Exhaust Catalysts Research Articles

Graphene-Based Material Supports for Ni- and Ru- Catalysts in CO2 Hydrogenation: Ruling out Performances and Impurity Role.

Laboratory-prepared Gnp using molten salt, commercial Gnp and reduced graphene oxide (rGO) have been characterized and utilized as support for CO2 hydrogenation catalysts. Ni- and Ru- catalysts supported over Gnp, commercial Gnp and rGO have been deeply characterized at different stages using Raman, IR, XRD, FE-SEM-EDXS, SEM-EDXS, XPS, and TEM, also addressing carbon loss before reaction and evolved species, thus allowing a better comprehension of the produced materials. Ni and Ru/rGO were inactive while Gnp-supported ones were active. Ru has been found almost completely selective toward reverse Water Gas Shift to CO, approaching the forecasted thermodynamic equilibrium at 723 K, in the tested conditions (YCO~55 %), with an apparent activation energy in the range of 70-90 kJ/mol. Exhaust catalysts pointed out the presence of sulfur partially linked to the carbon matrix and partially producing the corresponding metal sulfide with the detection of surface oxidized species in the cationic form and adsorbed species as well. The metal-based nanoparticles displayed a quite narrow size distribution, confirming the promising behavior of these catalytic systems for CO2 utilization.

Analysis of Dimethylsiloxanes in Hydrocarbon Matrices like Marine Fuels Applying a Novel Enrichment Procedure and a Two-Column Gas Chromatography – Mass Spectrometry Measurement

Marine fuels are consumed worldwide in quantities of more than 200 million tons per year. It is not a uniform product, but rather heterogeneous mixtures of hydrocarbons with a wide range of viscosities. Due to the production processes, marine diesel contains dimethylsiloxanes. These lead to damage to marine exhaust catalysts in connection with combustion reactions in the ships’ engines. A novel analytical method, presented here, was developed that allows to investigate these processes and to monitor the dimethylsiloxane contents in complex marine fuel matrices. The key steps of the analytical procedure are analyte enrichment by solid phase extraction (SPE) using thermally activated silica gel and chromatographic separation and measurement by heart-cutting gas chromatography - mass spectrometry. Authentic reference substances for quantification by standard addition are used for the dimethylsiloxane analytes. The clean-up enabled a 90% reduction of the matrix content in the analysis solutions compared to the initial sample. Recovery rates in the range of 87.8% to 111.4% were determined for all analytes (Si3 to Si9). The detection limits of analytes ranged from 0.06 μg/L to 5.68 μg/L. Values of 0.71 μg/L to 23.6 μg/L were determined for the limits of quantification. The newly designed analytical method was successfully applied to real marine fuel samples. The analytical procedure is to be made available to commercial and industrial laboratories as a practical method for controlling siloxane contents in marine fuels to contribute this way to efficiently functioning marine exhaust gas purification.

Improving the anti-coking ability in the Ni-M(M = Ce, Zr, Co)@SiO2 yolk-shell catalysts for dry reforming of methane

Dry methane reforming (DRM) represents a highly promising approach to greenhouse gas conversion (CO2 and CH4) to valuable byproducts. However, severe carbon deposition and catalyst deactivation inhibit large-scale applications. The work designed new catalysts with a yolk-shell structure using the water-in-oil microemulsion method. The catalysts were composed of a yolk-shell structure, with Ni-M as the active point and silica as the shell. The catalytic performance evaluation indicates that the Ni-M @SiO2 catalysts show higher CH4 and CO2 conversion compared with the Ni@SiO2 and conventional catalysts at 750 ℃, suggesting the yolk-shell structure and added M species enhance the DRM activity. The XRD, HRTEM, XPS, BET, H2-TPR, and CO2-TPD analysis confirmed the existence of yolk-shell configuration and evident electronic effect among Ni, M species, and SiO2. The long term measurements indicate that the added M species also bring higher carbon deposition tolerance for DRM, where Ni-Ce@SiO2 and Ni-Zr@SiO2 exhibit good structural and catalytic stability for DRM over 100 h. Through XRD, TEM, and TGA characterizations of the exhausted catalysts, it is determined that the coke deposition resistance of the catalyst is improved as a result of increased oxygen mobility and enhanced Ni dispersion on the catalytic surface, both of which are enhanced by the added Ce species. The structural analysis of the spent catalysts indicates that the tolerance of carbon deposition is improved by the yolk-shell samples. This study can offer valuable insights for the development of Ni-based catalysts with exceptional carbon deposition capability for DRM.

