Light off temperature based approach to determine diesel oxidation catalyst effectiveness level and the corresponding outlet NO and NO2 characteristics

According to the latest EPA emission regulations, the NOx (Nitrogen oxide compounds) emissions from heavy duty compression ignition engines need to see a dramatic reduction. The current technology used for this purpose is the selective catalytic reduction (SCR) system, which achieves NOx reduction of around 90% [9]. This involves urea injection which is influenced by the NO: NO2 ratio at the inlet to the SCR. Thus, the role of the DOC (Diesel Oxidation Catalyst) where most of the oxidation of the NOx compounds takes place, comes to fore. The focus is also on the effectiveness of the catalyst as it thermally ages. Therefore, the aim of this research project is to correlate the aging in the DOC with the light off temperature of the catalyst and subsequent variation in the NO and NO2 concentration at the outlet of the DOC. This shall be achieved through means of a model developed after extensive experimental procedures. Also, further exhaustive experiments to validate the model over multiple aging cycles of the catalyst shall be undertaken. ^ The DOC was subjected to 2 rigorous kinds of experiments aimed at determining the light off temperature shift as the catalyst aged and to determine the NO and NO2 concentrations at the DOC outlet as it aged. Exhaust stream compounds were measured using exhaust analyzers and DOC temperatures were determined using thermocouples installed inside the DOC and at its inlet and outlet. ^ The data thus obtained was then analyzed and 2 separate models were developed, one for the light off experiments, and the other for the NOx experiments. Aging procedures were carried out at an oven according to prescribed techniques and the DOC was subjected to similar experiments again. Analysis was carried out on the data. From the light off experiments and the model analysis, a clear positive shift in light off temperatures was observed from one aging level to another across the range of set points. It was also observed that even after subjecting the DOC to three thermal aging exercises, its conversion efficiency went up to 90%. Also, as the DOC aged, the NO concentration at the DOC outlet showed a downward trend which was observed across the spectrum of engine set points and aging levels. These experiments were repeated for consistency so that the models could be rendered more useful

Advanced Transmission Electron Microscopy Studies of Induced Interactions of Metallic Species with Perovskite Oxide Hosts.

Catalysts are used to remove detrimental gases from the automobile exhaust stream, thus fulfilling an essential need in increasingly environmentally conscious times. The constituent functional materials – some combination of Pt, Pd, and Rh – that compose the catalyst nanoparticles are both rare and expensive, and their performance degrades throughout the catalytic converter lifetime via thermodynamically driven losses of the catalytically active surface area during prolonged exposure to high exhaust temperatures. Conventional oxide powder supports, used to stabilize the catalyst nanoparticles against migration and coarsening, retard coarsening to some degree, but coarsening is nonetheless irreversible on these supports. We report here on microscopy and density functional theory studies of a new class of self-regenerative catalyst/support systems, wherein the catalyst absorbs into a specially selected perovskite oxide support (e.g. LaFeO3 for Pd; CaTiO3 for Pt, Rh) and re-emerges as nanoparticles in a high dispersion. Utilizing ab initio modeling, we find that this behavior is the result of balanced thermodynamic equilibria in which the normal stoichiometric oscillations of the air-fuel mixture alternately favor the catalyst existing as a metallic phase and as a solid solution within the perovskite. Using ex-situ and in-situ transmission electron microscopy experiments on model thin films and powders to study the phenomenology, we find that the movement of catalyst atoms along the self-regenerative dissolution/extrusion route is slower than expected, however, and much of the metal may fail to reach the support surface upon regeneration. The coarsening of catalyst particles on the surface, however, is significantly retarded with respect to its behavior on traditional automotive catalyst supports. Therefore, the morphology of the catalyst support must be carefully engineered for the self-regenerative catalyst to be effective and practical.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98073/1/mbkatz_1.pd

