Automotive Three-way Catalysts Research Articles

Sustainable Recovery of Platinum Group Metals from Spent Automotive Three-Way Catalysts through a Biogenic Thiosulfate-Copper-Ammonia System.

This study explores an eco-friendly method for recovering platinum group metals from a synthetic automotive three-way catalyst (TWC). Bioleaching of palladium (Pd) using the thiosulfate-copper-ammonia leaching processes, with biogenic thiosulfate sourced from a bioreactor used for biogas biodesulfurization, is proposed as a sustainable alternative to conventional methods. Biogenic thiosulfate production was optimized in a gas-lift bioreactor by studying the pH (8-10) and operation modes (batch and continuous) under anoxic and microaerobic conditions for 35 d. The maximum concentration of 4.9 g S2O32- L-1 of biogenic thiosulfate was reached under optimal conditions (batch mode, pH = 10, and airflow rate 0.033 vvm). To optimize Pd bioleaching from a ground TWC, screening through a Plackett-Burman design determined that oxygen and temperature significantly affected the leaching yield negatively and positively, respectively. Based on these results, an optimization through an experimental design was performed, indicating the optimal conditions to be Na2S2O3 1.2 M, CuSO4 0.03 M, (NH4)2SO4 1.5 M, Na2SO3 0.2 M, pH 8, and 60 °C. A remarkable 96.2 and 93.2% of the total Pd was successfully extracted from the solid at 5% pulp density using both commercially available and biogenic thiosulfate, highlighting the method's versatility for Pd bioleaching from both thiosulfate sources.

Pt-Doped Lanthanum Ferrites as Versatile Electrode Material for Solid Oxide Cells

La0.6Sr0.4Fe0.8Co0.2O3-δ (LSCF) alone or mixed with doped ceria represents the reference air electrode material for IT-SOFC/SOEC, thanks to its intrinsic MIEC nature and unrivaled catalytic activity towards oxygen exchange reactions. Nevertheless, a steep growth in cobalt demand for automotive (EVs) and storage applications is expected in the next decades, and ethical issues related to cobalt mining in politically unstable countries endanger cobalt supply chain [1]. Noble metal doping to a low extent ( ≤ 5% mol) has drawn attention as a valid strategy to provide the parent oxide structure with high catalytic activity [2][3]. Such amounts of platinum-group-metals (PGM) could be profitably harvested from secondary sources, such as spent automotive three-way catalysts (TWCs) [4], rendering their supply less dependent from localized low-grade ores. In particular, due to the tendency of PGM to be easily reduced to the metallic state, PGM-doped perovskites have found application mainly as fuel electrode materials. Noble metal exsolution endows the parent perovskite with finely dispersed nanoparticles firmly anchored to the oxide substrate, that display high catalytic activity and stability [5].Here, platinum-doping on strontium-substituted lanthanum ferrites is explored as an innovative strategy to enhance the parent perovskite catalytic activity both in reducing and oxidizing environment. The ultimate goal is the design of a multi-functional electrode for Reversible Solid Oxide Cells (r-SOCs). La0.6Sr0.4Fe1-xPtxO3-δ, X = 0.005, 0.01, 0.05 (LSFPtX) stoichiometries were successfully synthesized and characterized by means of X-ray Powder Diffraction (XPRD) (Fig. 1), thermogravimetric analysis (TG), oxygen temperature-programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). LSFPtX were tested in symmetric cells to evaluate their activity as air electrode materials in terms of polarization resistance vs. temperature and vs. pO2. The rate-limiting steps of oxygen exchange reactions were investigated by means of electrochemical impedance spectroscopy (EIS) fitting experimental data with equivalent circuit (EC) modelling and distribution of relaxation times (DRT). Results were compared both to the undoped (LSF) and to a commercially available state-of-art 20 mol% Co-substituted LSCF. LSFPtX structural evolution is evaluated at different pO2 and in several SOCs operational environments (5%H2/Ar, 100% CO2 and 50% CO2 : 50% CO). B-site exsolution was studied by means of temperature-programmed reduction (H2-TPR) and scanning electron microscopy (FE-SEM) to assess their applicability as fuel electrode materials as well. Finally, LSGM-based symmetric cells were tested as SOFC and CO2-SOEC, evaluating the operational reversibility and the long-term stability.[1] IEA, Total Cobalt Demand by Sector and Scenario, October 2022, pp. 2020–2040.[2] Marcucci, A., Zurlo, F., Sora, I. N., Placidi, E., Casciardi, S., Licoccia, S., & Di Bartolomeo, E. (2019). A redox stable Pd-doped perovskite for SOFC applications. Journal of Materials Chemistry A, 7(10), 5344-5352.[3] Marasi, M., Duranti, L., Luisetto, I., Fabbri, E., Licoccia, S., & Di Bartolomeo, E. (2023). Ru-doped lanthanum ferrite as a stable and versatile electrode for reversible symmetric solid oxide cells (r-SSOCs). Journal of Power Sources, 555, 232399.[4] Karim, S., & Ting, Y. P. (2021). Recycling pathways for platinum group metals from spent automotive catalyst: A review on conventional approaches and bio-processes. Resources, Conservation and Recycling, 170, 105588.[5] Kothari, M., Jeon, Y., Miller, D. N., Pascui, A. E., Kilmartin, J., Wails, D., ... & Irvine, J. T. (2021). Platinum incorporation into titanate perovskites to deliver emergent active and stable platinum nanoparticles. Nature Chemistry, 13(7), 677-682. Figure 1

