Noncontact In Situ Multidiagnostic NMR/Dielectric Spectroscopy.

Introduction of a dielectric material in a nuclear magnetic resonance (NMR) probe head modifies the frequency response of the probe circuit, a phenomenon revealed by detuning of the probe. For NMR spectroscopy, this detuning is corrected for by tuning and matching the probe head prior to the NMR measurement. The magnitude of the probe detuning, "the dielectric shift", provides direct access to the dielectric properties of the sample, enabling NMR spectrometers to simultaneously perform both dielectric and NMR spectroscopy. By measuring sample dielectric permittivity as a function of frequency, dielectric permittivity spectroscopy can be performed using the new methodology. As a proof of concept, this was evaluated on methanol, ethanol, 1-propanol, 1-pentanol, and 1-octanol using a commercial cross-polarization magic angle spinning (CPMAS) NMR probe head. The results accurately match the literature data collected by standard dielectric spectroscopy techniques. Subsequently, the method was also applied to investigate the solvent-surface interactions of water confined in the micropores of an MFI-type, hydrophilic zeolite with a Si/Al ratio of 11.5. In the micropores, water adsorbs to BroÌ·nsted acid sites and defect sites, resulting in a drastically decreased dielectric permittivity of the nanoconfined water. Theoretical background for the new methodology is provided using an effective electric circuit model of a CPMAS probe head with a solenoid coil, describing the detuning resulting from the insertion of dielectric samples in the probe head.

Prediction of Cu Zeolite NH3-SCR Activity from Variable Temperature 1H NMR Spectroscopy.

Selective catalytic reduction (SCR) of NOx by ammonia is one of the dominant pollution abatement technologies for near-zero NOx emission diesel engines. A crucial step in the reduction of NOx to N2 with Cu zeolite NH3-SCR catalysts is the generation of a multi-electron donating active site, implying the permanent or transient dimerization of Cu ions. Cu atom mobility has been implicated by computational chemistry as a key factor in this process. This report demonstrates how variable temperature 1H NMR reveals the Cu induced generation of sharp 1H resonances associated with a low concentration of sites on the zeolite. The onset temperature of the appearance of these signals was found to strongly correlate with the NH3-SCR activity and was observed for a range of catalysts covering multiple frameworks (CHA, AEI, AFX, ERI, ERI-CHA, ERI-OFF, *BEA), with different Si/Al ratios and different Cu contents. The results point towards universal applicability of variable temperature NMR to predict the activity of a Cu-zeolite SCR catalyst. The unique relationship of a spectroscopic feature with catalytic behavior for zeolites with different structures and chemical compositions is exceptional in heterogeneous catalysis.

Hydrogen bonding to oxygen in siloxane bonds drives liquid phase adsorption of primary alcohols in high-silica zeolites.

Upon liquid phase adsorption of C1-C5 primary alcohols on high silica MFI zeolites (Si/Al = 11.5-140), the concentration of adsorbed molecules largely exceeds the concentration of traditional adsorption sites: Brønsted acid and defect sites. Combining quantitative in situ1H MAS NMR, qualitative multinuclear NMR and IR spectroscopy, hydrogen bonding of the alcohol function to oxygen atoms of the zeolite siloxane bridges (Si-O-Si) was shown to drive the additional adsorption. This mechanism co-exists with chemi- and physi-sorption on Brønsted acid and defect sites and does not exclude cooperative effects from dispersive interactions.

Enabling hydrate-based methane storage under mild operating conditions by periodic mesoporous organosilica nanotubes.

Biomethane is a renewable natural gas substitute produced from biogas. Storage of this sustainable energy vector in confined clathrate hydrates, encapsulated in the pores of a host material, is a highly promising avenue to improve storage capacity and energy efficiency. Herein, a new type of periodic mesoporous organosilica (PMO) nanotubes, referred to as hollow ring PMO (HR-PMO), capable of promoting methane clathrate hydrate formation under mild working conditions (273 K, 3.5 MPa) and at high water loading (5.1 g water/g HR-PMO) is reported. Gravimetric uptake measurements reveal a steep single-stepped isotherm and a noticeably high methane storage capacity (0.55 g methane/g HR-PMO; 0.11 g methane/g water at 3.5 MPa). The large working capacity throughout consecutive pressure-induced clathrate hydrate formation-dissociation cycles demonstrates the material's excellent recyclability (97% preservation of capacity). Supported by ex situ cryo-electron tomography and x-ray diffraction, HR-PMO nanotubes are hypothesized to promote clathrate hydrate nucleation and growth by distribution and confinement of water in the mesopores of their outer wall, along the central channels of the nanotubes and on the external nanotube surface. These findings showcase the potential for application of organosilica materials with hierarchical and interconnected pore systems for pressure-based storage of biomethane in confined clathrate hydrates.

