Targeting the complete range of soot components through the catalytic oxidation of diesel particulates

While total exhaust emissions from individual road vehicles continue to be reduced, it is becoming increasingly important to identify and quantify the residual chemical compounds in tail-pipe emissions that are potential hazards to the environment and to human health. Diesel particulate matter (DPM) is known to consist mostly of carbonaceous soot together with minor components, such as volatile organic fractions (from unburned fuel), lubricating oil, and inorganic compounds that include ash and sulphur compounds. Polycyclic aromatic hydrocarbons (PAHs) are invoked as the key intermediates in diesel soot formation. These are mutagenic air pollutants formed as by-products of combustion. PAH-precursors identified in soot include single ring structures such as benzene and toluene. Soot nucleation and growth gradually leads to the formation of five to six membered ring structures, such as benzopyrene, dibenzopyrene and coronene. Several methods have been devised to reduce the emissions of DPM, which include the use of a diesel particulate filter, or a technology which combines selective catalytic reduction of NOx with a regenerating particulate trap in a single unit. These oxidise the combustible content of the particulate matter collected on the filter through a non-catalytic reaction with NO2. As an alternative, the more difficult catalysed oxidation of soot by direct reaction with O2 has been gaining a lot of attention. Several studies have shown that the oxidation of soot requires a redox catalyst, such as CeO2, CeO2-ZrO2 and CeO2-ZrO2-Al2O3, or other reducible metal oxides including perovskites and spinels. In the past, proposed mechanisms have assumed that exhaust soot is simply graphitic carbon, and so have not taken into account the other organic components. In this work, we have carried out a speciation of soot that has been sourced from a diesel particulate trap. The soluble components have been identified by GC-MS, following extraction by Soxhlet and ultrasonication techniques. The speciation has been repeated as a function of temperature during the non-catalysed and catalysed combustion of the soot, allowing the conversion of individual components to be tracked. The results provide important catalyst design information, which should allow the formulation of materials that will be catalytically active in the combustion both of graphitic carbon and the complete range of retained organic species

Assessing the Oxidative Degradation of N-methyl Pyrrolidone (NMP) in Microelectronic Fabrication Processes by using a Multi-platform Analytical Approach

During the construction of recording head devices, corrosion of metal features and subsequent deposition of corrosion by-products have been observed. Previous studies have determined that the use of N-methylpyrrolidone (NMP) may be a contributing factor. In this study, we report the use of a novel multiplatform analytical approach comprising of pH, liquid chromatography/UV detection (LC/UV), inductively coupled plasma optical emission spectroscopy (ICP-OES), and LC/mass spectrometry (LC/MS) to demonstrate that reaction conditions mimicking those of general photoresist removal processes can invoke the oxidation of NMP during the photolithography lift-off process. For the first time, we have confirmed that the oxidation of NMP lowers the pH, facilitating the dissolution of transition metals deposited on wafer substrates during post-mask and pre-lift-off processes in microelectronic fabrication. This negatively impacts upon the performance of the microelectronic device. Furthermore, it was shown that, by performing the process in an inert atmosphere, the oxidation of NMP was suppressed and the pH was stabilized, suggesting an affordable modification of the photolithography lift-off stage to enhance the quality of recording heads. This novel study has provided key data that may have a significant impact on current and future fabrication process design, optimization, and control. Results here suggest the inclusion of pH as a key process input variable (KPIV) during the design of new photoresist removal processes

Using real particulate matter to evaluate combustion catalysts for direct regeneration of diesel soot filters

The particulate produced by internal combustion engines has a complex composition that includes a large proportion of porous soot within which condensed and adsorbed organic molecules are trapped. However, many studies of the catalytic combustion of particulate are based on the assumption that commercially produced carbon can be used as a reliable mimic of engine soot. Here we show that soot removed from a diesel particulate filter is rich in the polyaromatic molecules that are the precursors of the solid particulate. Through a combination of solvent extraction and evolved gas analysis, we have been able to track the release and transformation of these molecules in the absence and presence of combustion catalysts. Our results reveal that, although the rate of combustion of the elemental carbon in diesel soot is higher than that of graphite, deep oxidation of the polyaromatic molecules is a more demanding reaction. An active and stable Ag–K catalyst lowers the combustion temperature for elemental carbon by >200 °C, but has little effect on the condensed polyaromatic molecules. The addition of a secondary catalyst component, with aromatic-oxidation functionality is required to target these molecules. Although the combined catalyst would not enable a completely passive regeneration system for diesel passenger cars, it would improve the efficiency of existing active systems by reducing the amount of fuel-injection required for trap regeneration