Reactivity of Re2O7 in aromatic solvents – Cleavage of a β-O-4 lignin model substrate by Lewis-acidic rhenium oxide nanoparticles

First Evidence of the Double-Bond Formation by Deoxydehydration of Glycerol and 1,2-Propanediol in Ionic Liquids

Deoxydehydration (DODH) reaction of glycerol (GL) and 1,2-propanediol (1,2-PD), in ionic liquids (ILs), catalyzed by methyltrioxorhenium (MTO) and Re₂O₇, was studied in detail. To better understand the ability of ILs to improve the catalytic performance of the rhenium catalyst, several experiments, employing eight different cations and two different anions, were carried out. Among the anions, bis(trifluoromethylsulfonyl)imide (TFSI) appears to be more appropriate than PF₆ ^-, for its relatively lower volatility of the resulting IL. Regarding the choice of the most appropriate cation, the presence of a single aromatic ring seems to be a necessary requirement for a satisfying and convenient reactivity. With the aim to extend the recyclability of the catalyst, experiments involving the readdition of polyol to the terminal reaction mixture were carried out. Worthy of interest is the fact that the presence of the IL prevents the inertization process of the catalyst, allowing us to obtain the alkene also after a readdition of fresh polyol.

In situ growth gold nanoparticles in three-dimensional sugarcane membrane for flow catalytical and antibacterial application

In this work, we decorated gold nanoparticles (Au NPs) in the porous, three-dimensional sugarcane membrane for the flow catalytical and antibacterial application. Due to the uniformly distributed Au NPs in sugarcane channels and the porous structure of sugarcane, the interaction between contaminant and catalysis was enhanced as water flowing through the Au NPs/sugarcane membrane. The Au NPs/sugarcane membrane exhibited superior catalytical efficiency for removing methylene blue (MB) with a turn over frequency of 0.27 mol_MB·mol_Au^-1·min^-1 and the water treatment rate reached up to 1.15×10⁵ L/m² h with >98.3 % MB removal efficiency. The Au NPs/sugarcane membrane also exhibited superior bacterial removal efficiency as E. coli suspension flowing through it, due to the superimposition effects of physical barrier in sugarcane and the antibacterial property of Au NPs. The tremendous catalytical and antibacterial performance of Au NPs/sugarcane membrane provides a promising potential for the rational design of flow catalytical membrane reactor to purify the microbial contaminated water.

One-Pot Conversion of Lignin into Naphthenes Catalyzed by a Heterogeneous Rhenium Oxide-Modified Iridium Compound

The direct transformation of lignin into fuels and chemicals remains a huge challenge because of the recalcitrant and complicated structure of lignin. In this study, rhenium oxide-modified iridium supported on SiO₂ (Ir-ReO_x /SiO₂ ) is employed for the one-pot conversion of various lignin model compounds and lignin feedstocks into naphthenes. Up to 100 % yield of cyclohexane from model compounds and 44.3 % yield of naphthenes from lignin feedstocks are achieved. 2 D HSQC NMR spectroscopy before and after the reaction confirms the activity of Ir-ReO_x /SiO₂ in the cleavage of the C-O bonds and hydrodeoxygenation of the depolymerized products. H₂ temperature-programmed reduction, temperature-programmed desorption of NH₃ , IR spectroscopy of pyridine adsorption, X-ray photoelectron spectroscopy, X-ray absorption fine structure analysis, and control experiments reveal that a synergistic effect between Ir and ReO_x in Ir-ReO_x /SiO₂ plays a crucial role in the high performance; ReO_x is mainly responsible for the cleavage of C-O bonds, whereas Ir is responsible for hydrodeoxygenation and saturation of the benzene rings. This methodology opens up an energy-efficient route for the direct conversion of lignin into valuable naphthenes.

Colloidal ReO3 Nanocrystals: Extra Re d-Electron Instigating a Plasmonic Response

Rhenium (+6) oxide (ReO₃) is metallic in nature, which means it can sustain localized surface plasmon resonance (LSPR) in its nanocrystalline form. Herein, we describe the colloidal synthesis of nanocrystals (NCs) of this compound, through a hot-injection route entailing the reduction of rhenium (+7) oxide with a long chain ether. This synthetic protocol is fundamentally different from the more widely employed nucleophilic lysing of metal alkylcarboxylates for other metal oxide NCs. Owing to this difference, the NC surfaces are populated by ether molecules through an L-type coordination along with covalently bound (X-type) hydroxyl moieties, which enables easy switching from nonpolar to polar solvents without resorting to cumbersome ligand exchange procedures. These as-synthesized NCs exhibit absorption bands at around 590 nm (∼2.1 eV) and 410 nm (∼3 eV), which were respectively ascribed to their LSPR and interband absorptions by Mie theory simulations and Drude modeling. The LSPR response arises from the oscillation of free electron density created by the extra Re d-electron per ReO₃ unit in the NC lattice, which resides in the conduction band. Further, the LSPR contribution facilitates the observation of dynamic optical modulation of the NC films as they undergo progressive electrochemical charging via ion (de)insertion. Ion (de)insertion leads to distinct dynamic optical signatures, and these changes are reversible in a wide potential range depending on the choice of the ion (lithium or tetrabutylammonium). Nanostructuring in ReO₃ and the description of the associated plasmonic properties of these NCs made this optical modulation feasible, which were hitherto not reported for the bulk material. We envisage that the synthetic protocol described here will facilitate further exploration of such applications and fundamental studies of these plasmonic NCs.