Base-catalyzed Research Articles

Study on acid-base coupled catalytic pyrolysis of heavy crude oil to light olefins and aromatics by Py-GC/MS and fixed bed reactor

Direct catalytic cracking of heavy crude oil has gained attention as an alternative and cheapest method of producing raw materials for the petrochemical industry. The Py-GC/MS technique was used to study the effects of calcium aluminate base catalysts and ZSM-5 acid zeolites on heavy crude oil conversion. The results showed that ZSM-5 with a Si/Al ratio of 40 (40Z) outperformed zeolites with Si/Al ratios of 80 and 200, with a maximum selectivity of 65% for light olefins and BTX (benzene, toluene and xylene). Among all base catalysts studied, calcium aluminate (CaAl-3) had the highest selectivity of 23% of C2-C4 olefins and BTX. The “Mix” model outperformed the “Base + Acid” or “Acid + Base” models in terms of minimizing hydrogen transfer reactions and maximizing the yield and selectivity of light olefins. The 30 C catalyst (30%CaAl-3 +70%40Z) exhibited significant co-effect of basic and acidic catalysis, with maximum light olefin selectivity and total olefinicity of 72% and 81%, respectively. The results of the present work showed that acid-base coupled catalytic pyrolysis was a viable approach for improving the yield of light olefins and aromatics.

How Bases Catalyze Diels-Alder Reactions.

We have quantum chemically studied the base-catalyzed Diels-Alder (DA) reaction between 3-hydroxy-2-pyrone and N-methylmaleimide using dispersion-corrected density functional theory. The uncatalyzed reaction is slow and is preceded by the extrusion of CO2 via a retro-DA reaction. Base catalysis, for example, by triethylamine, lowers the reaction barrier up to 10 kcal mol-1 , causing the reaction to proceed smoothly at low temperature, which quenches the expulsion of CO2 , yielding efficient access to polyoxygenated natural compounds. Our activation strain analyses reveal that the base accelerates the DA reaction via two distinct electronic mechanisms: i) by the HOMO-raising effect, which enhances the normal electron demand orbital interaction; and ii) by donating charge into 3-hydroxy-2-pyrone which accumulates in its reactive region and promotes strongly stabilizing secondary electrostatic interactions with N-methylmaleimide.

A broad specificity β-propeller enzyme from Rhodopseudomonas palustris that hydrolyzes many lactones including γ-valerolactone

Lactones are prevalent in biological and industrial settings, yet there is a lack of information regarding enzymes used to metabolize these compounds. One compound, γ-valerolactone (GVL), is used as a solvent to dissolve plant cell walls into sugars and aromatic molecules for subsequent microbial conversion to fuels and chemicals. Despite the promise of GVL as a renewable solvent for biomass deconstruction, residual GVL can be toxic to microbial fermentation. Here, we identified a Ca2+-dependent enzyme from Rhodopseudomonas palustris (Rpa3624) and showed that it can hydrolyze aliphatic and aromatic lactones and esters, including GVL. Maximum-likelihood phylogenetic analysis of other related lactonases with experimentally determined substrate preferences shows that Rpa3624 separates by sequence motifs into a subclade with preference for hydrophobic substrates. Additionally, we solved crystal structures of this β-propeller enzyme separately with either phosphate, an inhibitor, or a mixture of GVL and products to define an active site where calcium-bound water and calcium-bound aspartic and glutamic acid residues make close contact with substrate and product. Our kinetic characterization of WT and mutant enzymes combined with structural insights inform a reaction mechanism that centers around activation of a calcium-bound water molecule promoted by general base catalysis and close contacts with substrate and a potential intermediate. Similarity of Rpa3624 with other β-propeller lactonases suggests this mechanism may be relevant for other members of this emerging class of versatile catalysts.

Crystal structure of a pre-chemistry viral RNA-dependent RNA polymerase suggests participation of two basic residues in catalysis.

