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Multiple-phase hydrogen storage materials such as metal alanates and borohydrides, and destabilized systems offer the possibility of high hydrogen storage capacity with favorable thermodynamics. However, the multiphase nature of these materials intrinsically limits the kinetics due to the required transport of species between phases, which are typically in dry powder form. To address this limitation, the influence of added electrolytes is explored. This approach is motivated by analogy with similar multiphase battery reactions that show reduced kinetic limitations while necessarily containing electrolytes. Previous experimental results showing improved kinetics for MgH2/Sn (using a LiBH4/KBH4 eutectic electrolyte) and NaAlH4 (using a diglyme electrolyte) are further analyzed in terms of this analogy. The results show that the analogy is useful and rate constants are increased. Importantly, the inclusion of an electrolyte also appears to alleviate the continuously decreasing rates with the extent of reaction, which is characteristic of many multiphase hydrides. Instead, reaction rates are approximately constant until near completion. Together, these effects can lead to >10× shorter overall reaction times. In addition, new results are presented for the hydrogenation of MgB2 using Li/K/CsI and Li/K/CsCl eutectic electrolytes, where >60% conversion to Mg(BH4)2 was demonstrated at 350 bar.

Direct synthesis of delaminated layered zeolitic materials aims to synthesize confined catalysts for reactions involving sterically bulky reactants, which are too large to benefit from conventional three-dimensional confinement in micropores.

In this work, we evaluate the electrochemical properties of MBH4-C60 (M = Li+, Na+) nanocomposites for potential use as a solid-state electrolyte in alkali-ion batteries. The enhancement of ionic conductivity for MBH4 was achieved through the addition of C60 and partial dehydrogenation, resulting in an electrolyte with significantly higher ionic conductivity when compared to the pure MBH4. This improvement is attributed to the nanoionic destabilization of the MBH4 salt due to the affinity of the BH4− anion for C60 and partial dehydrogenation of the MBH4 through heating. The LiBH4-C60 nanocomposite was successfully paired with two anodes (graphite and lithium titanate) and two cathodes (LiFePO4 and TiS2) and galvanostatically cycled. The NaBH4-C60 nanocomposite showed nearly a 4-order-of-magnitude increase in ionic conductivity versus pure NaBH4 and demonstrated reversible sodium stripping and plating in a symmetric cell.

Low-silica faujasite (FAU) zeolites (with Si/Al ratio of ca. 1.2–1.8) sustain framework integrity and porosity upon moderate ion exchange (0.01 M NH₄NO₃ solution for 1 h at ambient temperature), which introduces two kinds of protons, distinctive in reactivity and coordination to the zeolite framework, within supercages (HSUP). Moderate ion exchange limited within supercages transpires while maintaining full occupancy of Na⁺ cations within associated sodalite cages; this in turn helps stabilize the framework of low-silica H-FAU zeolites. Protons located on site II (H₃₆₃₀) and site III (H₃₆₅₀) within supercages on low-silica FAU zeolites can be classified and enumerated by virtue of infrared spectroscopy, providing an opportunity to compare reactivities of these distinct protons for monomolecular protolytic reactions of propane. Protons on site II exhibit prominently higher reactivity for monomolecular propane dehydrogenation and cracking than protons on site III. Low-silica proton-form FAU zeolites (zeolite X) upon moderate ion exchange possess protons on site III that are unavailable on high-silica FAU zeolites (zeolite Y) and limit ion exchange within supercages, providing unprecedented high-temperature structural and chemical stability (>773 K) and enabling their application as solid-acid catalysts.

Faujasite (FAU) zeolites (with Si/Al ratio of ca. 1.7) undergo mild dealumination at moderate ion exchange conditions (0.01 to 0.6 M of NH 4 NO 3 solutions) resulting in protons circumscribed by sodalite cages becoming accessible for reaction without conspicuous changes to bulk crystallinity. The ratio of protons in sodalite cages (H SOD ) to supercages (H SUP ) can be systematically manipulated from 0 to ca. 1 by adjusting ammonium concentrations used in ion exchange. The fraction of accessible protons in the sodalite cages is assessed by virtue of infrared spectra for H-D exchange of deuterated propane based on the band area ratio of OD 2620 / OD 2680 (OD SOD / OD SUP ). Protons in sodalite cages (H SOD ) show higher rate constants of propane dehydrogenation ( k D ) and cracking ( k C ) than protons in supercages (H SUP ) plausibly due to confinement effects being more prominent in smaller voids. Rate constants of dehydrogenation and cracking including k D / k C ratios are also augmented as the fraction of accessible protons in the sodalite cages is enhanced. These effects of accessibility and reactivity of protons in sodalite cages hitherto inconspicuous are revealed herein via methods that systematically increase accessibility of cations located in sodalite cages.

Modern H2-based energy storage and conversion devices require a polymer electrolyte membrane (PEM) fuel cell–based integrated power system with synergistic heat integration. The key issue in integrated power systems is developing a PEM that can operate at 200–300 °C. However, currently used phosphoric-acid-based high-temperature PEM fuel cells limited stability at higher operating temperatures. Herein, we introduce a cerium hydrogen phosphate (CeHP) PEM that conducts protons above 200 °C through a self-assembled network (SAN). The SAN-CeHP-PBI reached maximum power densities of 2.4 W cm-2 and operate stably for over 7000 minute without any voltage decay at 250 ℃ under H2/O2 and anhydrous conditions. The developed fuel cell can be combined with an external hydrogen generator that uses a liquid hydrogen carrier such as N-ethylcarbazole and methanol as fuel, thus achieving a high energy efficiency. The thermal stability and fuel flexibility of these SAN-CeHP-PBI demonstrate potential for commercial applications.

