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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Pilot Plant Reliability Metrics for Grinding and Fast Pyrolysis of Woody Residues

The reliability of biomass size reduction, feeding, and conversion processes remains a critical technical hurdle and important cost driver for biomass conversion systems. While Biorefinery projects have typically focused on scaling up conversion technologies that maximize yield of desired products, e.g. fuels and chemicals, solids handling and reactor feeding systems are often considered secondarily. These are frequently scaled down or adapted from other industries, without a full appreciation of how biomass heterogeneity and variability impact process reliability. Here we present the effects of feedstock variability on relative throughput, mass loss, plant uptime, operator intervention, product yield, and product quality for grinding and fast pyrolysis operations at the pilot scale. Loblolly pine residues were sourced and collected using commercial harvesting techniques. Grinding and pyrolysis experiments were performed at INL's Biomass Feedstock National User Facility and NREL's Thermal and Catalytic Process Development Unit, respectively. Preprocessing throughput using a hammer mill varied between 31-48% of nameplate capacity (5 tons/hr), and fast pyrolysis throughput varied between 57-72% of nameplate capacity (20 kg/hr) for an overall system throughput of 18-35% of nameplate capacity across biomass preprocessing and conversion to pyrolysis oil. Pyrolysis oil yields varied between 46-53% (feedstock carbon to oil, dry basis). Grinder overloads in the size reduction step were more prevalent for lower ash and higher moisture materials. During fast pyrolysis operations, downtime was caused by bridging in the feed and char removal systems and plugging in the condensation system, and significant variation in the type and frequency of operator intervention was observed between feedstocks. Cohesion of solids (feedstock and char) leading to system plugging appeared less problematic for higher ash feedstocks, and differences in condenser plugging behavior between high and low ash feedstocks indicates the composition and physical nature of the deposited material is important for process reliability and is feedstock dependent.

09 BIOMASS FUELS↗
DOE OSTI2016

National Synchrotron Light Source II storage ring vacuum systems

The National Synchrotron Light Source II, completed in 2014, is a 3-GeV synchrotron radiation (SR) facility at Brookhaven National Laboratory and has been in steady operation since. With a design electron current of 500 mA and subnanometer radians horizontal emittance, this 792-m circumference storage ring is providing the highest flux and brightness x-ray beam for SR users. The majority of the storage ring vacuum chambers are made of extruded aluminium. Chamber sections are interconnected using low-impedance radiofrequency shielded bellows. SR from the bending magnets is intercepted by water-cooled compact photon absorbers resided in the storage ring chambers. This paper presents the design of the storage ring vacuum system, the fabrication of vacuum chambers and other hardware, the installation, the commissioning, and the continuing beam conditioning of the vacuum systems.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

A common intermediate for N2 formation in enzymes and zeolites: side-on Cu-nitrosyl complexes

Understanding the mechanisms of catalytic processes requires the identification of reaction centers and key intermediates, both of which are often achieved by the use of spectroscopic characterization tools. Due to the heterogeneity of active centers in heterogeneous catalysts, it is frequently difficult to identify the specific sites that are responsible for the overall activity. Furthermore, the simultaneous presence of a large number of surface species on the catalyst surface often poses a great challenge for the unambiguous determination of the relevant species in the reaction mechanism. In contrast, enzymes possess catalytically active centers with precisely defined coordination environments that are only able to accommodate intermediates relevant to the specific catalytic process. Here we show that side-on Cu+-NO+ complexes characterized by high magnetic field solid state magic angle spinning nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies are the key intermediates in the selective catalytic reduction of NO over Cu-SSZ-13 zeolite catalysts. Analogous intermediates have been observed and characterized in nitrite reductase enzymes, and shown to be the critical intermediates in the formation of N2 for anaerobic ammonium oxidation reactions.[1] The identification of this key reaction intermediate, combined with the results of our prior kinetic studies, allows us to propose a new reaction mechanism for the selective catalytic reduction of NO with NH3 under oxygen-rich environments over Cu-SSZ-13 zeolites, a key reaction in automotive emission control. The authors acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy/Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Where does the sulphur go? Deactivation of a low temperature CO oxidation catalyst by sulphur poisoning

