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In this paper, the development of catalytic technologies used aboard a vehicle for purifying exhaust gases is estimated and forecasted. According to forecasts, in the next decade, the total production of vehicles will exceed 1 billion units and 75% of them will be equipped with internal combustion engines, which should necessarily be accompanied by an exhaust gas purification system. The development of catalytic technologies for purifying vehicle exhaust gases is mutually stimulated by the tightening of environmental standards and improving the internal combustion engines. For example, to date, the European standards have gone from Euro 1 to Euro 6d. The introduction of Euro 7 standards in Europe and the introduction of their counterparts in a number of countries by 2025 is planned. In addition, this paper discusses the concepts of systems that purify the exhaust gases of gasoline and diesel engines to meet the Euro 7 standards. [ABSTRACT FROM AUTHOR]

Over the last few decades, Pd-based three-way catalysts (TWCs) have been more extensively used than Pt-based TWCs because of their higher thermal stability. In this study, the addition of CeO2 to a Pt-based TWC was performed to improve the reductivity and dispersion of Pt particles after aging at 1000 °C. The aged dispersion of the Pt-loaded CeO2 was much higher than that of a commonly used La2O3–CeO2–ZrO2 catalyst. Furthermore, the hydrogen temperature-programmed reduction conducted on Pt/CeO2 revealed that the Pt-loaded highly crystalline CeO2 (HC–CeO2) exhibited a higher reductivity as compared with that of the high surface area CeO2 (HS–CeO2). Adding a small amount of HC–CeO2 to the Pt-based TWC increased both the Pt dispersion and reductivity after aging. Owing to the high dispersion and reductivity of Pt, Rh/Pt-based TWCs with HC–CeO2 used as an additive to the Pt catalyst layer demonstrated a higher catalytic activity than that of the Rh/Pd-based TWCs even after aging at 1000 °C in an exhaust gas. [ABSTRACT FROM AUTHOR]

Gasoline engine vehicle emissions, such as nitrogen oxides (NOx), CO and hydrocarbons (HCs), are a major source of air pollution, and require improved emission control systems. By-product NH3 and N2O emissions, which come from low N2 selectivity in the emission control system, are also a major concern. The current study has comprehensively investigated the impact of the Pt-substitution in commercial Pd/Rh-based three-way catalyst (TWC) formulations with respect to catalytic performance. TWC performance was systematically evaluated with respect to the warm-up catalytic converter (WCC) and the under-floor catalytic converter (UCC). This included evaluating TWC activity under realistic simulated exhaust conditions including fuel-rich, stoichiometric and fuel-lean (0.99≤λ≤1.01). Pt-substituted TWCs outperformed Pd-based counterparts, regardless of the converter type (WCC or UCC), in CO, C3H6 and C3H8 oxidation and NO reduction reactions under the simulated exhaust conditions tested. Moreover, Pt-substituted TWCs exhibited significant stability upon hydrothermal aging at 1,050 °C. The results show that after aging the Pt-substituted catalyst retained higher N2 selectivity than the Pd-based TWC. Over Pd-based TWCs, N2 selectivity drastically dropped from 70–80% to 15–35% after aging, while Pt-substituted TWCs N2 selectivity dropped from 80–100% to only 60–80%. The key finding from this study is that Pt incorporation in a Pd/Rh TWC improves the emission control from gasoline vehicles in terms of both CO and HC oxidation and NOx reduction. [ABSTRACT FROM AUTHOR]

We synthesized three-way catalysts consisting of rhodium, platinum, or palladium clusters confined in zeolites produced by pulsed laser ablation (LA) in liquid acetone. A plate of the catalytic metals was irradiated with a pulsed laser in an acetone suspension of zeolite powder. The catalytic properties of the samples were evaluated for the three-way reaction, CO oxidation reaction, and NO–CO reaction. The zeolite-confined clusters generated by LA had higher thermal stability than those supported on α-Quartz (αQ) particles produced by LA. The cluster size matched those of the pores, resulting in a large contact area with the surface of the pores. Therefore, the metal clusters supported by zeolite were efficiently stabilized in the zeolite pores by a larger number of Rh–O–Si bonds than those supported on αQ particles produced by LA. Moreover, the zeolite-confined clusters generated by LA had higher catalytic activity than clusters on zeolite produced by traditional metal-ion exchange followed by reduction. [ABSTRACT FROM AUTHOR]

