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Three‐way catalysis represents a pivotal technology for converting automobile exhaust pollutants into non‐toxic gases. Substituting some noble metals with transition metals is considered a promising way to reduce catalyst costs. Herein, we have investigated the catalytic potential of different configurations of Pd−Cu catalysts prepared by impregnation (PdCu/MA), sol‐gel (PdCu‐MA), impregnation with physical mixing (Pd/Cu/MA) and sol‐gel with physical mixing (Pd/Cu‐MA) to modify the interaction of Pd/Cu and MgAl1.82Ce0.18O4 (MA) spinel in this comparative study. The different structures in these catalysts lead to different catalytic performances. PdCu/MA exhibits the best three‐way catalytic performance, which owe to the small‐sized PdCu particles with high Pd2+ content (45.3 %) and optimal interaction of Pd/Cu particles and MgAl1.82Ce0.18O4 support. Furthermore, comprehensive CO‐DRIFTS, H2‐TPR, and O2‐TPD analyses discover that the metal‐support interaction is beneficial to enhance the catalytic performance in three‐way catalysis. Overall, we demonstrated that the interaction between PdCu bimetals and support can regulate the electronic state of Pd, thereby enhancing the use and efficiency of noble metals. [ABSTRACT FROM AUTHOR]

Copyright of Precious Metals / Guijinshu is the property of Precious Metals Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A multi-layer membrane has been fabricated to integrate a Three-Way Catalyst (TWC) and Gasoline Particulate Filter (GPF) into one device, called a four-way catalytic converter. The top layer, made of nano-scale potassium catalyst particles, traps Particulate Matter (PM) with almost 100% filtration efficiency at all times and oxidizes PM (mostly soot) with a significantly reduced temperature of 476°C at the oxidation peak. Moreover, the bottom layer catalyst is comprised of sub-micro TWC particles to combine NO reduction and CO oxidation capabilities. The effective temperature range for the simultaneous removal of all pollutants was between 420°C–500°C. [ABSTRACT FROM AUTHOR]

Methane is one of the main components of automobile exhaust and has 25 times higher greenhouse effect than CO2. Methane is difficult to be purified by three-way catalyst (TWC) because of its stable chemical property. However lean / rich lambda oscillation improves methane purification rate. In this study we clarified CO, NO, and H2O in the exhaust and CeZr oxide in catalyst play a crucial role in improving the methane purification rate under lambda oscillation. [ABSTRACT FROM AUTHOR]

Three‐way catalysts (TWC) have been extensively studied and practically applied as a promising approach to mitigate vehicular exhaust emissions. However, the current TWC still suffer from issues such as the poor low‐temperature activity and stability. In this paper, the PdRh‐CeZrCo7 catalyst was synthesized by modifying CeZr solid solution with cobalt (Co) doping and PdRh bimetallic alloy loading. This catalyst exhibits superior TWC performance with T50 (temperature required to achieve a 50 % conversion rate) for CO, NO, and C3H6 at 172 °C, 175 °C, and 169 °C, respectively, and maintains excellent catalytic performance after 600 minutes of continuous TWC reaction at elevated temperatures. Experimental and mechanistic studies indicate that the doping of Co adjusts the electronic state of the support, exposes more oxygen vacancies, promotes the transition of the precious metal to the lower state, and then improves catalytic activity and stability for the TWC reaction. This work offers a viable strategy for the synergistic modulation of noble metals and composite oxide supports within the realm of TWC reactions, thereby significantly reducing environmental pollution associated with energy utilization. [ABSTRACT FROM AUTHOR]

This study aims to examine the particle number (PN) emissions of a retrofitted heavy-duty spark ignition (HD-SI) engine powered by liquefied petroleum gas (LPG) under both steady-state and transient conditions. The engine was tested under seven steady-state operating points to investigate the PN behavior and particle size distribution (PSD) upstream and downstream of the three-way catalyst (TWC). This analysis intends to assess the impact of including particles with diameters ranging from 10 nm to 23 nm on the total particle count, a consideration for future regulations. The study employed the World Harmonized Transient Cycle (WHTC) for transient conditions to encompass the same engine working region as is used in the steady-state analysis. A Dekati FPS-4000 diluted the exhaust sample to measure the PSD and PN for particle diameters between 5.6 nm and 560 nm using the TSI-Engine Exhaust Particle Sizer (EEPS) 3090. The findings indicate that PN levels tend to increase downstream of the TWC under steady-state conditions in operating points with low exhaust gas temperatures and flows (equal to or less than 500 °C and 120 kg/h). Furthermore, the inclusion of particles with diameters between 10 nm and 23 nm leads to an increase in PN emissions by 17.70% to 40.84% under steady conditions and by an average of 40.06% under transient conditions, compared to measurements that only consider particles larger than 23 nm. Notably, in transient conditions, most PN emissions occur during the final 600 s of the cycle, linked to the most intense phase of the WHTC. [ABSTRACT FROM AUTHOR]

