Measurements of the size distribution of particles emitted from a modern heavy duty diesel engine using fuel with a sulfur content of between 0.03 and 0.05% by mass have been made under constant engine operating conditions, but with variations in the humidity of dilution air and dilution rato prior to particle size measurement. The results show clearly that the measured size distribution is crucially dependent upon the conditions of dilution, hence real difficulties for comparison of data between different investigators. Conditions of high dilution ratio and high relative humidity both tend to favor the production of nanoparticles, especially within the range below 50 nm diameter. Application of homogeneous nucleation theory shows that nanoparticle production during dilution is qualitatively consistent with the production of sulfuric acid, but the predicted nucleation rates are lower than those measured, in common with studies of nucleation in the atmosphere. Chemical analysis of size-fractionated particles shows enhancement of sulfate concentrations in humid dilution conditions and at high dilution ratios consistent with the above mechanism. The possible role of semivolatile organic compounds in these processes has not been investigated. (A)

Investigation of ultrafine particle formation during diesel exhaust dilution

Solid-state lithium (Li)–air batteries are recognized as a next-generation solution for energy storage to address the safety and electrochemical stability issues that are encountered in liquid battery systems1–4. However, conventional solid electrolytes are unsuitable for use in solid-state Li–air systems owing to their instability towards lithium metal and/or air, as well as the difficulty in constructing low-resistance interfaces5. Here we present an integrated solid-state Li–air battery that contains an ultrathin, high-ion-conductive lithium-ion-exchanged zeolite X (LiX) membrane as the sole solid electrolyte. This electrolyte is integrated with cast lithium as the anode and carbon nanotubes as the cathode using an in situ assembly strategy. Owing to the intrinsic chemical stability of the zeolite, degeneration of the electrolyte from the effects of lithium or air is effectively suppressed. The battery has a capacity of 12,020 milliamp hours per gram of carbon nanotubes, and has a cycle life of 149 cycles at a current density of 500 milliamps per gram and at a capacity of 1,000 milliamp hours per gram. This cycle life is greater than those of batteries based on lithium aluminium germanium phosphate (12 cycles) and organic electrolytes (102 cycles) under the same conditions. The electrochemical performance, flexibility and stability of zeolite-based Li–air batteries confer practical applicability that could extend to other energy-storage systems, such as Li–ion, Na–air and Na–ion batteries. Flexible, stable and energy-dense solid-state Li–air batteries are realised using ultrathin, chemically inert ion-conductive zeolite membranes as a solid electrolyte.

A highly stable and flexible zeolite electrolyte solid-state Li-air battery.

In situ synchrotron X-ray powder diffraction and 133Cs and 23Na MAS NMR have been used to investigate the cation migration and ordering in samples of cesium-exchanged zeolite NaY as a function of temperature and cesium cation-exchange level and during dehydration. Samples were prepared with cesium-exchange levels varying from 68 to 83% of the total cation content by carrying out repeated ion-exchange and calcination steps. Lower cesium content samples contain sodium cations in the sodalite cages and cesium cations in the supercages (SII and SIII) directly after the ion-exchange process. After dehydration at 350 °C and above, sodium cations are observed in the supercages (in SII) and in the double 6-rings (SI). A maximum of 8 cesium cations/unit cell (1/sodalite cage) migrate from the super to the sodalite cages, occupying SII‘ and SI‘ positions. The supercage sodium cations are then exchanged for cesium in the subsequent ion-exchange steps, increasing the cesium content. In situ X-ray data, collected duri...

Cation Migration in Zeolites: An in Situ Powder Diffraction and MAS NMR Study of the Structure of Zeolite Cs(Na)−Y during Dehydration

The integration of metal atoms and clusters in well-defined dielectric cavities is a powerful strategy to impart new properties to them that depend on the size and geometry of the confined space as well as on metal-host electrostatic interactions. Here, we unravel the dependence of the electronic properties of metal clusters on space confinement by studying the ionization potential of silver clusters embedded in four different zeolite environments over a range of silver concentrations. Extensive characterization reveals a strong influence of silver loading and host environment on the cluster ionization potential, which is also correlated to the cluster's optical and structural properties. Through fine-tuning of the zeolite host environment, we demonstrate photoluminescence quantum yields approaching unity. This work extends our understanding of structure-property relationships of small metal clusters and applies this understanding to develop highly photoluminescent materials with potential applications in optoelectronics and bioimaging.

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Tuning the energetics and tailoring the optical properties of silver clusters confined in zeolites

Electrical properties of nanoscaled host/guest compounds

The electrical conductivity of anhydrous Linde zeolite types A, X, and Y in various cationic forms has been measured between 20 and 400°C. The conductivity is ohmic, essentially noncapacitive, and appears to be strictly ionic with unusually low activation energy. From the effect of zeolite channel size, type of cation and cation density on ΔH, ΔG, and ΔS for the conduction process, some conclusions as to the zeolite internal structure and surface energy have been obtained. The heterogeneity of the internal surface energy found by the measurement of adsorption heats is discussed in the light of these conclusions.

Electrical Conductivity of Synthetic Crystalline Zeolites

Electro-conductive zeolitic molecular sieve compacts are prepared without the presence of a binder by a process which comprises dehydrating a crystalline zeolitic molecular sieve until 80-95% of its moisture content is removed by heating at a temperature from 100-400 DEG C., preferably from 150-200 DEG C. and in a vacuum, preferably 100 microns of mercury and applying a mechanical pressure of at least 680 atmospheres, preferably 2720-4075 atmospheres to the zeolitic molecular sieve and thereafter allowing the compact to cool. The dehydration may be effected prior or during the application of pressure. The zeolite which may be treated by the process include naturally occurring zeolites and synthetic zeolits A, X, D, L, R, S, T and Y which are disclosed in the following Specifications 777,232, 777,233, 841,812, 868,846, 909,264, 909,265, 909,266 and 912,936. The zeolite may be partially ion exchanged with a reducible metal cation. The products of the invention form the basis of solid state batteries, electric hygrometers, and gamma radiation transducers.

Donald Chester Jr Freeman

Papers

Electrical Conductivity of Synthetic Crystalline Zeolites

Improvements in and relating to compacts