This study examines the catalytic performance of copper-alumina (CuAl) aerogel which is a possible alternative to the use of precious metals in automotive exhaust treatment systems which require simultaneous conversion of carbon monoxide, unburnt hydrocarbons and nitrogen oxides. To be a viable alternative, the aerogel materials need to withstand a slurrying process to enable coating onto a substrate and they need to maintain performance in a humid environment typical of what is seen in automotive exhaust. In this study, we slurried heat-treated copper-alumina aerogels in an acidic (pH ~4) aqueous solution under mechanical stirring. The solution was subsequently dried at 60 °C under ambient pressure conditions. Physical properties of slurried CuAl aerogel (surface area, X-ray diffraction, morphology) were similar to those of non-slurried materials. Catalytic testing in a simulated automotive exhaust environment demonstrated that the aerogels can survive exposure to humidity. The ability of the slurried and non-slurried aerogels to oxidize propene and carbon monoxide was similar under dry and humid conditions. In a high-O2 environment adding humidity degraded catalytic performance while in a low-O2 environment the humidity improved performance. The catalytic performance toward nitrogen monoxide was less consistent: the slurried sample did not perform as well as the non-slurried sample under any conditions. Highlights: Slurried copper-alumina aerogel largely maintains its physical structure. Slurried copper-alumina aerogel shows three-way catalytic activity. Copper-alumina aerogel is catalytically active in a humid simulated exhaust stream. Light-off temperatures for copper-alumina aerogel are higher in humid exhaust. [ABSTRACT FROM AUTHOR]

Development of automotive three-way catalysts (TWC) is a critical research topic owing to the increasingly stringent emission regulations together with the price and scarcity of precious metals. Among different materials classes, perovskite-type oxides are known to be valuable alternatives because of their high catalytic activities and thermal stability. The interest in doped lanthanum ferrite perovskite as a catalyst is the concept of regeneration of catalyst nanoparticles, which makes it be used efficiently in automobile exhaust for longer duration in comparison to the conventional TWCs. B-site cation regeneration prevents particle growth and sulfur poisoning; hence, the consumption of precious metals will be reduced without lowering the catalytic performance. The aim of this study is to optimize the characteristics of a LaFe0.6Co0.4O3 (LFC) washcoat layer on a cordierite (2MgO.2Al2O3.5SiO2) monolithic substrate through dip coating of the slurry of amorphous and calcined nano-sized LFC particles. Experiments have been conducted to find the optimum amount of viscosity of the slurry, number of dipping repetitions, and suspension time in order to get the highest specific surface area and adherence to the substrate. Also, differences between a slurry with amorphous and calcined powder, precipitation agent and calcination temperature are investigated. It was found that a slurry with 8% w/w of LFC powder, 2% w/w of PVA, 1% w/w of HNO3, and 7.8% w/w of glycerol in water yields suitable slurry characteristics for the dip-coating purpose. SEM pictures were acquired to find out the morphology of the washcoat layer. By repeating the dip-coating process for two times with the calcined powder, a uniform and porous layer is formed on the monolithic substrate with particle size of around 200 nm after sintering at 900 °C. [ABSTRACT FROM AUTHOR]

Pd-only three-way catalysts with improved catalytic activity for NO elimination were prepared. In order to explore the catalytic reaction rules of NO reduction under a three-way catalytic system, a series of single reactions related to NO reduction were evaluated. It was found that the reaction temperatures of NO + H2 or NO + CO or NO + C3H6 reactions were below 250 °C, while that of NO + C3H8 was up to 350 °C. Thus, the reaction NO + C3H8 served as the key reaction in determining the purification efficiency of NO at the high-temperature stage. By in situ FTIR, we proposed that three possible steps were involved in NO + C3H8 reaction. The first step was the oxidation of C3H8 and NO to acetone and nitrate species by active oxygen species, respectively (C3H8 + O* → C3H6O, NO + O* → NO3−). XPS results revealed that the amount of active oxygen species in Pd/CeO2-ZrO2-Al2O3 (Pd/CZA, 73.7%) was much higher than that in Pd/CexZr1−xO2+Al2O3 (Pd/CZ+A, 64.1%). This was in line with the higher reaction efficiency of the first step over Pd/CZA. Then the NO + C3H8 reaction was accelerated by the first step, which consequently contributed to the higher NO elimination efficiency of Pd/CZA. [ABSTRACT FROM AUTHOR]

