The catalytic sites of acidic zeolite are profoundly altered by the presence of water changing the nature of the Brønsted acid site. High-resolution solid-state NMR spectroscopy shows water interacting with zeolite Brønsted acid sites, converting them to hydrated hydronium ions over a wide range of temperature and thermodynamic activity of water. A signal at 9 ppm was observed at loadings of 2–9 water molecules per Brønsted acid site and is assigned to hydrated hydronium ions on the basis of the evolution of the signal with increasing water content, chemical shift calculations, and the direct comparison with HClO4 in water. The intensity of 1H–29Si cross-polarization signal first increased and then decreased with increasing water chemical potential. This indicates that hydrogen bonds between water molecules and the tetrahedrally coordinated aluminum in the zeolite lattice weaken with the formation of hydronium ion–water clusters and increase the mobility of protons. DFT-based ab initio molecular dynamics studies at multiple temperatures and water concentrations agree well with this interpretation. Above 140 °C, however, fast proton exchange between bridging hydroxyl groups and water occurs even in the presence of only one water molecule per acid site.

Li-S batteries have been extensively studied using rigid carbon as the host for sulfur encapsulation, but improving the properties with a reduced electrolyte amount remains a significant challenge. This is critical for achieving high energy density. Here, we developed a soft PEOLiTFSI polymer swellable gel as a nanoscale reservoir to trap the polysulfides under lean electrolyte conditions. The PEOLiTFSI gel immobilizes the electrolyte and confines polysulfides within the ion conducting phase. The Li-S cell with a much lower electrolyte to sulfur ratio (E/S) of 4 g/g (3.3 mL/g) could deliver a capacity of 1200 mA h/g, 4.6 mA h/cm, and good cycle life. The accumulation of polysulfide reduction products, such as LiS, on the cathode, is identified as the potential mechanism for capacity fading under lean electrolyte conditions.

August 24, 1998This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. PREPRINTThis paper was prepared for submittal to the DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. ABSTRACTMany studies suggest that lean-NO x SCR proceeds via oxidation of NO to NO 2 by oxygen, followed by the reaction of the NO 2 with hydrocarbons. On catalysts that are not very effective in catalyzing the equilibration of NO+O 2 and NO 2 , the rate of N 2 formation is substantially higher when the input NO x is NO 2 instead of NO. The apparent bifunctional mechanism in the SCR of NO x has prompted the use of mechanically mixed catalyst components, in which one component is used to accelerate the oxidation of NO to NO 2 , and another component catalyzes the reaction between NO 2 and the hydrocarbon. Catalysts that previously were regarded as inactive for NO x reduction could therefore become efficient when mixed with an oxidation catalyst. Preconverting NO to NO 2 opens the opportunity for a wider range of SCR catalysts and perhaps improves the durability of these catalysts. This paper describes the use of a non-thermal plasma as an efficient means for selective partial oxidation of NO to NO 2 . When combined with some types of SCR catalyst, the plasma can greatly enhance the NO x reduction and eliminate some of the deficiencies encountered in an entirely catalyst-based approach.

Natural abundance 17 O and 6 Li NMR experiments, quantum chemistry and molecular dynamics studies were employed to investigate the solvation structures of Li + at various concentrations of LiFSI in DME electrolytes. It was found that the chemical shifts of both 17 O and 6 Li changed with the concentration of LiFSI, indicating the changes of solvation structures with concentration. For the quantum chemistry calculations, the coordinated cluster LiFSI(DME) 2 forms at first, and its relative ratio increases with increasing LiFSI concentration to 1 M. Then the solvation structure LiFSI(DME) become the dominant component. As a result, the coordination of forming contact ion pairs between Li + and FSIion increases, but the association between Li + and DME molecule decreases. Furthermore, at LiFSI concentration of 4 M the solvation structures associated with Li + (FSI-) 2 (DME), Li + 2 (FSI-)(DME) 4 and (LiFSI) 2 (DME) 3 become the dominant components. For the molecular dynamics simulation, with increasing concentration, the association between DME and Li + decreases, and the coordinated number of FSIincreases, which is in perfect accord with the DFT results.

