Search

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.

The mechanism of the selective catalytic reduction (SCR) of NO by C3H6 on Cu−Al2O3 catalysts, which consist of highly dispersed Cu2+ ions in the surface aluminate phase, are investigated by in-situ FTIR spectroscopy. During NO + C3H6 + O2 reaction, the acetate is produced via the partial oxidation of C3H6 and becomes the predominant adspecies in the steady-state condition at 473−623 K. The acetate, which is stable in NO, is quite reactive with NO + O2, leading to the formation of isocyanate species (Cu−NCO) on the surface and N2 and CO2 in the gas phase. The rate of acetate reaction in NO + O2 is close to the steady-state rate of NO reduction over wide range of temperature, indicating that the acetate is an intermediate in the SCR and takes part in the rate-determining stage. A mechanism is proposed; the acetate and nitrates, formed by NO + O2, react to generate the Cu−NCO species, then Cu−NCO reacts with nitrates or NO to produce N2 and CO2. This mechanism explains the role of oxygen in facilitating SCR....

The mechanism of the selective catalytic reduction (SCR) of NO by C3H6 on Al2O3 was investigated using in situ IR spectroscopy. Attention was focused on the reactivity of the adsorbed acetate and n...

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.

This study demonstrates the intrinsic factors affecting the activity of transition metal oxide catalysts for C3H6-SCR. On the basis of the molecular information from XAFS and in-situ FTIR spectroscopies, the structure - activity relationship is examined in a molecular level to obtain intrinsic factors affecting the catalytic activity. The activity of metal oxide catalysts was determined not only by the kind of metal oxides but also by the dispersion, coordination, and local electronic states of the metal cation, which can be influenced by the surrounding oxide matrix. The results provide a criterion for a rational design of effective HC-SCR catalysts.