The impact of acetylene on the NO reduction mechanism was investigated on a Pd-Rh/CeO2-ZrO2 catalyst. Temperature Program Reaction revealed that C2H2 has a detrimental effect on NO reduction by both H2 and CO. Stationary regime perturbed by C2H2 pulse at different temperatures showed that surface species issued from C2H2 strongly compete with NO and CO for adsorption on metal particles, but also poison both the metal surface and the support which thus respectively prevents the O spillover and the ceria re-oxidation. The only positive effect of C2H2 was detected at 325 °C under rich condition. [ABSTRACT FROM AUTHOR]

Catalytic, copper-impregnated alumina and silica aerogels were prepared. Alumina gels were prepared from a solution of aluminum chloride via an epoxide-assisted synthesis. Silica gels were fabricated from tetramethyl orthosilicate using a base-catalyzed approach to the hydrolysis and polycondensation reactions. Copper was introduced into the alumina and silica gels through exposure of the wet gel to a solution of copper(II) nitrate during a solvent-exchange step prior to aerogel formation via rapid supercritical extraction. Undoped silica and alumina aerogels were fabricated for comparison. A barrage of physical characterization methods were employed to analyze the aerogels as-prepared, following heat-treatment and following catalytic testing. These include bulk density, Brunauer-Emmett-Teller surface area, Barrett-Joyner-Halenda pore distribution, infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. As-prepared copper-silica aerogels have density 0.11 g/cm, surface area 780 m/g, and 9-nm average pore diameter. As-prepared copper-alumina aerogels have density 0.09-0.11 g/cm, surface area 430 m/g, and 23-nm average pore diameter. Calcining to 800 °C results in 10% lower surface area and average pore size 22 nm for copper-silica aerogels, 70% lower surface area for copper-alumina aerogels and, in both types of materials, yields microcrystalline CuO. A catalytic testbed was employed to assess the suitability of the copper-alumina and copper-silica aerogels as three-way catalysts for eventual application in automotive pollution mitigation. Both copper-silica and copper-alumina aerogels performed as three-way catalysts. Graphical Abstract: [ABSTRACT FROM AUTHOR]

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

Pd-only three-way catalyst (TWC), Pd supported on washcoating (the mixture of alumina and Ce-Zr solid solution)/cordierite, was prepared and its catalytic performance and the operation window ( λ-value) at 450 °C were evaluated with the simulated automotive exhaust feed gas. Surfactants such as Tween-80 and Span-20 were added in the process of preparing the catalyst in order to improve the thermal stability and catalytic performance of Pd-only TWC. The fresh and aged catalysts at 1000 °C for 4 h were characterized by low-temperature N2 adsorption, XRD, XPS, and H-TPR techniques. The results show that the presence of surfactants in the synthesis slurry could influence the physicochemical properties of the final Pd-only TWC. The FTS catalyst prepared with the mixed surfactant of Tween-80 and Span-20 exhibited excellent three-way catalytic performance. After being aged at 1000 °C for 4 h, the catalytic performances of Pd-only TWCs slightly decreased, but the FTS catalyst still demonstrated higher catalytic performance and better thermal stability compared with the Pd-only catalysts prepared with single surfactant or without any surfactant. And the FTS catalyst has a wider λ value (operation window) than other catalysts, even after being aged at 1000 °C. [ABSTRACT FROM AUTHOR]

A novel Ultrasonic Assisted Membrane Reduction (UAMR)-hydrothermal method was used to prepare flower-like Pt/CeO catalysts. The texture, physical/chemical properties, and reducibility of the flower-like Pt/CeO catalysts were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), N adsorption, and hydrogen temperature programmed reduction (H-TPR) techniques. The catalytic performance of the catalysts for treating automobile emission was studied relative to samples prepared by the conventional wetness impregnation method. The Pt/CeO catalysts fabricated by this novel method showed high specific surface area and metal dispersion, excellent three-way catalytic activity, and good thermal stability. The strong interaction between the Pt nanoparticles and CeO improved the thermal stability. The Ce ions were incorporated into the surfactant chains and the Pt nanoparticles were stabilized through an exchange reaction of the surface hydroxyl groups. The SEM results demonstrated that the Pt/CeO catalysts had a typical three-dimensional (3D) hierarchical porous structure, which was favorable for surface reaction and enhanced the exposure degree of the Pt nanoparticles. In brief, the flower-like Pt/CeO catalysts prepared by UAMR-hydrothermal method exhibited a higher Pt metal dispersion, smaller particle size, better three-way catalytic activity, and improved thermal stability versus conventional materials. [ABSTRACT FROM AUTHOR]

