Determination of Pt and Pd in particles emitted from automobile exhaust catalysts using ion-exchange matrix separation and voltammetric detection

We report on the ion-exchange separation of Pt and Pd from the main elements emitted from catalysts of gasoline-fueled cars by exploiting the selective chelating ion exchanger Lewatit MonoPlus TP-214. Pt and Pd were then eluted with a recovery of 92% and 96%, respectively, using an acidified solution of thiourea, and the eluent was analyzed by sequential voltammetry. The detection limits are 0.04 μg L^?1 and 1 μg L^?1 for Pt and Pd, respectively, and the relative standard deviation is about 4.0% (for n?=?10). The procedure was successfully applied to particles emitted from automobile exhaust catalysts of four capacity engine vehicles. Graphite furnace atomic absorption spectrometry was also employed for reasons of comparison. Emission by four vehicles with 1400, 2600, 3200, and 4800 cc engines, respectively, ranged from 19 to 28 ng km^?1 for Pt, and from 102 to 150 ng km^?1 for Pd.

Determination of Platinum-Group Elements (PGE) from catalytic converters in soil by means of docimasy and INAA

The nickelsulfide fire assay (docimasy) for the enrichment of platinum-group elements (PGEs) has been modified for the use with small samples and combined with instrumental neutron-activation analysis (INAA). This procedure has been applied to the determination of PGEs exhausted from catalytic converters and deposited in soil near the Wiesbadener Kreuz (highway A3, Frankfurt-Köln). Our results show a considerable enhancement of the Pt (up to 330 ng/g), Pd (6.6 ng/g) and Rh (7.5 ng/g) contents close to the highway.     

The use of cation exchange matrix separation coupled with ICP-MS to directly determine platinum group element (PGE) and other trace element emissions from passenger cars equipped with diesel particulate filters (DPF)

Inductively coupled plasma-mass spectrometry coupled with cation exchange matrix separation has been optimised for the direct determination of platinum group element (PGE) and trace element emissions from a diesel engine car. After matrix separation method detection limits of 1.6 ng g(-1) for Pd, 0.4 ng g(-1) for Rh and 4.3 ng g(-1) for Pt were achieved, the method was validated against the certified reference material BCR 723, urban road dust. The test vehicle was fitted with new and aged catalytic converters with and without diesel particulate filters (DPF). Samples were collected after three consecutive New European Driving Cycle (NEDC) of the particulate and "soluble" phases using a home-made sampler optimised for trace element analysis. Emission factors for the PGEs ranged from 0.021 ng km(-1) for Rh to 70.5 ng km(-1) for Pt; when a DPF was fitted, the emission factors for the PGEs actually used in the catalysts dropped by up to 97% (for Pt). Trace element emission factors were found to drop by a maximum of 92% for Ni to a minimum of 18% for Y when a DPF was fitted; a new DPF was also found to cause a reduction of up to 86% in the emission of particulate matter.     

Rhenium- and ruthenium-containing catalysts for neutralization of automobile exhaust

The rhenium- and ruthenium-containing catalysts are active in the oxidation of CH _x and CO and in the reduction of NO _x . Comparative testing of catalyst samples under laboratory conditions and on an engine stand demonstrated that these catalysts outperform the known commercial catalysts in the neutralization of exhaust gas from automotive gasoline engines. It is, therefore, possible to completely replace expensive Rh and partially replace Pt and Pd with cheaper components—Re and Rh—in the manufacturing of catalytic converters.     

Assessment of environmental contamination risk by Pt, Rh and Pd from automobile catalyst

The main active components of present-day car catalysts are the noble metals Pt, Pd and Rh, belonging to the platinum group elements (PGEs). It is recognized that these elements are being spread into the environment to an as-yet incompletely known extent, mainly due to surface abrasion of the catalyst during car operation. These new pollutants have motivated extensive research on PGE determination. Our work is planned to ascertain the health and ecosystem risks of these PGEs emitted through a series of interrelated objectives that address the pathway of these elements from the catalyst to the different environmental compartments. Combined studies of catalyst surface abrasion and exhaust fumes analysis, the monitoring of Pt, Pd and Rh in airborne particles and road dust sediments and bioaccumulation studies in aquatic organisms, plants and urine enable a realistic assessment of the risk that this release represents for man and environment. In this work some previous results are presented.     

Dispersion dans l’environnement routier et urbain de Pt,Pd, et Rh émis par les pots d’échappement catalytiques. Étude de la spéciation des éléments

This study highlights the dispersion into the French urban environment of platinum group elements (PGEs) used in catalytic converters. Differences were observed between Pt and Rh on the one hand, and Pd on the other one. One experiment, consisting in passing the corrosive gas emissions from engines over the metals heated to 1000 °C, showed that Pd was severely corroded by nitrogen oxides. It was concluded that Pd is emitted in nitrate form. Hydrolysis of this nitrate form leads to the formation of soluble species. In situ pH and E_h measurements in the soils concerned confirm this theory when the results are compared with the Pd species predominance diagram.     