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis

BackgroundDriven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. ResultsIn this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SignificanceThis analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

Recovery of Platinum Group Metals from Spent Automobile Exhaust Catalysts

Recovery of Platinum Group Metals from Spent Automobile Exhaust Catalysts

Intermetallic based materials for Sabatier reaction: Surface understanding, performance assessment and comparison with commercial catalyst

Ni-based intermetallics and commercial CO2 hydrogenation catalysts have been compared in Sabatier’s reaction. For RENi5 intermetallics (RE = La, Ce), the analysis of the chemical bonding shows a charge transfer from the RE to the Ni species and the formation of polar two- and four-atomic RE-Ni and four-atomic Ni bonds. Surface simulations and chemical understanding based on the ELI-D mapping approach indicate that dangling bonds originate from the multi-atomic ones and they are the preferred adsorption sites for H2 molecules. This leads to H2 dissociation, its reduction to hydrides, Ni QTAIM-anion oxidation to the metallic state, and diffusion toward the surface. LaNi5 is active toward rWGS while the best catalytic activity is obtained over CeNi5 (49% methane yield) at 723 K; the exhaust catalyst is composed of Ni particles supported over CeO2 with a mean size of 10 nm and thus, promising material could be developed on intermetallic based compounds.

Novel Concentration Process for Platinum Group Metals in Automotive Exhaust Catalyst Using Electroless Copper Plating, Sulfurization, and Flotation

Platinum group metals (PGMs) are primarily used in automotive exhaust catalysts (autocatalysits). Spent autocatalysts are the most important secondary resource for PGMs. However, transporting autocatalyst scraps and recovering PGMs from the scraps are costly and time-consuming, owing to the low PGM content in spent autocatalysts. Thus, an effective PGM-concentration technology for the pretreatment of scrap prior to transport is required. This study develops a new pretreatment technique that is applied prior to the flotation concentration of PGMs in autocatalysts. This method utilizes electroless Cu plating followed by sulfurization. In the electroless Cu-plating process, which uses glyoxylic acid as a reducing agent, Cu is deposited on the PGM particles in the washcoat of the autocatalyst. During the sulfurization process, S vapor sulfurizes the deposited Cu into copper sulfide, which is hydrophobic. Prior to the experiments, thermodynamic considerations were made to predict the reactivity of Cu and the representative elements constituting the autocatalyst with S vapor, and the sulfurization conditions were designed. Sulfurization experiments were performed at 850 K (577 °C) in the presence of carbon (C), and the results show the successful conversion of only Cu to copper sulfide without sulfurizing the representative oxides (MgO, Al2O3, SiO2, CeO2, and ZrO2) present in the autocatalyst. Finally, in the flotation process, the copper sulfide-coated PGMs are separated from the ceramic components of the autocatalyst, which is hydrophilic; thus, it is concentrated in the froth. Flotation experiments utilizing a microbubble flotation method were successfully performed to recover the PGM concentrates. This innovative pretreatment technique is expected to reduce the cost and time required for the entire PGM recycling process.

Performance evaluation of methane oxidation catalyst for marine gas-engine in actual exhaust and simulated gas

To reduce methane slip from marine gas engines installed in gas fuelled ships, it is necessary to understand the effects of exhaust composition and temperature on the activity of the methane oxidation catalysts in the marine gas engine exhaust. A comparative study was performed to evaluate catalyst performance in both actual engine exhaust and the simulated gas under the same flow conditions. The test using actual exhaust gas test showed that despite the lower exhaust temperatures during low load operation, the catalyst exhibited an extremely high performance, achieving approximately 100% CH4 conversion. In contrast, at high load, despite high exhaust temperatures, the CH4 conversion was decreased to 50-60%. In the simulated gas test showed that the catalyst’ activity was declined with increasing concentration of H2O and NO, whereas it was improved by CH4 and CO oxidation. The results showed that high CH4 concentrations under low load conditions enhanced catalyst activity owing to the exothermic reaction, which increased the catalyst temperature despite the low exhaust temperature and the presence of H2O vapour. Furthermore, during actual engine operation, the catalytic performance at a high load was improved by controlling the air excess ratio.