High oxygen storage capacity (OSC) materials are very much demanded for catalytic applications and ceria is one of the promising OSC materials widely used in three-way catalysts. The objective of the present work is to overcome the inherent limitations of ceria by doping Al and Zr into its lattice and optimize the concentration of dopant based on its OSC. A solid solution of CeZrAlO (CZA) (0.0 ≤ x ≤ 0.4) was synthesized by sol-gel technique and the concentration of Zr and Al was optimized based on the maximum OSC of CZA. In all the samples, the lattice defects on the structure were observed and confirmed by HRTEM and Raman spectroscopy. The crystal size of CZA samples was observed to be varied from 2.7 to 7.5 nm. The crystallite growth of CZA was observed to be less compared to that of ceria-zirconia solid solution after the ageing treatment. The OSC of the sample was calculated by the cyclic heating and cooling process in the temperature range of 30-800 °C using Thermogravimetric analysis and the same was observed to be varied from 0.108 to 0.230 μmol g of CeO. The coefficient of thermal expansion, which was qualitatively used to confirm the OSC, was measured using the thermomechanical analyser and it was observed to be high in CeZrAlO compared to that of CeZrO and the same was found to be significant after 600 °C. It is concluded that CeZrAlO has the highest OSC among all the samples, which could be explored for the potential catalytic applications. [ABSTRACT FROM AUTHOR]

Three-way catalyst-based automotive exhaust gas aftertreatment is of high importance to meet today's emission standards. To determine in situ the oxygen loading state of three-way catalysts, a microwave cavity perturbation method is used. In this study, it is investigated whether this measurement setup that had originally been described for full-sized catalysts can be transferred to a lab test bench using cores of 1″ diameter. The initial tests were successful and a high correlation between the oxygen loading degree dependent resonance frequency and the conversion was found. As an application example of the new in situ characterization technique, the steady state degree of oxidation of a three way catalyst was measured as a function of the exhaust stoichiometry. The experimental results are compared with the prediction of a recently published improved kinetic model that takes into account the oxidation of reduced ceria by HO and CO. It is shown that the experimental observations agree very well with this improved model. This result provides evidence that under typical operating conditions, the degree of oxidation of the three way catalyst is controlled by equilibrium effects. [ABSTRACT FROM AUTHOR]

The present work is focused on applying washing treatments using Cl-containing reagents, such as di-chloroacetic acid (DCA) for the first time, and 1,2-di-chloropropane, DCP (0.1 M) solutions in regaining the activity and oxygen storage capacity (OSC) of an aged commercial Pd-based TWC. Segments extracted from an aged (56,000 km) commercial Pd/Rh-based (9:1) TWC after washing with DCA resulted in 100 % removal of Pb and about 43 % of P, while washing with DCP solution was ineffective in removing these specific contaminants. DCA-washing regeneration method was found to increase Pd surface concentration by four times compared to the aged TWC, whereas DCP-washing was considerably less effective than DCA in recovering Pd active sites. The OSC of the aged catalyst was significantly improved by the use of DCA-washing, whereas no improvement was observed by DCP-washing. Nevertheless, DCP-washing was found to be more effective in improving the performance of aged TWC towards CO oxidation. The removal of Pb is likely a reason for the DCA-washing being more effective in improving CH and NO conversions and OSC. [ABSTRACT FROM AUTHOR]

The oxidation state of palladium in a model Pd/ACZ three-way catalyst was monitored by synchronous XANES and mass spectrometry during two consecutive heating (to 850 °C) and cooling (to 100 °C) cycles under stoichiometric conditions simulating exhaust after treatment of a natural gas engine. During heating in the first cycle, PdO reduction occurred around 500 °C and the initial fully oxidized state of Pd was never recovered upon heating and cooling cycles. A mixed Pd/Pd oxidation state was at work in the second cycle. Hence, the operando XANES study reveals that the PdO/Pd pair exists in a working catalyst but is less active than the catalyst in its initial state of fully oxidized palladium. It is also evident from XANES spectra that ceria-zirconia promotes re-oxidation of metallic Pd, thus reasonably sustaining catalytic activity after exposure to high temperatures. [ABSTRACT FROM AUTHOR]