Sulphate formation, occurring preferentially at the CuO/CeOx-ZrOx interface, is responsible for the deactivation of low temperature CO oxidation catalysts. XRD, FTIR and isotope exchange experiments, as well as DFT calculations, reveal the poisoning mechanism of sulphate formation on the CeOx/ZrOx support material. JS, DM, TV and CHFP gratefully acknowledge the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program for the support of their participation in this work. Their studies were performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research, and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the U.S. DOE by Battelle under contract number DE-AC05-76RL01830.

Szanyi, Janos↗
DOE OSTI2013

Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

The structure-reactivity relationships of model BaO-based NOx storage/reduction catalysts were investigated under well controlled experimental conditions using surface science analysis techniques. The reactivity of BaO toward NO2, CO2, and H2O was studied as a function of BaO layer thickness [0\hBaO\30 monolayer (ML)], sample temperature, reactant partial pressure, and the nature of the substrate the NOx storage material was deposited onto. Most of the efforts focused on understanding the mechanism of NO2 storage either on pure BaO, or on BaO exposed to CO2 or H2O prior to NO2 exposure. The interaction of NO2 with a pure BaO film results in the initial formation of nitrite/nitrate ion pairs by a cooperative adsorption mechanism predicted by prior theoretical calculations. The nitrites are then further oxidized to nitrates to produce a fully nitrated surface. The mechanism of NO2 uptake on thin BaO films (\4 ML), BaO clusters (\1 ML) and mixed BaO/Al2O3 layers are fundamentally different: in these systems initially nitrites are formed only, and then converted to nitrates at longer NO2 exposure times. These results clarify the contradicting mechanisms presented in prior studies in the literature. After the formation of a nitrate layer the further conversion of the underlying BaO is slow, and strongly depends on both the sample temperature and the NO2 partial pressure. At 300 K sample temperature amorphous Ba(NO3)2 forms that then can be converted to crystalline nitrates at elevated temperatures. The reaction between BaO and H2O is facile, a series of Ba(OH)2 phases form under the temperature and H2O partial pressure regimes studied. Both amorphous and crystalline Ba(OH)2 phases react with NO2, and initially form nitrites only that can be converted to nitrates. The NO2 adsorption capacities of BaO and Ba(OH)2 are identical, i.e., both of these phases can completely be converted to Ba(NO3)2. In contrast, the interaction of CO2 with pure BaO results in the formation of a BaCO3 layer that prevents to complete carbonation of the entire BaO film under the experimental conditions applied in these studies. However, these ‘‘carbonated’’ BaO layers readily react with NO2, and at elevated sample temperature even the carbonate layer is converted to nitrates. The importance of the metal oxide/metal interface in the chemistry on NOx storage-reduction catalysts was studied on BaO(\1 ML)/Pt(111) reverse model catalysts. In comparison to the clean Pt(111), new oxygen adsorption phases were identified on the BaO/Pt(111) surface that can be associated with oxygen atoms strongly adsorbed on Pt atoms at the peripheries of BaO particles. A simple kinetic model developed helped explain the observed thermal desorption results. The role of the oxide/metal interface in the reduction of Ba(NO3)2 was also substantiated in experiments where Ba(NO3)2/O/Pt(111) samples were exposed to CO at elevated sample temperature. The catalytic decomposition of the nitrate phase occurred as soon as metal sites opened up by the removal of interfacial oxygen via CO oxidation from the O/Pt(111) surface. The temperature for catalytic nitrate reduction was found to be significantly lower than the onset temperature of thermal nitrate decomposition. We gratefully acknowledge the US Department of Energy (DOE), Office of Science, Division of Chemical Sciences, Geosciences, and Biosciences for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national user facility sponsored by the DOE Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle under contract number DE-AC05-76RL01830.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