As a clean and efficient advanced power generation equipment, the solid oxide fuel cell (SOFC) has the structural advantages of separation of air and fuel gas, which makes it easy to enrich the CO2 in the tail gas of the fuel side. In order to improve the CO2 concentration in SOFC anode tail gas, a steady-state multi-physical coupled model was established for the commercial three-way catalysts, considering the mass transfer, heat transfer, and chemical reaction processes in the catalytic combustion of SOFC anode tail gas. Based on this model, the catalytic combustion characteristics of SOFC anode tail gas were simulated. The effects of different inlet temperature, reaction space velocities and catalyst sizes on combustion temperature, wall temperature, H2 conversion, CO conversion and outlet CO2 concentration were studied, and the change trend of each parameter was obtained. Based on the existing experiments, the outlet CO2 volume fraction could be increased from 94.72% to 95.33% by optimizing the space velocity, and the outlet CO2 concentration could be increased from 94.72% to 95.64% by optimizing the catalyst size. By analyzing the variation characteristics of outlet CO2 concentration under different working conditions in the catalytic combustion of tail gas, the guidance for the commercial three-way catalyst to be used in the catalytic conversion of anode tail gas and CO2 enrichment in the tail gas of SOFC system was provided.

ABSTRACTMultimetallic nanoparticles (MNPs) have appeared as promising catalysts for important catalytic reactions such as three-way catalysis (TWC) due to their synergistic effects. Herein, a comprehensive process of preparing and evaluating MNPs and supported catalysts using high-throughput experimentation (HTE) for TWC is demonstrated. The synthesis of MNPs via a hot-injection method is performed using a homemade parallel reactor. The prepared MNPs are impregnated in parallel on alumina and examined for TWC. An in-house fixed-bed reactor equipped with a quadrupole mass spectrometer was employed for catalyst evaluation, taking advantage of the rapid screening of 20 catalysts and multiple reaction conditions. The overall HTE system can facilitate the synthesis and evaluation of 51 multimetallic catalysts for TWC in less than 2 weeks, and also appear to be a flexible and versatile system for other applications.

This study demonstrates the reaction behavior during the purification of model automotive exhaust gases over Pd catalysts before and after thermal degradation. In particular, to investigate the relationship between the Pd state and the reaction behavior of Pd/Al2O3 and Pd/CeO2−ZrO2 (CZ), operando X‐ray absorption spectroscopy measurements were performed during purifying exhaust gases over real and model catalysts mimicking the degradation of Pd particles and CZ supports after accelerated aging tests. The NO reduction activity of the aggregated Pd metal species was as high as that of the highly dispersed Pd species, but hydrocarbon (HC) poisoning was significantly enhanced by the aggregation of Pd metal particles caused by thermal aging. The existence of a three‐phase boundary (TPB) between the CZ, the Pd particles, and the gas phase strongly affected the catalytic activity at low temperatures, and the presence of a sufficient TPB facilitated the combustion of unburned HCs owing to the oxygen storage performance of CZ. Thus, the TPB reduced the poisoning of the precious metal surface by HC species at low temperatures. Therefore, the findings of this study will facilitate the development of next‐generation gas purification catalysts with high activity and durability. [ABSTRACT FROM AUTHOR]

CeO2-ZrO2-La2O3 supported Pt-Pd bimetallic three-way catalysts (0.6Pt-0.4Pd/CZL) were synthesized through the conventional impregnation method and then subjected to severe thermal aging. Reactivating treatments under different temperatures were then applied to the aged catalysts above. Three-way catalytic performance evaluations and dynamic operation window tests along with detailed physio-chemical characterizations were carried out to explore possible structure–activity evolutions during the reactivating process. Results show that the reactivating process conducted at proper temperatures (500~550 °C) could effectively restore the TWC catalytic performance and widen the operation window width. The suitable reactivating temperature ranges are mainly determined by the decomposing temperature of PMOx species, the thermal stability of PM-O-Ce species, and the encapsulation temperature of precious metals by CZL support. Reactivating under appropriate temperature helps to restore the interaction between Pt and CZL support to a certain extent and to re-expose part of the encapsulated precious metals. Therefore, the dynamic oxygen storage/release capacity, redox ability, as well as thermal stability of PtOx species, can be improved, thus benefiting the TWC catalytic performances. However, the excessively high reactivating temperature would cause further embedment of Pd by CZL support, thus leading to a further decrease in both dynamic oxygen storage/release capacity and the TWC catalytic performance after reactivating treatment. [ABSTRACT FROM AUTHOR]

Rh performance may not correlate with Rh particle size in automotive catalysts. Therefore, we studied the relation between Rh surface state and catalyst light-off performance by XPS analysis to find the cause. As a result, we found that there were metal Rh state, oxidized Rh state and highly oxidized Rh state in Rh surface state. In addition, we found that more metal Rh particles were produced by reduction treatment when the catalysts had both more oxidized Rh particles and less highly oxidized Rh particles. Furthermore, we found that Rh performance correlated with proportion of metal Rh particles. [ABSTRACT FROM AUTHOR]

