Wang L.,Tsinghua University |
Gaudet J.R.,Optimal CAE Inc. |
Gaudet J.R.,University of Michigan |
Li W.,General Motors |
Weng D.,Tsinghua University
Journal of Catalysis | Year: 2013
In the present work, we report the migration of copper species in Cu/SAPO-34 during hydrothermal aging and its role in selective catalytic reduction (SCR) of NOx. Two Cu/SAPO-34 catalysts, prepared by ion-exchange and precipitation methods, were hydrothermally aged at 700 C for 48 h and characterized in detail. The aged ion-exchanged catalyst exhibited little deterioration in NH3-SCR activity; however, the catalytic activity of the precipitated catalyst, which showed inferior activity for the fresh sample, was markedly improved after hydrothermal treatment and became comparable to that of the ion-exchanged sample. A detailed characterization of the Cu species before, during, and after the hydrothermal treatment using a combination of experimental techniques clearly demonstrated that the copper species in the precipitated sample, which initially existed as CuO clusters on the external surface of SAPO-34, migrated to the ion-exchanged sites as isolated ions after aging. The change in copper oxidation states and coordination environment during the aging process was probed by in situ X-ray absorption spectroscopy, and a possible mechanism of Cu migration involving metallic Cu species was proposed. © 2013 Elsevier Inc. All rights reserved.
Xiao Q.,Optimal CAE Inc. |
Cai M.,General Motors |
Balogh M.P.,General Motors |
Tessema M.M.,Optimal CAE Inc. |
Lu Y.,University of California at Los Angeles
Nano Research | Year: 2012
This work demonstrates the synthesis of Pt ultrathin nanowires assisted by chromium hexacarbonyl [Cr(CO) 6]. The nanowires exhibit a uniform diameter of 2-3 nm. The length can reach up to several microns. It was found that Cr species produced dumbbell-like nuclei which play a pivotal role in the formation of the Pt nanowires. Such Pt nanowires can be tuned to nanocubes by simply decreasing the concentration of [Cr(CO) 6]. Compared to a commercial Pt/C catalyst (45 wt%, Vulcan, Tanaka) and Pt black (fuel cell grade, Sigma), the synthesized Pt nanowires exhibit superior performance in electrocatalytic oxygen reduction with a specific activity of 0.368 mA/cm 2, which was 2.7 and 1.8 times greater than that of Pt/C (0.138 mA/cm 2) and Pt black (0.202 mA/cm 2), respectively. The mass activity of Pt nanowires (0.088 mA/μg) is 2.3 times that of Pt black (0.038 mA/μg) and comparable to that of Pt/C (0.085 mA/μg). © 2012 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
Raju M.,Optimal CAE Inc. |
Kumar Khaitan S.,Iowa State University
Applied Energy | Year: 2012
An accurate dynamic simulation model for compressed air energy storage (CAES) inside caverns has been developed. Huntorf gas turbine plant is taken as the case study to validate the model. Accurate dynamic modeling of CAES involves formulating both the mass and energy balance inside the storage. In the ground reservoir based storage bed, the heat transfer from the ground reservoir plays an important role in predicting the cavern storage behavior and is therefore taken into account. The heat transfer coefficient between the cavern walls and the air inside the cavern is accurately modeled based on the real tests data obtained from the Huntorf plant trial tests. Finally the model is validated based on a typical daily schedule operation of the Huntorf plant. A comparison is also made with the results obtained from adiabatic and isothermal assumptions inside the cavern to gain further insights. Such accurate modeling of cavern dynamics will affect the design of the cavern storage beds for future explorations. © 2011 Elsevier Ltd.
Khaitan S.K.,Iowa State University |
Raju M.,Optimal CAE Inc.
International Journal of Energy Research | Year: 2013
Cavern storage is a proven energy storage technology, capable of storing energy in the form of compressed air inside a cavern. The Huntorf plant and the Alabama plants use this technology to store electrical energy during the off-peak load hours by compressing the air inside a cavern and then using this compressed air during gas turbine operation to generate electricity during peak load demand hours. The advantage of doing this is that it increases the efficiency of gas turbine operation while meeting the grid generation and the load balance. The operation of a typical compressed air energy storage (CAES)-based gas turbine plant involves the operation of several components, including the compressor, the cavern storage, the combustor, the turbine, and so on. The dynamics of the plant as a whole depends on the performance of the individual components. The focus of this article is to develop a Simulink-based models for each of the individual components, which can then be assembled appropriately to design an entire CAES plant. As an illustration, a case study for the Huntorf CAES plant is presented with the developed models. A typical daily operation of the Huntorf plant is simulated and compared with the reported Huntorf plant data. The model accurately captures the reported dynamics of the cavern storage. In addition, the reported quantities like the compressor power consumption, the turbine power generation, and the temperature at different junctions of the CAES plant match well with the simulated results. © 2011 John Wiley & Sons, Ltd.
Beckner M.,Optimal CAE Inc. |
Dailly A.,General Motors
International Journal of Energy Research | Year: 2015
A huge obstacle to replacing gasoline as the main energy carrier in automotive applications is the relatively low energy density of suitable replacements. Gaseous energy carriers must be stored at high pressure or very low temperature in order to obtain an energy density suitable for vehicular use. High pressure gas storage requires large, cylindrical containers that occupy large amounts of cargo of passenger space. On the other hand, low-temperature storage requires expensive, heavy cooling systems to keep the gas in a liquid or high-density gaseous state. Adsorbent materials are becoming an attractive option to solve the energy density problem. Porous materials with a high surface area to volume ratio are desirable because of the large number of adsorption sites per volume of adsorbent, and, to this end, much research has focused on porous carbons and metal-organic frameworks. Research into adsorbent materials has focused on increasing the specific surface area, increasing the adsorption energy, and optimizing the pore structure. Here, we review current progress in adsorbent materials' development and discuss challenges in moving from laboratory scale to full-scale implementation including material packing and compatibility. In particular, we discuss the difference between using a material's crystal density and its bulk density to characterize gas storage and give estimates for the performance of current benchmark materials in an 8 gallon gasoline equivalent storage system. © 2015 John Wiley & Sons, Ltd.