Hydrothermal Aging Effects on Fe/SSZ-13 and Fe/Beta NH3–SCR Catalysts

Cu/SSZ-13 has been successfully commercialized as a diesel engine exhaust aftertreatment SCR catalyst in the past few years. This catalyst, however, displays undesirable NH3-SCR selectivity at elevated reaction temperature (≥ 350 C) after hydrothermal aging. Fe/zeolites, despite the fact that most of them degrade beyond tolerance after hydrothermal aging at temperatures ≥ 650 C, typically maintain good SCR selectivities. In recent years, Fe/beta has been identified as one of the more robust Fe/zeolites for use in NH3-SCR, where activity maintains even after hydrothermal aging at 750 C. Very recently, we, for the first time, synthesized and tested NH3-SCR performance for fresh and hydrothermally aged Fe/SSZ-13 catalysts. This study demonstrated that Fe/SSZ-13 is also a promising robust SCR catalyst, especially for high-temperature applications. In the present study, we compare catalytic performance between Fe/SSZ-13 and Fe/beta with similar Fe loadings and Si/Al ratios. Special attention is paid to effects from hydrothermal aging, aiming to understanding similarities and differences between these two catalysts. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

On the hydrothermal stability of Cu/SSZ-13 SCR catalysts

Cu/SSZ-13 SCR catalysts have been extensively studied in the past decade or so. Hydrothermal stability of these catalysts has been identified as the most important criterion for application. In this perspective, we describe recent atomic-level understanding of their hydrothermal stability. In particular, electron paramagnetic resonance (EPR) is shown to rather accurately quantify isolated Cu(II) ions and CuO clusters in fresh and aged catalysts to demonstrate the remarkable hydrothermal stability for Cu2+ ions located in 6-membered ring windows, and the conversion of [Cu(OH)]+ ions in Chabazite cages to CuO clusters. The hydrothermal stability difference of the two isolated Cu(II) ions is confirmed with DFT simulations and the conversion of [Cu(OH)]+ to CuO is proposed to involve formation, migration and condensation of Cu(OH)2 intermediates. The structural destructive role of CuO clusters is attributed to mesopore formation from their migration, which more severely damages the catalysts than dealumination. Finally, perspectives are given on new strategies for low-temperature NOx removal, rational design and refinement of Cu/SSZ-13, and development of new Cu/zeolite SCR catalysts with even better performance than the state-of-the-art Cu/SSZ-13. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

Chabazite, SSZ-13, hydrothermal aging, selective c↗
DOE OSTI2018

Catalytic N 2 O decomposition and reduction by NH 3 over Fe/Beta and Fe/SSZ-13 catalysts

Fe/zeolites are important N 2 O abatement catalysts, efficient in direct N 2 O decomposition and (selective) catalytic N 2 O reduction. In this study, Fe/Beta and Fe/SSZ-13 were synthesized via solution ion-exchange and used to catalyze these two reactions. Nature of the Fe species was probed with UV-vis, Mössbauer and EPR spectroscopies and H2-TPR. The characterizations collectively indicate that isolated and dinuclear Fe sites dominate in Fe/SSZ-13, whereas Fe/Beta contains higher concentrations of oligomeric Fe x O y species. H 2 -TPR results suggest that Fe-O interactions are weaker in Fe/SSZ-13, as evidenced by the lower reduction temperatures and higher extents of autoreduction during high-temperature pretreatments in inert gas. Kinetic measurements show that Fe/SSZ-13 has higher activity in catalytic N 2 O decomposition, thus demonstrating a positive correlation between activity and Fe-O binding, consistent with O 2 desorption being rate-limiting for this reaction. However, Fe/Beta was found to be more active in catalyzing N 2 O reduction by NH 3 . This indicates that larger active ensembles (i.e., oligomers) are more active for this reaction, consistent with the fact that both N 2 O and NH 3 need to be activated in this case. The authors from PNNL gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle. Aiyong Wang gratefully acknowledges the China Scholarship Council for the Joint-Training Scholarship Program with the Pacific Northwest National Laboratory (PNNL). The authors from East China University of Science and Technology acknowledge National Basic Research Program of China (2013CB933200), National Natural Science Foundation of China (21577035, 21577034), Commission of Science and Technology of Shanghai Municipality (15DZ1205305) and 111 Project (B08021) for supports.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Elementary Steps of Faujasite Formation Followed by in Situ Spectroscopy