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Oxidation enhancement by a Three-Way Catalyst (TWC) porous particles membrane filter was investigated through a comparison with a TWC solid particles one. The TWC porous particle was fabricated through agglomeration of TWC and PMMA nanometer-sized particulates and then pyrolysis of PMMA. It was confirmed that some pores are connecting from the surface to the center of the porous TWC particle by observation of the cross-sectional area using a scanning electron microscope. Using a temperature programed oxidation experiment by only CO (44 ppm, N2 balance) supply, the light-off temperature defined as a 50 % oxidation temperature by the TWC porous particles membrane filter is 149 °C which is lower than 182 °C by the TWC solid particles membrane filter though the total weight of TWC in the case of porous particles membrane is approximately 5 times smaller than that of solid one. This is because the specific surface area of the porous particle is more than 2 times larger than that of the solid one and all TWC material will be used effectively while the TWC material emerged inside of the particle is not used in the case of solid particle. [ABSTRACT FROM AUTHOR]

High exhaust temperature is an intrinsic nature of natural gas engines which underlies power de-rating and thermal aging of after-treatment system; therefore, this study integrates an organic Rankine cycle (ORC) system between engine and it's three-way catalyst (TWC) to address these challenges. ORC facilitates power output enhancement through exhaust energy recovery and alleviates thermal aging by reducing exhaust temperature. To estimate the effectiveness of this hypothesized system, a simulation-based investigation is performed. First, simulation models, including engine, TWC, and vehicle dynamic models, are built and validated by experimental data. According to the temperature characteristics of different TWCs, three scenarios, representing old, current, and prospective TWC technology, are formulated to estimate the ORC performance under Worldwide Harmonized Light Vehicles Test Cycle. Results show that ORC system can substantially alleviate the thermal damage caused by high exhaust temperature and extend TWC lifespan. It is estimated that over 98.5 % of thermal damage can be decreased by proper ORC setting, and the average TWC lifespan extension can be at least 55.4, making a reduced noble metal usage and cost of TWC. Meanwhile, with the decrease of the working temperature of TWC, ORC can recover exhaust energy under more road conditions, further improving the net power and shortening the payback period of extra ORC hardware costs. A reduction in the working temperature of TWC from 770.5 K to 618 K yields a 109 % enhancement in maximum power, coupled with a 62.30 % reduction in the payback period. These findings fully reflect the advantage of ORC-TWC coupling and indicate that ORC is supposed to be used more for the TWC with a low working temperature to maximize economic effectiveness. This study provides a novel pathway for thermal aging alleviation of TWC and a valuable reference for prospective studies on matching ORC with TWC under road conditions.

With the Euro 7 pollutant emission legislation currently under discussion, advanced and more efficient exhaust aftertreatment systems are being developed. The technologies required for these are leading to an increase in the number of components and control systems requiring diagnoses strategies under the on-board diagnostics (OBD) legislation. With concurrent shorter development times and significant reductions in budgets allocated to conventional powertrain development, challenges in the field of OBD calibration and verification are already rising sharply. In response to these challenges, hardware-in-the-loop (HiL) approaches have been successfully introduced to support and replace conventional development methods. The use of complex simulation models significantly improves the quality of calibrations while minimizing the number of required prototype vehicles and test resources, thus reducing development costs. This paper presents a feasibility study for moving OBD-related calibration and validation tasks from the vehicle to a HiL platform. In this context, the calibration and verification process of an active diagnostic for monitoring the condition of the three-way catalyst (TWC) and the oxygen sensors in the exhaust aftertreatment system is presented. It is shown that all relevant signals are simulated with sufficient accuracy to ensure a robust transfer from the vehicle to a HiL test bench. Special attention is given to the simulation of aged components and their influence on the emission behavior of the system. Furthermore, it is discussed that transferring OBD tasks from the vehicle to the HiL test bench could result in significant savings in development time and a reduction in the number of physical prototype vehicles and test resources required. [ABSTRACT FROM AUTHOR]

Three-way catalyst (TWC) is the mainstream technology for stoichiometric natural gas vehicle gas emission purification to meet the China VI emission standard for heavy-duty vehicles. Due to the high price of Pd-Rh TWC widely used at present, it is of great significance to develop cheaper Pt-only catalysts as substitutes. However, there are few studies on Pt-only TWC, especially for natural gas vehicles. It remains a formidable challenge to develop Pt-only TWC with excellent activity and stability. In this study, we significantly improved the catalytic performance of Pt/CeO2 TWC through thermal treatment, especially steam treatment at 800 °C, and used XRD, TEM, H2-TPR, and XPS techniques to investigate how Pt/CeO2 can be activated via these treatments. Our results suggested that after these treatments, CeO2 crystallites sintered slightly, while platinum particles remained highly dispersed. Moreover, these treatments also weakened the Pt-CeO2 interaction, promoted the formation of oxygen vacancies in CeO2 support, and generated a new type of active surface oxygen in the vicinity of Ptδ+, thus improving the activity of the catalyst. After 800 °C steam treatment, the T50 of CH4 and NO decreased by 31 and 36 °C, respectively. The results obtained in this study provide implications for the synthesis of efficient Pt-based catalysts. [ABSTRACT FROM AUTHOR]