No abstract

High field quantitative 27 Al single pulse (SP) MASNMR combined with temperature programmed desorption (TPD) of ethanol are used to study the surface of γ−Al 2 O 3 during phase transformationprocessesinduced by calcinationin the temperature range of 500 to1300 °C.Following ethanol adsorption,ethylene is generated during TPD with a desorption temperature above 200 °C.The amount of ethylene decreases monotonically with increasing calcination temperature prior to TPD. Significantly, 27 Al SP MAS NMR revealsthat the amount of pentacoordinated Al 3+ ions also decreases with increasing calcination temperature. Aquantitative (within experimental error)correlation between the amount of penta-coordinated Al 3+ ions and the amount of strongly adsorbed ethanol molecules(i.e., the ones that convert to ethylene during TPD) is obtained. These resultsprovide good evidence for a proposalthat the penta-coordinated aluminum sites are the catalytic active sites on alumina surfacesduring ethanol dehydration reaction across the entire course of γ−tο−α Al 2 O 3 phase transformations.

Mechanisms of nucleation and growth of Al hydroxides such as gibbsite from aqueous solution, particularly in highly alkaline conditions, remain poorly understood. In this work, quantitative 27Al and 23Na MAS NMR experiments were conducted on solid samples extracted from the crystallization of gibbsite from an amorphous aluminum hydroxide gel precursor. The use of a high magnetic field and a moderate sample spinning rate of 20 kHz allowed transitional tetrahedral (AlT) and pentahedral (AlP) aluminum species to be observed along with the octahedral aluminum (AlO) that dominates the gibbsite product. Low-coordinated Al species could be detected at concentrations as low as 0.1% of the total Al sites. The following results have been established: (a) AlT and AlP coexist on the surface of growing gibbsites even with a combined percentage over the total Al sites of less than 1%. (b) Different synthesis methods generate gibbsite with varying amounts of low-coordinated Al. (c) The amorphous gel precursor contains a significant amount of low-coordinated Al sites with an AlO:AlP:AlT ratio of approximately 4:2:1. (d) Upon hydration, the external, low-coordinated Al sites become 6-fold coordinated by interacting with the oxygen in H2O, and the 27Al MAS NMR peak position shifts to that for the AlO sites. (e) Gibbsite with increased long-range order is synthesized over longer times by gradually incorporating residual AlP and AlT sites into octahedrally coordinated AlO sites. (f) Trace Na is predominantly a surface species on gibbsite particles. These findings provide a basis for understanding the gibbsite crystallization mechanism, along with a general means of characterizing gibbsite surface properties that are of equal importance for understanding related processes such as dissolution behavior.

Alpine ecosystems are harsh environments where low temperatures are generally a limiting factor. Predicted global warming is thus expected to have a profound impact on alpine ecosystems in the future. This study was conducted to compare the effect of experimental warming on soils in two contrasting forest ecosystems (a dragon spruce plantation and a natural forest) using the open top chamber (OTC) method in the Eastern Tibetan Plateau of China. The OTC enhanced average daily mean soil temperatures by 0.61°C (plantation) and 0.55°C (natural forest), respectively, throughout the growing season. Conversely, soil volumetric moisture declined by 4.10% in the plantation and by 2.55% in the natural forest. Across all measuring dates, warming increased average soil CO 2 efflux by 10.6% in the plantation and by 15.4% in the natural forest. However, elevated temperatures did not affect the respiration quotient in either forest. Two-stage sulfuric acid hydrolysis was used to quantify labile and recalcitrant C and N fractions in the two contrasting soils. Warming significantly reduced labile C and N fractions in both ecosystems but did not influence the total, recalcitrant and microbial biomass C and N pools. Labile C, N and microbial biomass C showed significant interactions in warming × forest type × season. Irrespective of warming treatments, all measured pools were significantly larger in the natural forest compared to the plantation. Taken together, our results indicate that the lowered soil labile C and N pools may be induced by the increased soil CO 2 efflux. The responses of the natural forest soil were more sensitive to experimental warming than those of the plantation. We conclude that reforestation dramatically lowers soil C and N pools, further affecting the responses of forest soils to future global warming.