Reversible Parahydrogen Induced Hyperpolarization of 15 N in Unmodified Amino Acids Unraveled at High Magnetic Field.

Amino acids (AAs) and ammonia are metabolic markers essential for nitrogen metabolism and cell regulation in both plants and humans. NMR provides interesting opportunities to investigate these metabolic pathways, yet lacks sensitivity, especially in case of 15 N. In this study, spin order embedded in p-H2 is used to produce on-demand reversible hyperpolarization in 15 N of pristine alanine and ammonia under ambient protic conditions directly in the NMR spectrometer. This is made possible by designing a mixed-ligand Ir-catalyst, selectively ligating the amino group of AA by exploiting ammonia as a strongly competitive co-ligand and preventing deactivation of Ir by bidentate ligation of AA. The stereoisomerism of the catalyst complexes is determined by hydride fingerprinting using 1 H/D scrambling of the associated N-functional groups on the catalyst (i.e., isotopological fingerprinting), and unravelled by 2D-ZQ-NMR. Monitoring the transfer of spin order from p-H2 to 15 N nuclei of ligated and free alanine and ammonia targets using SABRE-INEPT with variable exchange delays pinpoints the monodentate elucidated catalyst complexes to be most SABRE active. Also RF-spin locking (SABRE-SLIC) enables transfer of hyperpolarization to 15 N. The presented high-field approach can be a valuable alternative to SABRE-SHEATH techniques since the obtained catalytic insights (stereochemistry and kinetics) will remain valid at ultra-low magnetic fields.

Absolute Quantification of Residual Solvent in Mesoporous Silica Drug Formulations Using Magic-Angle Spinning NMR Spectroscopy.

Porous silica is used as a drug delivery agent to improve the bioavailability of sparsely soluble compounds. In this approach, the active pharmaceutical ingredient (API) is commonly loaded into the porous silica by incipient wetness impregnation using organic solvents. Subsequent solvent elimination is critical as the residual solvent concentration cannot exceed threshold values set by health and safety regulations (e.g., EMA/CHMP/ICH/82260/2006). For dichloromethane and methanol, for example, residual concentrations must be below 600 and 3000 ppm, respectively. Today, EU and USA Pharmacopoeias recommend tedious procedures for residual solvent quantification, requiring extraction of the solvent and subsequent quantification using capillary gas chromatography with static headspace sampling (sHS-GC). This work presents a new method based on the combination of standard addition and absolute quantification using magic-angle spinning nuclear magnetic resonance spectroscopy (MAS qNMR). The methodology was originally developed for absolute quantification of water in zeolites and has now been validated for quantification of residual solvent in drug formations using mesoporous silica loaded with ibuprofen dissolved in DCM and MeOH as test samples. Interestingly, formulations prepared using as-received or predried mesoporous silica contained 5465 versus 484.9 ppm DCM, respectively. This implies that the initial water content of the silica carrier can impact the residual solvent concentration in drug-loaded materials. This observation could provide new options to minimize the occurrence of these undesired solvents in the final formulation.

How Water and Ion Mobility Affect the NMR Fingerprints of the Hydrated JBW Zeolite: A Combined Computational-Experimental Investigation.

An important aspect within zeolite synthesis is to make fully tunable framework materials with controlled aluminium distribution. A major challenge in characterising these zeolites at operating conditions is the presence of water. In this work, we investigate the effect of hydration on the 27 Al NMR parameters of the ultracrystalline K,Na-compensated aluminosilicate JBW zeolite using experimental and computational techniques. The JBW framework, with Si/Al ratio of 1, is an ideal benchmark system as a stepping stone towards more complicated zeolites. The presence and mobility of water and extraframework species directly affect NMR fingerprints. Excellent agreement between theoretical and experimental spectra is obtained provided dynamic methods are employed with hydrated structural models. This work shows how NMR is instrumental in characterising aluminium distributions in zeolites at operating conditions.

Hydration of Wheat Flour Water-Unextractable Cell Wall Material Enables Structural Analysis of Its Arabinoxylan by High-Resolution Solid-State 13C MAS NMR Spectroscopy.