Density functional theory is used to compare the catalytic performance of PtPdRhFeCo(100) high entropy alloy (HEA) three‐way catalyst (TWC) to the conventional Pt(100) in the NO reduction step during NH3 production that supplies to passive NH3‐SCR. Stronger adsorption of NO on the HEA(100) surface is beneficial to capture NO. During adsorption, the catalyst surface acts as an electron donor while the adsorbate is the acceptor on both HEA(100) and Pt(100) systems. Herein, the reaction mechanism of NO reduction can be classified into two steps: 1) NO activation and 2) product formation. During NO activation, direct NO dissociation is the preferable pathway on both HEA(100) and Pt(100) surfaces with the same Ea, whereas HNO and NOH pathways on HEA(100) are suppressed. For NH3, N2, and N2O production on HEA(100) is found to be more difficult than on Pt(100). However, the thermodynamic driving force of all reactions on HEA(100) is more spontaneous than on Pt(100). Also, the rate‐determining step on HEA(100) is found to be NH3 formation different from the Pt(100), while difficult H diffusion on HEA(100) is the key factor that reduces NH3 production. [ABSTRACT FROM AUTHOR]

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]

This study aims to examine the particle number (PN) emissions of a retrofitted heavy-duty spark ignition (HD-SI) engine powered by liquefied petroleum gas (LPG) under both steady-state and transient conditions. The engine was tested under seven steady-state operating points to investigate the PN behavior and particle size distribution (PSD) upstream and downstream of the three-way catalyst (TWC). This analysis intends to assess the impact of including particles with diameters ranging from 10 nm to 23 nm on the total particle count, a consideration for future regulations. The study employed the World Harmonized Transient Cycle (WHTC) for transient conditions to encompass the same engine working region as is used in the steady-state analysis. A Dekati FPS-4000 diluted the exhaust sample to measure the PSD and PN for particle diameters between 5.6 nm and 560 nm using the TSI-Engine Exhaust Particle Sizer (EEPS) 3090. The findings indicate that PN levels tend to increase downstream of the TWC under steady-state conditions in operating points with low exhaust gas temperatures and flows (equal to or less than 500 °C and 120 kg/h). Furthermore, the inclusion of particles with diameters between 10 nm and 23 nm leads to an increase in PN emissions by 17.70% to 40.84% under steady conditions and by an average of 40.06% under transient conditions, compared to measurements that only consider particles larger than 23 nm. Notably, in transient conditions, most PN emissions occur during the final 600 s of the cycle, linked to the most intense phase of the WHTC.

This work investigates oxygen-storage capacity (OSC) changes during thermal degradation in modern three-way catalysts. Two experiments are performed using catalysts with different degradation degrees to evaluate OSC and reaction rates. The CO2 production test, where CO and O2 are supplied at a constant temperature, shows decreased CO2 production with more degraded catalysts and reduced purification. The CO2 production test is conducted using transient temperature increases, showing that the maximum CO2 production temperature increases with catalyst degradation. The results reveal an increase in activation energy in the oxygen desorption reaction caused by thermal degradation progresses and a decrease in OSC, resulting in temperature increases in the oxygen storage reaction. In the surface reaction and mass transport model considering the 30 elementary reactions, the predicted results are well-validated for CO2 production, enabling good oxygen storage predictions based on actual data. These results can be used to predict OSC by formulating the changes in active site density and activation energy due to degradation.

Although most of the currently used solid catalysts possess a three‐dimensional structure of nanoparticles dispersed on a porous support, the nanoparticle structure should not be considered the optimal structure for all catalytic reactions due to some disadvantages such as thermal instability and catalyst poisoning. Herein, we present the unique catalytic performance of a two‐dimensional metal foil‐supported nanometric Rh thin film, referred to as the "Rh overlayer", for a catalytic CO−NO reaction and a stoichiometric three‐way catalytic reaction under practical conditions. The extremely high turnover frequency for NO reduction using two‐dimensional Rh is a key to understanding this phenomenon, the detailed mechanism of which can be explained by theoretical calculations. [ABSTRACT FROM AUTHOR]