Kim J.-H.,General Motors |
Pieczonka N.P.W.,Optimal CAE Inc. |
Yang L.,General Motors
ChemPhysChem | Year: 2014
Lithium-ion (Li-ion) batteries have been developed for electric vehicle (EV) applications, owing to their high energy density. Recent research and development efforts have been devoted to finding the next generation of cathode materials for Li-ion batteries to extend the driving distance of EVs and lower their cost. LiNi0.5Mn1.5O4 (LNMO) high-voltage spinel is a promising candidate for a next-generation cathode material based on its high operating voltage (4.75 V vs. Li), potentially low material cost, and excellent rate capability. Over the last decade, much research effort has focused on achieving a fundamental understanding of the structure-property relationship in LNMO materials. Recent studies, however, demonstrated that the most critical barrier for the commercialization of high-voltage spinel Li-ion batteries is electrolyte decomposition and concurrent degradative reactions at electrode/electrolyte interfaces, which results in poor cycle life for LNMO/graphite full cells. Despite scattered reports addressing these processes in high-voltage spinel full cells, they have not been consolidated into a systematic review article. With this perspective, emphasis is placed herein on describing the challenges and the various approaches to mitigate electrolyte decomposition and other degradative reactions in high-voltage spinel cathodes in full cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Raju M.,Optimal CAE Inc. |
Raju M.,General Motors |
Kumar S.,General Motors
International Journal of Hydrogen Energy | Year: 2012
Design of the heat exchanger in a metal hydride based hydrogen storage system influences the storage capacity, gravimetric hydrogen storage density, and refueling time for automotive on-board hydrogen storage systems. The choice of a storage bed design incorporating the heat exchanger and the corresponding geometrical design parameters is not obvious. A systematic study is presented to optimize the heat exchanger design using computational fluid dynamics (CFD) modeling. Three different shell and tube heat exchanger designs are chosen. In the first design, metal hydride is present in the shell and heat transfer fluid flows through straight parallel cooling tubes placed inside the bed. The cooling tubes are interconnected by conducting fins. In the second design, heat transfer fluid flows through helical tubes in the bed. The helical tube design permits use of a specific maximum distance between the metal hydride and the coolant for removing heat during refueling. In the third design, the metal hydride is present in the tubes and the fluid flows through the shell. An automated tool is generated using COMSOL-MATLAB integration to arrive at the optimal geometric parameters for each design type. Using sodium alanate as the reference storage material, the relative merits of each design are analyzed and a comparison of the gravimetric and volumetric hydrogen storage densities for the three designs is presented. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Han K.,Central South University |
Liu Z.,Northwestern University |
Ye H.,Central South University |
Dai F.,Optimal CAE Inc.
Journal of Power Sources | Year: 2014
A flexible, self-standing graphene-Se@CNT composite film has been synthesized by a facile two-step assembly process. The film is directly employed as cathode for rechargeable Li-Se batteries without extra binders and conductive additives. It exhibits much higher reversible capacity and cycling stability (315 mAh g-1 after 100 cycles at 0.1 C) than graphene-Se composite film. The improved electrochemical performance is mainly attributed to the synergistic effects of graphene and CNT, which not only function as a flexible scaffold for strains/stresses release and volume expansion, but also offer a three-dimensional conductive architecture with open channels for electron transfer and Li ion diffusion, as well as strong confinement of soluble polyselenides. © 2014 Elsevier B.V. All rights reserved.
Oh S.H.,General Motors |
Triplett T.,Optimal CAE Inc.
Catalysis Today | Year: 2014
In-situ ammonia generation over a three-way catalyst is an important part of the "passive ammonia SCR" technology being developed at GM Global R&D as a low-cost alternative to the current lean NOx emission control technologies. The purpose of this laboratory reactor study is to clarify the reaction pathways and to identify/quantify the key controlling factors for the formation and destruction of ammonia over Pd-based three-way catalysts under realistic feedstream conditions simulating the exhaust from a lean gasoline engine operating at fuel-rich air-fuel ratios. In addition to the "full-feed" experiments, we also conducted some "simple- feed" experiments to better understand the NH3 formation process (via the NO + H2 reaction with and without CO) as well as the possible removal process of the NH3 formed (via the NH3 + O2 reaction or NH3 decomposition). Of particular interest in this study are the multiple roles that CO plays in both the formation and destruction of NH3. It is also found that the presence of Rh and/or Ce in a Pd-based three-way catalyst decreases the amount of NH3 formation significantly under fuel-rich (net-reducing) conditions of practical interest. © 2014 Elsevier B.V.
Raju M.,Optimal CAE Inc. |
Kumar S.,General Motor Randchnical Center
International Journal of Hydrogen Energy | Year: 2011
In this paper, we examine the feasibility of an on-board hydrogen storage system using sodium alanate as the hydrogen storage material. A two-dimensional model is used for evaluating refueling dynamics as well as heat transfer coefficients for the system level model. A parametric study is conducted to understand the influence of different operating parameters on the refueling time. System level performance of this storage system during driving conditions is evaluated using a simulation model developed in Matlab/Simulink platform. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.