To enable its structural characterization by nuclear magnetic resonance (NMR) spectroscopy, the native structure of cereal water-unextractable arabinoxylan (WU-AX) is typically disrupted by alkali or enzymatic treatments. Here, WU-AX in the wheat flour unextractable cell wall material (UCWM) containing 40.9% ± 1.5 arabinoxylan with an arabinose-to-xylose ratio of 0.62 ± 0.04 was characterized by high-resolution solid-state NMR without disrupting its native structure. Hydration of the UCWM (1.7 mg H2O/mg UCWM) in combination with specific optimizations in the NMR methodology enabled analysis by solid-state 13C NMR with magic angle spinning and 1H high-power decoupling (13C HPDEC MAS NMR) which provided sufficiently high resolution to allow for carbon atom assignments. Spectral resonances of C-1 from arabinose and xylose residues of WU-AX were here assigned to the solid state. The proportions of un-, mono-, and di-substituted xyloses were 59.2, 19.5, and 21.2%, respectively. 13C HPDEC MAS NMR showed the presence of solid-state fractions with different mobilities in the UCWM. This study presents the first solid-state NMR spectrum of wheat WU-AX with sufficient resolution to enable assignment without prior WU-AX solubilization.

HSIL-Based Synthesis of Ultracrystalline K,Na-JBW, a Zeolite Exhibiting Exceptional Framework Ordering and Flexibility.

A reproducible synthesis strategy for ultracrystalline K,Na-aluminosilicate JBW zeolite is reported. The synthesis uses a Na-based hydrated silicate ionic liquid (HSIL) as a silicon source and gibbsite as the aluminum source. 27Al and 23Na NMR spectra exhibit crystalline second-order quadrupole patterns in the hydrated as well as dehydrated states and distinct resonances for different T-sites demonstrating an exceptional degree of order of the elements of the JBW framework, observed for the first time in a zeolite. Detailed structural analysis via NMR crystallography, combining powder X-ray diffraction and solid-state NMR of all elements (27Al, 29Si, 23Na, 39K, and 1H), reveals remarkable de- and rehydration behavior of the JBW framework, transforming from its as-made hydrated structure via a modified anhydrous state into a different rehydrated symmetry while showing astonishing flexibility for a semicondensed aluminosilicate. Its crystallinity, exceptional degree of ordering of the T atoms and sodium cations, and the fully documented structure qualify this defect-free K,Na-aluminosilicate JBW zeolite as a suitable model system for developing NMR modeling methods.

Ion-Pairs in Aluminosilicate-Alkali Synthesis Liquids Determine the Aluminum Content and Topology of Crystallizing Zeolites.

Using hydrated silicate ionic liquids, phase selection and framework silicon-to-aluminum ratio during inorganic zeolite synthesis were studied as a function of batch composition. Consisting of homogeneous single phasic liquids, this synthesis concept allows careful control of crystallization parameters and evaluation of yield and sample homogeneity. Ternary phase diagrams were constructed for syntheses at 90 °C for 1 week. The results reveal a cation-dependent continuous relation between batch stoichiometry and framework aluminum content, valid across the phase boundaries of all different zeolites formed in the system. The framework aluminum content directly correlates to the type of alkali cation and gradually changes with batch alkalinity and dilution. This suggests that the observed zeolites form through a solution-mediated mechanism involving the concerted assembly of soluble cation-oligomer ion pairs. Phase selection is a consequence of the stability for a particular framework at the given aluminum content and alkali type.

Nucleation of Porous Crystals from Ion-Paired Prenucleation Clusters.

Current nucleation models propose manifold options for the formation of crystalline materials. Exploring and distinguishing between different crystallization pathways on the molecular level however remain a challenge, especially for complex porous materials. These usually consist of large unit cells with an ordered framework and pore components and often nucleate in complex, multiphasic synthesis media, restricting in-depth characterization. This work shows how aluminosilicate speciation during crystallization can be documented in detail in monophasic hydrated silicate ionic liquids (HSILs). The observations reveal that zeolites can form via supramolecular organization of ion-paired prenucleation clusters, consisting of aluminosilicate anions, ion-paired to alkali cations, and imply that zeolite crystallization from HSILs can be described within the spectrum of modern nucleation theory.

A multi-perspective analysis of microclimate dynamics for air-based solar hydrogen production.