Reduction of NO by Propene Over Pt, Pd and Rh-Based ZSM-5 Under Lean-Burn Conditions

Selective catalytic reduction of NO by propene has been investigated over noble metal (Pt, Pd, Rh)-based ZSM-5 catalysts. These samples were tested in a gas mixture system in the presence of excess oxygen, simulating lean-burn exhaust gases. The sequence in activity for NO reduction was Pt > Rh Pd. Regarding the selectivity of the reaction to N₂, an opposite trend was observed: Rh > Pd Pt. The catalytic systems have presented stable operation under isothermal conditions during time-on-stream experiments.     

Determination of Platinum-Group Elements (PGE) from catalytic converters in soil by means of docimasy and INAA

The nickelsulfide fire assay (docimasy) for the enrichment of platinum-group elements (PGEs) has been modified for the use with small samples and combined with instrumental neutron-activation analysis (INAA). This procedure has been applied to the determination of PGEs exhausted from catalytic converters and deposited in soil near the Wiesbadener Kreuz (highway A3, Frankfurt-Köln). Our results show a considerable enhancement of the Pt (up to 330 ng/g), Pd (6.6 ng/g) and Rh (7.5 ng/g) contents close to the highway.     

Development of an analytical method for monitoring worker populations exposed to platinum-group elements

The increasing industrial use of platinum-group elements (PGEs), namely Ir, Pd, Pt and Rh, and related allergies such as rhinitis, conjunctivitis, asthma, urticaria and contact dermatitis, have led to a growing need to monitor selected populations of exposed workers. In this study, the levels of PGEs were measured in indoor airborne particulate matter and in biological samples taken from employees of a plant where car catalytic converters are produced and precious metals are recovered from spent carbon catalysts. The development of an analytical procedure based on quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) for the analysis of PGEs in airborne particulate matter and on sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) for the analysis of PGEs in blood, serum, urine and hair is described. For airborne particulate matter deposited on filters, the limits of detection (LoDs) were found to be 0.006 ng m⁻³, 0.020 ng m⁻³, 0.018 ng m⁻³ and 0.006 ng m⁻³ for Ir, Pd, Pt and Rh, respectively. Repeatability of measurements ranged from 1.8 to 8.5%, while recovery was in the range from 92 to 102%. For biological samples LoDs in blood, serum, urine and hair ranged from (in ng l⁻¹) 0.2–0.6 for Ir, 5–10 for Pd, 1–3 for Pt and 2–3 for Rh. For all biological materials, the repeatability varied from 1.1 to 12% for the four elements. Recovery data for the determination of PGEs in biological matrices were found to range from 84.0 to 107.8%. The method was applied to the determination of either total or respirable airborne PGEs collected from five different work areas in the plant. The difference between areas with high and low exposure correlates closely with metal levels in hair, blood and urine. The correlation coefficients between Pt in airborne particulate matter and Pt in biological materials was 0.994, 0.991 and 0.970 for blood, hair and urine, respectively.     

富氧条件下贵金属催化剂上丙烯选择性还原NO研究

用溶胶-凝胶(Sol-gel)法制备了以γ-Al₂O₃为载体,以Pt,Pd和Rh等为活性组分的单组分及双组分催化剂,在稀燃汽油机条件下评价了丙烯对NO的选择性催化还原活性.结果表明,在单组分催化剂中,催化剂的活性及顺序为Rh(73%)>Pt(65%)>Pd(47%),最高活性对应的温度分别为Pt(225℃),Pd(275℃)和Rh(375℃),N₂选择性顺序为Rh,Pd(>80%)>Pt(48%),氧化性顺序为Pt>Rh>Pd.Sol-gel制备的双组分催化剂中的不同贵金属活性位具有一定的协同效应,可明显拓宽活性温度范围,其中以Pt-Rh组合活性最好.Rh/Al₂O₃和Pt/Al₂O₃两种催化剂分层有序填装时,可提高C₃H₆的利用率,在200～450℃范围内,可有效地催化净化NO.     

Pd black decorated by Pt sub-monolayers as an electrocatalyst for the HCOOH oxidation

Pd black was modified by a very low amount of Pt corresponding to a sub-monolayer (ML). Spontaneous displacement method was employed. The catalysts with 0.02–0.12 ML were characterized by cyclic voltammetry and CO_ads stripping and were tested for HCOOH oxidation under the potentiodynamic and potentiostatic conditions. All the Pt@Pd catalysts were more active for HCOOH oxidation than Pd black. The Pt@Pd with 0.08 ML of Pt exhibited the highest activity with the maximum current density under the potentiodynamic conditions of 8 mA cm^?2 (vs. 2.7 mA cm^?2 on Pd black). Contrasting HCOOH oxidation kinetics on Pt@Pd and Pt@Au catalysts revealed that the current densities are higher, and the poisoning rate is lower on Pt@Pd catalyst. This was ascribed to an optimal strength of the Pt–adsorbate bond when Pt is supported on Pd and to a possible influence of the Pt atoms on the Pd substrate.     