The search for structurally relevant Al arrangements in zeolites is an important endeavor for single-site catalysis. Little is known about the mechanisms and zeolite dynamics during synthesis that are responsible for creating those Al ensembles. Here, new synthetic strategies for creating Al hosts in small-pore zeolites suitable for divalent cation catalysis are uncovered, leading to a mechanistic proposal for Al organization during crystallization. As such, unique synthesis–structure–activity relations are demonstrated for the partial oxidation of methane on Fe-exchanged CHA zeolites. With modified interzeolite conversions, the divalent cation capacity of the resulting high-Si SSZ-13 zeolites (Si/Al ∼ 35) can be reproducibly controlled in a range between 0.04 and 0.34 Co2+/Al. This capacity is a proxy for the distribution of framework aluminum in pairs and correlates with the methanol production per Al when these zeolites host the α-FeII redox active site. The uncovered interzeolite conversion synthesis–structure relations paint an Al-distribution hypothesis, where incongruent dissolution of the starting USY zeolite and fast synthesis kinetics with atypical growth modes allow assembling specific Al arrangements, resulting in a high divalent cation capacity. Prolonged synthesis times and high temperatures overcome the energetic barriers for T-atom reshuffling favoring Al isolation. These mechanisms and the relations uncovered in this work will guide the search for relevant Al ensembles in a range of zeolite catalysts where controlling the environment for a single active site is crucial. ispartof: Chemistry Of Materials vol:32 issue:1 pages:273-285 status: Published online

We investigated the substitution of structure-directing agent diisobutylimidazolium hydroxide with cetyltrimethylammonium hydroxide (CTA+OH−) surfactant in the synthesis gel of layered-zeotype-precursor B-SSZ-70(P). At low substitution levels, CTA+ interacts with the external-zeotype surface, where it assembles. At higher surfactant amounts, CTA+ intercalation occurs, leading to swelling of the precursor material, as evidenced by powder X-ray diffraction. Characterization of adsorbed CTA+ cations by 13C MAS NMR spectroscopy demonstrates unique broad resonances in the intercalated layers, which represent a more rigid environment than in the external-surface assemblies. At still higher CTA+ substitution levels in the synthesis gel, we observe the formation of amorphous mesoporous silica. We attempted to delaminate materials synthesized with varying CTA+ substitution levels using mild conditions, in which the conventional sonication step is replaced with an easy-to-scale high-shear mixing, and in which the use of halide reagents, which are corrosive and have been required in the past, is also avoided. Our data demonstrate that synthesis of a swollen material per se is not essential as an intermediate for delamination, and that layered zeolite precursor swelling can actually undermine zeolite delamination. Our results instead point to the CTA+ external-surface assemblies as facilitating ease of SSZ-70 delamination under these mild conditions. When calcined and functionalized with grafted titanium centers, the delaminated materials are highly active and selective olefin epoxidation catalysts with organic hydroperoxides, showing a 40% higher epoxide conversion than a catalyst prepared from conventional B-SSZ-70.

Integration of sensory and molecular inputs from the environment shapes animal behaviour. A major site of exposure to environmental molecules is the gastrointestinal tract, in which dietary components are chemically transformed by the microbiota1 and gut-derived metabolites are disseminated to all organs, including the brain2. In mice, the gut microbiota impacts behaviour3, modulates neurotransmitter production in the gut and brain4,5, and influences brain development and myelination patterns6,7. The mechanisms that mediate the gut-brain interactions remain poorly defined, although they broadly involve humoral or neuronal connections. We previously reported that the levels of the microbial metabolite 4-ethylphenyl sulfate (4EPS) were increased in a mouse model of atypical neurodevelopment8. Here we identified biosynthetic genes from the gut microbiome that mediate the conversion of dietary tyrosine to 4-ethylphenol (4EP), and bioengineered gut bacteria to selectively produce 4EPS in mice. 4EPS entered the brain and was associated with changes in region-specific activity and functional connectivity. Gene expression signatures revealed altered oligodendrocyte function in the brain, and 4EPS impaired oligodendrocyte maturation in mice and decreased oligodendrocyte-neuron interactions in ex vivo brain cultures. Mice colonized with 4EP-producing bacteria exhibited reduced myelination of neuronal axons. Altered myelination dynamics in the brain have been associated with behavioural outcomes7,9-14. Accordingly, we observed that mice exposed to 4EPS displayed anxiety-like behaviours, and pharmacological treatments that promote oligodendrocyte differentiation prevented the behavioural effects of 4EPS. These findings reveal that a gut-derived molecule influences complex behaviours in mice through effects on oligodendrocyte function and myelin patterning in the brain.

In this contribution, we extend some of the explorations in using ionic liquids as both solution media and organic–guest contributors to the eventual crystallizing structure, when attempts are made synthesize MAPO molecular sieves. We synthesize a family of imidazolium bromides for this purpose and demonstrated a trend toward increasing substituent length on the nitrogen sites. These materials are run as reaction systems using 5 inorganic situations: metals Ni, Zn, Co and Mg substituting in part for Al, and then a 5th reaction where there is no metal added. A variety of MAPO products are made and there are some correlati ons for the size of the imidazolium guest and the internal void space of the microporous material. Further analysis of some of the details of the products was carried out using solid state MAS NMR and focusing on Al, P and F nuclei in the products. There are some interesting observations found as to deviation from simple tetrahedral coordination for the Al and P, depending upon the imidazolium guest and the metal incorporated. Then, more attention was also focused on the reactions for Ni where once the guests became large enough the products seemed to be the 12-ring structure AFI which has parallel one dimensional pores. It seemed to be that the Ni is not able to be part of the lattice in these instances, and in fact, AFI is the product for a variety of the larger imidazolium guest molecules in the reaction run without any metal added for substitution.