Cr-Fe-Ni-Cu Quaternary Nanostructure as a Substitute for Precious Metals in Automotive Three-Way Catalysts.

The replacement of precious metals (Rh, Pd, and Pt) in three-way catalysts with inexpensive and earth-abundant metal alternatives is an ongoing challenge. In this research, we examined various quaternary metal catalysts by selecting from six 3d transition metals, i.e., Cr, Mn, Fe, Co, Ni, and Cu, equimolar amounts (0.1 mol each), which were prepared on the Al2O3 support (1 mol Al) using H2 reduction treatment at 900 °C. Among 15 combinations, the best catalytic performance was achieved by the CrFeNiCu system. Light-off of NO-CO-C3H6-O2-H2O mixtures proceeded at the lowest temperature of ≤200 °C for CO, ≤300 °C for C3H6, and ≤400 °C for NO when the molar fraction of Cr in Cr x Fe0.1Ni0.1Cu0.1 was around x = 0.1. The activity for CO/C3H6 oxidation was superior to that of reference Pt/Al2O3 catalysts but was less active for NO reduction. The structural analysis using scanning transmission electron microscopy and X-ray absorption spectroscopy showed that the as-prepared catalyst consisted of FeNiCu alloy nanoparticles dispersed on the Cr2O3-Al2O3 support. However, the structural change occurred under a catalytic reaction atmosphere, i.e., producing NiCu alloy nanoparticles dispersed on a NiFe2O4 moiety and Cr2O3-Al2O3 support. The oxidation of CO/C3H6 can be significantly enhanced in the presence of Cr oxide, resulting in a faster decrease in O2 concentration and thus regenerating the NiCu metallic surface, which is active for NO reduction to N2.

Effects of co-precipitation temperature on structure and properties of La and Y doped cerium zirconium mixed oxides

Due to the oxygen storage and release properties, cerium zirconium mixed oxides are recognized as the key material in automotive three-way catalysts. To reveal the effects of co-precipitation temperature on structure, physical and chemical properties of multi-doped cerium zirconium mixed oxides, a series of La and Y doped cerium zirconium mixed oxides (CZLYs) were synthesized via a co-precipitation method, and the physical and chemical properties of CZLYs were systemically characterized by XRD, N2 adsorption–desorption, TEM, XPS, oxygen storage capacity (OSC) and hydrogen temperature programmed reduction (H2-TPR). The results show that co-precipitation temperature is an important parameter to influence the crystal size, oxygen storage capacity and thermal stability of CZLYs. When the co-precipitation temperature was 60 °C, the best redox properties and thermal stability of CZLYs were obtained. After thermal treatment at 1100 °C for 10 h, the specific surface area and oxygen storage capacity of the corresponding aged sample were 15.42 m2/g and 497.7 μmol/g, respectively. In addition, a mechanism was proposed to reveal the effects of co-precipitation temperature on the structure and properties of CZLYs.

