An Isomorphously Substituted Fe-BEA Zeolite with High Fe Content: Facile Synthesis and Characterization.

An isomorphously substituted Al-free Fe-BEA zeolite with extremely high Fe content (~7 wt.%) was synthesized by a facile and industrially friendly method using an excess amount of NaOH. The obtained Fe-BEA zeolite was highly crystalline and showed a well-facetted bipyramidal morphology, similarly to beta zeolites synthesized in a fluoride medium. The chemical states of Fe in the above zeolite were investigated by diffuse reflectance ultraviolet-visible (UV-Vis) absorption spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. The observed chemical states were similar to those of the Fe-BEA zeolite synthesized in the presence of fluoride (Fe-BEA-F). Considering the fact that more than 88% of the micropore volume of the calcined Fe-BEA zeolite was retained after hydrothermal treatment at 1000 °C for 5 h, and 53% of the tetrahedrally coordinated Fe3+ was retained after hydrothermal treatment at 700 °C for 20 h, the obtained Fe-BEA zeolite was concluded to be highly hydrothermally stable. The synthesized zeolite was evaluated in the selective catalytic reduction of NOx by ammonia (NH3-SCR), exhibiting greater catalytic activity than Fe-BEA-F throughout the reaction temperature range. Moreover, the potential of this catalyst as a hydrocarbon adsorbent for cold-start emission control was characterized by dynamic adsorption-desorption of toluene. Interestingly, only 66% of adsorbed toluene was desorbed from the Fe-BEA zeolite (cf. 96% for commercial beta zeolite), even though the gas stream did not contain oxygen, suggesting that hydrocarbon oxidation involved oxygen stored inside the Fe-BEA zeolite.

Elastic rotation of Escherichia coli F(O)F(1) having ε subunit fused with cytochrome b(562) or flavodoxin reductase.

Intra-molecular rotation of FOF1 ATP synthase enables cooperative synthesis and hydrolysis of ATP. In this study, using a small gold bead probe, we observed fast rotation close to the real rate that would be exhibited without probes. Using this experimental system, we tested the rotation of FOF1 with the ε subunit connected to a globular protein [cytochrome b562 (ε-Cyt) or flavodoxin reductase (ε-FlavR)], which is apparently larger than the space between the central and the peripheral stalks. The enzymes containing ε-Cyt and ε-FlavR showed continual rotations with average rates of 185 and 148 rps, respectively, similar to the wild type (172 rps). However, the enzymes with ε-Cyt or ε-FlavR showed a reduced proton transport. These results indicate that the intra-molecular rotation is elastic but proton transport requires more strict subunit/subunit interaction.

Structural analysis of high-silica ferrierite with different structure-directing agents by solid-state NMR and ab initio calculations.

The host-guest interaction in high-silica ferrierite (FER) with different structure-directing agents (SDA), pyridine and piperidine, was analyzed by solid-state (29)Si NMR relaxation experiments and molecular-orbital calculations. Qualitative and quantitative knowledge of the SDA structure obtained by these methods provides significant insight for understanding the functions in a template, and the stabilizing role of the SDA. Relaxation experiments show a larger magnetic dipolar interaction between the silicon and hydrogen atoms in piperidine as compared to that in pyridine, and the results correlate with the bonding property in terms of the distance between the zeolite framework and the SDA. The (1)H MAS NMR spectrum shows that the pyridine molecules mainly act as pore fillers in the pyridine-FER. In contrast, it was presumed that piperidine, adjacent to the aluminosilicate framework and framework defects, acted as a counter cation to balance the charge in the piperidine-FER. H(+)-FER synthesized with piperidine shows a lower hydrothermal stability as compared to that synthesized with pyridine. The hydrothermal stability of H(+)-FER is discussed by considering the contributions of framework defects and the different properties pertaining to the bonding between the zeolite framework and the SDA.