Use of electrolytes, in the form of LiBH_4/KBH_4 and LiI/KI/CsI eutectics, is shown to significantly improve (by more than a factor of 10) both the dehydrogenation and full rehydrogenation of the MgH_2/Sn destabilized hydride system and the hydrogenation of MgB_2 to Mg(BH_4)_2. The improvement revealed that interparticle transport of atoms heavier than hydrogen can be an important rate-limiting step during hydrogen cycling in hydrogen storage materials consisting of multiple phases in powder form. Electrolytes enable solubilizing heavy ions into a liquid environment and thereby facilitate the reaction over full surface areas of interacting particles. The examples presented suggest that use of electrolytes in the form of eutectics, ionic liquids, or solvents containing dissolved salts may be generally applicable for increasing reaction rates in complex and destabilized hydride materials.

The structural changes underlying the deactivation of Sn-Beta zeolites under aqueous-phase reaction conditions at elevated temperatures (373 K) are investigated using spectroscopic characterization and site titration techniques together with turnover rates for glucose isomerization, a well-understood probe reaction for which changes in measured rates can be ascribed to specific changes in catalyst structure. In the case of hydrophobic, low-defect Sn-Beta zeolites (Sn-Beta-F), treatment in hot liquid water (373 K) for short times (3 h) to hot liquid water causes turnover rates to decrease and approach values characteristic of hydrophilic, defect-rich Sn-Beta zeolites (Sn-Beta-OH). In contrast, turnover rates on hydrophilic Sn-Beta-OH zeolites are insensitive to the duration of hot liquid water exposure prior to reaction. Activation and deactivation phenomena on Sn-Beta-F zeolites occur concomitantly with the formation of silanol defects (by ∼2–10×) with increasing durations (0–24 h) of hot water treatment, despite negligible differences in open and closed Sn site speciation as quantified ex situ by CD_3CN IR spectra. Mechanistic interpretations of these phenomena suggest that silanol groups present at low densities serve as binding sites for water molecules and clusters, which confer enthalpic stability to kinetically-relevant hydride-shift transition states and increase turnover rates, while silanol groups present in higher densities stabilize extended hydrogen-bonded water networks, which entropically destabilize kinetically-relevant transition states and decrease turnover rates. Intraporous voids within hydrophobic Sn-Beta-F zeolites become increasingly hydrophilic as silanol groups are formed by hydrolysis of framework siloxane bridges with increasing durations of water treatment, thereby decreasing aqueous-phase glucose isomerization turnover rates (per open Sn site). These findings suggest design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media.

Micro/meso/macroporous (hierarchical) zeolites show remarkable catalytic performance for reactions involving bulky reactants. However, quantitative assessment of the microstructural characteristics contributing to the observed performance remains elusive. Here, structure–activity relationships are established for a set of micro/mesoporous self‐pillared pentasil (SPP) zeolites using two parallel liquid‐phase reactions (benzyl alcohol alkylation and self‐etherification) based on analysis of mass transport and reaction kinetics. A reaction–diffusion mathematical model is developed that quantitatively assigns the catalytic contributions of the external surface and micropores of SPP zeolites for these reactions. In addition, the effect of the zeolite external surface structure on the corresponding catalytic activity is quantitatively assessed by comparing SPP zeolites (with MFI structure) with MCM‐22 (with MWW structure). This work demonstrates that reaction–diffusion modeling allows quantitative description of the catalytic performance of hierarchical zeolites and provides a model reaction to assess nm‐sized characteristic diffusion lengths in MFI.

Aqueous amines are currently the most promising solution for large-scale CO_2 capture from industrial sources. However, molecular design and optimization of amine-based solvents have proceeded slowly due to a lack of understanding of the underlying reaction mechanisms. Unique and unexpected reaction mechanisms involved in CO_2 absorption into aqueous hydrazine are identified using ^1H, ^(13)C, and ^(15)N NMR spectroscopy combined with first-principles quantum-mechanical simulations. We find production of both hydrazine mono-carbamate (NH_2-NH-COO^−) and hydrazine di-carbamate (^−OOC-NH-NH-COO^−), with the latter becoming more populated with increasing CO_2 loading. Exchange NMR spectroscopy also demonstrates that the reaction products are in dynamic equilibrium under ambient conditions due to CO_2 exchange between mono-carbamate and di-carbamate as well as fast proton transfer between un-protonated free hydrazine and mono-carbamate. The exchange rate rises steeply at high CO_2 loadings, enhancing CO_2 release, which appears to be a unique property of hydrazine in aqueous solution. The underlying mechanisms of these processes are further evaluated using quantum mechanical calculations. We also analyze and discuss reversible precipitation of carbamate and conversion of bicarbonate to carbamates. The comprehensive mechanistic study provides useful guidance for optimal design of amine-based solvents and processes to reduce the cost of carbon capture. Moreover, this work demonstrates the value of a combined experimental and computational approach for exploring the complex reaction dynamics of CO_2 in aqueous amines.