Navigating the microclimatic environment for the optimal control of water-from-air devices could be a challenge. An example of such a device is an air-based solar hydrogen production device. Such a device promises the ability for off-grid, easily deployable and modular hydrogen production for on-site consumption. Novel analysis techniques, such as wavelet transform coherence analysis, could assist in better understanding the microclimate in which air-based hydrogen production devices might function. The analysis becomes complicated when a system is evaluated at the microclimatic level, especially when it is considered that the performance of air-based solar hydrogen devices are not only dependent on solar radiation, but also on humidity levels in the air. To get a grasp of the interactions that take place within a microclimatic system, a two-tiered approach is presented. It has been shown that relative humidity and temperature is stratified close to the ground, and that the stratification undergoes an inversion twice per day. A possible link between absolute humidity and wind direction is observed and humidity rallies are identified. Using microclimate monitoring and wavelet transform coherence analysis, an attempt is made to disentangle microclimatic variables by pointing out regions of high coherence and regions of low coherence between different variables. It is furthermore suggested that the propagation direction of a humidification process within the microclimate can be determined by considering the phase angle between relative humidity timeseries at different heights above the ground, using wavelet transform coherence analysis. It has been demonstrated that wavelet transform coherence analysis, in conjunction with a comprehensive microclimate monitoring process, could support the understanding of the complex processes that occur within the microclimatic environment and therefore support the management of water-from-air systems. In this regard a management framework is also presented.

A zeolite crystallisation model confirmed by in situ observation.

Probing nucleation and growth of porous crystals at a molecular level remains a cumbersome experimental endeavour due to the complexity of the synthesis media involved. In particular, the study of zeolite formation is hindered as these typically form in multiphasic synthesis media, which restricts experimental access to crystallisation processes. Zeolite formation from single phasic hydrated silicate ionic liquids (HSiL) opens new possibilities. In this work, HSiL zeolite crystallisation is investigated in situ using a specifically designed conductivity measurement set-up yielding access to crystallisation kinetics. Based on the conductivity data and final yields, a crystallisation model explaining the results based on a surface growth mechanism was derived. The excellent agreement between experiment and theory indicates zeolite crystallisation from highly ionic media proceeds via a multi-step mechanism, involving an initial reversible surface condensation of a growth unit, followed by incorporation of that unit into the growing crystal. The first step is governed by the liquid phase concentration and surface energy, while the final step shows a correlation to the mobility of the cation involved.

Selective catalytic reduction of NOx with ammonia (NH3-SCR) over copper loaded LEV type zeolites synthesized with different templates.

LEV type zeolites were synthesized with four different structure-directing agents and converted to copper loaded NH3-SCR catalysts. The synthesis recipe was found to impact the respective Al population in the two topologically different framework sites in double and single 6-rings, resolvable by 27Al MAS NMR spectroscopy. Hydrothermal stability was found to be related to the silanol concentration, Si/Al ratio, particle size, crystal morphology, crystal defects, external surface area, and microporosity. Catalytic activity in NH3-SCR was dependent on preferential Al siting in the double 6-rings. Levinite synthesized using adamantylamine showed the strongest preference for Al atoms sitting in double 6-ring sites, and showed the highest catalytic turnover frequency. Unfortunately, because of the large crystal size, copper loading of this sample was limited to 0.6 wt% while other samples could be loaded with copper up to 3.3 wt%. An optimum combination of hydrothermal stability and catalytic activity was obtained with N,N'-bis-dimethylpentanediyldiammonium dibromide as structure-directing agent.

Dispersing carbomers, mixing technology matters!

Mixing dry carbomer powder with water using magneto-hydrodynamic mixing yielded carbomer dispersions with higher viscosity and increased storage modulus as compared to conventional high shear mixing. 1H NMR spectroscopy demonstrated this to be induced by a different water distribution, accompanied by lower ionization and higher degradation of the polymer in case of high shear mixing. This investigation reveals 1H MAS NMR to provide suitable sensitivity and resolution to detect structural changes induced in organic polymers during their hydration.

Isotopological Fingerprinting Using 1H/D Scrambling Identifies the Stereochemistry of Hyperpolarization Catalysts Transferring Spin Polarization from Parahydrogen to Substrates Using Signal Amplification by Reversible Exchange.

Hyperpolarization using signal amplification by reversible exchange (SABRE) relies on target molecules and parahydrogen coordinating to a transition metal catalyst. Identification of this coordinated state becomes increasingly important, especially since bio-relevant targets such as pyruvate and amino acids exhibiting multiple binding sites are becoming compatible with SABRE. In this report, we present a fingerprinting method to discriminate and identify ligand binding sites without requiring the presence of a sensitive or isotope-labeled heteroatom. Adding a small concentration of protons to a deuterated medium, spontaneous 1H/D scrambling of exchangeable protons encodes the ligands each with an isotopological fingerprint. By use of rapid 2D zero quantum NMR, the binding sites are decoded from the hydrides in less than a minute. The new methodology is explained and demonstrated on Ir mixed complexes with pyridine, benzylamine, and ammonia as common N-functional ligands.