This study investigated the redox behaviour of Rh in three‐way catalysts (TWC) using time‐resolved in situ diffuse reflectance UV‐vis spectroscopy in different modes with air‐to‐fuel ratio (A/F) step, A/F perturbation, and temperature ramping. When Rh/ZrO2−CeO2 (Rh/ZC) and Rh/ZrO2 (Rh/Z) containing fully oxidised Rh were treated at 400 °C under simulated TWC conditions with A/F stepping from 15.0 (fuel‐lean) to 14.1 (fuel‐rich), a steep increase in the metallic fraction (Rh0/Rh) and a simultaneous increase in Kubelka–Munk function (ΔKM) at λ=450 nm occurred near the stoichiometric point (A/F=14.6). Metallic Rh became abundant until A/F=14.1, where the largest ΔKM was attained. In the A/F perturbation mode, the Rh oxidation state fluctuated with repetitious switching of rich and lean gas feeds, but the ΔKM oscillation amplitude was lessened for Rh/ZC compared to Rh/Z because of the oxygen‐scavenging function of ZC. Furthermore, the changes in Rh oxidation state during TWC light‐off were analysed in the temperature‐ramping mode. Under rich conditions, Rh0/Rh and ΔKM increased after 200 °C, where the formation of Rh metal led to efficient conversions of CO and NO. However, metallic Rh did not appear during light‐off under the lean condition, where NO conversion was negligible. [ABSTRACT FROM AUTHOR]

Modification of the applied Pt-containing catalysts with rare-earth metals is one of effective ways to increase their activity and resistance to thermal deactivation, which is associated with both an increase in thermal stability of the texture and structure of the carrier material and an increase in the degree of dispersion and resistance to sintering of the applied platinum metals (PM) when exposed to high temperatures. Conflicting data make it difficult to select a suitable modifier for the use as part of a three-way catalyst in the exhaust treatment system of gasoline-powered cars, whose function is to simultaneously convert CO, CxHy and NOx. In this work, the effect of europium-modified Pt-containing γ-Al2O3 -based catalyst on its physicochemical properties and activity in the oxidation of CO, CxHy, and NOx reduction processes was evaluated. The catalytic activity was evaluated by passing a gas mixture simulating the exhaust of a gasoline-powered car through the catalyst applied onto the surface of a cylindrical honeycomb block with simultaneous measurement of the degree of conversion of toxic components into relatively non-toxic CO2, N2 and H2O in the temperature range from 1000C to 4000C. The modification of the Pt/γ-Al2O3 catalytic system with europium was shown to enhance the activity in all three reactions studied, indicating a great potential for the use as a modifier of a three-way catalyst. [ABSTRACT FROM AUTHOR]

Nanometric metal overlayer catalysts have been developed as novel catalyst structures with high three-way catalytic performance for practical applications. The metal overlayer is prepared via a dry process using pulsed arc plasma deposition, unlike wet coating processes for conventional powder catalysts containing nanoparticles. The key point to achieving high performance is the extremely high turnover frequencies for specific chemical reactions catalyzed by a large two-dimensional surface compared with metal nanoparticles. This overview study presents the preparation, structure, performance, reaction mechanism, and thermal stability of metal overlayer catalysts, focusing on rhodium (Rh) and catalytic conversion of nitric oxide (NO). Rh plays a pivotal role in the reduction of NO to N2 in automotive three-way catalytic converters. The potential benefit of the overlayer structure is the minimum loading of precious metal, such as Rh, which is limited and expensive. [ABSTRACT FROM AUTHOR]

Over the past decade, the three-way catalyst (TWC) has become a critical technology for reducing pollutant emissions from gasoline-powered vehicles. Due to the global rise in the number of vehicles and limited resources, it is necessary to operate a TWC at high space velocities (SVs) to minimize the usage of expensive metals and reduce catalyst consumption. However, the mass transfer limitation within the nanostructure of TWC particles hinders the full utilization of their active surfaces, limiting their performance, particularly at high SVs. To address this challenge, our study focused on the development of particles derived from TWC nanoparticles with a hierarchically ordered macroporous structure via a template (polymer–particle)-assisted spray method, followed by a reheating process. Spherical catalyst particles with a macropore size of approximately 150 nm and a specific surface area of 79.9 m2 g–1 were successfully synthesized by optimizing the reheating conditions (i.e., temperature and time). The catalytic evaluation of the model reaction (CO oxidation) revealed that the TWC particles with the macroporous structure exhibited better catalytic performance than those without the structure (i.e., aggregate structures and nanoparticles). This improvement can be attributed to the enhancement of the mass transfer efficiency induced by the macropores. Our findings provide valuable insights for developing efficient material structures for future catalysts. [ABSTRACT FROM AUTHOR]

Methane (CH4) is one of the main constituents of the exhaust gas emitted by compressed natural gas (CNG) vehicles. CH4 has 25 times higher greenhouse effect than CO2. Furthermore, it is difficult to be purified by a three-way catalyst (TWC) because of its chemical stability. In this study we clarified that lean / rich lambda oscillation improves CH4 purification by contribution of oxygen storage capacity (OSC) of TWC. In addition, we investigated the mechanism of CH4 purification improvement by in situ FT-IR analysis. [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]

