEA zeolite (Fe-BEA) catalyst was studied by using a pulse reaction technique, temperature-programmed desorption (TPD) and infrared (IR) spectroscopy. N2O readily reacted with CH4 in the presence of an N2O + CH4 mixture above 200 °C, while both the O2 + CH4 reaction and the catalytic decomposition of N2O over the Fe-BEA catalyst required higher temperatures (above 400 °C). In the O2-TPD studies, a desorption peak of O2 was observed above 600 °C after O2 treatment at 250 °C, while a new O2 desorption peak appeared at the lower temperatures after N2O treatment at 250 °C. However, the new O(a) species resulting from the N2O treatment hardly reacted with CH4 even at 350 °C, which was confirmed by the CH4-pulsed experiments. On the other hand, a new IR band at 3683 cm−1, which can be assigned to the OH group on Fe ion species, was observed after O2 or N2O treatment. The peak intensity at 3683 cm−1 was not changed in the exposure of CH4 only, but decreased in the exposure of N2O + CH4 mixture above 150 °C. At the same time, the CHxOy(a) species such as Fe–OCH3 were formed, which were observed by IR measurements. The adsorbed surface species showed a high reactivity with N2O even at low temperatures (∼200 °C). A possible mechanism is discussed in terms of active oxygen species such as nascent oxygen transients (O*(a)), which are formed in the exposure of N2O + CH4 mixture, and may play an important role in the activation/oxidation of CH4 at initial steps to form CHxOy(a) species.

Steam reforming of methanol over Pt–Zn alloy catalyst supported on carbon black

Abstract Steam reforming of methanol over Zn-promoted Pt catalyst supported on an electrically conductive carbon black has been investigated after H2 reduction at 873 K. X-ray diffraction measurement showed that Pt–Zn alloy was formed on the carbon black (C). The Zn-promoted Pt/C catalyst showed higher activity and selectivity to CO2 compared with unpromoted Pt/C catalyst. Methyl formate was formed over the Zn-promoted Pt/C catalyst in decomposition of methanol (without water). This suggests that steam reforming of methanol over the Zn-promoted Pt/C catalyst can proceed via methyl formate, which is different from that of the unpromoted Pt/C catalyst.

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.

Plasma-induced nitrogen chemisorption on a ruthenium black catalyst: formation of NH3 by hydrogenation of the chemisorbed nitrogen

Nitrogen was chemisorbed on a ruthenium black catalyst by a plasma discharge of N2. Temperature-programmed desorption of nitrogen showed a broad peak at around 300 °C which showed a dependence on the duration and the wattage of the discharge. The chemisorbed nitrogen species was reacted with hydrogen to form NH3 even at room temperature.

Isotopic Study of N2O Decomposition on an Ion-Exchanged Fe-Zeolite Catalyst: Mechanism of O2 Formation

N2O decomposition on an ion-exchanged Fe-MFI catalyst has been studied using an 18O-tracer technique in order to reveal the reaction mechanism. N216O was pulsed onto an 18O2-treated Fe-MFI catalyst at 693 K, and the O2 molecules produced were monitored by means of mass spectrometry. The 18O fraction in the produced oxygen had almost half the value of that on the surface oxygen, and 18O18O was not detected. The result shows that O2 formation proceeds via the Eley–Rideal mechanism (N216O + 18O(a) → N2 + 16O18O).

Enhancement of C2H6 Oxidation by O2 in the Presence of N2O over Fe Ion-Exchanged BEA Zeolite Catalyst

Selective catalytic reduction (SCR) of N2O with C2H6 took place effectively over Fe ion-exchanged BEA zeolite catalyst (Fe-BEA) even in the presence of excess oxygen. The mechanism in the SCR of N2O with C2H6 over Fe-BEA catalyst was studied by a transient response experiment and an in situ DRIFT spectroscopy. No oxidation of C2H6 by O2 took place below 350 °C (in C2H6/O2). In the N2O/C2H6/O2 system, however, it was found that the reaction of C2H6 with O2 was drastically enhanced by the presence of N2O even at low temperatures (200-300 °C). Therefore, it was concluded that N2O played an important role in the oxidation of C2H6 (i.e., activation of C2H6 at an initial step). On the basis of these findings, the mechanism in the SCR of N2O with C2H6 is discussed.