Catalytic and Thermodynamic Studies of Supported Core-Shell Catalysts

Interactions between metal catalysts and oxide supports have been known to be important in modifying the catalyst properties for many years, and catalysts with core-shell nanostructures are promising for optimizing these metal-oxide interactions. In this dissertation, core-shell nanoparticles that consist of a metal core and a metal-oxide shell were synthesized and deposited onto an alumina support. These core-shell catalysts exhibit unique catalytic and thermodynamic properties, and were investigated with different core-shell compositions as part of this thesis. The first part of this dissertation focuses on a Pd@CeO2/Si-Al2O3 catalyst that has been developed and examined for methane-oxidation previously. To better understand this material, I investigated the catalytic, adsorption, and redox properties as they are related to the methane-steam-reforming. I also looked at the effect of calcination temperature on the catalytic properties since the catalysts were strongly influenced by the calcination temperatures, in a manner that is very different from that observed with conventional Pd/CeO2 catalysts. It was found that calcination to higher temperatures improved the performance of the Pd@CeO2 catalyst by modifying the redox properties of the ceria shell. In the second part of this dissertation, the synthesis and investigation of core-shell catalysts was extended to other precious-metal cores and metal-oxide shells. To determine the effect of shell material, a Pd@ZrO2/Si-Al2O3 catalyst was investigated. The ZrO2 in contact with Pd was found to be reducible and to enhance the methane-oxidation. A Au@TiO2/Si-Al2O3 catalyst was also synthesized and examined for CO oxidation. It was found that the strong interaction between Au and TiO2 not only enhanced the oxidation activity of Au but also effectively prevented Au sintering up to 873 K. Additionally, catalysts with Pd or Pt cores and ZnO shells were prepared. The formation of Pt-Zn alloy was suggested by in-situ TEM and coulometric titration results and by catalytic properties for methanol-steam-reforming. Finally, metal-oxide interactions were compared for Pd@CeO2 and Pt@CeO2. A very strong interaction between Pd and CeO2 helped to stabilize the core-shell structure at higher calcination temperatures and affected the CO accessibility of the core for catalyst calcined at lower temperatures, but these were not observed with Pt

Addressing the Mars ISRU Challenge: Production of Oxygen and Fuel from CO_2 using Sunlight

Advanced exploration of Mars, particularly human missions, will require vast amounts of fuel and oxygen for extended campaigns and the return of samples or humans back to Earth. If fuel and oxygen can be prepared on Mars from in-situ resources, this would greatly reduce the launch mass of the mission from Earth. In this Keck Institute for Space Sciences (KISS) study, the viability of Mars near-ambient temperature photoelectrochemical (PEC) or electrochemical (EC) production of fuel and oxygen from atmospheric carbon dioxide—with or without available water—was examined. With PEC devices incorporated into lightweight, large-area structures operating near 25°C and collecting solar energy to directly convert carbon dioxide into oxygen, it may be possible to reduce the launch mass (compared with bringing oxygen directly from Earth) by a factor of three or more. There are other numerous benefits of such a system relative to other in-situ resource utilization (ISRU) schemes, notably reduced thermal management (e.g., lower heating demand and decreased amplitude of thermal cycling) and the elimination of a need for a fission power source. However, there are considerable technical hurdles that must be surmounted before a PEC or EC ISRU system could be competitive with other more mature ISRU approaches, such as solid oxide electrolysis (SOXE) technology. Noteworthy challenges include: the identification of highly stable homogeneous or heterogeneous catalysts for oxygen evolution and carbon monoxide or methane evolution; quantification of long-term operation under the harsh Martian conditions; and appropriate coupled catalyst–light absorber systems that can be reliably stowed then deployed over large areas, among other challenges described herein. This report includes recommendations for future work to assess the viability of and advance the state-of-the-art for EC and PEC technologies for future ISRU applications. Importantly, the challenges of mining, transporting, purifying, and delivering water from Mars resources to a PEC or EC reactor system, development and demonstration of a low-temperature-capable, non-aqueous-based CO2 reduction scheme as described below is perhaps the first logical step toward implementing an efficient near-surface Mars temperature oxygen generation system on Mars

Prediction of Exhaust Skin Temperature Integrating 1D Model with Vehicle Level CFD Model

