Akihide Takami

Zeolite-supported precious metal catalysts for NOx reduction in lean burn engine exhaust

The effects of the zeolite-supported precious metal catalysts on NOx reduction in oxygen-rich exhaust have been investigated. It became clear that NOx conversion related the number of NO adsorption sites of precious metal and the number of HC (C3H6) adsorption of support (zeolite). PtIrRh/MFI zeolite catalyst showed higher performance and durability than the current PtRh supported on alumina and ceria catalyst.

Lowering Combustion Temperature of Carbon Particles on Pt-supported Ceria Series Oxides

ディーゼル車の排出ガスに含まれるカーボン微粒子を低減する手段として触媒担持ウォールフロー型ハニカムがあり，これにたい積したカーボン微粒子を効率良く酸化除去するために，Pt担持酸化物の検討を行った。その結果，カーボン微粒子の燃焼開始温度は同等だったが，燃焼開始後については，Pt担持Ce複合酸化物（Pt/Ce0.7Zr0.3O2およびPt/Ce0.9Pr0.1O2）を用いた場合にPt担持CeO2（Pt/CeO2）に比べ，より低温でカーボン微粒子が燃焼した。1073 K大気エージング後では，特にPt/Ce0.9Pr0.1O2において最も低温でカーボン微粒子が燃焼した。Pt/Ce0.9Pr0.1O2については，低温において担体からのO2の放出量が最も多く，またPt表面において吸着するCOの気相O2による酸化反応が進みやすい状態にあることが明らかになり，これらの特性がカーボン微粒子の燃焼特性を高めたと推定した。

Self-regeneration of three-way catalyst rhodium supported on La-containing ZrO2 in an oxidative atmosphere

Rhodium supported on lanthanoid (La, Ce, Pr, or Nd)-containing ZrO2 was investigated as a three-way catalyst following an aging treatment (oxidation at 1273 K) that simulates 80000 km of mileage in real vehicles. The properties of rhodium were assessed by transmission electron microscopy, CO chemisorption, and temperature-programmed reduction using CO. The oxidation states of rhodium before and after the aging treatment were evaluated using X-ray photoelectron spectroscopy. Rhodium supported on lanthanum-containing ZrO2 (Rh/Zr–La–O) was highly active for the removal of NOx and hydrocarbons from a synthetic auto exhaust. The support determined the oxidation state of rhodium after the aging treatment: rhodium supported on Zr–La–O maintained its low oxidation state during the three-way catalytic reaction and after the aging treatment, whereas rhodium supported on ZrO2 and other lanthanoid-containing ZrO2 was converted to the higher oxidation states. The Rh/Zr–La–O catalyst, following the aging treatment, exhibited superior activity for the steam reforming reaction. The hydrogen produced from the steam reforming reaction reduced the previously oxidized Rh in Rh/Zr–La–O, thereby regenerating the catalyst that was previously deactivated by an oxidation treatment. Self-regeneration of the Rh/Zr–La–O catalyst by the steam reforming reaction was more efficient when compared with that of the other lanthanoid-containing ZrO2 catalysts. These results highlight the potential of the present strategy for developing active three-way catalysts with high tolerance to oxidative conditions.

High three-way catalytic activity of rhodium particles on a Y-stabilized La-containing ZrO2 support: the effect of Y on the enhanced reducibility of rhodium and self-regeneration

A novel, highly active three-way catalyst, rhodium supported on Y- and La-added zirconia (Rh/Zr–Y–La–O), was found in this study. Rh/Zr–Y–La–O showed superior performance to a previously reported Rh on La-added ZrO2 (Rh/Zr–La–O) catalyst (Kawabata et al., Chem. Commun., 2013, 49(38), 4015; Catal. Sci. Technol. 2014, 4(3), 697).21,22 The effects of Y addition to ZrO2-based supports were investigated in detail. CO temperature-programmed reduction and in situ Fourier transform infrared spectra of adsorbed NO species indicated that Y addition to La-containing ZrO2 enhanced the reducibility of rhodium supported on the catalyst and that more metallic Rh was exposed on the surface after the oxidation of Rh/Zr–Y–La–O than of Rh/Zr–La–O. Before and after an aging treatment at 1273 K that simulated 80 000 km travelled by vehicles, Rh/Zr–Y–La–O showed high steam reforming activity. After the aging treatment, Rh/Zr–Y–La–O was deactivated using an oxidation treatment, but its three-way catalysis activity was completely regenerated after a short (5 min) exposure to steam reforming reaction conditions, demonstrating self-regeneration capability. After the aging treatment, Rh/Zr–Y–La–O showed higher rhodium dispersion than other catalysts. This was attributed to the high surface area of the support after aging and the stabilization of ZrO2 by the addition of Y. Our findings highlight the role of catalyst supports in designing effective three-way catalysts with high tolerance to the oxidative conditions in new vehicles and engines.

