NO CO C3H6 Research Articles

Highly Active and Durable Rh–Mo-Based Catalyst for the NO–CO–C3H6–O2 Reaction Prepared by Using Hybrid Clustering

We developed a method for preparing catalysts by using hybrid clustering to form a high density of metal/oxide interfacial active sites. A Rh–Mo hybrid clustering catalyst was prepared by using a hybrid cluster, [(RhCp*)4Mo4O16] (Cp* = η5-C5Me5), as the precursor. The activities of the Rh–Mo catalysts toward the NO–CO–C3H6–O2 reaction depended on the mixing method (hybrid clustering > coimpregnation ≈ pristine Rh). The hybrid clustering catalyst also exhibited high durability against thermal aging at 1273 K in air. The activity and durability were attributed to the formation of a high-density of Rh/MoOx interfacial sites. The NO reduction mechanism on the hybrid clustering catalyst was different from that on typical Rh catalysts, where the key step is the N–O cleavage of adsorbed NO. The reducibility of the Rh/MoOx interfacial sites contributed to the partial oxidation of C3H6 to form acetate species, which reacted with NO+O2 to form N2 via the adsorbed NCO species. The formation of reduced Rh on Rh4Mo4/Al2O3 was not as essential as that on typical Rh catalysts; this explained the improvement in durability.

Enhanced Catalytic NO Reduction in NO–CO–C3H6–O2 Reaction Using Pseudo-Spinel (NiCu)Al2O4 Supported on γ-Al2O3

Enhanced Catalytic NO Reduction in NO–CO–C₃H₆–O₂ Reaction Using Pseudo-Spinel (NiCu)Al₂O₄ Supported on γ-Al₂O₃

Change in the Pd Oxidation State during Light-Off of Three-Way Catalysis Analyzed by in situ Diffuse Reflectance Spectroscopy

The changes in the oxidation state of supported Pd catalysts during light-off of NO–CO–C3H6–O2 reactions were evaluated during temperature ramp up and down cycles (10 °C min–1) under fuel-rich (air...

Effect of Thermal Aging on Local Structure and Three-Way Catalysis of Cu/Al2O3

Cu supported on Al2O3, prepared by impregnation, was thermally aged at different temperatures, and the influence of thermal aging on the local structure, redox behavior of Cu, and catalytic activity for a stoichiometric NO–CO–C3H6–O2 reaction was investigated. Crystalline CuO was mainly formed on Al2O3 after thermal aging at ≤700 °C, whereas aging at higher temperatures induced Cu2+ incorporation into tetrahedral (Td-Cu2+) rather than octahedral (Oh-Cu2+) sites of γ-Al2O3. Despite its lower surface area, thermally aged Cu/Al2O3 with Td-Cu2+ sites showed higher catalytic performance for the stoichiometric NO–CO–C3H6–O2 reaction compared with the as-prepared catalyst, especially for NO reduction. Td-Cu2+ was reduced to Td-Cu+ during reaction with CO and/or C3H6, and NO could be reduced in subsequent reoxidation of Td-Cu+ to Td-Cu2+ by NO. This redox behavior is more probable on Td-Cu rather than crystalline CuO, resulting in enhancement of NO reduction during the three-way catalyst reaction.

Formation of Rhodium Metal Ensembles that Facilitate Nitric Oxide Reduction over Rhodium/Ceria in a Stoichiometric Nitric Oxide–Carbon Monoxide–Propene–Oxygen Reaction

AbstractA series of ceria‐supported Rh nanoparticles (NPs) that have various particle sizes of 2–7 nm was prepared to investigate the size effect of Rh NPs on NO reduction in NO–CO–C3H6–O2 under stoichiometric conditions. The turnover frequency (TOF) for NO reduction on Rh NPs increased drastically according to their particle size. The strong size dependence of the TOF was attributed to the oxidation states of Rh NPs but not to particle geometries, which include fractions of surface local sites (e.g., corner, edge, plane) and the surface crystal structures (e.g., Rh(1 1 1), (1 0 0)). The variation of the TOF with the Rh metal fraction suggested that Rh metal ensembles are highly active species for NO reduction.

Thermal Evolution of the Structure and Activity of Rh Overlayer Catalysts Prepared by Pulsed Arc-Plasma Deposition

Nanometric Rh overlayers were formed on Fe–Cr–Al stainless steel (SUS) foils by pulsed cathodic arc-plasma (AP) technique to investigate the thermal evolution of the structure and catalytic activity for stoichiometric NO–CO–C3H6–O2 reaction. As-prepared Rh overlayer catalysts (Rh/SUS) with 2000–8000 AP pulsing showed steep light-off of NO, CO and C3H6 at around 250 °C and their conversions soon reached to almost 100%. After thermal aging at 900 °C in H2O/air, however, the catalytic activity was decreased to the different extent depending on the number of AP pulsing. The most significant deactivation was observed for the smallest numbers of AP pulsing (2000), because Al in the foil was oxidized during the aging to form a passivation layer of α-Al2O3, which covered the surface of the foil and decreased the surface concentration of Rh. To overcome this deactivation, the Rh overlayer was formed by AP after preheating the foil at 1000 °C in air. This modified preparation process enables the deposition of Rh overlayer on the highly crystalline α-Al2O3 layer at the surface of the foil, which is found to be much more stable against thermal deactivation.