Heterogeneous catalytic ozonation of organic wastewater by using bimetallic catalysts supported on honeycomb‐structured activated carbon

AbstractHoneycomb‐structured activated carbon (HAC) is one of the most studied chemicals with large specific surface area, high porosity, unique adsorption properties, and other characteristics, which has been widely used in the fields of exhaust gas adsorption, wastewater adsorption, and catalyst support. However, the study and application of HAC in the field of wastewater treatment is not extensive. Herein, a novel HAC‐based bimetallic catalyst was prepared by incipient wetness co‐impregnation, which exhibited high catalytic activity in heterogeneous catalytic ozonation of methylene blue (MB) organic wastewater. A high MB removal of 95.43% and a chemical oxygen demand (COD) removal of 85.19% were achieved by using Cu‐La/HAC under optimized conditions. The inductively coupled plasma‐mass spectrometry (ICP‐MS) results showed that the metal dissolution concentration of Cu‐La/HAC was the lowest. Moreover, X‐ray photoelectron spectroscopy (XPS) characterization of copper‐containing catalysts indicated that the strong interaction between copper and lanthanum resulted in the low metal dissolution concentration.

Catalyst-heating operation in compression-ignition engines: A comprehensive understanding using large eddy simulations

Catalyst-heating operation in compression-ignition engines is critical to ensure rapid light-off of exhaust catalysts during cold-start. This is typically achieved by using late post injections for increased exhaust enthalpy, where retardability is constrained mainly by emissions due to inactivity of the oxidation catalyst at these conditions. Comprehensive understanding of formation mechanism of pollutant emissions is needed to optimize engine performance and minimize tailpipe harmful emissions. In this study, a computational fluid dynamics model of a medium-duty compression-ignition engine is developed and validated against with catalyst-heating operation experimental data using large eddy simulations. The engine is fueled with a full boiling-range diesel fuel and uses an optimized five-injections strategy that consists of two pilots, one main, and two post injections. Results show that, significant amounts of unburned hydrocarbons (UHCs) and oxygenated UHCs (OUHC) are formed by the pilot injections, which may persist until exhaust valve opening. UHCs accumulate mainly in the outer-upper part of the cylinder guided by the piston lip, in the inner-bowl due to the bowl geometry, near the injector nozzle by the fuel from the end-phase of injection, and in the space between spray plumes transported by the swirl motion. The main injection exhibits a short ignition delay and rapidly consumes most of UHC and OUHC, except for the central part of the chamber near the injector nozzle. The 1st post injection counteracts the expansion effect on temperature, plays a key role in increasing the exhaust enthalpy and reducing the harmful emissions by promoting combustion associated with the 2nd post injection. The fuel delivered by the 2nd post injection penetrates through the flame of the 1st post injection, creating cool flame clouds beyond the flame that eventually transition to a diffusion flame. Finally, a unique phenomenological model is proposed to better visualize the interactions of post injections.

Occurrence of palladium and platinum in human scalp hair of adolescents living in urban and industrial sites

Platinum group elements (PGEs) can be naturally found at very low concentrations in the Earth's crust. However, the increasing uses of PGEs in vehicle exhaust catalysts, in addition to some other applications (industry, jewelry, anticancer drugs) cause their anthropogenic emission and dispersion in the environment. The use of human hair samples analysis is considered a suitable biological indicator to assess human occupational and environmental exposure. It is an easily accessible material for individuals or population groups of non-invasive sampling. The aim of this study is a comparative analysis to investigate human hair content of Pd and Pt in adolescents, of both genders, residing near petrochemical plants of Augusta and Gela, in urban area of Palermo, and Lentini as control site (Sicily, Italy). A total of 108 samples were taken from school students (11–14 years old). Hair samples were cleaned, mineralized, and processed for analyses by inductively coupled plasma–mass spectrometry (ICP-MS).The samples from the industrial sites of Gela and Augusta do not have statistically significant differences between them for either Pd for Pt; however, they differ from the samples relating to the city of Palermo. Median Pd concentrations are higher than Pt in industrial sites and control site. In urban site the levels of both metals were comparable. The study does not reveal any statistically significant difference between Pd and Pt concentrations in female and male samples. The data confirm that the study areas are heavily affected by industrial and urban emissions of Pd and Pt, representing a potential hazard to the local population.

