Automotive Emission Control Research Articles

Atomic-Scale Behavior of Perovskite-Supported Ir-Pd-Ru Nanoparticles under Redox Atmospheres.

An advanced materials solution utilizing the concept of "smart catalysts" could be a game changer for today's automotive emission control technology, enabling the efficient use of precious metals via their two-way switching between metallic nanoparticle forms and ionic states in the host perovskite lattice as a result of the cyclical oxidizing/reducing atmospheres. However, direct evidence for such processes remains scarce; therefore, the underlying mechanism has been an unsettled debate. Here, we use advanced scanning transmission electron microscopy to reveal the atomic-scale behaviors for a LaFe0.95Pd0.05O3-supported Ir-Pd-Ru nanocatalyst under fluctuating redox conditions, thereby proving the reversible dissolution/exsolution for Ir and Ru but with a limited occurrence for Pd. Despite such selective dissolution during oxidation, all three elements remain cooperatively alloyed in the subsequent reduction, which is a key factor in preserving the catalytic activity of the ternary nanoalloy while displaying its self-regenerating functionality and control of particle agglomeration.

Energy, exergy, sustainability, thermoeconomic, exergoeconomic, environmental and environmental-economic effects of novel boron-containing open cell geopolymer filter of a diesel engine on exhaust emissions

In this study, the energy, exergy, sustainability, thermoeconomic, exergoeconomic, environmental and environmental-economic based analyses are applied to the experimentally developed (3 % boric acid based) boron-doped geopolymer filter used for the diesel engine to assess it in a large engineering point of view. In this context, novel boron-doped filter exhaust after treatment system (BDF EAS) is compared with catalytic exhaust after treatment system (catalytic EAS) and unfiltered option (filterless) with engine loads of 50 Nm, 75 Nm and 100 Nm, while engine speeds are 1500 rpm, 1700 rpm, and 1900 rpm. The utilization of the newly developed BDF EAS has a significant effect on the exhaust emission particles. It effectively filters the particles compared to the original catalytic EAS of the engine. On the other hand, the developed BDF EAS has effective oxidation process for the emissions. So, the newly developed boron-doped filter can be used as a single device that has both of the Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) specifications together. Hence, the new product of BDF EAS is environmentally benign system for the diesel engines and boron-doped geopolymer material can be used as an innovative material in the automotive industry's exhaust emission control system.

Rhodium and Rhodium-Alloy Films and Nanoparticles: Part I

Noble metals are key to various research fields and noble metal nanomaterials are directly relevant to optics, catalysis, medicine, sensing and many other applications. Rhodium-based nanomaterials have been less studied than metals such as gold, silver or platinum. There have been many improvements in characterisation tools over the years and knowledge about rhodium chemistry and nanomaterials is growing rapidly. Rhodium nanoparticles are widely used as catalysts for automotive emissions control and for hydrogen and oxygen precipitation reactions in electrolytic cells. Novel applications in electronics, anticancer drugs and aerospace are being revisited. In Part I of this two-part review, we cover different strategies for the synthesis of rhodium films and nanoparticles.

Continuous Unsteady-State De-NOx System via Tandem Water-Gas Shift, NH3 Synthesis, and NH3-SCR under Periodic Lean/Rich Conditions.

The development of urea-free and platinum group metal (PGM)-free catalytic systems for automotive emission control is a challenging task. Herein, we report a new de-NOx system using cyclic feeds of rich and lean gas mixtures with PGM-free catalysts. Initial catalyst screening tests showed that Cu/CeO2 with 5 wt % Cu loading was the most suitable for the water-gas shift reaction (WGS, CO + H2O → CO2 + H2), followed by the selective NH3 synthesis by the NO + H2 reaction. The unsteady-state system under alternating feeds of rich (0.1% NO + 0.5% CO + 1% H2O) and lean (0.1% NO + 2% O2 + 1% H2O) gas mixtures over a mixture of Cu/CeO2 and Cr-exchanged mordenite (CrMOR) showed higher NOx conversion than the steady-state (0.1% NO + 0.35% CO + 0.6% O2 + 1% H2O) reaction between 200 and 500 °C. The de-NOx mechanism under periodical rich/lean conditions was studied by operando infrared (IR) experiments. In the rich period, the WGS reaction on the Cu/CeO2 catalyst yield H2, which reduces NO to NH3 on the Cu/CeO2 catalyst. NH3 is then captured by the Brønsted acid sites of CrMOR. In the subsequent lean period, the adsorbed NH3 acts as a reductant for the selective catalytic reduction of NOx catalyzed by the Cr sites of CrMOR. This study demonstrates a new urea-free and PGM-free catalytic system that can provide an alternative de-NOx technology for automotive catalysis under periodic rich/lean conditions.