Studies involving flow and heat transfer in automotive exhaust systems are regularly employed in the design and optimization phases. Both internal as well as external heat transfer are key to provide a better understanding of the underbody heat transfer, cold start warm-up and thermal aging of the catalytic converter for gasoline engines and adequate thermal protection for the underbody components. The internal flow in a typical automobile exhaust system can be simplified using a 1D model employing correctional factors to encompass the three-dimensional effects. However, the external flow and heat transfer underbody of a vehicle is highly complex as it involves the overall front-end design of the car as well as the packaging of components underhood and underbody. This would require the use of a full scale 3D model of a vehicle. The proposed research involves the prediction of exhaust skin (outer surface) temperature combining a 1D model with a full vehicle 3D model as well as investigating heat transfer characteristics of the exhaust system. The 1D model is developed using a commercial code, GT-Power and the 3D vehicle level model is simulated using STAR-CCM+. The 1D and the 3Dmodel will provide a real time closed loop control system based on the combustion requirements and exhaust system readings for internal flow and external flow. In the first stage, the gas side internal heat transfer is simulated using the 1D model by adding available heat transfer correlations considering entrance effects, engine induced pulsation, geometrical effects and surface conditions. Initially, the model is simulated for steady state wide open throttle (WOT) cases and validated with results available from bench test. In the second stage, the use of the model is extended further in transient heat transfer studies. In the third stage, the 3D vehicle level model is simulated using the commercial code STAR-CCM+ at various wind speeds based on a set of cluster points representing a transient drive cycle. A Reynold Averaged Navier-Stokes (RANS) based k-ε turbulence model is used for modeling flow and turbulence. Thermal models for free convection and thermal radiation, are used to account for external heat transfer. The initial thermal boundary condition of the exhaust for the simulation is obtained from the preliminary 1D simulation data. The predicted external heat transfer coefficients from the 3D model are then used as a boundary condition for the 1D model for heat transfer as a third phase of the study. The iterative of the process of using the 3D model as boundary condition for the 1D model and vice versa until convergence will ensure a more accurate prediction of the exhaust skin temperature. Further a parametric study involving the influence of external emissivity on exhaust system heat transfer was carried out. The results indicate that the effect of the external emissivity is significant on the skin temperature and external heat transfer. The variation in emissivity is seen to contribute to more than 50% in the overall heat transfer. A temperature difference of up to 200oC was seen on the heat shields of the exhaust at high loads. Similar results were seen for the other components underbody close to the exhaust system. This would potentially be higher at idling after a drive cycle where free convection and radiation are seen to be more dominant, indicating a strong influence of external radiation as a key parameter in the heat transfer from an exhaust. Further the study revealed that the variation in emissivity does not influence the convective heat transfer by more than 4%

Perovskite Materials, Devices and Integration

Perovskites have attracted great attention in the fields of energy storage, pollutant degradation as well as optoelectronic devices due to their excellent properties. This kind of material can be divided into two categories; inorganic perovskite represented by perovskite oxide and organic-inorganic hybrid perovskite, which have described the recent advancement separately in terms of catalysis and photoelectron applications. This book systematically illustrates the crystal structures, physic-chemical properties, fabrication process, and perovskite-related devices. In a word, perovskite has broad application prospects. However, the current challenges cannot be ignored, such as toxicity and stability

Effects of Biodiesel Blends Varied by Cetane Numbers and Oxygen Contents on Stationary Diesel Engine Performance and Exhaust Emissions

This work investigated waste plastic pyrolysis oil (WPPO), 2-ethyl hexyl nitrate (EHN), and ethanol as sources of renewable energy, blending conventional diesel (CD), WPPO, and ethanol with EHN was to improve the combustion and performance characteristics of the WPPO blends. EHN has the potential to reduce emissions of CO, CO2, UHC, NOX, and PM. Ethanol improves viscosity, miscibility, and the oxygen content of WPPO. Mixing ratios were 50/WPPO25/E25, 60/WPPO20/E20, 70/WPPO15/E15, 80/WPPO10/E10, and 90/WPPO5/E5 for CD, waste plastic pyrolysis oil, and ethanol, respectively. The mixing ratio of EHN (0.01%) was based on the total quantity of blended fuel. Performance and emission characteristics of a stationary 4-cylinder water-cooled diesel Iveco power generator were evaluated with ASTM standards. At 1000 rpm, the BSFC was 0.043 kg/kWh compared to CD at 0.04 kg/kWh. Blend 90/WPPO5/E5 had the highest value of 14% for BTE, while the NOX emissions for 90/WPPO5/E5, 80/WPPO10/E10, and 70/WPPO15/E15 were 384, 395, and 414 ppm, respectively, compared to CD fuel at 424 ppm. This is due to their densities of 792 kg/m3, 825 kg/m3 which are close to CD fuel at 845 kg/m3 and the additive EHN. These results show blends of WPPO, ethanol and EHN reduce emissions, and improve engine performance, mimicking CD fuel