Present-day three-way catalysts operate in contact with exhaust gases whose temperature is as high as >1000°C, so the problem of developing thermally stable catalytic compositions is still topical. A series of AlO-CeZrO composites containing 0, 10, 25, and 50 wt % AlO has been synthesized by direct precipitation. The as-prepared composites and those calcined in air at 1000 and 1100°C have been characterized by BET, X-ray diffraction, transmission electron microscopy, and temperature-programmed reduction methods. The composites aged at 1050°C in a 2% O + 10% HO + 88% N atmosphere have been used to prepare monolith catalysts, and the oxygen storage capacity (OSC) of the latter has been measured using a gas analysis setup. As the proportion of AlO in the composite is raised, the mixing uniformity and degree of dispersion of CeZrO particles increase, their chemical composition becomes homogeneous, and the amount of cerium involved in oxidation and reduction increases. The composite containing 50 wt % AlO is a mixture of CeZrO and AlO crystallites, whose size is practically unaffected by calcination. The (Pt/AlO + AlO-CeZrO) based on this composite has the highest OSC and is the most active. For this reason, full-scale testing of this catalyst is recommended. [ABSTRACT FROM AUTHOR]

Praseodymium-Cerium Oxide (PrCeO; PCO), a potential three way catalyst oxygen storage material and solid oxide fuel cell (SOFC) cathode, exhibits surprisingly high levels of oxygen nonstoichiometry, even under oxidizing (e.g. air) conditions, resulting in mixed ionic electronic conductivity (MIEC). In this study we examine the redox kinetics of dense PCO thin films using impedance spectroscopy, for x = 0.01, 0.10 and 0.20, over the temperature range of 550 to 670°C, and the oxygen partial pressure range of 10 to 1 atm O. The electrode impedance was observed to be independent of electrode thickness and inversely proportional to electrode area, pointing to surface exchange rather than bulk diffusion limited kinetics. The large electrode capacitance (10F) was found to be consistent with an expected large electrochemically induced change in stoichiometry for x = 0.1 and x = 0.2 PCO. The PCO films showed surprisingly rapid oxygen exchange kinetics, comparable to other high performance SOFC cathode materials, from which values for the surface exchange coefficient, k, were calculated. This study confirms the suitability of PCO as a model MIEC cathode material compatible with both zirconia and ceria based solid oxide electrolytes. [ABSTRACT FROM AUTHOR]

Suppression of noble metal sintering is a very important approach in the development of automotive three-way catalysts. The investigation into the Pt sintering behavior revealed that the formed Pt–O–M (M: cation of oxide, i.e., cerium oxide) bond acted as an anchor to suppress the Pt sintering, and that the strength of the Pt-oxide-support interaction was well correlated with the electron density of oxygen in the support oxide. To achieve a good balance between catalytic activity and the sintering suppression, ceria based oxide support was verified to be suitable for Pt, and zirconia based oxide support was appropriate support for Rh. Through optimizing the configuration of Pt and Rh in the catalyst, a novel three-way catalyst was developed successfully, and this catalytic activity is far superior to the conventional catalyst, but with lower noble metal content. [ABSTRACT FROM AUTHOR]

The present work demonstrates for the first time that rejuvenation of the catalytic activity of full-scale aged commercial three-way catalytic (TWC) converters is feasible after treatment with weak oxalic acid solution (0.1 M). Up to 50% reduction in CO, 75% in NO x and 32% in HC emissions was attained under warm engine driving conditions following regeneration of three aged TWC converters with 42,500, 156,000 and 165,000 km mileage. Efforts to expand the durability of aged commercial TWC converters installed in gasoline-driven cars after applying specific treatments with weak oxalic acid-based solutions appear to be a very promising starting point in recovering to a very large degree their performance. [ABSTRACT FROM AUTHOR]

The role of cerium oxide on direct oxidation of perchloroethylene (PCE) by a three-way catalyst was explored. In the absence of an external oxidizing agent, PCE was oxidized over an alumina supported Pt/Rh three-way catalyst. We hypothesize that the chlorine atoms in the adsorbed PCE interact with oxygen in CeO2, reducing the cerium to create CeCl3. [ABSTRACT FROM AUTHOR]

This paper reviews the progress in our development of the three-way catalyst with a noble metal sintering suppression technology based on the support anchoring effect. The catalytic activity on this catalyst is far superior to the conventional catalyst, but with lower noble metal loading. [ABSTRACT FROM AUTHOR]