This manuscript develops a surface polymerization and cross-linking approach for the stabilization of single-site catalysts on solid surfaces, which is demonstrated here for grafted Ti(IV)-calixarene Lewis acids on silica. Our approach relies on cationic polymerization that is initiated by an adsorbed B(C_6F_5)_3 and uses styrene as the monomer and diisopropenylbenzene as the cross-linking agent. The mildness of this polymerization method is demonstrated by its lack of blocking micropores and only slight consumption of mesopore internal surface area on the basis of N2 physisorption data at 77 K, both of which are in contrast to previously reported surface-polymerization approaches. Catalysis of samples before and after polymerization and cross-linking was investigated with a probe reaction consisting of the epoxidation of 1-octene with tert-butyl hydroperoxide as oxidant, which is known to be catalyzed by Lewis-acid sites, and a comparison of catalyst hydrolytic stability was performed. Added water in the latter was used as a a trigger to induce site aggregation, as a stress test to determine the effectiveness of site protection by our polymerization approach. Consistent with the N2 physisorption data, catalysis data demonstrate that surface polymerization does not block small-molecule reactant and product access to Lewis-acid sites on the surface, since the conversion remains essentially unchanged before and after surface polymerization and cross-linking. DR UV–vis, TGA, and catalysis data reveal that the grafted Ti(IV)-calixarene sites on silica maintain their catalytic activity even after being treated with corrosive protic stress-test solution. In sharp contrast, grafted sites without the polymer layer leach nearly all of their calixarene and Ti contents during similar stress testing, resulting in the near complete loss of catalytic activity. We hypothesize that the surface polymer acts as a nanoreactor gatekeeper, which prevents the large Ti(IV)-calixarene site from leaching and keeps surface complexes as single sites grafted on the silica surface, by blocking access for the migration of sites from the surface to bulk solution.

Making cells magnetic is a long-standing goal of chemical biology, aiming to enable the separation of cells from complex biological samples and their visualization in vivo using magnetic resonance imaging (MRI). Previous efforts towards this goal, focused on engineering cells to biomineralize superparamagnetic or ferromagnetic iron oxides, have been largely unsuccessful due to the stringent required chemical conditions. Here, we introduce an alternative approach to making cells magnetic, focused on biochemically maximizing cellular paramagnetism. We show that a novel genetic construct combining the functions of ferroxidation and iron chelation enables engineered bacterial cells to accumulate iron in "ultraparamagnetic" macromolecular complexes, allowing these cells to be trapped with magnetic fields and imaged with MRI in vitro and in vivo. We characterize the properties of these cells and complexes using magnetometry, nuclear magnetic resonance, biochemical assays, and computational modeling to elucidate the unique mechanisms and capabilities of this paramagnetic concept.

The tetrairidium carbonyl cluster Ir_4L_3(CO)_9 (L = tert-butyl-calix[4]arene(OPr)_3(OCH_2PPh_2) (Ph = phenyl; Pr = propyl)) on a partially dehydroxylated silica support undergoes hydrogen activation at a rate and with a mechanism different from those pertaining to the cluster in alkane solution. These results are unobvious in view of the sterically bulky ligands protecting the cluster and the nearly identical CO band frequencies in the infrared spectra characterizing the supported and dissolved Ir_4L_3(CO)_9, both before reaction and during reaction involving decarbonylation in the presence of either helium or H_2 (and H2 reacted with the clusters to form hydrides with the same Ir–H band frequencies for clusters in alkane solvent and supported on silica). The initial rates of CO loss from the supported clusters in the presence of helium were the same as those in the presence of H_2. The comparison demonstrates that the rate-determining step for hydride formation on the silica-supported cluster is CO dissociation. In contrast, the comparable dissociation of CO from the cluster in n-decane solution requires a higher temperature, 343 K, and is at least an order of magnitude slower than when the clusters were supported on silica. CO dissociation is not the rate-determining step for hydrogen activation on the cluster in n-decane, as the rate is influenced by reactant H_2 as well.

A study exploring the use of ionic liquid reactions based on imidazolium halides in molecular sieve synthesis has produced a novel zincoaluminophosphate material with an open DFO-type framework structure. This framework structure had only been observed previously in the magnesioaluminophosphate system (Mg-DAF-1) where decamethonium was used as the structure directing agent. The new Zn-DAF-1 material has been characterized using chemical and thermogravimetric analysis and ^(13)C, ^(19)F, ^(27)Al and ^(31)P MAS NMR techniques. Structure analysis (P6/mcc, a = 22.2244(1) Å, c = 42.3293(3) Å) using synchrotron powder diffraction data not only confirmed the framework structure, but also revealed the locations of the Al, P and Zn atoms in the framework, the N,N′-di-isopropyl-imidazolium (DIPI) ions in the pores, some fluoride ions associated with double 4-rings, and some water molecules and anions filling the remaining space. This level of structural detail had not been possible in the Mg-DAF-1 material. Four different locations for the DIPI cation were found in the two 12-ring channels and Zn was found to substitute for only one of the six crystallographically distinct Al sites to yield the approximate crystal chemical formula |(DIPI)_(17)(OH,F)_(11)(H2O)_(23)|[Zn_6Al_(126)P_(132)O_(528)]-DFO.

Understanding of surface interactions between borohydride molecules and the surfaces of porous supports have gained growing attention for successful development of nano-confinement engineering. By use of in␣situ variable temperature (VT) magic angle spinning (MAS) NMR, molecular mobility changes of LiBH_4 crystalline solid has been investigated in the presence of silica based and carbonaceous surfaces. Spin–spin J-coupling of ^(1)H–^(11)B in LiBH_4 was monitored in series of VT NMR spectra to probe translational mobility of LiBH_4 that appeared to be greatly enhanced upon surface contact. Such enhanced diffusivity was found to be effective in the formation of solid solution and co-confinement with other metal borohydrides. Co-confinement of LiBH_4–Ca(BH_4)_2 mixture was demonstrated at temperature as low as 100 °C, much lower than the reported bulk eutectic melting temperature. The discovery adds a novel property of LiBH_4 that has been proven to be highly versatile in many energy related applications.