Exhaust Gases as Fluxing Agents for Palladium: Formation Enthalpies and Vapor Pressures of PdO, PdO2, Pd(CO)n (n = 1–3), Pd(NO)n (n = 1,2), Pd(OH)n (n = 1,2), HOPdNO, and 21 Other Species under Automotive Catalyst Aging Conditions

Catalyst deactivation by precious metal sintering is a major driver of cost in automotive emission control catalysts. In order to develop strategies to mitigate sintering and maintain higher activity from lower precious metal loading, it is necessary to first develop a more complete understanding of the sintering process. In particular, it is of interest to identify the mobile intermediates that are responsible for sintering via Ostwald ripening and the extent to which the identities and concentrations of these intermediates depend upon the composition of the contacting atmosphere during catalyst use. In this work, first-principles thermodynamic calculations have been conducted on a series of small palladium-containing molecules to assess the potential of these molecules to form over palladium catalysts in the presence of automotive exhaust and serve as mobile carriers during Ostwald ripening. Among the results obtained, three stand out: (1) while exposure to reducing atmospheres in general does not enhance palladium mobility, exposure to carbon monoxide in particular leads to a multiple order of magnitude increase in palladium mobility driven primarily by the formation of Pd(CO)2; (2) under hydrothermal aging conditions, the most abundant vapor species is neither Pd nor PdOx but PdOH; and (3) combination of the latter with traces of nitric oxide enables a significant increase in palladium mobility via the formation of HOPdNO. The impact of surface adsorption on stabilization of mobile intermediates is also considered; a simple non-specific adsorption model indicates that surface stabilization enhances Pd(OH)2 formation under hydrothermal aging conditions.

Iridium-Containing Automotive Emission Control Catalysts

Iridium-Containing Automotive Emission Control Catalysts

New Approaches to the Synthesis of Ultralow-Palladium Automotive Emission Control Catalysts

New Approaches to the Synthesis of Ultralow-Palladium Automotive Emission Control Catalysts

Pr-rich cerium-zirconium-praseodymium mixed oxides for automotive exhaust emission control

This study describes the textural, structural, redox properties, oxygen reactivity of two Pr-rich cerium-zirconium-praseodymium (CZP) oxides (Ce0.45Zr0.10Pr0.45O2−x and Ce0.475Zr0.05Pr0.475O2−x) and their catalytic activity for propane and CO oxidation in both stoichiometric and lean conditions, two important reactions for automotive exhaust emission control. The concentration of oxygen vacancies can be tuned by the quantity of Pr3+ cations which depend both on the preparation method and the composition. The Pr4+(4 f1)/Pr3+(4 f2) ratio was accurately determined by magnetic measurement. A highly energetic grinding step was found to double this Pr3+ concentration, resulting in a strong enhancement of the low-temperature reducibility, bulk oxygen mobility and catalytic activity for propane deep oxidation. Pr-rich CZP oxides seem to be less relevant for CO oxidation, which is mainly driven by the specific surface areas. These Pr-rich CZP mixed oxides present better performances for lean conditions, suggesting their possible role in diesel oxidation catalysts applications.