Copyright of Precious Metals / Guijinshu is the property of Precious Metals Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Full-scale monolithic three-way catalysts (TWCs) comprising Rh, oxygen-scavenging ZrO2–CeO2 (ZC), and γ-Al2O3 as a binder component were studied after real engine aging. The fatal irreversible deactivation that occurred under stoichiometric-lean-rich perturbation at 1000 °C for 40 h (SLR aging) was attributed to the complete encapsulation of Rh nanoparticles by ZC, leading to the physical blockage of gas adsorption. Preaging the catalyst under a rich condition at 1000 °C for 40 h (R aging) drastically mitigated this deactivation, i.e., the catalyst with R–SLR combined aging sustained its catalytic performance much better than the catalyst with SLR aging at the same temperature (1000 °C) and total time (80 h). X-ray mapping and high-temperature environmental electron microscopic analyses suggested that R aging promoted the migration of Rh nanoparticles across the ZC surface toward the boundary with the Al2O3 binder. Owing to the strong bonding with the Al2O3 surface, Rh nanoparticles were trapped at or near the boundary. Consequently, these Rh nanoparticles were unlikely to be fully covered by ZC even under the SLR aging condition because the encapsulation was induced through repetitive oxygen release/storage cycles at the Rh/ZC interface. Thus, we propose that Rh nanoparticles in contact with ZC and Al2O3 played crucial roles to hinder the encapsulation caused by SLR aging at 1000 °C. Rh nanoparticles supported on the dual-oxide support of ZC and Al2O3 were subjected to engine aging and chassis dynamometer tests. The deterioration extents of the TWC and oxygen storage capacity performances were successfully mitigated using this dual-oxide support formulation. [ABSTRACT FROM AUTHOR]

Precious metals, including Rh, are used practically in three-way catalytic converters of automobiles. An important role of Rh is the reduction of NOx to N2. Gas-phase clusters are used to study reactions relevant to heterogeneous catalysts because it is possible to define and detect the number of atoms included in the cluster and to obtain atomiclevel insights into the reactions. We have studied the adsorption forms of NO molecules on metal clusters by using infrared multiple photon dissociation (IRMPD) spectroscopy. We found that NO molecules adsorb on metal clusters molecularly or dissociatively depending on the element and the size of the clusters. For instance, NO adsorbs on Rhn+ clusters mainly in the molecular form (＞95％ on Rh6+), while more NO adsorbs dissociatively on Irn+ clusters (～50％ on Ir6+). In this review, the methodology and results of the identification of NO adsorption forms on Rh and related clusters are presented. [ABSTRACT FROM AUTHOR]

Most vehicle tailpipe emissions are related to the cold-start condition. In the present study, a novel methodology is introduced to trap the cold-start emissions. A numerical model is used to investigate the method implementation on the vehicle's cold-start emissions. Model is validated with the experimental data. Three different driving cycles are simulated to understand the effects of the employed method. The results show that the light-off temperature is independent of the driving cycle, while the light-off time is highly dependent on the driving behavior. The presented concept is more effective for traffic conditions and the low required powers of the vehicle. The most emission reduction is related to the emissions with moderate increment after catalyst light off. Therefore, the most considerable reduction is related to the NOx emission in all driving conditions, while method implementation is not beneficial for CO reduction compared to NOx. The emission reduction varies from 20% (WLTC) to 35% (NEDC) for CO emission, from 25% (WLTC) to 34% (NEDC and FTP75) for HC emission and 41% (FTP75) to 51% (NEDC) for NOX emission. This idea would help gasoline-powered vehicles to pass more strict emissions such as Euro7 in the coming future. [ABSTRACT FROM AUTHOR]

Fueling a compression-ignition engine with premixed natural gas offers the potential to combine a clean-burning, low-carbon fuel with a high compression ratio, high-efficiency engine. This work describes the development of a multi-cylinder 6.7 L diesel engine converted to run stoichiometric diesel micro-pilot/ natural gas premix combustion with a maximum diesel contribution target of 5% of the total fuel energy and a three-way catalyst aftertreatment system. Results are given by comparing the stoichiometric combustion to the diesel baseline operation, showing combustion characteristics differences, including the rapid two stage heat release. A high load output of 23 bar brake mean effective pressure was obtained with diesel-like brake thermal efficiency of 41%. This operating condition enabled a brake specific CO2 emissions reduction of up to 25% when compared to diesel. It was observed that the low load output is limited by combustion stability when operated at stoichiometric condition. The three-way catalyst is observed to run at peak efficiency with an equivalence ratio of 1.01. Injector fouling was observed through the inspection of the nozzle and its internal parts, indicating carbon build-up similar to that seen in injector coking mechanisms. A comparison of the developed engine to other engine technologies is given, showing that the diesel micro-pilot natural gas engine performance is in good standing among other diesel and gas engines in the market. [ABSTRACT FROM AUTHOR]

Emission reduction at cold start is a common challenge on gasoline engine vehicles even in recent years with advanced technologies. Focusing on an emission purification system used in series hybrid vehicles, optimal measures that can reduce emissions with less energy were investigated by numerical simulations, where a three-way catalyst purification reaction model that was verified to reproduce experimental results accurately was adopted and functionalized as an electrically heated catalyst. [ABSTRACT FROM AUTHOR]