Variable temperature (VT) ^2H magic angle spinning (MAS) spectroscopy was employed to measure deuterium diffusion behavior in the Zr_2NiD_(4.8) phase. ^2H MAS NMR spectrum at ∼190 K provides with well-resolved 4 different site occupancies which can be assigned based on the crystal structure (16k (Zr_2Ni_2), 32m (Zr_3Ni), Zr_4 (16/ and 4b)). As the temperature rises, the ^2H peaks sensitively reflect the exchange behavior among the sites with evident change at around 230 K and reaching a uniform distribution of site occupancies, indistinguishable in NMR timescale, above 245 K. This behavior is reflected by the collapse of the ^2H MAS spectrum into a single peak. From analyses of VT MAS NMR spectra, we were able to extract multiple hopping rates and activation energies among face sharing interstices: for example, 32m ↔ 16/ hopping shows _(τc)=2.8×10^(-4)s at 245 K and E_a = 62.2 kJ/mol.

Generation of fluidic LiBH_4 molecules, ƒ-LiBH_4, was demonstrated by NMR spectroscopy of LiBH_4 bulk powder mixed with silica scaffold surface materials under minor heat treatment. In the presence of the fumed silica or mesoporous MCM-41 and SBA-15, LiBH_4 shows increased translational mobility at relatively low temperature (ca. 95 °C) and becomes liquid-like by evidence from ^1H–^(11)B J-coupling in ^1H and ^(11)B MAS NMR or substantial line narrowing of ^7Li static NMR. This high diffusional mobility of LiBH_4 at the molecular level has never been seen for bulk LiBH_4, and the property is attributed to the interfacial interaction with the mesoporous scaffold surfaces. While ƒ-LiBH_4 facilitates the confinement of LiBH_4 itself into various scaffold materials, LiBH_4 migrates along the SBA-15 surface to reach other metal borohydride particles, Ca(BH_4)_2 in this case, and promotes the formation of similarly fluidic LiBH_4–Ca(BH_4)_2 composite (LC solid solution) for coconfinement into mesopores. In situ variable temperature (VT) NMR spectroscopy detects the co-infiltration process of eutectic LiBH_4–Ca(BH_4)_2 composite (LC) into mesopores of SBA-15. The infiltration rates measured for LiBH_4 bulk powder or LC composite showed dependence on pore sizes (MCM-41 vs SBA-15) and heat treatment conditions (static vs MAS).

High resolution, multi-nuclear solid state nuclear magnetic resonance (NMR) characterizations are carried out in order to obtain insights into the structural features of Sn-beta zeolites that catalyze glucose isomerization or epimerization reactions in water and methanol solvents. In particular, we focus on investigating the local structural changes to catalytically-active framework Sn sites of different ^(119)Sn-labeled beta zeolites, including the calcined, dehydrated, rehydrated, and post-sugar isomerization catalysis forms. Magic angle spinning (MAS) and cross polarization MAS (either from ^1H or ^(19)F) ^(119)Sn NMR spectra provide evidence for changes to the local framework Sn coordination in the presence of water and sugar molecules, and provide insights into structural features of adsorbed intermediates that may be relevant in sugar isomerization reaction pathways.

Metal dodecaborates M_2/_nB_(12)H_(12) (n denotes the valence of the metal M), containing icosahedral polyatomic anion [B_(12)H_(12)]^(2−), have been attracting increasing interest as potential energy materials, especially in the context of hydrogen storage and superionic conductivity. M_2/_nB_(12)H_(12) are commonly formed as dehydrogenation intermediates from metal borohydrides M(BH_4)_n, like LiBH_4 and Mg(BH_4)_2, which are well-known as potential high-density hydrogen storage materials. The strong B−B bond in the icosahedral [B_(12)H_(12)]^(2−), however, is regarded to be the key factor that prevents the rehydrogenation of dodecaborates. In order to elucidate the mechanism as well as to provide effective solutions to this problem, a novel solvent-free synthesis route of anhydrous M_2/nB_(12)H_(12) (here M means Li, Na, and K) has been developed. Thermal stability and transformations of the anhydrous single phase Li_2B_(12)H_(12) suggested the formation of the high temperature polymorph of Li_2B_(12)H_(12) during the dehydrogenation of LiBH_4, while concurrently emphasized the importance of further investigation on the decomposition mechanism of metal borohydrides and metal dodecaborates. The high stability of icosahedral [B_(12)H_(12)]^(2−), on the other hand, favors its potential application as solid electrolyte. Recently, Na^+ conductivity of Na_2B_(12)H_(12) was reported to be 0.1 S/cm above its order−disorder phase transition at ∼529 K, which is comparable to that of a polycrystalline β”-Al_2O_3 (0.24 S/cm at 573 K) solid state Na-electrolyte. Mechanistic understanding on the diffusion behavior of cation and further improvement of ionic conductivity at a lower temperature, however, are important in order to facilitate the practical application of metal dodecaborates as superionic conductors.

Aqueous amines are currently the most promising solution for large-scale CO

Dealuminated zeolite HY was used to support Ir(CO)_2 complexes formed from Ir(CO)_2(C_5H_7O_2). Infrared and X-ray absorption spectra and atomic resolution electron microscopy images identify these complexes, and the images and ^(27)Al NMR spectra identify impurity amorphous regions in the zeolite where the iridium is more susceptible to aggregation than in the crystalline regions. The results indicate the value of electron microscopy in characterizing the amorphous impurity regions of zeolites and a significant stability limitation of metals in these regions of zeolite catalyst supports.

