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Nanoparticles of Ce1-xMxO2-delta (M = Ca or Zr) coated with Al2O3 with average crystallite size of 10 nm have been synthesised via solution chemistry approach under controlled chemical and hydrodynamic conditions. Their synthesis has been accomplished in three major steps: (1) simultaneous co-precipitation of cations, (2) sequential precipitation of Al(OH)(3) over the former particles and (3) calcination of the precipitated precursors to the corresponding oxides. Several compositions have been synthesised and their physicochemical properties are compared with commercial state-of-the-art material. The Al2O3-coating hinders the particles growth at high temperatures, resulting in materials with a large specific surface area and a restrain in the decrease of their oxygen storage capacity.

Extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) studies on supported bimetallic Pt/Pd diesel oxidation catalyst (Pt:Pd weight ratio 2:1) after various treatments were compared with those of monometallic Pd and Pt catalysts prepared under similar conditions. After calcination and thermal ageing, the coexistence of alloyed bimetallic Pt/Pd particles and of tetragonal PdO has been found in the bimetallic Pt/Pd catalyst. PdO is present in form of crystals at the surface of the Pt/Pd particles or as isolated PdO crystals on the support oxide. Bimetallic Pt/Pd nanoparticles were already formed in the Pt/Pd catalyst after calcination. Hydrogen treatment causes the formation of randomly alloyed Pt/Pd nanoparticles. In the thermally aged catalyst, a strong indication for an enrichment of Pt in the interior of the particle and of Pd at its outer shell was found. In the monometallic catalyst, the Pd is found to be completely oxidised already after calcination and to consist of metallic Pd in zero-valent state exclusively after reductive treatment. Ageing under hydrothermal oxidative atmosphere leads to complete oxidation of the Pd species. After calcinations, the catalytic activity of the Pt/Pd catalyst studied is comparable to those of monometallic Pt catalysts. In contrast to monometallic Pt catalysts, the alloyed system show significant stabilisation against sintering and a much higher activity after the thermal ageing step. This stabilisation of dispersion and the presence of Pt atoms on the surface of the Pt/Pd particles are considered to cause the higher catalytic activity of metallic particles for the oxidation of carbon monoxide and propene after ageing.

In this paper the effect of the vanadium oxide loading on the surface vanadia structure and the activity as well as selectivity in the catalytic reduction of NO with NH3 was studied for a V2O5/TiO2 model system. A series of TiO2 (WO x stabilized anatase) supported vanadia catalysts with varying loadings were characterized by laser Raman spectroscopy, 51V MAS-NMR, V K XANES. To determine the acidic properties, DRIFTS measurements were done with pyridine adsorbed on the samples. The measurements indicate that with increasing active phase loading square pyramidal coordinated surface vanadia species are replaced by an amorphous highly dispersed vanadium oxide phase with a coordination like V2O5. In addition, the ratio of Bronsted to Lewis acid sites is shifted from a comparatively low to an equal level at high loadings. This structural change is accompanied by a clearly improved catalytic activity and selectivity.

Diesel engine exhaust particles were collected under controlled conditions with and without passing a Pt/Al2O3 exhaust after-treatment oxidation catalyst and were studied before and after extraction treatment. The surface compositions were analyzed by means of X-ray photoelectron spectrometry (XPS). The properties of the hydrogen containing carbonaceous part of the soot were selectively characterised by combining results from inelastic neutron scattering (INS) as a bulk technique and secondary ion mass spectrometry (SIMS) as a surface and selvedge related technique. The effect of the catalyst in reducing the overall hydrogen content, the relative amounts of poorly crystalline species and of polyaromatic and aliphatic contributions at the surface was observed for the original as well as for the extracted diesel soot. Complementary, INS revealed a high integral graphiticity together with the proton dynamics of the finely divided, fluffy soot as well as the changes of the amounts of polyaromatic and aliphatic species in the surface regions. The matrix dependencies of the yields of negatively charged C/H secondary ions of the diesel soot and their time profiles were compared in SIMS experiments together with related properties of selected carbon blacks of different hydrogen content and with purified activated carbon. The C2−/CH− and the C2−/C2H− fragment ion ratios were used as a sensitive measure to roughly differentiate between hydrogenous species associated with poorly crystalline contributions and with structures of enhanced graphiticity, respectively. The acetylene-like fragment ion C2H2− is helpful to indicate the progression of the erosion process from the topmost atomic layers into the near-surface regions. The combination of these surface and bulk related techniques is shown to be useful in monitoring the efficiency of the oxidizing exhaust gas purification catalyst in the abatement of polyaromatic contributions from residual particulate emissions of diesel-engine passenger cars in addition to the overall lessening of soot emission. The combination deserves more common use in characterising carbons and carbonaceous emissions from other sources as well as contributing to the evaluation of the performance of new catalysts for exhaust purification processes.

