Isomerization of sugars is used in a variety of industrially relevant processes and in glycolysis. Here, we show that hydrophobic zeolite beta with framework tin or titanium Lewis acid centers isomerizes sugars, e.g., glucose, via reaction pathways that are analogous to those of metalloenzymes. Specifically, experimental and theoretical investigations reveal that glucose partitions into the zeolite in the pyranose form, ring opens to the acyclic form in the presence of the Lewis acid center, isomerizes into the acyclic form of fructose, and finally ring closes to yield the furanose product. The zeolite catalysts provide processing advantages over metalloenzymes such as an ability to work at higher temperatures and in acidic conditions that allow for the isomerization reaction to be coupled with other important conversions.glucose isomerization | heterogeneous catalysis | reaction mechanism

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Molecular-level interactions at organic-inorganic interfaces play crucial roles in many fields including catalysis, drug delivery, and geological mineral precipitation in the presence of organic matter. To seek insights into organic-inorganic interactions in porous framework materials, we investigated the phase evolution and energetics of confinement of a rigid organic guest, N,N,N-trimethyl-1-adamantammonium iodide (TMAAI), in inorganic porous silica frameworks as a function of pore size (0.8 nm to 20.0 nm). We used hydrofluoric acid solution calorimetry to obtain the enthalpies of interaction between silica framework materials and TMAAI, and the values range from −56 to −177 kJ per mole of TMAAI. The phase evolution as a function of pore size was investigated by X-ray diffraction, IR, thermogravimetric differential scanning calorimetry, and solid-state NMR. The results suggest the existence of three types of inclusion depending on the pore size of the framework: single-molecule confinement in a small pore, multiple-molecule confinement/adsorption of an amorphous and possibly mobile assemblage of molecules near the pore walls, and nanocrystal confinement in the pore interior. These changes in structure probably represent equilibrium and minimize the free energy of the system for each pore size, as indicated by trends in the enthalpy of interaction and differential scanning calorimetry profiles, as well as the reversible changes in structure and mobility seen by variable temperature NMR.mesoporous silica | thermodynamics | porous materials K nowing both the structure and molecular mobility of guest matter in nanosized pores and channels, which often differ from those in the bulk unconfined material or solution, is essential for fundamental understanding of processes in both science and technology, with applications including natural processes such as biomineralization (1-3) and membrane transport (4, 5), engineering processes such as oil recovery (6-8), CO 2 sequestration (9-11), catalysis (12-14), and biomedical processes including diagnostics and drug delivery (15-17). Most of the pioneering research has used soft matter as guests, including gas and liquid phases, low-melting point organic solids, and longchain polymers (18)(19)(20).In our earlier studies, various calorimetric methods have been designed to investigate guest-host interactions. Piccione et al.(21) developed a novel system for hydrofluoric acid (HF) solution calorimetry to study the interactions of four different silica zeolite frameworks with several quaternary ammonium structure-directing agents (SDAs). The enthalpies of interaction were measured to be −32.0 to −181.0 kJ per mole of SDA. Slightly stronger interactions were found by Trofymluk et al. (22) for mesoporous silica phases containing long-chain molecules. Recently, Wu et al. (23) measured the enthalpy of interaction of various small molecules with mesoprous silicas using immersion calorimetry. The hydration enthalpies of a series of cation exchanged aluminosilicate or gallosilicate ze...

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In situ solid-state NMR methodologies have been employed to investigate the photocatalytic oxidation of ethanol (C 2 H 5 OH) over a TiO 2 -coated optical microfiber catalyst and two other TiO 2 -based catalysts. Adsorption of ethanol on the surface of the TiO 2 /optical microfiber catalyst formed a strongly hydrogen-bonded species and a Ti ethoxide species. In situ UV irradiation experiments under 13 C magic angle spinning (MAS) conditions reveal the formation of two main reaction intermediates, 1,1-diethoxyethane (CH 3 CH(OC 2 H 5 ) 2 ) and acetic acid, under dry conditions. The catalyst was shown to be highly effective for the degradation of ethanol as complete photooxidation of ethanol was observed to form acetic acid and CO 2 . These results were compared to those using a monolayer catalyst supported on porous Vycor glass and powdered TiO 2 . Solid-state NMR investigations on TiO 2 powder modeled after temperature-programmed desorption experiments confirm the identities of the hydrogen-bonded and Ti ethoxide species and show that the strongly bound ethoxide species has a number of adsorption sites. Kinetic experiments indicate this latter species reacts much more rapidly. Studies of the effect of surface hydration show that the presence of water decreases the rate of ethanol photodegradation. Water and ethanol compete for the same adsorption sites on the surface of the TiO 2 catalysts.

Complex metal hydrides are attracting much attention as a class of candidate materials for hydrogen storage. Lithium-based complex hydrides, including lithium aluminum hydrides (LiAlH4 and Li3AlH6), are among the most promising materials, owing to their high hydrogen contents. In the present work, we investigated the dehydrogenation/rehydrogenation reactions of a combined system of Li3AlH6 and Mg(NH2)2, which has a theoretical hydrogen capacity of 6.5 wt %. Thermogravimetric analysis of hydrogenated 2/3Al−Li2Mg(NH)2 (doped with 4 wt % TiCl3) indicated that a large amount of hydrogen (∼6.2 wt %) can be stored under 300 °C and 172 bar of hydrogen pressure. The FT-IR and NMR results showed that the reaction between Li3AlH6 and Mg(NH2)2 is reversible. Further, a short-cycle experiment has demonstrated that the new combined material system of alanates and amides can maintain its hydrogen storage capacity upon cycling of the dehydrogenation/rehydrogenation reactions.

Glasses and polycrystals in the series xNa 2 S + (1 -x)B 2 S 3 have been prepared and studied by magic angle spinning (MAS) NMR and by two-dimensional multiple-quantum (MQ) MAS NMR of 11 B and 23 Na. These techniques, when applied at various magnetic fields and combined with computer simulations of the spectra, provide new insights into the structure of the polycrystalline samples. Isotropic chemical shifts, quadrupolar parameters, and relative concentrations of the various boron sites are obtained by NMR and correlated with the known structures of boron trisulfide (x ) 0), sodium metathioborate (x ) 0.5) and sodium orthothioborate (x ) 0.75). A structural model of polycrystalline sodium dithioborate (x ) 0.33) is proposed. The MQMAS NMR method significantly enhanced the resolution in 11 B spectra of xNa 2 S + (1 -x)B 2 S 3 glasses and proved instrumental in finding and identifying various structural units present within these materials as the modification of the B 2 S 3 network progressed with increasing Na 2 S content. The dominant 11 B resonances observed in the glassy samples represent the same basic structural units that were observed in the polycrystalline compounds. In addition, several new resonances featuring trigonally and tetrahedrally coordinated boron atoms in various transitional structures between dithioborate and metathioborate, or between metathioborate and orthothioborate, were found. 23 Na NMR proved less informative, especially in the glassy samples where the motion of the sodium ions between various sites precluded the observation of well-resolved spectra.