Recovery of Platinum and Palladium from Spent Automotive Catalysts: Study of a New Leaching System Using a Complete Factorial Design

The recovery of materials and energy from end-of-life products is increasingly a fundamental factor in the sustainable development of various countries. Recovering metals from different types of waste is not only a practice in support of the environment, but is also a profitable economic activity. For this reason, exhausted automotive catalysts can become renewable sources of critical raw materials such as Pt, Pd, and Rh. However, recovering Pt and Pd from spent catalysts through an efficient, economical, and green method remains a challenge. This article presents a new leaching process for the hydrometallurgical recovery of Pt and Pd from exhausted automotive catalysts. The leaching solution consists of an aqueous mixture of hydrochloric acid, two organic acids (citric acid and acetic acid) and hydrogen peroxide. A complete factorial plan on two levels (2k) was performed in order to evaluate the main effects of the analyzed factors and their interactions. The factors that were presumed to be the most influential on the leaching of Pt and Pd were the concentrations of the different reagents and the reaction time. The optimal circumstances for achieving the largest recovery (over 80% Pt and 100% Pd) were achieved using the following conditions: a concentration of HCl of 5 M, a concentration of H2O2 of 10% wt./vol., a concentration of C2H4O2 of 10%vol./vol., and a reaction time of 3 h.

Short Pulse Reductive Activation of Pt/ceria for the Low-Temperature CO Abatement in Vehicles Operated with the Synthetic Diesel Fuel OME

The synthetic Diesel fuel oxymethylene ether (OME) is sulfur-free by nature, and due to the low soot formation, no active filter regeneration events are required, limiting the maximum temperatures seen by the exhaust catalysts to ~ 450 °C. These OME-specific ageing requirements will enable the application of new types of catalysts that cannot be used in conventional Diesel vehicles. Such new catalytic solutions will allow ultra-low emissions at a much-reduced cost and will hence contribute to the overall efficiency of the OME approach. In this contribution, we focus on CO abatement from OME exhaust. To enable an efficient evaluation of new catalysts under practically relevant conditions, a test bench was set up that can reproduce the transient temperature-, mass flow- and concentration profiles measured during real driving tests. In a first step, the transient test bench was used to compare CO oxidation over a commercial Diesel oxidation catalyst for OME- and conventional Diesel conditions. The same low-load cold-start drive cycle run with OME showed slightly lower raw emissions, but the CO emissions downstream of the catalyst increased by a factor of ~ 2. The main reason for the lower CO conversion is the lower temperature of the OME exhaust. In a second step, we investigated short-pulse reductive activation of Pt/ceria as a promising new technology that benefits from the OME-specific low ageing requirements. A Pt/ceria catalyst activated by a short 5–10 s reductive pulse achieved virtually 100% conversion even at exhaust temperatures below 80 °C. With one 5 s reductive activation pulse per 30-minute drive cycle, a CO conversion of > 99.9% is demonstrated over the low-load cold-start OME drive cycle, compared to 59% obtained with a standard commercial Diesel oxidation catalyst. To our knowledge, this is the first published demonstration of short pulse reductive activation of Pt/ceria for CO oxidation using realistic transient drive cycles.

Flotation Sludges from Precious Metal Recovery Processes: From Waste to Secondary Raw Material in Ceramics

In this study, we investigated flotation muds (FM) deriving from the recovery processes of precious metals contained in e-waste (wastes from electronics) and exhausted catalysts. FM consist of an amorphous phase, corresponding to a Ca- and Al-rich silicatic glass, potentially usable as a secondary raw material (SRM) to obtain a final ceramic product (CFM). A high FM amount was used in our ceramic tests, and suitably mixed with variable percentages of other phases. Chemical analysis, phase composition, microstructure, pore pattern and technological properties of the new ceramic products were determined using different analytical techniques, including bulk XRF, XRD, SEM-EDS and µCT. The CFM product predominantly consists of nepheline, pyroxene and wollastonite as the main crystalline phases, with a minor amorphous phase occurring as a compact interstitial matrix. The ceramic product has a porous interconnected microstructure. Nevertheless, this microstructure does not negatively affect the mechanical properties of the ceramic product, as testified by the geo-mechanical tests, revealing good properties in terms of bending and uniaxial strength. These preliminary results point out that FM recycling is feasible, at least at the laboratory scale.