Ex situ and in situ spectroscopy was used to identify the kinetics of processes during the formation of the faujasite (FAU) zeolite lattice from a hydrous gel. Using solid-state 27Al MAS NMR, the autocatalytic transformation from the amorphous gel into the crystalline material was monitored. Al-XANES shows that most Al already adopts a tetrahedral coordination in the X-ray-amorphous aluminosilicate at the beginning of the induction period, which hardly changes throughout the rest of the synthesis. Using 23Na NMR spectroscopy, environments in the growing zeolite crystal were identified and used to define the processes in the stepwise formation of the zeolite lattice. The end of the induction period was accompanied by a narrowing of the 27Al and 23Na MAS NMR peak widths, indicating the increased long-range order. The experiments show conclusively that the formation of faujasite occurs via the continuous formation and subsequent condensation of intermediary sodalite-like units that constitute the key building block of the zeolite. Acknowledgement The authors thank T. Huthwelker for assistance with XAFS experiment setup at the Swiss Light Source (PSI, Switzerland). Further, we would like to acknowledge V. Shutthanandan and B.W. Arey for performing Helium ion microscopy as well as Z. Zhao, N.R. Jaeger, M. Weng, C. Wan and M. Hu for aiding in the NMR experimental procedure. T. Varga is acknowledged for his help with the capillary XRD. A.V., D.M.C., J.H., J.L.F and J.A.L. were supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. S.P. and M.A.D. acknowledge support by the Materials Synthesis and Simulation Across Scales (MS3 Initiative) conducted under Laboratory Directed Research & Development Program at PNNL. The in situ NMR experiments were supported by the U. S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences. Part of the research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

faujasite↗
DOE OSTI2017

Low-Temperature Pd/Zeolite Passive NO x Adsorbers: Structure, Performance, and Adsorption Chemistry

Pd/zeolite passive NOx adsorber (PNA) materials were prepared with solution ion-exchange between NH4/zeolites (Beta, ZSM-5 and SSZ-13) and PdCl2 solutions. The nature of Pd (dispersion, distribution and oxidation states) in these materials was characterized with Na+ ion-exchange, TEM imaging, CO titration with FTIR and in situ XPS. The NOx trapping and release properties were tested using feeds with different compositions. It is concluded that multiple Pd species coexist in these materials: atomically dispersed Pd in the cationic sites of zeolites, and PdO2 and PdO particles on the external surfaces. While Pd is largely atomically dispersed in ZSM-5, the small pore opening for SSZ-13 inhibits Pd diffusion such that the majority of Pd stays as external surface PdO2 clusters. NOx trapping and release are not simple chemisorption and desorption events, but involve rather complex chemical reactions. In the absence of CO in the feed, cationic Pd(II) sites with oxygen ligands and PdO2 clusters are reduced by NO to Pd(I) and PdO clusters. These reduced sites are the primary NO adsorption sites. In the presence of H2O, the as-formed NO2 desorb immediately. In the presence of CO in the feed, metallic Pd, “naked” Pd2+, and Pd+ sites are responsible for NO adsorption. For Pd adsorption sites with the same oxidation states but in different zeolite frameworks, NO binding energies are not expected to vary greatly. However, NO release temperatures do vary substantially with different zeolite structures. This indicates that NO transport within these materials play an important role in determining release temperatures. Finally, some rational design principles on efficient PNA materials are suggested. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle. Discussions with Drs. A. Yezerets, J.Y. Luo, K. Kamasamudram and N. Currier Cummins, Inc., and H.Y. Chen from Johnson-Matthey are greatly appreciated.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