Pt/Rh and Pd/Rh catalysts used for ozone decomposition and simultaneous elimination of ozone and carbon monoxide

Summary Catalytic oxidation of CO in the gas phase with ozone was carried out at lower temperature. The catalytic activities of Pt/Rh and Pd/Rh monolith honeycomb catalysts for the catalytic thermal oxidation and catalytic ozone oxidation were compared.     

汽车尾气净化反应的UBI-QEP法研究

应用单位键指标-二次指数势(UBI-QEP)方法对汽车尾气净化反应中氮氧化物的分解进行了理论分析.结果表明,NOx的分解的可能途径为氮氧化物的直接分解、CO还原助解和氮助解离.在富氧条件下,以CO助解为主.NO的解离存在N2O中间态.Ni与Rh一样,也是优秀的还原NOx催化剂,若能有效克服表面氧的共吸附,Ni-Cu可能是良好的汽车尾气净化催化剂的主体成份.     

Effect of supports on activity and stability of Pt–Pd catalysts for oxygen reduction reaction in proton exchange membrane fuel cells

The platinum–palladium alloy (Pt–Pd) catalysts were prepared on various supports including Vulcan XC72, Hicon Black (HB), multiwalled carbon nanotubes (MWCNTs), and titanium dioxide (TiO₂) by a combined approach of impregnation and seeding using NaBH₄ reduction at low temperature. Their oxygen reduction reaction (ORR) activities in single proton exchange membrane fuel cell (PEMFC) under a H₂/O₂ environment and their stability in an acid electrolyte (0.5 M H₂SO₄) were tested and compared with the Vulcan XC72-supported Pt (Pt/C) catalysts. The presence of the Pd metal as well as different types of supports affected the ORR activity in H₂/O₂ environment and stability in the acid electrolyte. Overall, the HB-supported Pt–Pd (Pt–Pd/HB) catalysts provided the highest current density at 0.6 V under a H₂/O₂ environment, while the MWCNT-supported Pt–Pd (Pt–Pd/MWCNT) catalyst provided the best stability in an acid electrolyte.     

Monitoring of the exposure to platinum-group elements for two Italian population groups through urine analysis

It is well recognized that automobile catalytic converters are the main source of Pd, Pt and Rh (also called platinum-group elements (PGEs)) in an urban atmosphere. Over recent years, urinary biomonitoring of PGEs has gained considerable importance in assessing the individual human exposure to these elements. This paper reports the concentration ranges of PGEs in the urine of 257 Italian subjects, aged between 23 and 88 years. Subjects were selected on the basis of standardized criteria in two different Italian cities, so as to represent a small urban area surrounded by an essentially rural environment and characterized by low automobile-traffic density (Foligno) and a large urban area with almost constant high-traffic conditions (Rome). The determination of PGEs was performed by sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) after 1:4 (v/v) dilution of the samples. The 5th and 95th percentiles for PGEs in urine of subjects living in Foligno were the following (in ng l⁻¹): Pd 1.99-17.2, Pt 0.24-3.08 and Rh 0.53-14.8. The 5th and 95th percentiles in the urine of subjects from the area of Rome were (in ng l⁻¹): Pd 0.71-17.0, Pt 0.49-8.13 and Rh 4.10-38.6. Platinum and Rh median concentration values showed large and significant differences (P<0.0001) between the two urban settings considered (0.52 and 3.50 ng l⁻¹ for Pt and Rh in Foligno, respectively, and 1.70 and 12.85 ng l⁻¹ for Pt and Rh in Rome, respectively). On the other hand, no striking differences were found in the Pd concentration (median value of 6.02 ng l⁻¹ in Foligno versus 7.79 ng l⁻¹ in Rome). The sex variable correlates only with Pd concentration (P=0.05), pointing out that in males concentrations are higher than in females.     

Characteristic of hydrogen-saturated Pd-based alloys for the application in electrochemical capacitors

Hydrogen electrosorption was performed in thin electrodeposits of Pd alloys with Pt, Au, and Rh. The possibility of their application as phase charging–discharging systems was investigated. The values of specific pseudocapacitance, power, and energy were calculated for hydrogen-saturated Pd-rich electrodes for temperatures 283–313 K. The best working parameters are exhibited by Pd–Rh alloys with 85–95% Pd, and by Pd–Pt alloys with 90–95% Pd in the bulk. The maximum values of specific pseudocapacitance are ca. 4,500 F?g^?1, specific energy ca. 150 J?g^?1 and specific power up to 750 W?g^?1 (per the mass of the electroactive material). In the case of the alloy deposits on reticulated vitreous carbon, their characteristics related to the total mass of the electroactive material and the substrate are comparable with those for other supercapacitors utilizing various redox reactions.     