In spite of their technical use and relevance the structural properties of diesel engine exhaust gas catalysts are not yet understood on an atomic scale. This study investigates structural changes during aging of Pt/V2O5/TiO2 based catalysts in order to get insight into the mutual interaction of the active constituents. X-ray photoelectron spectrometry, secondary ion mass spectrometry and X-ray absorption fine structure measurements were used to characterize the chemical composition and the electronic and geometric structure of the catalyst's surface and bulk. In the freshly prepared catalyst the interaction among the active species turns out to be moderate, i.e. vanadium is present in a distorted 5+ state. TiO2, as expected, is present as in the precursor and Pt is found to form monometallic clusters of about 16 A diameter without any significant interaction with the other metal species. Particularly, no alloying is observed. Upon aging of the catalyst vanadium is reduced to 4+ and preferentially orders in a VO2 structure although other minor phases may also be present. This is accompanied by a partial transformation of TiO2 from the initial anatase to rutile. Like V, Pt undergoes a strong modification upon aging: Pt is partly oxidized but still forms metal particles with a slightly smaller size.

This paper reports on the investigation of the effect of noble metal precursor and support oxide on their catalytic activity for the conversion of diesel exhaust gas components. The noble metal precursors used in this investigation were hexachloroplatinic acid, platinum nitrate, and tetraammine platinum(II) hydroxide. As support metal oxides zirconia, a base metal doped alumina, alumina, and titania were used. Catalysts were prepared from all combinations of precursors and supports and were tested in an integral model gas test reactor both in the fresh and in the aged state. The catalysts were also characterized by various techniques including BET surface area, CO chemisorption, XRD, and TEM. The results indicate that the catalyst prepared from the tetraammine platinum(II) hydroxide precursor on the base metal doped alumina support shows the highest activity for the conversion of the gaseous exhaust components.

Here we show that neutron diffraction can experimentally measure distances involving hydrogen on real catalysts. This method is applicable to adsorbed hydrogen (and other hydrogenous species) on crystalline, nanocrystalline or amorphous materials, supported and unsupported metals as well as oxides and works at ambient temperature and pressure.

The sections in this article are Introduction Origin of Emissions Importance of Road Transport Legislation History Present and Future Measurement of Emissions Passenger Cars and Light Duty Vehicles Heavy Duty Trucks and Buses Technology to Meet Legislation Spark-Ignition Engines Compression-Ignition Engines Catalytic Systems for Gasoline-Fueled, Indirect Injection Spark-Ignition Engines Introduction Engine-Out Emissions Reactions Emission Control Concepts Aspects of Three-Way Catalyst Design General Aspects Bead Catalysts Ceramic Monolithic Substrates Metallic Monolithic Substrates Washcoat Precious Metals Aspects of Three-Way Catalyst Performance Introduction Measurement of Catalyst Performance Influence of Catalyst Operating Conditions Influence of Substrate and Converter Design Influence of Catalyst Formulation Deactivation of Three-Way Catalysts Introduction Assessment of Durability Selected Deactivation Phenomena Future Developments and Concepts Catalytic Systems for Gasoline-Fueled Direct Injection Spark-Ignition Engines Introduction Aspects of Operation of NOx-Adsorber Systems Aspects of Deactivation of NOx-Adsorber Systems Catalytic Systems for Diesel-Fueled Compression-Ignition Engines Introduction Diesel Oxidation Catalysts Aspects of Diesel Oxidation Catalyst Design Aspects of Deactivation Future Developments and Concepts Catalytic Diesel Particulate Filter Systems Aspects of Diesel Filter System Design Aspects of Filter System Operation Diesel NOx-Reduction Systems Introduction HC-DeNOx-Systems Diesel NOx-adsorber systems SCR Systems Future Developments and Concepts Conclusions and Outlook Acknowledgments List of Abbreviations and Symbols Keywords: emissions; road transport; legislation; converter; durability; three-way catalysts; adsorber systems; particulate filters; diesel oxidation catalyst; precious metals; selective catalytic reduction