In this study, fresh and aged Pd/(OSC–Al2O3) and Pd/(Al2O3–OSC–La2O3) metallic monoliths (OSC material Ce0.75Zr0.25O2) were used to find out the effect of La2O3 on the catalyst behaviour in dynamic oxygen storage capacity (OSC) measurements. In addition, the interaction of CO, NO and O2 reaction compounds over the studied catalysts was investigated in order to understand the effect of La2O3 in the oxidation and reduction reactions in lean automotive exhaust gas conditions. A FT-IR gas analyser was used to analyse the product gas composition. The presence of La2O3 on fresh and aged catalysts had negative effect on both the dynamic OSC and the activity of the catalyst. The reason for this is the different washcoat compositions between the studied catalysts which could explain the differences in BET surface areas. [ABSTRACT FROM AUTHOR]

A Pd catalyst is particularly effective for the oxidation of CO and C3H6 at low temperatures, while the Pt/Rh/Ce catalyst is active for NO reduction. The TWC activity of both catalysts generally decreased as the catalyst mileage increased. However, the NO reduction activity was less affected by catalyst aging compared to the oxidation reactions. The selectivity of the catalysts in favor of the CO–O2 reaction (vs. C3H6–O2 reaction) in the O2 partitioning experiments became less pronounced as the catalyst aged. The NO partitioning experiments reveal the superior capability of H2 in NO reduction to the other reductants (CO and C3H6) examined in the present study. The reactivities of NO with both H2 and CO were found to decrease upon catalyst aging, resulting in decreased overall NO removal activity. [ABSTRACT FROM AUTHOR]

To understand the effect of the NH3 emissions from vehicles, the NH4 + bulk deposition and concentrations of gaseous NH3 and particulate NH4 + were measured at two sites in Saitama prefecture, Japan, one at the roadside of an arterial road (Kounosu), and the other in an agricultural area (Kisai). We observed that the NH4 + bulk deposition and NH3 concentration were significantly increased in Kounosu; the effect of NH3 emissions from vehicles was confirmed. NOx was a primary pollutant mainly emitted by vehicle exhaust in the vicinity of arterial roads, and the relationship between NO x and sum of gaseous NH3 and particulate NH4 + (T-NH4 +) was examined. The [T-NH4 +/NO x ] ratios in Kounosu ranged from 0.08 to 0.23 (average 0.15), and in Kisai they ranged from 0.16 to 0.67 (average 0.39). In Kounosu, the effect of vehicle exhaust was great, but seasonal variation was small. The contribution ratio of NH3 from vehicle emissions increased at low temperatures, while that from the non-vehicle emissions increased at high temperatures. [ABSTRACT FROM AUTHOR]

Pt–Rh three-way catalysts (TWCs) of two formulations were examined by electron probe microanalysis (EPMA) and cross sectional transmission electron microscopy (TEM), in order to study the effect of accelerated aging on microstructure. Both formulations have Pt and Rh applied in separate washcoat layers, Rh in a zirconia-rich outer layer and Pt in an alumina-rich inner layer(s). Microstructural analyses show that in spite of the initial separation, the precious metals inter-diffuse between the washcoat layers and alloy during aging. Following dynamometer aging the two formulations exhibited significant differences in the precious metal (PM) particle size distributions and the correlation between PM particle size and composition. These differences are attributed to the increased transport of Pt due to the presence of ceria and zirconia in the alumina-rich inner washcoat of one formulation, compared to other formulation. The presence or absence of porosity > 1 μm in diameter and differences in initial Pt distributions in the inner washcoat were also noted as possibly contributing to the PM particle growth. The transition alumina of one formulation, containing Ba, partially transformed to corundum during aging. The other formulation utilized a La-stabilized alumina which did not transform to corundum after aging. [ABSTRACT FROM AUTHOR]

Recent studies relevant to the future use of gold catalysts in the automotive industry are summarized. Gold catalysts have been examined for their potential in low temperature activity to combat cold-start emission problems and removal of NOx from lean-burn gasoline and diesel engines. The justification for developing gold catalyst technologies is based both on their promising technical performance and the relatively stable price and greater availability of gold compared with the platinum group metals (PGMs). Use of gold catalysts under mild conditions could also produce lower proportions of CO in the hydrogen streams used for automotive fuel cells and they could be used for the selective oxidation of carbon monoxide in these hydrogen streams in order to increase the efficiency of these fuel cells. Technical barriers are indicated which still remain to be overcome before application of gold catalysts is successful in the automotive sphere. [ABSTRACT FROM AUTHOR]