First of Its Kind Automotive Catalyst Prepared by Recycled PGMs-Catalytic Performance

The production of new automotive catalytic converters requires the increase of the quantity of Platinum Group Metals in order to deal with the strict emission standards that are imposed for vehicles. The use of PGMs coming from the recycling of spent autocatalysts could greatly reduce the cost of catalyst production for the automotive industry. This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered PGMs, without further refinement steps. The catalysts were characterized and evaluated in terms of activity in comparison with benchmark catalysts produced using commercial metal precursors. The small-scale catalytic monoliths were successfully synthesized as evidenced by the characterization of the samples with XRF analysis, optical microscopy, and N2 physisorption. Hydrothermal ageing of the catalysts was performed and led to a significant decrease of the specific surface area of all catalysts (recycled and benchmarks) due to sintering of the support material and metal particles. The TWCs were studied for their activity in CO and unburned hydrocarbon oxidation reactions under a slightly lean environment of the gas mixture (λ > 1) as well as for their ability to reduce NOx under a slightly rich gas mixture (λ < 1). Recycled TWC fresh catalyst presented the best performance amongst the catalysts studied for the abatement of all pollutant gases, and they also showed the highest Oxygen Storage Capacity value. Moreover, comparing the aged samples, the catalyst produced from recycled PGMs presented higher activity than the one synthesized with the use of commercial PGM metal precursors. The results obtained for the DOC catalysts showed that the aged PLDOC catalyst outperformed both the fresh catalyst and the aged DOC catalyst prepared with the use of commercial metal precursors for the oxidation of CO, hydrocarbons, and NO. The latter reveals the effect of the presence of several impurities in the recovered PGMs solutions.

Microwave-Based State Diagnosis for Three-Way Catalysts – A Promising Technology for Future Gasoline Exhaust Gas Aftertreatment

Microwave-Based State Diagnosis for Three-Way Catalysts – A Promising Technology for Future Gasoline Exhaust Gas Aftertreatment

Calibration of the Oxygen Storage Reactions for the Modeling of an Automotive Three-Way Catalyst

Nowadays, numerical simulations play an important role during the design and optimization phase of the after-treatment system (ATS). Simulation tools, based on both simple 1D or detailed CFD approaches, are able to describe the chemical species transport through the system and the main reactions occurring in the catalytic devices. In this context, the availability of accurate kinetic schemes is of primary importance for the reliable prediction of the ATS performance. In this work, the theme of the calibration of the reaction scheme based on the available experimental measurement is investigated, with particular interest in the modeling of the three-way catalyst. Hence, a methodology for the calibration is proposed, based on a two-step calibration procedure, which exploits two different types of the experimental data set, namely, oxygen storage capacity tests and standard homologation cycles. The adoption of these two different data sets allows us to optimize separately the kinetics of the reactions occurring at high temperatures and low temperatures, with a specific focus on the oxygen storage mechanism at the basis of the operation of a three-way catalyst. The effectiveness of the developed calibration procedure is finally demonstrated, considering two different test cases.

NH3 formation pathways from NO reduction by CO in the presence of water over Rh/Al2O3

Steady-state kinetic measurements with varying NO (0.05−0.2 kPa), CO (0.2−0.5 kPa), and water (1.5–9 kPa) pressures at 598 K rationalize that N2/N2O selectivity is determined by NO pressure while the NH3/(N2O + N2) selectivity is a single-valued function of NO/CO ratio. The existence of NCO* species on Al2O3 is confirmed by IR spectra. Monotonically increasing NH3/Rh ratios from H2O recirculation over the NCO* accrued in transient reaction studies on Rh/Al2O3 upon exposure to NO/CO mixtures suggests NH3 formation occurs by hydrolysis of isocyanate species bound on Al2O3. These findings demonstrate the critical role of H2O and NO/CO ratio in determining NH3 selectivity for operation of three-way automotive exhaust catalysts at rich air/fuel ratios.