A three-way catalyst (TWC) and a TWC with a NOx storage component (NS-TWC) were evaluated on a lean spark ignition (SI) engine platform to reduce the fuel consumption and emissions of a passive selective catalytic reduction (pSCR) emission control system. The pSCR system is an approach for controlling NOx emissions from lean SI engines. It relies on onboard NH3 generation over a TWC during brief periods of fuel-rich operation. The NH3 is then stored on a downstream SCR catalyst and is available for NOx reduction during subsequent periods of lean engine operation. The NS-TWC addition enabled longer lean operation and more efficient NH3 use, which lowered fuel penalty of the pSCR system. Over a pseudo-transient drive cycle, the lean SI engine with pSCR that included NS-TWC demonstrated a 8.3% reduction in gasoline consumption over stoichiometric-only engine operation, and the NOx and non-CH4 organic gas emissions were consistent with Environmental Protection Agency (EPA) Tier 3 levels. The CO emissions, primarily from rich operation, exceeded the EPA Tier 3 levels. A cleanup catalyst (CUC) with high oxygen storage capacity was used to oxidize tailpipe CO during rich excursions by using the stored oxygen from the preceding lean operation. Although the CUC decreased CO emissions and reduced NH3 slip, some of the NH3 was converted back to NOx. Furthermore, rich CO control remains challenging. The results of this work demonstrate significant improvement in fuel consumption and emissions with a modified pSCR system architecture.

With the Euro 7 pollutant emission legislation currently under discussion, advanced and more efficient exhaust aftertreatment systems are being developed. The technologies required for these are leading to an increase in the number of components and control systems requiring diagnoses strategies under the on-board diagnostics (OBD) legislation. With concurrent shorter development times and significant reductions in budgets allocated to conventional powertrain development, challenges in the field of OBD calibration and verification are already rising sharply. In response to these challenges, hardware-in-the-loop (HiL) approaches have been successfully introduced to support and replace conventional development methods. The use of complex simulation models significantly improves the quality of calibrations while minimizing the number of required prototype vehicles and test resources, thus reducing development costs. This paper presents a feasibility study for moving OBD-related calibration and validation tasks from the vehicle to a HiL platform. In this context, the calibration and verification process of an active diagnostic for monitoring the condition of the three-way catalyst (TWC) and the oxygen sensors in the exhaust aftertreatment system is presented. It is shown that all relevant signals are simulated with sufficient accuracy to ensure a robust transfer from the vehicle to a HiL test bench. Special attention is given to the simulation of aged components and their influence on the emission behavior of the system. Furthermore, it is discussed that transferring OBD tasks from the vehicle to the HiL test bench could result in significant savings in development time and a reduction in the number of physical prototype vehicles and test resources required.

A nanometric Rh overlayer exhibits excellent three-way catalytic activity under stoichiometric conditions. However, dynamic changes in the air-to-fuel (A/F) ratio under experimental conditions deteriorates the catalytic activity caused by the lack of oxygen storage/release capability of Rh. In this study, we first report that the surface modification of the Rh overlayer by a small amount of Ce using a sequential metal deposition technique based on the pulsed arc-plasma method enhances its three-way catalytic activity under A/F perturbation conditions. X-ray photoelectron spectroscopy and X-ray absorption fine structure measurements revealed that the redox behavior of the surface Ce contributed to an oxygen storage/release and buffered the A/F change. The Ce-modified Rh overlayer with a metal honeycomb structure exhibited high activity for the three-way catalytic reaction even under A/F perturbation conditions at high space velocity. This novel catalytic converter is expected to be significantly process and energy saving compared to the conventional catalytic converter. Thus, the oxygen storage/release performance, heat resistance, and low-temperature activity can be improved by controlling the surface composition. [Display omitted] • Sequential metal deposition technique based on pulsed arc-plasma method. • Surface of the Rh overlayer was modified by a small amount of Ce. • Redox behavior of the Ce contributed to an oxygen storage/release. • Ce-modified Rh overlayer exhibited high activity for three-way catalytic reaction. [ABSTRACT FROM AUTHOR]

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A membrane filter was fabricated using gas dispersant micro-sized Three-way Catalyst (TWC) particles on the conventional filter substrate. The porosity of the cross-sectional area of the TWC-membrane was measured through electron microscopy image processing technique. In the membrane manufacturing process, a parametric study was conducted by comparing three mean particle sizes under three superficial velocities. According to high resolution electron micrographs, the cross-sectional view of a single TWC-particle was revealed as a homogeneously agglomerated particle. The porosity of the cross-sectional area of the membrane was measured as approximately 64.4% with a slight difference about 3% depending on varying mean particle sizes and superficial velocities. [ABSTRACT FROM AUTHOR]