The effect of nanocrystalline TiO2 on structure and catalytic activity of CuO–ZnO in combined methanol reforming

CuO–ZnO (CZ) and CuO–ZnO/TiO2 (CZT) catalysts have been prepared by co-precipitation, characterized by X-ray diffraction, surface area measurements and chemical analysis and tested in the combined methanol reforming reaction. Catalytic tests have been performed in the temperature range 200–400 °C with a GHSV = 55.000 h−1, after H2 reducing pretreatment at 250 °C or 450 °C. It is shown that nanocrystalline TiO2 influences the CuO–ZnO nanosized structure, reducibility and reactivity. TiO2 slightly increases ZnO crystallite size of the fresh catalyst. Moreover, it causes the CuO chemical reduction to nanosized Cu2O on exhaust catalyst pretreated in hydrogen at 250 °C, this improves the reaction with higher methanol conversion and hydrogen production. On the contrary, TiO2 reduces CuO to submicron Cu0 and greatly increases ZnO crystallite size on the exhaust catalyst pretreated in hydrogen at 450 °C, this treatment weakens the reaction, with lower methanol conversion and hydrogen production. In both cases, nanocrystalline TiO2 presence is able to decrease the CO formation: independently of the hydrogen pretreatment temperature. This ability of the nanocrystalline TiO2 is ascribed to the presence of the oxygen vacancies, which act as electron donors that contribute to hinder CO2 and H2 surface adsorption for steric, electrostatic and probabilistic factors.

Assessment of influence of the Common Rail system high-pressure fuel pump design on regularity of fuel supply to a fuel accumulator

BACKGROUND: At the present time all worldwide diesel engine manufacturers have directed their development strategies on the way of reduction of harmful emissions, fuel efficiency improving and increasing of the power per liter. Using only accumulator type system is not sufficient for the goals achievement. It is necessary to use new auxiliary units, such as an exhaust catalyst, an exhaust recirculation system, injection of additional liquids together with diesel fuel, as well as to improve the existing units. Increasing the accuracy of injection rate of a nozzle will make it possible to adjust the engine fuel system more precisely, that will have a positive effect on all development directions of diesel engine engineering. Injection rate of a nozzle is dependent on fuel pressure in the nozzle inlet and on control signal timing. Pressure pulsation with stable timing cause irregularity of injection rate of a nozzle. Possibility of decreasing of nozzle inlet pressure pulsation is mainly defined by design of a high-pressure fuel pump, as it supplies fuel partially. The design optimization will make it possible to increase the accuracy of injection rate, that will make a positive effect on development of the diesel engines promising areas.
 AIMS: Study of irregularity of fuel supply by fuel pumps of various diesel engines designs with the Common Rail fuel accumulation system, aimed to decrease fuel oscillations and to improve stability of injection rate of a nozzle.
 METHODS: In order to assess the efficiency of high-pressure fuel pump designs, these designs were simulated in the specialised software. Theoretical studies of fuel supply irregularity for various designs of the pumps were carried out.
 RESULTS: Graphs of non-uniformity of fuel supply of high-pressure pumps depending on their design are obtained.
 CONCLUSIONS: Based on simulations, the conclusions about design influence on fuel supply irregularity of various designs of pump are made, recommendations for use are given.

Effect of Hydrophobicity of Ionic Liquids on the Leaching Selectivity of Platinum from a Spent Automotive Catalyst

Recycling platinum group metals from secondary resources such as spent automotive exhaust catalysts is promising for the circular economy. However, the selective separation of Pt over massive amounts of impurity metals such as Mg and Al is particularly challenging. In this study, non-aqueous direct leaching of platinum from a spent automotive catalyst (SAC) using hydrophobic ionic liquids, namely, trihexyl(tetradecyl)phosphonium chloride (P66614Cl) and trioctyl(dodecyl)phosphonium chloride (P88812Cl) with the aid of pre-loading hydrochloric acid/hydrogen peroxide was proposed. The more hydrophobic P88812Cl exhibited more efficient and selective leaching of Pt over Mg and Al. The recovery of Pt from the metal-loaded P88812Cl, and the reusability of the IL for SAC leaching were also demonstrated.