Delaminated zeolite UCB-3 exhibits 2.4-fold greater catalytic activity relative to its three-dimensional (3D) zeolite counterpart, Al-SSZ-70, and 2.0-fold greater activity (per catalyst mass) when compared with industrial catalyst MCM-22, for the alkylation of toluene with propylene at 523 K. The former increase is nearly equal to the observed relative increase in external surface area and acid sites upon delamination. However, at 423 K for the same reaction, UCB-3 exhibits a 3.5-fold greater catalytic activity relative to 3D Al-SSZ-70. The higher relative rate enhancement for the delaminated material at lower temperature can be elucidated on the basis of increased contributions from internal acid sites. Evidence of possible contributions from such acid sites is obtained by performing catalysis after silanation treatment, which demonstrates that although virtually all catalysis in MCM-22 occurs on the external surface, catalysis also occurs on internal sites for 3D Al-SSZ-70. The additional observed enhancement at low temperatures can therefore be rationalized by greater access to internal active sites as a result of sheet breakage during delamination. Such breakage leads to shorter characteristic internal diffusion paths and was visualized using TEM comparisons of UCB-3 and 3D Al-SSZ-70.

Framework Lewis acidic tin sites in hydrophobic, pure-silica molecular sieves with the zeolite beta topology (Sn-Beta) have been reported previously to predominantly catalyze glucose−fructose isomerization via 1,2 intramolecular hydride shift in water and glucose–mannose epimerization via 1,2 intramolecular carbon shift in methanol. Here, we show that alkali-free Sn-Beta predominantly isomerizes glucose to fructose via 1,2 intramolecular hydride shift in both water and methanol. Increasing extents of postsynthetic Na+ exchange onto Sn-Beta, however, progressively shifts the reaction pathway toward glucose–mannose epimerization via 1,2 intramolecular carbon shift. Na^+ remains exchanged onto silanol groups proximal to Sn centers during reaction in methanol solvent, leading to nearly exclusive selectivity toward epimerization. In contrast, decationation occurs with increasing reaction time in aqueous solvent and gradually shifts the reaction selectivity to isomerization at the expense of epimerization. Decationation and the concomitant selectivity changes are mitigated by the addition of NaCl to the aqueous reaction solution. Preadsorption of ammonia onto Sn-Beta leads to near complete suppression of infrared and ^(119)Sn nuclear magnetic resonance spectroscopic signatures attributed to open Sn sites and of glucose−fructose isomerization pathways in water and methanol. These data provide evidence that Lewis acidic open Sn sites with either proximal silanol groups or Na-exchanged silanol groups are respectively the active sites for glucose–fructose isomerization and glucose–mannose epimerization.

We investigate grafting of poly(methylhydrosiloxane) (PMHS) onto Ti/SiO2 catalysts for improving their robustness to water, using olefin epoxidation catalysis with organic hydroperoxide as oxidant as a relevant probe reaction. Our approach involves triggering catalyst deactivation with added water in the reactants as a means to simulate catalyst deactivation, thereby causing grafted Ti-site aggregation. When using harsh aqueous Soxhlet extraction conditions as a trigger for this aggregation, significant differences are observed via diffuse-reflectance UV–vis spectrscopy on samples before and after treatment, for Ti/SiO2 catalysts containing grafted PMHS. Not only was there a lack of appearance of red-shifted bands in the UV-Vis spectrum following Soxhlet extraction, the batch catalytic activity for catalysts before and after PMHS grafting remained virtually unchanged. This was in stark contrast to an unmodified Ti/SiO2 catalyst, which showed a more than 60% decrease in catalytic activity following Soxhlet extraction as a result of aggregation, as ascertained by red shifts in its UV–vis spectrum after Soxhlet extraction. Similar red shifts were also observed for a hydrophobically modified TMS Ti/SiO2 catalyst. However, when comparing these catalysts under more gentle olefin epoxidation catalysis conditions with added water in a flow reactor, it was more difficult to differentiate the TMS Ti/SiO2 and grafted PMHS catalysts. Both catalysts exhibited similar activity and selectivity after a prolonged time on stream, though the rate of initial deactivation in the latter was less pronounced. Altogether, our data demonstrate that grafted PMHS catalysts are positively differentiated from conventional catalysts based on either TMS surface modification or no surface modification, under conditions involving aggregation induced via extreme hydrothermal environmentst. Thus, we expect that PMHS grafting of Lewis acid catalysts can offer an alternative approach for endowing hydrolytic stability to such catalysts, as demonstrated here for Ti/SiO2 epoxidation catalysts.

The work here describes the kinetic analyses of aluminum replacement for boron in a suite of borosilicate molecular sieves. While the method has been described before as a means of converting synthesized borosilicates (with weak inherent acidity) to aluminosilicates (with much stronger acid strength) when there are large pores in the structure, here we carry out the transformation under less than optimal replacement concentrations, in order to better follow the kinetics. We examined several zeolite structures with boundary conditions of boron MEL where there are only 10-ring (or intermediate) pore structures and no Al is taken up, to multidimensional large pore zeolites, like boron beta, where Al substitution can occur everywhere. We also studied materials with both intermediate and large pores, SSZ-56, 57, 70, and 82. In the case of 57 up to 90% of the structure is made up of boron MEL. We observe that the pH drop is proportional to the Al reinsertion and is the same for all zeolites we studied. In one case, we compared a zeolite (SSZ-24) with boron and then no boron sites and found that Al does not go into defect sites. It was again confirmed (shown in earlier work) that Al will go into nest sites created by boron hydrolysis out of the substrate before Al treatment. Along those lines we also made two new observations: (1) the profile for Al uptake, as followed by pH drop, is the same kinetically, whether the boron is there or not; and (2) NMR showed that the boron is leaving the structure faster than Al can go back in (SSZ-33 study), even when we treat a material with boron in the lattice.

