Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide ...variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.
Metallic nickel is known to efficiently catalyze hydrogenation reactions, but one of its major drawbacks lies in its lack of selectivity, linked to side-reactions of hydrogenolysis and ...over-hydrogenation. More selective hydrogenations can be obtained upon the introduction of a second metal in combination with Ni. Fe is an interesting choice, as it is a cheap and abundant metal. This review aims at discussing the advantages and constraints brought by the preparation procedures of bimetallic supported Ni–Fe nanoparticles, and at analyzing the benefits one can draw by substituting Ni–Fe supported catalysts for Ni monometallic systems for the catalytic hydrogenation of organic molecules. Specific formulations, such as Ni75Fe25, will be singled out for their high activity or selectivity, and the various hypotheses behind the roles played by Fe will be summarized.
Complete reduction of the metal phase in cobalt-containing catalysts is often difficult to reach and can be promoted by a small amount of noble metals. Because these costly promoters are introduced ...in a very low quantity, their speciation and their chemical interaction with cobalt have seldom been studied in detail. We present here a time-resolved in situ X-ray absorption spectroscopy investigation of the speciation of ruthenium, used as a reduction promoter of cobalt, throughout the preparation of Co/SiO2 catalysts. In the cobalt(II) nitrate impregnation solution, ruthenium is detected as hydrated Ru(OH)4 short-chain oligomers that are deposited on silica upon drying. Co3O4 forms during calcination in air and catalyzes the elimination in the gas phase of 60% of Ru. The addition of a polyol, sorbitol, in the impregnation solution stabilizes the whole of Ru on the catalyst. Upon calcination, Ru(IV) ions are inserted inside Co3O4 nanoparticles. Reduction of the oxidic phase takes place in two distinct steps, at approximately the same temperatures regardless of the ruthenium content: first to Ru(III)-containing CoO nanoparticles (Ru ions modifying the intrinsic electronic properties of the oxidic nanoparticles); then to bimetallic Co nanoparticles containing Ru(0) atoms, via an autocatalytic process. Ru loadings as low as 0.2 wt % are sufficient to afford complete reduction of cobalt. Close association between Ru and Co from the beginning of the synthesis is thus necessary for a maximum promoting effect.
•Sorbitol, glucose and citric acid are introduced as additives in impregnation solutions.•The main role played by these additives is to increase the solution viscosity.•In solution, the additives do ...not behave as stable ligands toward Ni2+ ions.•Crystallization of the precursor salt and formation of larger NiO nanoparticles are inhibited.•The reducibility of smaller nanoparticles compares well with reference Ni/Al2O3 catalyst.
The introduction of organic additives, such as polyols, sugars or polyacids, in impregnation solutions has been suggested to better control the size of nanoparticles on supported catalysts. The present paper focuses on the roles played by three of these additives, sorbitol, glucose and citric acid, in the preparation of Ni/Al2O3 catalysts. ATR-IR, circular dichroism spectroscopy and viscosity measurements show that the additives act as modifiers of the physical properties of the solutions, by increasing their viscosity via hydrogen bonding, rather than as stable ligands toward Ni2+ ions. Recrystallization of the nickel precursor salt is prevented upon drying. As a consequence, no population of large particles is evidenced by XRD and TPR on the catalysts prepared with additives, unlike reference catalysts prepared by conventional impregnation of nickel nitrate. Adding these organic molecules in the impregnation solution is thus an easy way to narrow the size distribution of NiO nanoparticles without significantly affecting their reducibility.
The effect of metal and support acidity on the hydroconversion of dimeric aryl ethers, used as model molecules for lignin, is still under debate, both in terms of hydrogenolysis (cleavage of the ...ether bond) and formation of by-products (coupling of aromatic monomers to dimers by alkylation reaction). Their role is investigated here in the conversion of three typical molecules representative of the α-O-4, β-O-4, and 4-O-5 ether linkages of lignin, respectively, benzyl phenyl ether (BPE), phenethoxybenzene (PEB), and diphenyl ether (DPE), at 503 K, under 18 bar of H2 in decalin. Ru- and Pd-based catalysts were synthesized on non-acidic SiO2 and on acidic HZSM5. Under these reaction conditions, the conversion of the ethers over the bare supports was observed in the presence of acidic sites; the effect decreased as the ether bond strength increased. The results also suggest that the product distribution is directly affected both by the support acidity and by the oxophilicity of Ru. Alkylated products from isomerization reactions, which are reported to be formed only over acidic sites, were also produced on the surface of the Ru nanoparticles.
Summary
Objective
A common rodent model in epilepsy research employs the muscarinic acetylcholine receptor (mAChR) agonist pilocarpine, yet the mechanisms underlying the induction of ...pilocarpine‐induced seizures (PISs) remain unclear. Global M1 mAChR (M1R) knockout mice are resistant to PISs, implying that M1R activation disrupts excitation/inhibition balance. Parvalbumin‐positive (PV) inhibitory neurons express M1Rs, participate in cholinergically induced oscillations, and can enter a state of depolarization block (DB) during epileptiform activity. Here, we test the hypothesis that pilocarpine activation of M1Rs expressed on PV cells contributes to PISs.
Methods
CA1 PV cells in PV‐CRE mice were visualized with a floxed YFP or hM3Dq‐mCherry adeno‐associated virus, or by crossing PV‐CRE mice with the RosaYFP reporter line. To eliminate M1Rs from PV cells, we generated PV‐M1knockout (KO) mice by crossing PV‐CRE and floxed M1 mice. Action potential (AP) frequency was monitored during application of pilocarpine (200 μm). In behavioral experiments, locomotion and seizure symptoms were recorded in wild‐type (WT) or PV‐M1KO mice during PISs.
Results
Pilocarpine significantly increased AP frequency in CA1 PV cells into the gamma range. In the continued presence of pilocarpine, a subset (5/7) of PV cells progressed to DB, which was mimicked by hM3Dq activation of Gq‐receptor signaling. Pilocarpine‐induced depolarization, AP firing at gamma frequency, and progression to DB were prevented in CA1 PV cells of PV‐M1KO mice. Finally, compared to WT mice, PV‐M1KO mice were associated with reduced severity of PISs.
Significance
Pilocarpine can directly depolarize PV+ cells via M1R activation, but a subset of these cells progress to DB. Our electrophysiologic and behavioral results suggest that this mechanism is active during PISs, contributing to a collapse of PV‐mediated γ‐aminobutyric acid (GABA)ergic inhibition, dysregulation of excitation/inhibition balance, and increased susceptibility to PISs.
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