Development of lean NOx catalyst for lean burn gasoline engine

Abstract Lean NOx catalyst for a lean burn gasoline engine was developed. This catalyst could constantly reduce NOx under lean burn driving condition by using hydrocarbon as a reducing agent. This catalyst consists of platinum (Pt), iridium (Ir) and rhodium (Rh) as active metals and H-MFI type zeolite as a support material. This catalyst had high thermal durability that was caused by Pt-Ir-Rh composite that suppressed the growth of particle size of itself during thermal aging and MFI zeolite that had high thermal durability and HC trap activity. Lean burn vehicle with this developed catalyst achieved emission legislation limit after an engine endurance test and improved 16% of fuel economy at JPN 10-15 mode.

Mazda’s LNT

The new shape ceria-based support material for a lean Nitrogen oxide (NOx) trap catalyst (LNT) was developed by Mazda. It has a unique shape that each fine particle of raw material is formed into hollow sphere. Samples of platinum loaded powder catalysts were obtained with either the hollow sphere ceria-based material or two kinds of the conventional shape one and their catalytic activities were evaluated with the synthetic gas. The characterisation results indicate that the hollow sphere ceria-based material had high thermal stability [1].

Mazda-LNT. Katalytische Eigenschaften des neu geformten Traegermaterials

Die Reduktion von NOx wird am effizientesten durch die Reduzierung der NOx-Emissionen waehrend der fetten Betriebsphase gefoerdert. Einer der Schluesselfaktoren ist das Beguenstigen dieser Reaktion zur Erhoehung der thermischen Bestaendigkeit des Traegermaterials, auf welchem die Edelmetalle und NOx-Speichermaterialien aufgebracht sind. Mazda hat dazu ein neu geformtes Traegermaterial auf Ceroxid-Basis fuer einen Stickoxid-Speicherkatalysator entwickelt und seine katalytischen Eigenschaften untersucht. Es besitzt eine einzigartige Form, durch die jeder feine Partikel des Ausgangsstoffes zu einer Hohlkugel geformt wird. Drei Proben platinbeladener Pulverkatalysatoren auf Ceroxid-Basis wurden vorbereitet: eine mit dem neuen Hohlkugelmaterial und zwei Proben mit herkoemmlicher Form. Ihre katalytischen Eigenschaften wurden dann mit synthetischem Gas ausgewertet. Die Analyseergebnisse zeigten, dass das Hohlkugelmaterial auf Ceroxid-Basis eine hohe thermische Bestaendigkeit aufweist. Die Katalysatorleistung wurde an einem Pt-Katalysator untersucht.

Applications of Ceramics for the Rotary Engine

To meet ever-stringent requirements for higher power and lower lubrication oil consumption on rotary engines, the wear resistance of apex seals and housing surfaces is a critical subject. The authors have been attempting to apply ceramic-based materials to these parts. Through the study on the material composition and production processes, the authors developed a ceramic material with high strength, high toughness and high wear resistance for the apex seals, which is silicon carbide whisker reinforced silicon nitride. As a result of the rig tests, the detonation gun spray of Cr3C2/Ni-Cr was found appropriate for the coating of side housings. In consideration of its potential productivity, the spray method was changed to the plasma spray method. The plasma sprayed Cr3C2/Ni-Cr showed the wear resistance equivalent to that of the detonation gun sprayed coating as a result of the optimization of material powder granulation and the spray conditions.