Simultaneous IR spectroscopic and catalytic measurements have been performed in order to investigate the nature of adsorbed species involved in the formation of N2O on Rh/Al2O3 in the course of the CO + NO reaction. Only nitrosyl species have been isolated that could be involved in the formation of N2 and N2O in accordance with previous kinetic investigations [Granger et al. J. Catal. 175(1998) 194]. Sequential and simultaneous NO and CO exposures lead to the observation of different nitrosyl species that could act as intermediates in the formation of N2 and N2O. Correlations between the appearance/disappearance of Rh(NO)δ+ species and an extra formation of N2O have been established. [ABSTRACT FROM AUTHOR]

Deactivation of Pd/Rh monoliths is considered. Based on the results of different characterization techniques, a deactivation correlation between laboratory scale ageing, engine bench ageing, and vehicle ageing is proposed. [ABSTRACT FROM AUTHOR]

The individual and combined effects of phosphorus and calcium on Rh-containing catalyst powders have been studied. The results showed a strong deactivating impact of phosphorus on the catalytic activity of these powders. The effect of calcium poisoning was not as significant. By contrast, the presence of calcium even restored the activity of the catalyst powders poisoned by phosphorus. [ABSTRACT FROM AUTHOR]

This review summarises catalyst-based strategies and techniques for efficient control of automotive emissions with focus on methods that increase the catalytic activity at low temperatures. Technical solutions, which more indirectly improve the function of the catalyst, are briefly discussed. [ABSTRACT FROM AUTHOR]

SPring-8 is the largest third-generation synchrotron radiation facility in the world. Synchrotron radiation is the most powerful light source currently available, especially in the EUV and X-ray regions, and in the research area of catalysis synchrotron radiation offers a very useful analysis method, i.e. XAFS. This spectroscopic investigative technique enables the determination of the chemical states and local structure of the atoms in the specific elements of a sample. Here, we introduce the SPring-8 facility and report how synchrotron radiation XAFS spectroscopy is utilized for the characterization and analysis of catalysts. [ABSTRACT FROM AUTHOR]

This paper reviews progress in the development of oxygen storage materials for automotive exhaust catalysts. The research was mainly conducted as a study and development exercise in the author's laboratory in Japan. Ceria-lanthana solid solutions (CL) and the first generation of ceriazirconia solid solutions (CZ) were developed as excellent oxygen storage materials for automotive catalysts in the 1980s. These materials consist of ceria doped with less than 20 mol% of La4+ or Zr4+. An increase in oxygen defects in CL and CZ under reductive conditions is responsible for an enhanced oxygen storage capability on the cerium atoms. An accurate measure of the oxygen storage capacity (OSC) per cerium is very important for theoretical and practical treatments of the catalyst. The term “partial OSC” was introduced to describe this capacity and to differentiate it from the usual definition of the OSC, known also as the “total OSC”. After the development of CL and CZ, a new technology was developed to dissolve more than 20 mol% of zirconia in the ceria, allowing second generation CZ and third generation CZ (known as ACZ, which is doped with alumina) to be successfully developed in the 1990s. The partial OSC of these materials increases with increasing amounts of zirconia dissolved in the ceria, and also with decreasing material particle size after an engine durability test. In the case of ACZ, alumina was added to CZ based on the “diffusion barrier concept”, in which a diffusion barrier layer inhibits the coagulation of CZ and A when the material is required for duty at high temperature in air. Furthermore, the relationship between the total or partial OSC and the structure of the ceriazirconia solid solutions is explained in this paper. For ceriazirconia solid solutions composed of equimolar CeO2 and ZrO2(Ce/Zr=1), the total or partial OSC of the κ-phase CeZrO4, in which the cerium and zirconium ions are regularly distributed, was about twice as large as that of a ceriazirconia solid solution with a relatively irregular distribution of cerium and zirconium ions, and about five times larger than that of a mixture of ceria powder and zirconia containing only a small amount of ceriazirconia solid solution. It corresponds to about 89% of the theoretical maximum value. For a ceriazirconia solid solution composed of non-equimolar CeO2 and ZrO2(Ce/Zr ≠ 1), the partial OSC of a ceria-κ-phase solid solution with a zirconia content of between 30 and 50mol% is much higher than that of a ceriazirconia solid solution of the same zirconia content. The partial OSC of a κ-phase and zirconia mixed oxide, which is formed by reducing the material at 1200 °C, reaches a value above 0.20 mol-O2/mol-Ce (about 80% of the theoretical maximum value of the partial OSC), when the zirconia content is between 50 and 80 mol%. The Toyota Motor Corp. has put automotive three-way catalysts containing the first, second and third generations of CZ into practical use on a global basis. [ABSTRACT FROM AUTHOR]