An attempt to stabilize supported Ru catalysts against oxidative volatilization

Ru/Al2O3 is an active catalyst for the stoichiometric NO–CO–C3H6–O2 reaction, whereas >90% of the loaded Ru was volatized during thermal ageing in airflow at 1000°C for 100h, resulting in considerable catalyst deactivation. Using α-Fe2O3 as support, the Ru volatilization was suppressed to a significant extent, because Ru oxide was stabilized by dissolving into Fe2O3 to form a solid solution. Nevertheless, this metal-support interaction decreased the Ru concentration on the catalyst surface, thus leading to another catalyst deactivation route. The catalytic activity can be regenerated by applying H2-reduction treatment to the aged Ru/Fe2O3 catalyst.

Effect of Rare Earth Additives on the Catalytic Performance of Rh/ZrO2 Three-Way Catalyst

The catalytic activity of Rh/ZrO2 for NO–CO–C3H6–O2 reaction under stoichiometric conditions was significantly improved by addition of rare earth. Among the catalysts tested here, Y-doped Rh/ZrO2 (Rh/Y/ZrO2) showed the highest three-way catalytic performance. The catalytic activity of rare earth-doped Rh/ZrO2 was strongly related to the Rh dispersion, which was improved by using rare earth-doped ZrO2 with large amount of surface basic sites. The role of rare earth additive was considered to control the surface basicity of ZrO2 and stabilize the Rh species in high dispersion state. Y-stabilized ZrO2 was found to be effective support for Rh catalyst in NO–CO–C3H6–O2 reaction. The site geometry and the surface electric state of Rh can be altered by interacting with Y2O3, leading us to consideration that the presence of suitable Rh–Y2O3 interaction is responsible for high NO reduction activity of Rh/Y–ZrO2.

Rh Supported on LaPO4/SiO2 Nanocomposites as Thermally Stable Catalysts for TWC Applications

Hydrothermally synthesized LaPO4/SiO2 nanocomposites were investigated as thermally stable support materials for Rh catalysts. The nanocomposites were composed of macroporous SiO2 and highly dispersed columnar LaPO4 crystallites of approximately 20 nm in thickness and 100 nm in length, the surface of which anchored Rh nanoparticles via Rh–O–P interfacial bonding. The microstructure was useful to prevent agglomeration and sintering of LaPO4 during high-temperature thermal aging under both oxidizing and reducing atmospheres. The Rh catalyst supported on the LaPO4/SiO2 composite exhibited higher catalytic activities for simulated NO–CO–C3H6–O2 reactions over a wide Rh loading range (0.01–0.4 wt%), compared to those of Rh catalysts supported on the individual components (LaPO4 and SiO2), and on ZrO2, which is widely used as a support for Rh in commercial three-way catalysts. Enhanced catalytic activities for elementary CO–O2, CO–H2O, and CO–NO reactions were achieved while maintaining the activity toward C3H6 as an advanced feature of phosphate supports.

Surface Properties of Rh/AlPO4 Catalyst Providing High Resistance to Sulfur and Phosphorus Poisoning

A rhodium catalyst supported on AlPO4 exhibited a much higher resistance to sulfur and phosphorus poisoning compared with a reference catalyst (Rh/Al2O3). The acidic surface of AlPO4 was effective in preventing the adsorption of sulfur oxides (SO2), whereas Lewis acid/base sites on Al2O3 favored SO2 adsorption followed by the formation of sulfite, leading to deterioration of the activity of Rh/Al2O3 for the model NO–CO–C3H6–O2 reaction. Similarly, the AlPO4 support suppressed the extent of phosphorus poisoning caused by dimethylphosphite (DMP) (CH3O)2POH, which was used as a model phosphorus source. A greater amount of inactive phosphate overlayers were deposited from the gas feed containing DMP and O2 on Rh/Al2O3 than Rh/AlPO4 because of the reaction between P2O5 vapors and Al2O3. Consequently, the active Rh surface was covered to a greater extent for Rh/Al2O3 than Rh/AlPO4.