Knock Mitigation Effectiveness of EGR across the Pressure-Temperature Domain

<div class="section abstract"><div class="htmlview paragraph">Exhaust gas recirculation (EGR) has been shown to enable efficiency improvements in SI engines through multiple different mechanisms, including decreasing the knock propensity at high load, which allows higher compression ratio. While many of the benefits of EGR are applicable to both low and high power density engines, including reductions in pumping work and improved specific heat ratio, the knock benefits and corresponding compression ratio increases have been limited to low power density naturally aspirated engines primarily intended for hybrid vehicle architectures. An earlier study [<span class="xref">1</span>] indicated that there may be a kinetic limitation for the ability of EGR to mitigate knock under these conditions, but that study only considered a small number of conditions. This investigation expands on that study while also providing data for model validation for the new light-duty combustion consortium from the U.S. Department of Energy: Partnership for Advancing Combustion Engines (PACE). In this investigation, the effectiveness of EGR to mitigate knock is studied with regards to the effect of engine speed (1,500 and 3,000 rpm), changing trajectory in the pressure-temperature domain by varying the intake manifold temperature (35, 60, and 90 deg C), and by considering the effect of minor species by studying the effect of untreated EGR vs. EGR that has been treated by an automotive three-way catalyst. Additionally, to increase the relevance of these data for future modeling studies, the performance of the full boiling range gasoline was compared relative to a surrogate formulation. The study found that the fuel surrogate performs well, confirmed the kinetic limitations of EGR to mitigate knock under boost, and showed improvements in EGR performance with catalyzed EGR.</div></div>

Physicochemical Properties of LaFeO3 Perovskite Prepared by Various Methods and Its Activity in the Oxidation of Hydrocarbons

LaFeO3 perovskites, obtained through co-precipitation of carbonates with (NH4)2CO3, co-precipitation of hydroxides with NaOH, citrate method, and through solid-state reaction using metal nitrates as precursors, were deposited on a heat-resistant foil support. Their physicochemical properties were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry and thermogravimetric analysis (DSC/TGA), and specific surface area measurements. DSC/TGA showed that phase transitions took place in the LaFeO3 perovskite up to 800–840 °C. Pure LaFeO3 perovskite phase was obtained only when the citrate method was used. The following decreasing order of methane and hexane oxidation activity at 700 °C was determined for the catalysts with the LaFeO3 perovskite obtained by different methods: citric acid > ammonium carbonate ∼ metal nitrates > sodium hydroxide. LaFeO3 catalysts obtained at 700 °C in the presence of citric acid or ammonium carbonate can be used as three-way automotive exhaust catalysts or as catalysts in environmental protection.

Effects of ammonia concentration in hydrothermal treatment on structure and redox properties of cerium zirconium solid solution

Cerium zirconium solid solution is a key washcoat material for automotive three-way catalysts (TWCs). However, improving the redox ability and high temperature thermal stability of cerium zirconium solid solution is still a challenge. In this paper, the cerium zirconium solid solution was prepared by a coprecipitation-hydrothermal method, and the effects of the ammonia concentration on their structures and redox properties were investigated. The results show that when the ammonia concentration is 0.8 mol/L, the aged sample (1100 °C/10 h) of cerium zirconium solid solution has the highest specific surface area of 23.01 m2/g. Additionally, the increase of ammonia concentration improves the uniformity of phase compositions and increases the oxygen vacancies. When the ammonia concentration reaches 0.4 mol/L, the cerium zirconium solid solution exhibits the best redox activity, with the lowest reduction temperature of 565 °C. Therefore, increasing ammonia concentration in the hydrothermal treatment is beneficial to the thermal stability and redox performance of cerium zirconium solid solution.

Synthesis of high stability nanosized Rh/CeO2–ZrO2 three-way automotive catalysts by Rh chemical state regulation

The chemical state of precious metals plays an important role in redox reaction. In order to maintain rhodium (Rh) at metallic state, which is recognized as reactive center in three-way catalytic reactions, we synthesized Rh/CeO2–ZrO2 (Rh/CZ) catalyst by liquid phase reduction adsorption with glycerol as reductant (Rh/CZ-g). Detailed characterizations were conducted to investigate the chemical state of Rh species, and the CO-FTIR and XPS results indicated that Rh species mainly existed in metallic state for Rh/CZ-g. Through CO chemisorption and H2-TPR, it’s proved that the liquid phase reduction treatment would weaken the interaction between Rh species and CeO2–ZrO2 support, avoiding the supply of oxygen species from CeO2–ZrO2 to Rh in some degree. Compared with Rh/CeO2–ZrO2 catalyst prepared by incipient wetness impregnation, Rh/CZ-g exactly had superior activity in three-way catalytic process. Combined with in situ DRIFTS, some important intermediate species, such as Rh–CN, Rh-(NO)2, formates and acetates, preferred to adsorb and transform on Rh/CZ-g with larger proportion of metallic Rh, which determined Rh/CZ-g was more favorable for three-way catalytic reactions, even after aged at 950 °C for 5 h. The purpose of this work is to inspire researchers use simple and valid methods to synthesize highly efficient three-way catalysts.

