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In this work, we investigated the mechanisms for the high activity and durability of Rh single nanosized catalysts for the CO–NO reaction in three-way catalysis. For this, we analyzed the relations...

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.

自動車排出ガス浄化用Pd系触媒において, 助触媒である酸素貯蔵剤 (Oxygen Storage Component : OSC) が, 熱エージング後のNOx浄化特性へ及ぼす影響をCeO2とCeZr複合酸化物を用いて, 触媒の構造, 状態, 酸素貯蔵能 (OSC能) , NO吸着特性の点から解析した.CeO2へZrを添加することにより, CeO2と比較して熱エージング後もOSC能が維持され, NOx浄化性能も向上した. 種々の解析結果より, これは, 以前から報告されているZr添加によるシンタリング抑制効果のほかに, CeZr複合酸化物には立方晶系構造と正方晶系構造の2相が存在し, このうちの正方晶系構造を持つ相が酸素の吸蔵, 放出を促進する効果があると考察した. その結果助触媒としてCeZr複合酸化物を用いると, 自動車排ガスのように酸素濃度が変動する雰囲気においても, 活性種に吸着した酸素がOSCへスピルオーバーし活性種の還元状態を維持できるので, NOを吸着, 浄化できるものと推察した.

酸化セリウムを酸素貯蔵材として使用したパラジウム担持触媒の二酸化硫黄 (SO2) ガスによる被毒現象を検討した. 還元雰囲気下において, 酸化セリウムに担持したパラジウムに吸着した硫黄の脱離温度は, 酸化アルミニウムに比較して高温化しており, 被毒状態からの触媒活性の回復に影響を与えていることが判明した. この高温化は, 吸着した硫黄量と触媒の状態変化の解析から, 還元されたパラジウムと酸化セリウム間における酸化セリウムの還元性に基づく栢互作用が原因であると推察された. また, 573Kにおける, パラジウム担持酸化セリウムのSO2被毒に対する酸化, 還元雰囲気の影響を検討した結果, 酸化雰囲気では, SO2の吸着が酸化セリウムの酸素貯蔵を阻害し, 還元雰囲気では, パラジウム表面を不活性化しているものと推論した.

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.

Rhodium on a La-containing ZrO2 support effectively eliminated NOx from a synthetic auto exhaust gas under fluctuating oxygen conditions. Rhodium particles maintained a low oxidation state on the ZrO2–La2O3 mixed oxide even after treatment with 5% O2 at 773 K, highlighting the significant effect of the La addition.

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.

Conception d'une chambre tourbillonnaire entierement en ceramique pour moteur diesel a injection indirecte. Problemes dus aux materiaux