The metallic palladium-rhodium solution in interaction with oxygen: The Pd-Rh-O phase diagram and thermodynamics

Palladium and rhodium are two platinum group metals (PGMs) widely operated in the industry because of their high electrical and thermal conductivity. They are also widely used for their catalytic activity for automotive emission control. In the nuclear field, both elements are also known as metallic fission products. Due to their sensitivity towards oxygen, the thermodynamic equilibria of the Pd-Rh-O system have been assessed in this paper thanks to the Calphad method.From this thermodynamic assessment, the linear fit of the Gibbs free energy of PdO is ΔfG°TPdO=-115.8+0.102·T (kJ·mol−1) and its calculated heat of formation is –58.994 kJ·mol−1·at−1. The assessed Pd(g) equilibrium pressure under 1 bar of O2 is:log10pPdbar=6.560-19046.9TThe Pd(g) and PdO(g) equilibrium pressures at PdO decomposition are respectively:log10pPdbar=6.7269-19339.0Tlog10pPdObar=8.55-23649.7TIn the Rh-O system, the Rh2O3 and RhO2 heat of formation were reassessed. The new enthalpy values are –79698 kJ·mol−1·at−1 and –80142 kJ·mol−1·at−1, respectively. The calculated Gibbs energy of formation of RhO2 and Rh2O3 can be expressed as ΔGfRhO2=-234.44+0.1751·T and ΔGfRh2O3=-389.51+0.2737·T (in kJ·mol−1), respectively.

Mechanistic study on three-way catalysis over Pd/La/Al2O3 with high La loading

Although La-loaded Al2O3 (La/Al2O3) is a widely used support material for three-way catalysis (TWC), little is known about the promotional effect of La in the La/Al2O3 supported Pd catalyst (Pd/La/Al2O3) in the catalytic NO reduction (DeNOx) for automotive emission control. Previously (Jing et al., 2020 [1]), we assessed the promotional effect of La and observed that the supported metallic Pd nanoparticles on the La/Al2O3 support were more electron-deficient than those on Al2O3 without La, which led to suppression of CO poisoning and a higher catalytic activity for NO reduction. Here, we further investigated the role of La in Pd/La/Al2O3 for the DeNOx process by various spectroscopic methods. The results obtained suggest that the efficient generation of nitrite species and its facile reactivity are important for the promotional effect of La in NO reduction. In addition, we investigated the effects of hydrothermal aging. For the TWC, Pd/La/Al2O3 with high La loading (15 wt%) was identified to be superior to the conventional industrial catalyst having a loading of 5 wt%. It was also found to show relatively high Pd dispersion even after aging at 800 °C. The observed stabilizing effect is an important benefit of the addition of La.

Perspectives on Current and Future Requirements of Advanced Analytical and Characterization Methods in the Automotive Emissions Control Industry

Perspectives on Current and Future Requirements of Advanced Analytical and Characterization Methods in the Automotive Emissions Control Industry

PROMETHEUS: A Copper-Based Polymetallic Catalyst for Automotive Applications. Part II: Catalytic Efficiency an Endurance as Compared with Original Catalysts.

PROMETHEUS catalyst, a copper-based polymetallic nano-catalyst has been proven to be suitable for automotive emission control applications. This novel catalyst consists of copper, palladium and rhodium nanoparticles as active phases, impregnated on an inorganic oxide substrate, CeO2/ZrO2 (75%, 25%). The aim of PROMETHEUS catalyst’s development is the substitution of a significant amount (85%) of Platinum Group Metals (PGMs) with copper nanoparticles while, at the same time, presenting high catalytic efficiency with respect to the commercial catalysts. In this work, an extensive investigation of the catalytic activity of full scale PROMETHEUS fresh and aged catalyst deposited on ceramic cordierites is presented and discussed. The catalytic activity was tested on an Synthetic Gas Bench (SGB) towards the oxidation of CO and CH4 and the reduction of NO. The loading of the washcoat was 2 wt% (metal content) on Cu, Pd, Rh with the corresponding metal ratio at 21:7:1. The concentration of the full-scale monolithic catalysts to be 0.032% total PGM loading for meeting Euro III standard and 0.089% for meeting Euro IV to Euro VIb standards. The catalytic activity of all catalysts was tested both in rich-burn (λ = 0.99) and lean-burn conditions (λ = 1.03).