PREPARATION AND PROPERTIES OF PT-RH-PD / CEO2-ZRO2-LA2O3-AL2O3 FIBROUS CATALYST VIA ELECTROSPINNING

In order to increase the specific surface area of Pt-Rh-Pd / Al2O3 automotive three-way catalyst and improve its low-temperature reduction performance, Ce, Zr, and La were added to the Pt-Rh-Pd / Al2O3 catalyst to prepare the fibrous Pt-Rh-Pd / CeO2-ZrO2-La2O3-Al2O3 catalyst via an electrospinning technique. The fibrous catalysts were characterized by XRD, FT-IR, SEM-EDS, H2-TPR and BET analysis. The catalytic effect of the catalyst on automobile exhaust was also studied. Results revealed that the surface of catalysts is mainly mesoporous. Ce, Zr and La can remarkably increase the specific surface area of the Pt-Rh-Pd / Al2O3 catalyst. The specific surface area of the catalyst prepared with Pt Rh Pd molar ratio of 0.75:0.01:1 is 301.5816 m2 g-1, and the average diameter of which is 790 nm. In addition, the reaction temperature of the catalyst is approximately 220 °C, which shows good low-temperature reduction performance. Moreover, the Pt-Rh-Pd / CeO2-ZrO2-La2O3-Al2O3 catalyst has a catalytic conversion efficiency for NOX of 90.0% in automobile exhaust, a catalytic conversion efficiency for CO of 88.8%, and a catalytic conversion efficiency for SO2 of 75%.

Characterization of LaFe0.6Co0.4O3 washcoat layer on a monolithic substrate

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.

Effects of precursor moisture calcination on the properties of CeZrLaPr solid solution and catalytic behavior of Pd supported catalysts

Abstract CeO2-ZrO2 solid solution is widely used in automotive three-way catalysts. In this work, Ce0.35Zr0.55La0.05Pr0.05O2 solid solutions were prepared by a co-precipitation method. The effects of precursor moisture calcination on the properties of cerium zirconium solid solution and catalytic behavior of Pd supported catalysts were investigated systematically. The results show that the moisture (content of 66.58 wt%) in precursor promotes the crystal grain growth of the cerium zirconium solid solution, enriches the pore channels, and enhances the dispersion of cerium zirconium particles, leading to high thermal stability. After thermal treatment at 1000 °C for 4 h, the aged surface area reaches 48.32 m2 g−1 (a 14.86% increase compared with the common sample). The oxygen storage capacity is also improved by the precursor moisture calcination, with high oxygen storage capacity of 599.08 μmolO2.g−1. The precursor moisture calcination obviously broadens the air/fuel ratio window and improves the catalytic performance of the aged palladium supported catalyst.

Sustainable Inorganic Chemistry: Metal Separations for Recycling.

Inorganic materials are critical components of clean energy technology. For example, rare earths are key for the function of electric car batteries and in permanent magnets used in wind turbines, and palladium helps to reduce harmful exhaust in automotive three-way catalysts. Many of the critical elements for these materials are of low abundance in the earth's crust, found in few places globally, and/or require energy- and resource-intensive purification. By comparison, many of these elements are concentrated in waste electrical and electronic equipment, which represents an attractive secondary resource. Inorganic chemists are ideally positioned to develop new chemistry and greener processes that are more efficient and use less hazardous reagents to separate high-value metals from waste electronics. The purpose of this Viewpoint is to highlight recent discoveries in fundamental inorganic chemistry that can contribute to new recycling technologies for gold, lithium, palladium, germanium, and rare earths, especially using simple approaches in solid-liquid extraction. Such fundamental studies are expected to help close metal supply chain loops and create circular economies.

Fabrication of FeOx-ZrO2 nanostructures for automotive three-way catalysts by supercritical hydrothermal synthesis with supercritical CO2 drying

In this study, an inexpensive and abundant FeOx-based catalyst was developed as a three-way catalyst (TWC). The deactivation associated with the fusion and aggregation of metallic iron under high-temperature reducing conditions was solved by the formation of FeOx-ZrO2 nanostructures. Furthermore, high dispersibility of FeOx in the nanostructures and multiple pores were successfully formed using a supercritical CO2 drying. As a result, the oxygen storage capacity of the FeOx increased dramatically and high stability was obtained.In a TWC reactivity evaluation, the FeZr-TWC showed a high performance similar to that of the commercially available CeO2-based TWC. Even after aging treatment for 20 h at 1000 °C under a 10 vol% steam condition, an NOx (T80, NOx) conversion of greater than 80% was successfully achieved, whereas it was not achieved by the standard TWC. Therefore, the FeZr nanostructures are expected to have sufficient capacity to replace the conventional CeO2-based TWCs.