The role of the substrate porosity, Cu loading and redox state of CuO/CeO2/Al2O3 catalysts in the CO Preferential Oxidation in H2-rich mixtures

The Preferential Oxidation of carbon monoxide (CO-PROX) reaction is meaningful processes for CO removal in trace amounts from a reformate stream rich in H2 to be further utilized in Fuel Cell applications. Catalysts based on transition metal oxides (e.g CuO/CeO2/Al2O3) were identified as potential candidates for CO-PROX in H2-rich reformate gas thanks to their high activity towards CO oxidation and their crucial role in the reduction or replacement of platinum-group metal (PGMs)- based catalysts. In this work, six catalytic matirial were provided by National Center for Scientific Research “Domokritos” (NCSRD) as a part f an active collaboration. The catalyst were synthesised with two methods(ADP and EISA), which differ in the methodology employed for the deposition of CuO-Cu on the surface of the catalytic substrate. ADP catalysts differed according to the loading of copper oxide (15,20 and 30%), while EISA catalysts were calcined at different temperatures (400,550 and 900°C). A fixed GHSV value (20000h−1) and a specific thermal ramp (up to 280°C) were taken into account for the verification of the catalytic activity. Activity experiments in a standard plug-flow reactor showed that 20% CuO loading has the highest performance among the ADP samples, with a maximum CO conversion of 80% at 185°C and 100% selectivity for CO oxidation up to 170°C. However, the 20% sample synthesized with EISA and calcined at 900°C showed the highest activity among all the samples, with 90% of CO conversion at 210°C and H2 conversion lower than 0.5% from 250°C. A weak deactivation of the 20% CuO/CeO2/Al2O3-ADP sample was obtained as higher temperatures were needed to achieve the same performance of the fresh catalyst. In the operational range of the reaction, the catalyst is subjected to a continuous cycle of reduction and oxidation, due to the high presence of hydrogen (a strong reducing agent) and the fact that the most stable form of the catalyst is the oxidized state. This redox cycle causes the catalyst to consume some of the oxygen in the mixture and thus reduce the possible conversion of CO WGS reaction cannot take place for temperature below to 155°C because the catalyst is not active towards the hydrogen oxidation.The Preferential Oxidation of carbon monoxide (CO-PROX) reaction is meaningful processes for CO removal in trace amounts from a reformate stream rich in H2 to be further utilized in Fuel Cell applications. Catalysts based on transition metal oxides (e.g CuO/CeO2/Al2O3) were identified as potential candidates for CO-PROX in H2-rich reformate gas thanks to their high activity towards CO oxidation and their crucial role in the reduction or replacement of platinum-group metal (PGMs)- based catalysts. In this work, six catalytic matirial were provided by National Center for Scientific Research “Domokritos” (NCSRD) as a part f an active collaboration. The catalyst were synthesised with two methods(ADP and EISA), which differ in the methodology employed for the deposition of CuO-Cu on the surface of the catalytic substrate. ADP catalysts differed according to the loading of copper oxide (15,20 and 30%), while EISA catalysts were calcined at different temperatures (400,550 and 900°C). A fixed GHSV value (20000h−1) and a specific thermal ramp (up to 280°C) were taken into account for the verification of the catalytic activity. Activity experiments in a standard plug-flow reactor showed that 20% CuO loading has the highest performance among the ADP samples, with a maximum CO conversion of 80% at 185°C and 100% selectivity for CO oxidation up to 170°C. However, the 20% sample synthesized with EISA and calcined at 900°C showed the highest activity among all the samples, with 90% of CO conversion at 210°C and H2 conversion lower than 0.5% from 250°C. A weak deactivation of the 20% CuO/CeO2/Al2O3-ADP sample was obtained as higher temperatures were needed to achieve the same performance of the fresh catalyst. In the operational range of the reaction, the catalyst is subjected to a continuous cycle of reduction and oxidation, due to the high presence of hydrogen (a strong reducing agent) and the fact that the most stable form of the catalyst is the oxidized state. This redox cycle causes the catalyst to consume some of the oxygen in the mixture and thus reduce the possible conversion of CO WGS reaction cannot take place for temperature below to 155°C because the catalyst is not active towards the hydrogen oxidation