PROMETHEUS: A Copper-Based Polymetallic Catalyst for Automotive Applications. Part I: Synthesis and Characterization.

According to the strict European exhaust emissions standards that have been imposed by European legislation there is an elevated need for the decrease of the toxic gas emissions from vehicles. Therefore, car manufacturers have implemented a series of catalytic devices in the aftertreatment of the engine to comply with the standards. All catalytic devices (such as three-way catalysts, diesel particulate filters and diesel oxidation catalysts) accumulate concentrated loading of platinum group metals (PGMs, platinum, palladium, rhodium) as the active catalytic phase. Thus, the demand for PGMs is constantly increasing with a subsequent increase in their market prices. As a result, the research on catalytic converters of high activity and reduced cost/PGM loading is of great interest. In the present work, the Prometheus catalyst, a polymetallic nanosized copper-based catalyst for automotive emission control applications, is presented in two different metal loadings (2 wt% and 5 wt%) and metal ratios (Cu/Pd/Rh = 21/7/1 and Cu/Pd/Rh = 21/7/3). For the first time, a three-metal (copper, palladium, rhodium) nano-catalyst has been synthesized and characterized on a large scale. By using copper as an active catalytic phase, a reduction of PGMs loading is achieved (up to 85%) resulting in a novel catalytic device with similar or improved catalytic performance compared to commercial ones. The Prometheus catalyst is prepared by a wet impregnation method, using as a carrier an inorganic mixed oxide (CeZrO4) exhibiting elevated oxygen storage capacity (OSC). The heterogeneous catalytic powders produced were characterized by both spectroscopic and analytical methods. The metal content and ratio were determined by inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF) and energy-dispersive X-ray spectroscopy (EDS). The morphology and the catalyst particle size were determined with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The investigation revealed homogeneous particle formation and dispersion. The deposition of the metal nanoparticles on the porous inorganic carrier was verified with N2 sorption. Catalytic performance and reactivity of a catalyst (pure wash coat) with molar ratio 21/7/1 and a full-scale Prometheus catalyst with the desired loading of 15 g/ft3 were tested on an in-house synthetic gas bench (SGB) for the abatement of CO, CH4 and NO, both presenting high catalytic activity.

Nanoparticle Ex-solution for Supported Catalysts: Materials Design, Mechanism and Future Perspectives.

Supported metal catalysts represent one of the major milestones in heterogeneous catalysis. Such catalytic systems are feasible for use in a broad range of applications, including renewable energy devices, sensors, automotive emission control systems, and chemical reformers. The lifetimes of these catalytic platforms depend strongly on the stability of the supported nanoparticles. With this regard, nanoparticles synthesized via ex-solution process emphasize exceptional robustness as they are socketed in the host oxide. Ex-solution refers to a phenomenon which yields selective growth of fine and uniformly distributed metal nanocatalysts on oxide supports upon partial reduction. This type of advanced structural engineering is a game-changer in the field of heterogeneous catalysis with numerous studies showing the benefits of ex-solution process. In this review, we highlight the latest research efforts regarding the origin of the ex-solution phenomenon and the mechanism underpinning particle formation. We also propose research directions to expand the utility and functionality of the current ex-solution techniques.

Recent advances in catalytic automotive emission control: Passive NO storage at low temperatures

AbstractIn the practical applications, a high portion of the NOx is emitted without purification in the cold start period of engine because the selective catalytic reduction (SCR) or NOx storage and reduction (NSR) catalysts are not warmed up. Passive NOx absorbers (PNA) were proposed earlier to store the NOx at low temperatures and release the stored NOx during warm‐up period when the SCR and NSR catalysts downstream are functional, while this concept just attracted great interests recently to meet the extra stringent requirement of governmental emissions regulations. A plant of PNA catalysts, showing different NO adsorption/release characteristics, was disclosed. This review summarizes the recent progress in the development of PNA catalysts. The characteristics of NO adsorption/release on precious metal (i.e., Pt, Pd) loading Al2O3 support catalysts, CeO2 support catalysts, and zeolite support catalysts are summarized and compared.