Sensitivity of Three-Way Catalyst Light-Off Temperature to Air-Fuel Ratio

The operating conditions of the automotive three-way catalyst (TWC) are characterized by continuous variation of the air-fuel ratio (λ) that determines the composition of the exhaust supplied to the catalyst. It is well known that the ability of the TWC to simultaneously catalyze reduction of NOx and oxidation of CO and hydrocarbons is sensitive to the air-fuel ratio. In efforts to formulate improved TWCs with greater activity at lower temperatures, the impact of air-fuel ratio on light-off temperature must therefore be considered. This paper reports an investigation of the impact of air-fuel ratio on the temperatures at which representative exhaust species in a simulated exhaust mixture reach 90% conversion (T90) over a family of rhodium-based model catalysts, with focus on the performance of a recently developed catalyst comprising rhodium supported on titania-modified alumina with exceptional light-off performance. Over a range of air-fuel ratios 0.977 200 °C between 0.995 1.001; and the T90s for representative hydrocarbons ethylene, propylene, and propane decrease by more than 100 °C between 0.977 < λ < 0.995, then increase again by 30 °C (propylene) to 180 °C (propane) between 0.998 < λ < 1.001. These dramatic shifts in T90 over a small range of air-fuel ratio are attributed to facile conversion of CO and olefins by oxidation, facile conversion of propane by steam reforming, and inhibition of propane steam reforming by both oxygen and CO. Balancing these factors leads to optimal conversion of all exhaust components at an air-fuel ratio λ ~ 0.995.

Promotional effect of alkyl acids on thermal stability of nanostructured CeO2-ZrO2-Y2O3-La2O3 and its application in automotive three-way catalysts

A series of nanostructured CeO2-ZrO2-Y2O3-La2O3 quaternary solid solutions (CZ-C10, CZ-C12, CZ-C14 and CZ-C16) were synthesized by simultaneous co-precipitation method with the assistance of alkyl acids CnH2n+1COOH (n=9, 11, 13 and 15). The obtained materials exhibit greatly enhanced oxygen storage capacity, textural properties and thermal stability. After aging at 1000°C, CZ-C12-a presents a high surface area of 47m2g−1 and a large cumulative pore volume of 0.28mLg−1. A comparison between CZ-C12 and the commercial material SO-2 in terms of the catalytic performance of supported Rh-only three-way catalysts indicates that Rh/CZ-C12 owns significantly higher catalytic activity than Rh/SO-2. After aging at 1050°C for 12h, the light-off temperatures (T50) of C3H8, CO and NO for Rh/CZ-C12-a are 314°C, 263°C and 322°C, respectively, which are much lower than those (360°C, 290°C and 386°C) for Rh/SO-2-a.

Comparison between a Water-Based and a Solvent-Based Impregnation Method towards Dispersed CuO/SBA-15 Catalysts: Texture, Structure and Catalytic Performance in Automotive Exhaust Gas Abatement

Supported copper oxide nanoparticles are a potential candidate for replacing the rare and expensive precious metals within the automotive three-way catalyst. However, a well-designed dispersion method is necessary to allow a stable high loading of active material, compensating its lower intrinsic activity and stability. In this work, a CuO-loaded SBA-15 catalyst has been manufactured by two methods. The ammonia-driven deposition precipitation (ADP) and the molecular designed dispersion (MDD) methods are both considered as efficient deposition methods to provide well-dispersed copper oxide-based catalysts. Their morphology, copper dispersion and the chemical state of copper were characterized and compared. Due to the differences in the synthesis approach, a difference in the obtained copper oxide phases has been observed, leading to a distinct behavior in the catalytic performance. The structure-activity correlation of both catalysts has also been revealed for automotive exhaust gas abatement. Results demonstrate that various copper species can be formed depending on the precursor–support interaction, affecting selectivity and conversion during the catalytic reaction.