Shinichi Nakata

Effect of vanadium on USY zeolite destruction in the presence of sodium ions and steam—studies by solid-state NMR

Abstract The effect of deposited vanadium on the thermal destruction of ultra stable Y (USY) zeolite in the presence of sodium ions and steam was investigated by solid-state NMR. When USY zeolite containing few sodium ions was heated in a dry atmosphere, Siue5f8OH groups, which corresponded to defect sites, and strong adsorption sites were formed by the dealumination. The former mainly caused an increase in the mean void volume per supercage and the latter originated from cationic extra framework Al in the supercages. Furthermore, in the dry atmosphere, the sodium ions inhibited the dealumination; the effect of the deposited vanadium on the structural change was not large. After the heat treatment in 100% steam, in case of USY zeolite containing few sodium ions, the crystallinity and the supercage structure hardly changed although the dealumination occurred remarkably. This process did not depend on the deposited vanadium. Data suggested that the heat treatment in 100% steam causes the framework stabilization. In case of USY zeolite containing a number of sodium ions, the synergistic effect between a few deposited vanadium ions and the sodium ions on the framework destruction in 100% steam was tremendous. We propose that the deposited vanadium functions as vanadic acid and catalyzes the conversion of the sodium ions into NaOH. Thus, an increase in the NaOH content promotes the ‘dissolution’ of the zeolite crystal, i.e. the framework destruction. In addition, when the sample containing both a few vanadium ions and a number of sodium ions was heated in 100% steam, the supercage was plugged partially. We believe that the blockage compounds in the supercage are sodium vanadates.

Water-tolerant catalysis of a silica composite of a sulfonic acid resin, Aciplex

Abstract A silica composite of a perfluorocarbonsulfonic acid resin, Aciplex, has been used as a solid acid catalyst for a variety of reactions concerning water. The Aciplex–SiO 2 composite containing 20xa0wt% Aciplex has a surface area of 1.3xa0m 2 xa0g −1 and possesses an ion-exchanged capacity of 0.46xa0meq.xa0g −1 after pretreatment at 423xa0K, which is higher than that of 13xa0wt% Nafion–SiO 2 (0.12xa0meq.xa0g −1 ). The acid strengths estimated from an initial heat of adsorption of NH 3 were similar for these polymer resin composites. It was found that the Aciplex–SiO 2 was more active than typical solid acids such as Cs 2.5 H 0.5 PW 12 O 40 , H-ZSM-5, and SO 4 2− /ZrO 2 for hydrolysis of ethyl acetate in excess water and esterification of acrylic acid with 1-butanol, while it was less active than Cs 2.5 H 0.5 PW 12 O 40 for N -alkylation of acrylonitrile with 1-adamantanol and solid–solid hydrolysis of 2-naphthyl acetate. The Aciplex–SiO 2 was superior in activity to Nafion–SiO 2 for all the above reactions and in thermal stability. These results indicate that Aciplex–SiO 2 is a promising solid acid catalyst for reactions involving liquid phase water.

Synthesis and oxide ion conductivity of new layered perovskite La1−xSr1+xInO4−d

Abstract New La 1− x Sr 1+ x InO 4− d compounds were synthesized and identified by the powder X-ray diffraction (XRD) method. In the composition range of 0≤ x ≤0.2, La 1− x Sr 1+ x InO 4− d compounds were prepared by heating at 1573 K in air for 36 h as single phase. Rietveld analysis of their XRD data revealed that La 1− x Sr 1+ x InO 4− d compounds possess the orthorhombic K 2 NiF 4 -type structure. Measurement of electrical conductivity as a function of oxygen partial pressure ( P O 2 ) showed oxide ion conduction for the samples below P O 2 =10 −12 atm for x =0 and below 10 −5 atm for x =0.1 and 0.2. At high oxygen partial pressure, it also showed contribution of hole conduction for the samples.

Preparation of apatite-type-silicate-supported precious metal catalysts for selective catalytic reduction of NOx

Apatite-type silicate supported precious metal catalysts were prepared and investigated for their catalytic activity in selective catalytic NO reduction. Single-phase La9.33Si6O26 and La8.33ASi6O25.5 (A=Ca, Sr, Ba) were obtained by a sol-gel method. Pd/La9.33Si6O26 catalyst exhibited high activity for oxidation of C3H6, comparable to Pd/Al2O3 catalyst, although the specific surface area of La9.33Si6O26 was lower than that of Al2O3. In addition, Pt/La9.33Si6O26 catalyst exhibited higher activity for selective catalytic reduction of NO than Pt/Al2O3 catalyst. Substitution of Ba2+ for La3+ of La9.33Si6O26 led to increased catalytic activity at low temperature.

Oxygen storage and release behavior of delafossite-type CuFe1−xAlxO2

Delafossite-type solid solution, CuFe1−xAlxO2, was synthesized and its oxygen storage capacity (OSC) was investigated under oxidation/reduction cycle using a pulse injection method. CuFe1−xAlxO2 was synthesized by heating at 1100–1150xa0°C in N2 flow. OSC values for xxa0=xa00.1 and 0.3 were larger than that for xxa0=xa00 above 500xa0°C, indicating that substitution of Fe3+ by Al3+ improved OSC. For xxa0=xa00.5–1.0, temperature at which OSC increased steeply shifted upward. Results of X-ray diffraction (XRD) after the thermogravimetry and differential thermal analysis (TG–DTA) measurement in air for CuFe1−xAlxO2 (xxa0=xa00–0.7) indicated that oxidative decomposition of delafossite phases to CuO and spinel-type phase occurred. In addition, Cu reduction temperature estimated by the temperature programmed reduction using H2 (H2-TPR) shifted to higher temperature with increasing Al content. The XRD results of the samples after H2 and O2/He pulse injection suggested that the oxygen storage/release behavior was caused by reversible oxidation/reduction process between CuFe1−xAlxO2 delafossite and (Fe1−xAlx)3O4 spinel phase +Cu.

Effect of Aging Atmosphere on Catalytic Activity for NO–CO–C3H6–O2 Reaction of CeO2-Containing Oxide Supported Pd Catalysts

The catalytic activity for CO, hydrocarbon and NO removal on Al2O3 and CeO2 based oxides supported Pd catalysts were studied under switching of aging condition between air and N2 atmosphere. For CeO2-containing Pd catalysts, the deterioration of catalytic activities by aging in N2 was improved by oxidative treatment. Based on results of XPS and FT-IR measurements, it was presumed that the catalytic activity of Pd catalysts was strongly affected by the adsorbed form of CO on Pd, which occurs owing to a change of the chemical state of Pd.Graphical Abstract