Bimetallic IrRh/CeO2–ZrO2 as a Highly Active Catalyst for NO–CO–C3H6–H2–O2 Reactions under Stoichiometric Conditions

Abstract The catalytic activity of Rh/CeO2–ZrO2 for NO–CO–C3H6–H2–O2 reactions under stoichiometric conditions was significantly improved by the addition of Ir. The optimum Ir/Rh atomic ratio was 1/9. The improvement was ascribed to the formation of finely divided Ir species on the surface of Rh particles. IrRh/CeO2–ZrO2 with an IrRh loading of 0.3 wt % showed high catalytic performance, which is comparable with that of 0.5 wt % Rh/CeO2–ZrO2, leading to minimize the Rh usage.

Catalytic NO–CO–C3H6–O2 reactions over hydrothermally stable Rh-supported ZrP2O7 catalyst

A novel and facile hydrothermal synthetic route for ZrP2O7 from ZrO(OH)2 and H3PO4 has been developed to use this as an active support for Rh catalyst. Temperature-programmed reactions of mixtures of NO, CO, C3H6 and O2 with a stoichiometric A/F ratio (14.6) were investigated over Rh-supported ZrP2O7 catalyst. A lower amount of Rh (0.4 wt.%) loaded to ZrP2O7 exhibited satisfactory light-off at lower temperature (T50% = 312 °C) with a steep rise in conversion efficiency after ageing the catalyst at 900 °C for 25 h in a stream of 10% H2O/air. Rh particle growth was not so significant even after 500 h of ageing at 900 °C in the stream of 10% H2O/air, which is one of the reasons for exhibiting adequate catalytic activity of this catalyst after long-term exposure in H2O/air. Reducibility of Rh oxide was enhanced substantially by this support which is believed to be the key factor for exhibiting good catalytic activity after ageing in an oxidizing environment. This newly developed Rh/ZrP2O7 catalyst with minimum Rh loading, having high thermal stability up to 1200 °C along with outstanding capacity to resist sintering at high temperature, has the potential to serve as a new generation deNOx catalyst.

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.

Promoting Effect of CeO2 on the Catalytic Activity of Rhodium Supported on Y-Stabilized ZrO2 for NO–CO–C3H6–O2 Reactions

Abstract The catalytic activity of Rh supported on Y-stabilized ZrO2 for NO–CO–C3H6–O2 reactions under stoichiometric conditions was improved by the addition of 5 mol % CeO2, whereas an excess amount of CeO2 of more than 10 mol % caused a decrease in the NO reduction activity. The improvement was ascribed to the formation of easily reducible Rh species through interaction with a Ce–Zr solid solution.

Structure and Catalytic Properties of Pd/10Al2O3·2B2O3. Effect of Preparation Routes and Additives

Abstract The synthesis route of 10Al2O3·2B2O3 (10A2B) and effect of additives were studied to use this compound as a thermally stable support material for Pd catalysts. The preparation by reverse coprecipitation was found to have a beneficial effect on the BET surface area of 10A2B and thus Pd metal dispersion, compared to other preparation routes via solid-state reaction and hydrolysis of metal alkoxides. The addition of 3 wt % BaO suppressed the sintering of 10A2B and Pd during thermal aging at 900 °C in a stream of air containing 10% H2O. Although direct interactions between Pd and the support material were not detected by EXAFS, the catalytic performance for NO–CO–C3H6–O2–H2O reactions under modulated air-to-fuel ratio (A/F) conditions was strongly influenced by the Ba additive. The activity for NO and C3H6 in a rich region (A/F < 14.6) was especially enhanced in the presence of Ba because of accelerated elemental reactions including NO–CO and NO–C3H6. In situ FT-IR of CO suggested that the Pd electronic state changed by electrostatic effect of Ba additives would activate NO and weaken the self-poisoning effect of C3H6.

Thermostable Rh Catalysts Supported on Metal Phosphates: Effect of Aging on Catalytic Activity for NO–CO–C3H6–O2 Reactions

Abstract The catalytic activity and thermostability of Rh catalysts (0.4% loading) have been studied using various metal phosphates (B, Al, Ga, Y, La, Pr, Zr, and Ce) as support materials. Temperature-programmed reactions of mixtures of NO, CO, C3H6, and O2 with the stoichiometric A/F ratio (14.6) exhibited a steep rise in conversion efficiency as a common feature of Rh supported on metal phosphates. The activity of Rh/AlPO4 was found to be the highest even after aging at 900 °C for 25 h in a stream of 10% H2O/air. Among four types of AlPO4 polymorphs having different BET surface area, i.e, berlinite (5 m2 g−1), cristobalite (1 m2 g−1), tridymite (82 m2 g−1), and microporous AlPO4-5 (330 m2 g−1), tridymite AlPO4 achieved the lowest light-off temperature. The slow grain growth of tridymite AlPO4 at ≤1000 °C is a possible reason for the stability against sintering, whereas one-dimensional micropores of AlPO4-5 are unstable in the high-temperature steam.