Single-atom site catalysts for environmental catalysis

In recent decades, the environmental protection and long-term sustainability have become the focus of attention due to the increasing pollution generated by the intense industrialization. To overcome these issues, environmental catalysis has increasingly been used to solve the negative impact of pollutants emission on the global environment and human health. Supported platinum-metal-group (PGM) materials are commonly utilized as the state-of-the-art catalysts to eliminate gaseous pollutants but large quantities of PGMs are required. By comparison, single-atom site catalysts (SACs) have attracted much attention in catalysis owing to their 100% atom efficiency and unique catalytic performances towards various reactions. Over the past decade, we have witnessed burgeoning interests of SACs in heterogeneous catalysis. However, to the best of our knowledge, the systematic summary and analysis of SACs in catalytic elimination of environmental pollutants has not yet been reported. In this paper, we summarize and discuss the environmental catalysis applications of SACs. Particular focus was paid to automotive and stationary emission control, including model reaction (CO oxidation, NO reduction and hydrocarbon oxidation), overall reaction (three-way catalytic and diesel oxidation reaction), elimination of volatile organic compounds (formaldehyde, benzene, and toluene), and removal/decomposition of other pollutants (Hg0 and SO3). Perspectives related to further challenges, directions and design strategies of single-atom site catalysts in environmental catalysis were also provided.

Framing Contests and Emerging Institutional Landscape for Automotive Emission Control

By conceptualizing institutional opportunity landscape as an unfolding emerging space that is shaped and reshaped within multiple actors’ framing strategies over time, this study in particular examine how framing contests unfold as a sequential process. Using a combined data set of semi-interviews and various sources of archival data, the findings add to the extant research by providing unique insights on how independent strategic actions of marginalized actors triggered social activists framing contests on automotive emission control unintendedly, as a consequence, disrupting the existing institutional opportunity structure.

A comparative study of Rh-only, Pd-only and Pd/Rh catalysts

With the increase in worldwide automobile usage and the tightening of associated emissions legislation, the total demand of PGMs for use in automotive emission control catalysts is growing. Reducing the amount of required PGM in automotive catalysts as well as maintaining or improving the associated catalytic performance is an area of significant focus. This work presents a comparative study of the catalytic activity of Pd-only, Pd/Rh and Rh-only catalyst systems with respect to CO, HC and NOx conversion. The Rh-only catalyst has been shown to have the potential to improve CO and NOx conversions when functioning as a downstream catalyst compared with a Pd/Rh catalyst as well as reducing the usage of precious metals. In addition the formation of the three way catalysis by-products N2O and NH3 in different catalyst systems was investigated. The temperature of N2O and NH3 formation was shown to correlate with NOx light off temperatures and to vary depending upon the catalyst system employed and ageing conditions. The Rh-only catalyst was shown to generate the highest amount of N2O and the Pd-only catalyst the highest amount of NH3.

Synergism of Iron and Platinum Species for Low-Temperature CO Oxidation: From Two-Dimensional Surface to Nanoparticle and Single-Atom Catalysts.

CO oxidation is one of the most studied reactions in heterogeneous catalysis. It is present in air cleaning and automotive emission control. It also participates in the removal of CO from streams of hydrogen used in fuel cells. Because of the competitive adsorption of CO and O2 over active sites, the use of Pt-based catalysts for low-temperature CO oxidation remains a challenge. Recently, great progress has been made with catalysts containing Pt-Fe species because of the contribution of Fe species to O2 activation. The structure-activity relationship and reaction mechanisms have been investigated with various Pt-Fe catalysts. In this Perspective, we give a summary of the recent advances of low-temperature CO oxidation over Pt-Fe catalysts with a focus on the synergistic effect of Pt and Fe species in the CO and O2 activation of catalytic reactions. Future prospects for the preparation of highly effective Pt-Fe catalysts are also proposed.

Thermally Induced Restructuring of Pd@CeO2 and Pd@SiO2 Nanoparticles as a Strategy for Enhancing Low-Temperature Catalytic Activity

Retaining high catalytic activity after exposure to elevated temperatures remains a crucial challenge for applications such as automotive emissions control. While catalysts generally sinter and los...