The three-way catalyst promoters (Ce-Zr)O2, (Pr-Ce-Zr)O2 and (Pr-Zr)O2 were prepared by the sol-gel method. The reduction/oxidation behavior of these mixed oxides was compared. It is shown that the formation of (Pr-Zr)O2 cubic solid solution at high temperature up to 800 °C makes it more reducible, and that the ternary solid solution that formed in (Pr-Ce-Zr)O2 mixed oxides plays an important role in the reduction process. The catalytic performance tests reveal that the introduction of a small amount of praseodymium into (Ce-Zr)O2 favors the light-off temperature of C3H6 and NO and the effectiveness for NO conversion at the lean region. [ABSTRACT FROM AUTHOR]

An asymmetry in NO conversion efficiency is apparent during trans-stoichiometric air–fuel ratio steps over a three-way catalyst. After a lean-to-rich step, NO conversion becomes high very rapidly and asymptotes to a higher value, followed by a reduction to a high, but reduced level. Following a rich-to-lean step, conversion remains high for a period before gradually decreasing to the low level seen at steady lean operation. This dynamic response in NO conversion can be modelled by a three-way catalyst model which includes ceria reoxidation by way of NO dissociative adsorption. Five, periodic, different aspect triangular waveforms were tested to try to exploit the asymmetry by waveform shaping. No strong trends in average NO conversion efficiency resulted; however, some shapes seemed to give a better overall conversion. [ABSTRACT FROM AUTHOR]

A novel preparation route of TWC, which is combined with the synthesis of nanosized (Ce–Zr–M)O2 (M = La, Pr) solid solution by modified sol–gel method, is introduced. The TWC precursor shows high thermal stability and possesses high OSC. High thermally stable TWCs with this kind of precursors are also exhibited. The main reason is discussed. [ABSTRACT FROM AUTHOR]

We have attempted to model the rate of NO transformation on a sintered Pt–Rh/Al2O3 three-way catalyst (TWC) in various temperature and conversion conditions close to the actual ones in TWCs. For this purpose a rate expression, previously established from kinetic measurements performed at a single temperature of 300°C, was used. The temperature dependency of the kinetic and thermodynamic parameters, using a non-linear optimisation, has been previously determined. Then, temperature-programmed experiments, performed in a fixed-bed flow reactor at atmospheric pressure under differential conditions, have been modelled using such parameters. A similar procedure has been achieved for modelling the TP experiments on Rh/Al2O3. Both results have been compared and discussed in the light of previous surface characterisations. [ABSTRACT FROM AUTHOR]

Recent studies suggest that microwave energy can be employed in catalysis and that the results differ from “conventional” heating. The influence of microwave energy on automotive exhaust catalysis in the presence and absence of a catalyst poison (SO2) was studied. The conclusion is that microwave energy can induce carbon monoxide (CO) lightoff (the temperature where 50% of final conversion is achieved) more efficiently than conventional heating and can reverse the poisoning by SO2 for a commercial three-way catalyst. [ABSTRACT FROM AUTHOR]

A simple hydrothermal procedure is introduced, which leads to the successful synthesis of a new composite material with fine CeO2-ZrO2 nanocrystallites embedded in amorphous and porous SiO2 matrices. The composite material possesses an extraordinary high thermal stability. After being calcined at 1000 °C, it retains CeO2-ZrO2 nanocrystallites of the size around 5 nm, a BET-specific surface area of 165 m2/g, and an oxygen storage capacity of 468 μmol/g. No phase segregation for CeO2-ZrO2 nanocrystallites is detected and the SiO2 matrices remain not crystallized. The composite material shows a great potential as a support of three-way catalyst, as evidenced in catalytic tests with supported Pt. [ABSTRACT FROM AUTHOR]