We describe a new zeolite catalyst where we develop only a portion of the structure for strong acid sites. This is achieved using zeolite SSZ-57 in boron lattice substitution (weak acid sites) and then replacing the boron sites in the large pore segments of this novel zeolite, while the intermediate pores (with MEL topology) remain unchanged. We can achieve the creation of such a novel catalyst system due to the inherent structure of SSZ-57 (repeat domains of MEL topology, periodically interrupted by a short segment of large pores) because the re-insertion of aluminum for boron requires that the pores be large to effect substitution. In this work, we describe the preparation and characterization of the novel material designated as SSZ-57LP. We use three model compound reactions to demonstrate the unique behavior for this novel large pore (but short path) zeolite and contrast it with intermediate pore zeolite Al-ZSM-11 (MEL topology) and the Al-SSZ-57 where the strong acid sites are in both intermediate and large pore regions (from direct zeolite synthesis with aluminum in the gel). The reactions studied are the Constraint Index probing reactant selectivity for cracking n-hexane and 3-methylpentane, the hydroisomerization of n-hexane where the formation of dimethylbutanes is examined for large pore space within a zeolite, and then finally, the isomerization and disproportionation of 1,3-diethylbenzene, again as a probe for large enough transition state selectivity within a given zeolite.

The recent discovery of a new class of negative ions called hyperhalogens allows us to characterize this complex as belonging to a unique class of materials called hypersalts. Hyperhalogen materials are important while serving as the building blocks for the development of new materials having enhanced magnetic or oxidative properties. One prime example of a hydperhalogen is the Al(BH_4)_4^– anion. Aluminum borohydride (17 wt % H) in itself is a volatile, pyrophoric compound that has a tendency to release diborane at room temperature, making its handling difficult and very undesirable for use in practical applications. Here we report that the combination of Al(BH_4)_3 with the alkaline metal borohydride KBH_4 results in the formation of a new compound KAl(BH_4)_4 which is a white solid that exhibits remarkable thermal stability up to 154 °C and has the typical makeup of a hypersalt material. Using a variety of characterization tools and theoretical calculations, we study and analyze the physical characteristics of this compound and show its potential for stabilizing high hydrogen capacity, energetic materials.

The synthesis of the first delaminated borosilicate layered zeolite precursor is described, along with its aluminosilicate analogue, which consists of Al-containing UCB-3 and B-containing UCB-4 from as-made SSZ-70. In addition, the delamination of PREFER (which is the precursor to ferrierite zeolite) under similar conditions yields delaminated layered zeolite precursors consisting of Al-containing UCB-5 and Ti-containing UCB-6. Multinuclear solid-state NMR spectroscopy (^(11)B and ^(27)Al), diffuse-reflectance UV-vis spectroscopy, and heteroatom/Si ratios measured via elemental analysis are consistent with a lack of heteroatom leaching from the framework following delamination. Such mild delamination conditions are achieved by swelling the zeolite precursor in a fluoride/chloride surfactant mixture in DMF solvent, followed by sonication. Powder X-ray diffraction, argon gas physisorption, and chemisorption of bulky base probes strongly suggest delamination, and demonstrate a 1.5-fold increase in the number density of external acid sites and surface area of calcined UCB-3, relative to calcined Al-SSZ-70. The synthesis of microporous pockets in materials UCB-3–UCB-5 suggests the possibility of interlayer porosity in SSZ-70, which is a layered zeolite precursor material whose structure remains currently unknown. The mildness of the delamination method presented here, as well as the lack of need for acidification in the synthesis procedure, enables the delamination of heteroatom-containing zeolites while preserving the framework integrity of labile heteroatoms, which could otherwise be leached under harsher conditions.

The effect of calixarene ligand symmetry, as dictated by lower-rim substitution pattern, on the coordination to a Ti(IV) cation is assessed in solution and when grafted on SiO_2, and its effect on epoxidation catalysis by Ti(IV)-calixarene grafted on SiO_2 is investigated. C_(2v) symmetric Ti-tert-butylcalix[4]arene complexes that are 1,3-alkyl disubstituted at the lower rim (di-R-Ti) are compared to previously reported grafted C_s symmetric complexes, which are singly substituted at the lower rim (mono-R-Ti). ^(13)C MAS NMR spectra of complexes isotopically enriched at the lower-rim alkyl position indicate that di-R-Ti predominantly grafts onto silica as the conformation found in solution, exhibiting a deshielded alkyl resonance compared to the grafted mono-R-Ti complexes, which is consistent with stronger alkyl ether→Ti dative interactions that are hypothesized to result in higher electron density at the Ti center. Moreover, ^(13)C MAS NMR spectroscopy detects an additional contribution from an “endo” conformer for grafted di-R-Ti sites, which is not observed in solution. Based on prior molecular modeling studies and on ^(13)C MAS NMR spectroscopy chemical shifts, this “endo” conformer is proposed to have similar Ti–(alkyl ether) distances at the lower-rim and electron density at the Ti center relative to grafted mono-R-Ti complexes. Differences between grafted mono-R-Ti and di-R-Ti sites can be observed by ligand-to-metal charge transfer edge-energies, calculated from diffuse-reflectance UV–visible spectroscopy at 2.24 ± 0.02 and 2.16 ± 0.02 eV, respectively. However, rates of tert-butyl hydroperoxide consumption in the epoxidation of 1-octene are found to be largely unchanged when compared to those of the grafted mono-R-Ti complexes, with average rate constants of ~1.5 M^(−2) s^(−1) and initial TOF of ~4 ks^(−1) at 323 K. This suggests that an “endo” conformation of grafted di-R-Ti may prevail during catalysis. Despite this, grafted di-C_1-Ti complexes can be more selective than mono-C_1-Ti complexes (45 vs. 34 % at a 50 % conversion at 338 and 353 K), illustrating the importance of the Ti coordination environment on epoxidation catalysis.