The launching of direct injection gasoline engines is currently one of the major challenges for the automotive industry in the European Union. Besides its potential for a notable reduction of fuel consumption, the enginewith direct gasoline injection also offers increased power during stoichiometric and stratified operation. These advantages will most probably lead to a significant market potential of the direct injection concept in the near future. In order to meet the increasingly more stringent European emission levels (EURO IV), new strategies for the exhaust gas aftertreatment are required. The most promising technique developed in recent years, especially for NO x conversion in lean exhaust gases, is the so-called NO x storage catalyst. The NO x storage technology achieves a high level of NO x conversion by storing nitrogen oxides reversibly as nitrates during lean operating conditions, while the periodic regeneration of the NO x storage components takes place under rich, i.e. under reducing conditions. In order to take full advantage of the fuel savings over the entire life-time of the vehicle, the most important task for the car and the catalyst manufacturers is the application and improvement of the thermal aging stability of this catalyst technology. The present paper focuses on the application of a NO x storage catalyst system on a new supercharged 4-cylinder engine with direct gasoline injection and also on the progress of NO x storage catalysts' development. On the basis of model gas tests and detailed studies at the engine test bench different NO x storage catalyst generations are compared. The key criteria to evaluate the different catalyst generations are on one hand the thermal aging stability and on the other hand the NO x storage capacity as a function of temperature under dynamic engine operating. Both, the model gas tests as well as the tests at the engine bench show that the new NO x storage technology possesses a notable improved stability with respect to thermal stress and also that the NO x storage window has been extended in the higher temperature range. Due to an intelligent combination of active components the improvement of the NO x conversion was achieved without any loss in the overall behavior of the catalyst. The temperature for a complete desulfation of the new catalyst generation is in the range of 600°C which is comparable to commercial NO x storage catalysts. Under oxidizing conditions as well as during the NO x regeneration phases the hydrocarbon oxidation activity remains at a high level.

The selective reduction of NO with propene in the presence of oxygen over a Pt/alumina catalyst has been investigated using TAP and model gas equipment. Experiments with different gas compositions (stoichiometric and overstoichiometric with respect to the complete oxidation of propene) were carried out at temperatures between 473 and 673 K. Additionally, the NO decomposition on reduced and oxidised Pt/alumina was studied. It is shown that N 2 is generated due to NO dissociation and following recombination of N-adatoms. Associatively adsorbed NO needs to be present on the surface to form N 2 O.

The nanocomposite Pt · 62 SiO2 was prepared by sol-gel processing of Pt(acac)2, two equivalents of H2 NCH2 CH2 NH(CH2)3Si(OEt)3 and 60 equivalents of Si(OEt)4, followed by heating of the obtained metal complex-containing gel in air. When the temperature treatment is performed at T ≥ 550°C, elemental Pt is the only crystalline phase. The influence of the calcination conditions (maximum temperature, period of heating) on the size and size distribution of the resulting Pt particles and on the morphology of the SiO2 matrix (surface area, pore volume) was investigated. When the temperature does not exceed 550°C, small Pt particles (3-5 nm) are formed which have a very narrow size distribution. Their size and size distribution are not affected by the period of heating. Gels heated to 550°C still contain about 0.1 - 0.25 wt% carbon. Carbon-free particles are obtained at 950°C However, at temperatures between 750°C and 950°C the average size of the particle increases considerably, and the size distribution gets very broad, particularly for rxtended periods of heating. The specific surface area increases from about 50 m2 /g in the metal complex-containing gel to about 230 m2/g during the oxidation step. At temperatures above 500°C considerable sintering of the matrix occurs. The pore volumes show the same trend. Heating the gels to 500°C results in the formation of nanopores with radii below 2 nm, which disappear again on heating to higher temperatures.