Energy-Efficient Small-Scale Ammonia Synthesis Process with Plasma-Enabled Nitrogen Oxidation and Catalytic Reduction of Adsorbed NOx.

Industrial ammonia production without CO2 emission and with low energy consumption is one of the technological grand challenges of this age. Current Haber-Bosch ammonia mass production processes work with a thermally activated iron catalyst needing high pressure. The need for large volumes of hydrogen gas and the continuous operation mode render electrification of Haber-Bosch plants difficult to achieve. Electrochemical solutions at low pressure and temperature are faced with the problematic inertness of the nitrogen molecule on electrodes. Direct reduction of N2 to ammonia is only possible with very reactive chemicals such as lithium metal, the regeneration of which is energy intensive. Here, the attractiveness of an oxidative route for N2 activation was presented. N2 conversion to NOx in a plasma reactor followed by reduction with H2 on a heterogeneous catalyst at low pressure could be an energy-efficient option for small-scale distributed ammonia production with renewable electricity and without intrinsic CO2 footprint.

Super-ions of sodium cations with hydrated hydroxide anions: inorganic structure-directing agents in zeolite synthesis.

In inorganic zeolite formation, a direct correspondence between liquid state species in the synthesis and the supramolecular decoration of the pores in the as-made final zeolite has never been reported. In this paper, a direct link between the sodium speciation in the synthesis mixture and the pore structure and content of the final zeolite is demonstrated in the example of hydroxysodalite. Super-ions with 4 sodium cations bound by mono- and bihydrated hydroxide are identified as structure-directing agents for the formation of this zeolite. This documentation of inorganic solution species acting as a templating agent in zeolite formation opens new horizons for zeolite synthesis by design.

Fresh water production from atmospheric air: Technology and innovation outlook.

Capturing water vapor from atmospheric air is a possible solution to local water scarcity, but it is very energy demanding. Energy consumption estimates of water-from-air technologies involving adsorption processes, thermo-responsive hydrophilicity switching polymers, air cooling processes, and reverse osmosis of deliquescent salt solutions reveal that these technologies are not competitive when compared with seawater desalination, and the use of fresh water and wastewater sources. They only become a viable option in the absence of local liquid water sources and when long-distance transport for socio-economic reasons is not an option. Of interest, direct solar-driven technology for water-from-air production is an attractive means to disentangle the local water-energy nexus. It is expected that climate change will accelerate the introduction of water-from-air technologies in local water supply schemes. The optimal water-from-air technology depends on the climate, relative humidity, and temperature profiles. A world map is presented, indicating the optimal geographic location for each technology.

NMR Crystallography Reveals Carbonate Induced Al-Ordering in ZnAl Layered Double Hydroxide.

Layered double hydroxides (LDHs) serve a score of applications in catalysis, drug delivery, and environmental remediation. Smarter crystallography, combining X-ray diffraction and NMR spectroscopy revealed how interplay between carbonate and pH determines the LDH structure and Al ordering in ZnAl LDH. Carbonate intercalated ZnAl LDHs were synthesized at different pH (pH 8.5, pH 10.0, pH 12.5) with a Zn/Al ratio of 2, without subsequent hydrothermal treatment to avoid extensive recrystallisation. In ideal configuration, all Al cations should be part of the LDH and be coordinated with 6 Zn atoms, but NMR revealed two different Al local environments were present in all samples in a ratio dependent on synthesis pH. NMR-crystallography, integrating NMR spectroscopy and X-ray diffraction, succeeded to identify them as Al residing in the highly ordered crystalline phase, next to Al in disordered material. With increasing synthesis pH, crystallinity increased, and the side phase fraction decreased. Using 1 H-13 C, 13 C-27 Al HETCOR NMR in combination with 27 Al MQMAS, 27 Al-DQ-SQ measurements and Rietveld refinement on high-resolution PXRD data, the extreme anion exchange selectivity of these LDHs for CO3 2- over HCO3 - was linked to strict Al and CO3 2- ordering in the crystalline LDH. Even upon equilibration of the LDH in pure NaHCO3 solutions, only CO3 2- was adsorbed by the LDH. This reveals the structure directing role of bivalent cations such as CO3 2- during crystallization of [M2+ 4 M3+ 2 (OH)2 ]2+ [A2- ]1 ⋅yH2 O LDH phases.