A re-examination of platinum-group element concentrations in the environmental certified reference material BCR-723

A detailed statistical examination of replicated data used to certify platinum-group elements (PGEs) in environmental reference material BCR-723 is presented. Certification of Pt, Pd, and Rh concentrations in BCR-723 was based on 16, eight, and nine accepted data sets, respectively. Each accepted data set contained six replicated measurements for each PGE, and the statistical properties of these concentration data were examined, i.e. 96 for Pt, 48 for Pd, and 54 for Rh. This level of investigation has received limited attention but is critical in furthering our understanding of PGE variability and representativeness. Concentrations of Pt, Pd, and Rh were shown to differ significantly between accepted data sets. Palladium and Pt differed in their quantification between detection techniques. Additionally, Pd and Pt concentrations varied significantly between laboratories using a similar definitive method (inductively coupled plasma-isotope dilution mass spectrometry). The distribution of Pd concentrations was found to be bimodal, with a secondary population exhibiting a contamination signal of about 15%. The secondary population, not previously reported in BCR-723, is likely a measurement artifact and not due to a nugget effect. Comparisons of BCR-723 with other environmental media from Europe, i.e. airborne particulate matter, tunnel dust, and road-deposited sediment, indicated that Pd is uncommonly low in BCR-723 (6.0?ng?g^?1) and is generally not representative in terms of its distribution relative to Pt and Rh. Serious consideration should be given to developing a new PGE certified environmental reference material.     

Determination of Rh, Pd and Pt in urine samples using a pre-concentration sequential injection analysis system coupled to a quadrupole-inductively coupled plasma-mass spectrometer

The proposed flow system was developed in order to minimize the drawbacks related to the PGEs determination by quadrupole-inductively coupled plasma-mass spectrometry (Q-ICP-MS). It was intended not only to lower the limits of detection (LODs) but also to eliminate the interferences originating from some atomic and molecular ions produced in the argon plasma. This was accomplished by means of an on-line sample clean-up/pre-concentration step, using a chelating resin (Metalfix™ Chelamine™) in which Rh, Pd and Pt were preferably retained when compared with the interfering species.

The results obtained by using the developed flow system in the analysis of urine samples are presented. With a sampling rate of 9 samples h⁻¹ (i.e., 27 determinations) and a sample consumption of ca. 10 mL, the developed flow system allowed linear calibration plots up to 100 ng L⁻¹ with detection limits of 1.2 ng L⁻¹ (Rh), 0.4 ng L⁻¹ (Pd) and 0.9 ng L⁻¹ (Pt). Repeatability studies showed good precision (R.S.D.%, n = 5): 3.7% (Rh); 2.6% (Pd) and 2.4% (Pt), for 10 ng L⁻¹; 2.4% (Rh); 1.4% (Pd) and 1.9% (Pt), for 50 ng L⁻¹; and 1.3% (Rh); 0.58% (Pd) and 0.62% (Pt), for 100 ng L⁻¹. By spiking human urine samples, recovery tests were performed, and the values obtained ranged between 89% and 105% (Rh); 90% and 104% (Pd); and 93% and 105% (Pt).     

Analytical Determination and Bio-Monitoring of Platinum Group Elements in Roadside Grass Using Microwave Assisted Digestion and Electrothermal Atomic Absorption Spectrometry

The analytical conditions that enable the determination of traffic related platinum group elements (PGEs) in roadside grass using microwave digestion and electrothermal atomic absorption spectrometry were evaluated as an alternative to the biomonitoring of traffic related PGEs and Pb levels in urban areas. To optimize the analytical conditions and account for matrix effects that could import error in the analysis, method optimization was based on matrix simulation through analyte recovery from spiked unpolluted samples against a matrix blank. A mixture of nitric and hydrofluoric acid under progressively increasing microwave irradiation was optimized to afford the quantitative extraction of platinum group elements from plant matrix. Due to the low levels of platinum group elements in real samples, preconcentration was accomplished using sample evaporation followed by dissolution in dilute nitric acid prior to deliverance to the atomic detector. Quantitation limits below 1 ng g^?1 for Pd and Rh and lower than 2 ng g^?1 for Pt, were accomplished, enabling the monitoring of platinum group elements bioaccumulation in roadside grass with satisfactory recoveries, as determined from the analysis of spiked samples. The results from method application in an annual monitoring survey of PGEs and Pb levels in urban flora and other roadside media are presented and discussed.