- NSF-PAR ID:
- 10163197
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 55
- Issue:
- 64
- ISSN:
- 1359-7345
- Page Range / eLocation ID:
- 9440 to 9443
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Indium on silica, alumina and zeolite chabazite (CHA), with a range of In/Al ratios and Si/Al ratios, have been investigated to understand the effect of the support on indium speciation and its corresponding influence on propane dehydrogenation (PDH). It is found that In 2 O 3 is formed on the external surface of the zeolite crystal after the addition of In(NO 3 ) 3 to H-CHA by incipient wetness impregnation and calcination. Upon reduction in H 2 gas (550 °C), indium displaces the proton in Brønsted acid sites (BASs), forming extra-framework In + species (In-CHA). A stoichiometric ratio of 1.5 of formed H 2 O to consumed H 2 during H 2 pulsed reduction experiments confirms the indium oxidation state of +1. The reduced indium is different from the indium species observed on samples of 10In/SiO 2 , 10In/Al 2 O 3 ( i.e. , 10 wt% indium) and bulk In 2 O 3 , in which In 2 O 3 was reduced to In(0), as determined from the X-ray diffraction patterns of the product, H 2 temperature-programmed reduction (H 2 -TPR) profiles, pulse reactor investigations and in situ transmission FTIR spectroscopy. The BASs in H-CHA facilitate the formation and stabilization of In + cations in extra-framework positions, and prevent the deep reduction of In 2 O 3 to In(0). In + cations in the CHA zeolite can be oxidized with O 2 to form indium oxide species and can be reduced again with H 2 quantitatively. At comparable conversion, In-CHA shows better stability and C 3 H 6 selectivity (∼85%) than In 2 O 3 , 10In/SiO 2 and 10In/Al 2 O 3 , consistent with a low C 3 H 8 dehydrogenation activation energy (94.3 kJ mol −1 ) and high C 3 H 8 cracking activation energy (206 kJ mol −1 ) in the In-CHA catalyst. A high Si/Al ratio in CHA seems beneficial for PDH by decreasing the fraction of CHA cages containing multiple In + cations. Other small-pore zeolite-stabilized metal cation sites could form highly stable and selective catalysts for this and facilitate other alkane dehydrogenation reactions.more » « less
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Summary In plants, 24 nucleotide long heterochromatic si
RNA s (het‐siRNA s) transcriptionally regulate gene expression byRNA ‐directedDNA methylation (RdDM ). The biogenesis of most het‐siRNA s depends on the plant‐specificRNA polymeraseIV (PolIV ), andARGONAUTE 4 (AGO 4) is a major het‐siRNA effector protein. Through genome‐wide analysis ofsRNA ‐seq data sets, we found that is required for the accumulation of a small subset of het‐siAGO 4RNA s. The accumulation of ‐dependent het‐siAGO 4RNA s also requires several factors known to participate in the effector portion of the RdDM pathway, includingRNA POLYMERASE V (POL V),DOMAINS REARRANGED METHYLTRANSFERASE 2 (DRM 2) andSAWADEE HOMEODOMAIN HOMOLOGUE 1 (SHH 1). Like manyAGO proteins,AGO 4 is an endonuclease that can ‘slice’RNA s. We found that a slicing‐defectiveAGO 4 was unable to fully recover dependent het‐siAGO 4‐RNA accumulation fromago4 mutant plants. Collectively, our data suggest that ‐dependent siAGO 4RNA s are secondary siRNA s dependent on the prior activity of the RdDM pathway at certain loci. -
Abstract The presence of molecular monolayers on semiconductor surfaces can improve the stability of semiconductor interfaces by inhibiting the growth of native oxides and defects which affect the materials’ electronic properties. The development of catalytically active passivated interfaces on semiconductor materials presents a useful material design for value‐added product conversion. Herein, an iron‐based catalyst covalently attached to silicon (Si) is reported for the investigation of activity and electrochemical decomposition pathways of diiron hydrogenase enzyme mimics. The employed catalyst, Fe2(CO)6(µ‐S‐C6H4‐p‐OH)2([FeFe]), mimics the active sites of these enzymes. Surface modification using this catalyst passivates the interface, hindering the formation of native SiO2for more than 300 h. [FeFe] modification improves the overpotential required to produce 10 mA cm–2by 100 mV, with a hydrogen evolution rate of 2.31 × 10–5 mol h–1 cm–2 (−0.78 V versus RHE). However, structural rearrangement transpires within 1 h of electrolysis, where Fe‐S bond dissociates at the catalytic center, resulting in an aromatic linkage modified Si interface. While semiconductor−catalyst interfaces have often been reported in the literature, their decomposition pathways have received limited discussion. Herein, this Si−[FeFe] interface is used as a tool for understanding the activity and decomposition mechanisms of the attached molecular catalyst.
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Summary Plants have mechanisms to recognize and reject pollen from other species. Although widespread, these mechanisms are less well understood than the self‐incompatibility (
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The efficient production of green hydrogen via electrochemical water splitting is important for improving the sustainability and enabling the electrification of the chemical industry. One of the major goals of water electrolysis is to utilize non-precious metal catalysts, which can be accomplished with alkaline electrolyzer technologies. However, there is a continuing need for designing catalysts that can operate in alkaline environments with high efficiencies under high current densities. Here we describe a simple, aqueous-based synthesis method to incorporate sulfur into NiFe-based electrocatalysts for the oxygen evolution reaction (OER). Sulfur incorporation was able to reduce the overpotential for the OER from ca. 350 mV on a NiFe catalyst to ca. 290 mV on the NiFeS catalyst at 100 mA cm −2 on a flat supporting electrode. Electrochemical impedance spectroscopy data showed a small decrease in the charge transfer resistance of the NiFeS catalysts, showing that sulfur incorporation may improve the electronic conductivity. Surface-interrogation scanning electrochemical microscopy (SI-SECM) studies combined with Tafel slope analysis suggested that the NiFeS catalyst was able to have vacant surface sites available under OER conditions and was able to maintain a Tafel slope of 39 mV dec −1 . This is in contrast to the NiFe catalyst, for which the SI-SECM studies showed a saturated surface under OER conditions with the Tafel slope transitioning from 39 mV dec −1 to 118 mV dec −1 . The low Tafel slope enabled the NiFeS catalyst to maintain low overpotentials under high current densities, which we attribute to the ability of the NiFeS catalyst to maintain vacant sites during the OER.more » « less