This paper presents the results of technological development research to safely and efficiently reduce substances contained in combustion emissions, which may impair the growth of crops and the health of workers, below the permissible limit. There are carbon monoxide and nitrogen oxides. Agricultural crop production factories, including greenhouses and glass greenhouses, may use the combustion emissions of hydrocarbon fuels as a carbon dioxide source to promote photosynthesis. In this study, the upper limit concentration of chemical substances permitted for emissions of the gas-fired water heater was calculated by model calculation, and it was set as the target purification. (1) A system using catalyst and air dilution was constructed, and it was shown that the target purification was satisfied. (2) The constructed combustion emissions purification system was verified under automatic cultivation operation of lettuce for eating raw. It was confirmed that the quality and yield of the fertilization method were equivalent to those of the vaporization type carbon dioxide fertilization method, and that the system exerted its effect stably. [ABSTRACT FROM AUTHOR]

A novel approach to optimize the cold start performance of Pd- and Pt-based three-way catalysts in stoichiometric natural gas engine tailpipes is presented, utilizing temperature-dependent frequency control of lambda switches. In comparison to Pt/Al 2 O 3 , Pd/Al 2 O 3 exhibits a lower optimal frequency at the same inlet temperature, which can be attributed to the differing noble metal-specific adsorption–desorption energies of CO and O, which can inhibit the catalytic activity by surface poisoning, lower exothermicity evolving due to its lower catalytic activity and its higher oxygen storage capacity. Catalyst operation at a fixed frequency during light-off resulted in improved pollutant conversion only within a specific temperature range and relevant NH 3 slip was observed at elevated temperatures compared to conventional stoichiometric steady-state operation. In contrast, controlling the frequency as a function of the catalyst inlet temperature enabled a substantial decrease of the light-off temperature of CH 4 and NO x and an increase in N 2 selectivity. [Display omitted] • T 50 of CH 4 and NO x conversion can be decreased by 60 K and 335 K on Pd/Al 2 O 3. • T 50 of CH 4 and NO x conversion can be decreased by 120 K and 210 K on Pt/Al 2 O 3. • Optimal frequency depends on different adsorption–desorption energies. • Optimal frequency depends on the applied gas mixtures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inhibition and thermal durability affect Pd/CeO 2 activity during gasoline cold start. • Representative catalyst testing and redox ageing is needed during catalyst development to probe inhibition and thermal durability. • Complex gas mix testing with inhibitors aims to replicate the actual gasoline exhaust stream. • Hydrothermal ageing is not representative of conditions on a gasoline vehicle. This paper shares with the academic community crucial considerations for laboratory research of components for TWCs during cold start operation. Model Pd/CeO 2 catalysts demonstrate the importance of testing in realistic gas mixtures and after harsh, perturbed ageing to accurately understand the limitations of these systems such as inhibition and thermal durability. Notably, the testing gas feed must be representative of a gasoline exhaust by including inhibiting species such as hydrocarbons, water and NO. Catalyst ageing protocols must use these complex gas mixtures whilst perturbing between lean and rich conditions at high temperatures in order to more closely mimic the conditions experienced by the catalyst on a gasoline vehicle. CeO 2 sintering is accelerated under rich (reducing) conditions and thus occurs to a greater extent during realistic redox ageing compared to simple lean (oxidising) hydrothermal ageing. Future studies that adopt the testing and ageing guidelines shared herein will accelerate the development of the next generation of gasoline autocatalysts. [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]

In view of the increasingly stringent emission regulations, the automotive sector needs considerable support from the development of robust and reliable engine and aftertreatment models. Accurate reproduction of engine-out and tailpipe pollutants plays a crucial role in complying with these legislations. Given the difficulty in characterizing some critical phenomena, frequently caused by strong dynamics and related to experimental uncertainties, communication between several calibrated and reliable models is mandatory. This is certainly valid for powertrains that will be powered with alternative gas fuels such as natural gas, bio-methane and hydrogen in the future. This paper describes a methodology to co-simulate a 1D CNG HD 6-cyl engine model and a 1D quasi-steady Three-Way Catalyst model in a global framework for high-fidelity virtual prototyping of the vehicle system. Through the implementation of a dedicated control logic in MATLAB/Simulink, the modeling architecture allows for the reproduction of the engine performance parameters together with the evaluation of the TWC pollutants' conversion efficiency. An extensive database of experimental tests was used to assess the model response. The latter was validated in multiple steady-state operating conditions of the engine workplan. Using a semi-predictive combustion model, the validation was carried out over a wide range of different air-to-fuel ratios and during fast rich/lean transitions to evaluate the formation and conversion phenomena of the main chemical species, both engine-out and tailpipe. Subsequently, the complete model was validated in dynamic conditions throughout a WHTC, accurately reproducing the cut-off phases and their sudden accelerations. The numerical–experimental agreement on pollutant reproduction is generally good and globally below 3%. Larger deviations occur in extremely rich conditions and in CH4 emission evaluation due to the lack of information related to the combustion process and chemical mechanisms involving the Pd surface. [ABSTRACT FROM AUTHOR]