The dehydrogenation reactions of Ca(BH_4)_2 are investigated under different isobaric conditions using in situ synchrotron radiation powder X-ray diffraction and nuclear magnetic resonance measurements. Ca(BH_4)_2 dissociates in multiple steps, and several intermediate phases, such as an amorphous phase(s), CaB_2Hx, and CaB_(12)H_(12), are observed during dehydrogenation. Among the intermediate phases, it is known that CaB_2Hx is fully reversible, while the more stable CaB_(12)H_(12) with an icosahedral structure hinders reversible reactions. Here, we try to control the dehydrogenation reaction pathway of Ca(BH_4)_2 by applying different hydrogen back-pressures. The decomposition reaction of Ca(BH_4)_2 in the absence of a catalyst was found to be sensitive to the H_2 back-pressure. At p(H_2) = 1 bar, Ca(BH_4)_2 decomposes via two competitive dehydrogenation reaction routes to form CaB_2H_x or CaB_(12)H_(12). At p(H_2) = 10 bar, the overall dehydrogenation reaction remains unchanged. However, the formation of CaB_2H_x is reduced, and amorphous elemental boron is observed as a final dehydrogenation product. At p(H_2) = 20 bar, the elemental boron formation is significantly increased, and the formation of the CaB_2H_x phase is suppressed. Possible routes to form CaH_2 and elemental boron are discussed.

The dehydrogenation reaction pathway of Ca(BH_4)_2 has been investigated under an isobaric condition of 1 bar of hydrogen. β-Ca(BH_4)_2 gradually transforms into the (XRD invisible) amorphous phase at the initial stage. Upon further heating, it decomposes into CaB_2H_x or CaB_(12)H_(12), indicating that there is a subtle competition between two different dehydrogenation routes: (i) Ca(BH_4)_2 → amorphous phase → CaB_2H_x + (4 – x)/2H_2 → 2/3CaH_2 + 1/3CaB_6 + 10/3H_2 and (ii) Ca(BH_4)_2 → amorphous phase → 1/6CaB_(12)H_(12) + 5/6CaH_2 + 13/6H_2. It has also been concluded that CaB_2H_x as well as the CaB_6 + CaH_2 mixture can be rehydrogenated at 330 °C under 90 bar of hydrogen without any catalytic additive, whereas CaB_(12)H_(12) hardly rehydrogenated under the same conditions.

Alteration of the thermodynamic stability of selected borohydride/alanate systems, including the combination of LiBH_4 with NaAlH_4 and LiBH_4 with CaCl_2 and LiAlH_4, was investigated to determine the possibility of forming intermediate stability mixed AlH_(4)^(−)–BH_(4)^(−) phase. Facile metathesis exchange reactions were observed when NaAlH_4 was combined with LiBH_4 resulting in the formation of LiAlH_4 and NaBH_4. Thermal analysis of this system showed that the 1st and 2nd decomposition of LiAlH_4 occurred irrespective of NaBH_4 illustrating the absence molecular level interaction between the AlH_(4)^(−) and the BH_(4)^(−) anions. On the other hand, in the case of CaCl_2, LiAlH_4, LiBH_4 combination, the results showed the formation of a calcium alanate type phase. Evaluation of the thermal property of this system showed an endothermic one step decomposition between 130 °C and 200 °C (2.3 wt% loss). Structural examination of this calcium alanate type phase revealed a different local coordination geometry of AlH_(4)^(−) from that observed in calcium alanate. The formation and properties of this phase are being attributed to molecular level AlH_(4)^(−)–BH_(4)^(−) interactions. These findings provide a pathway toward designing novel alanates-borohydrides systems for hydrogen storage applications. This article will show the methodologies followed and explain the results obtained.

Solid state NMR is widely applied in studies of solid state chemistries for hydrogen storage reactions. Use of ^(11)B MAS NMR in studies of metal borohydrides (BH_4) is mainly focused, revisiting the issue of dodecaborane formation and observation of ^(11)B{^1H} Nuclear Overhauser Effect.

A synthetic route to borosilicate zeolites is described which yields relatively boron-rich products. The reaction takes place under high reactant concentrations and utilizes fluoride delivered as the ammonium fluoride salt rather than as hydrofluoric acid. The reaction is an adaptation of the conditions (HF) initially used to discover zeolite SSZ-70. Exploring a range of structure-directing agents (SDA), several boron-rich phases crystallized. Reactions are generally quite slow, however. A more in-depth study with an adamantyl SDA finds zeolite SSZ-23 favored over SSZ-13. Multinuclear NMR experiments were carried out to better understand the boron substitution in SSZ-23 and to probe if there are key B–F interactions in its formation. Finally, providing alkali cation sources of fluoride shifts the product selectivity away from SSZ-23 and back toward SSZ-13.

In Part 1, the promising hydrogen storage properties of the combined systems of Li3AlH6/LiBH4 and Al/LiBH4, exhibiting the favorable formation of AlB2 during dehydrogenation, were presented based on TGA and XRD analyses. The present Part 2 describes the characterization of the intermediate and final products of the dehydrogenation and rehydrogenation of the above systems by multinuclear solid-state NMR characterization. This work has also verified that the presence of Al resulted in the re-formation of LiBH4 occurring at a much lower temperature and H2 pressure, under which conditions the dehydrogenation product from LiBH4 alone does not show any degree of rehydrogenation. NMR studies mainly identified various reaction intermediates for LiBH4 dehydrogenation/rehydrogenation reactions. Unlike the XRD studies, the AlB2 formation, in particular, could not be unambiguously confirmed by NMR. 27Al NMR showed that aluminum was mainly involved in various Li—Al alloy formations. The catalytic role of Al in the LiB...