Bio‑hydrogen and valuable chemicals from industrial waste glycerol via catalytic aqueous-phase transformation

Waste glycerol obtained as by-product of biodiesel production has been submitted to a sequential physico-chemical treatment in order to make it suitable for continuous Aqueous-Phase Reforming (APR) in a tubular reactor. Special focus was given to the impact of impurities. APR was performed using 0.3%Pt/CoAl2O4 catalyst, at 260 °C and 50 bar within WHSV range 6–55 h−1 to cover whole conversion ranges. Glycerol conversion and yield to hydrogen reached 99.7% and 45.4%, respectively at WHSV = 6 h−1. The liquid product distribution strongly varied with glycerol conversion, maximum C-yield to 1,2-propylene glycol was attained in the 60–90% glycerol conversion range. APR of methanol and acetic acid aqueous feedstreams were investigated independently. It was concluded that acetic acid exerts a negative influence on catalyst stability since glycerol conversion decreased by 41% after 5 h TOS. Extensive characterization of fresh and exhausted catalysts revealed strong Co leaching, especially for acetic acid APR, oxidation of metals, and carbonaceous deposits. The basis for the regeneration of the spent catalyst, consisting of a reductive treatment at 500 °C, has been established. This work is expected to have significant implications for the development of APR technology for crude glycerol from biodiesel industry.

Ni and Co-based catalysts supported on ITQ-6 zeolite for hydrogen production by steam reforming of ethanol

Ni and Co catalysts supported on ITQ-6 zeolite have been synthesized and evaluated in the steam reforming of ethanol (SRE). Catalysts were also characterized by means of N2 adsorption-desorption, XRD, H2-TPR, and H2-chemisorption. ITQ-6 containing Co (Co/ITQ-6) presented a higher conversion of ethanol and production of hydrogen than ITQ-6 containing Ni (Ni/ITQ-6). The lower size of the metallic cobalt particles shown in Co/ITQ-6 seems to be the major responsible of its higher catalytic performance. Regarding the reaction by-products (CO, CH4, C2H4O and CO2), Co/ITQ-6 showed the lowest selectivity at medium and high temperatures (773 and 873 K). At low reaction temperatures (673 K) the dehydrogenation reaction predominates in the Co/ITQ-6, what it is supported by the high concentration of acetaldehyde detected at this temperature. In the case of the Ni/ITQ-6 the main side reaction at 673 K seems to be the methanation reaction since large concentrations of methane are detected. Stability studies were also carried out showing lower deactivation of Co/ITQ-6 at large reaction times (24 h). Characterization of the exhausted catalysts after reaction showed the presence of coke in both catalysts. Nevertheless, Co/ITQ-6 presented the lowest coke deposition. In addition, Co/ITQ-6 exhibited the lowest metal sinterization, what could be also account for the lower deactivation exhibited by this sample. This fact could be related to the higher interaction between the cobalt metallic particles and the ITQ-6 support as the H2-TPR studies demonstrate.

Platinum Nanoparticle Extraction, Quantification, and Characterization in Sediments by Single-Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry.

Particulate emissions from vehicle exhaust catalysts are the primary contributors to platinum group elements (PGEs) being released into roadside environments, especially platinum (Pt) particles. With increasing traffic density, it is essential to quantify the emission, accumulation, and potential health effects of traffic-emitted Pt particles. In this study, three procedures were investigated to extract Pt nanoparticles (NPs) from sediments and characterize them by single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOF-MS). For this purpose, a reference sediment sample was spiked with manufactured Pt NPs. Pt NPs’ extraction recoveries reached from 50% up to 102%, depending on the extraction procedure and whether the particle mass or number was used as the metric. Between 17% and 35% of the Pt NPs were found as unassociated Pt NPs and between 31% and 78% as Pt NPs hetero-aggregated with other sediment particles. Multi-elemental analysis of Pt-containing NPs in the pristine sediment revealed frequently co-occurring elements such as Au, Bi, and Ir, which can be used to determine a natural background baseline. Our results demonstrated that spICP-TOF-MS elemental characterization allows for distinguishing anthropogenic Pt NPs from the natural background. In the future, this could enable the sensitive monitoring of PGE release from anthropogenic sources such as vehicle exhausts.