The nucleic acid polymerase-catalyzed nucleotidyl transfer reaction associated with polymerase active site closure is a key step in the nucleotide addition cycle (NAC). Two proton transfer events can occur in such a nucleotidyl transfer: deprotonation of the priming nucleotide 3'-hydroxyl nucleophile and protonation of the pyrophosphate (PPi) leaving group. In viral RNA-dependent RNA polymerases (RdRPs), whether and how active site residues participate in this two-proton transfer reaction remained to be clarified. Here we report a 2.5 Å resolution crystal structure of enterovirus 71 (EV71) RdRP in a catalytically closed pre-chemistry conformation, with a proposed proton donor candidate K360 in close contact with the NTP γ-phosphate. Enzymology data reveal that K360 mutations not only reduce RdRP catalytic efficiency but also alter pH dependency profiles in both elongation and pre-elongation synthesis modes. Interestingly, mutations at R174, an RdRP-invariant residue in motif F, had similar effects with additional impact on the Michaelis constant of NTP (KM,NTP). However, direct participation in protonation was not evident for K360 or R174. Our data suggest that both K360 and R174 participate in nucleotidyl transfer, while their possible roles in acid-base or positional catalysis are discussed in comparison with other classes of nucleic acid polymerases.

Talc modified by milling and alkali activation: Physico-chemical characterization and application in base catalysis

The work aimed at the development of benign solid base catalysts as alternatives for presently used noxious liquid bases. Talc, possessing intrinsic basic properties, was chosen as a particularly attractive and cost-effective precursor. Activation of talc by grinding in a planetary mill followed by treatment with 2 M NaOH was employed as means for basicity enhancement. Such protocol enabled profound modification of talc structure, otherwise resistant to treatment with a basic solution. Deep changes, not addressed in the literature reports so far, took place in the course of combined mechanical and alkali treatment. The amorphized ground talc transformed to the magnesium silicate hydrate (MSH) phase and brucite. Treatment with NaOH led to significant enhancement of surface basicity with respect to the parent materials. The effect was particularly spectacular for alkali-treated, strongly ground talc samples, containing the MSH component. The materials were tested in a base-catalyzed reaction of aldol condensation of acetone. The trend of catalytic activity followed closely the order of surface basicity, which pointed to the key role of MSH as a catalytically active phase in the modified talc solids. Joint mechanical and alkali activation of talc proved to be a simple, yet promising way of developing solid base materials for catalytic applications.

Synthesis of 5‐ethoxymethylfurfural from glucose catalyzed by porous tetra‐component metal oxides solid acid

AbstractThe production of 5‐ethoxymethylfurfural (EMF) from cheap and abundant glucose feedstock has attracted a great deal of attention because of its potential applications. Herein, three porous tetra‐component metal oxide solid acid catalysts (SO42−/ZFSA‐A, SO42−/ZFSA‐F‐10, SO42−/ZFSA‐F‐20) containing both Brønsted and Lewis acid sites have been successfully synthesized and can efficiently catalyze the synthesis of EMF from glucose. Particularly, the SO42−/ZFSA‐A, SO42−/ZFSA‐F‐10, and SO42−/ZFSA‐F‐20 catalysts were prepared under the template of sodium alginate, 10% F127, and 20% F127, respectively. The prepared catalysts were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), N2‐adsorption–desorption isotherm, X‐ray photoelectron spectroscopy (XPS), thermogravimetry (TG), temperature‐programmed desorption of ammonia (NH3‐TPD), and pyridine infrared spectra (Py‐FTIR). The characterization results indicated that all three catalysts have a porous structure. The pore distribution of the SO42−/ZFSA‐A catalyst is mainly macroporous and mesoporous, while the SO42−/ZFSA‐F‐10 and SO42−/ZFSA‐F‐20 catalysts are mainly mesoporous. The SO42−/ZFSA‐F‐20 catalyst exhibited the highest catalytic performance due to its large specific surface area, desirable mesoporous structure, high total acidity (especially strong and super strong acidity), and appropriate Lewis/Brønsted acid ratio. By applying SO42−/ZFSA‐F‐20, the formation of EMF from glucose was successfully catalyzed and EMF was obtained at a yield of 34.56% after 12 h at 160°C. This yield is much higher compared with most other results achieved by solid acids catalysis. In addition, the reaction parameters such as reaction temperature, reaction time, glucose amount, and catalyst dosage were shown to have a significant effect on the catalytic performance. Notably, the SO42−/ZFSA‐F‐20 catalyst exhibited good reusability, as its activity did not significantly diminish after four rounds of repeated experiments and was successfully reactivated after calcination.

A cell-based bioluminescence reporter assay of human Sonic Hedgehog protein autoprocessing to identify inhibitors and activators

The Sonic Hedgehog (SHh) precursor protein undergoes biosynthetic autoprocessing to cleave off and covalently attach cholesterol to the SHh signaling ligand, a vital morphogen and oncogenic effector protein. Autoprocessing is self-catalyzed by SHhC, the SHh precursor's C-terminal enzymatic domain. A method to screen for small molecule regulators of this process may be of therapeutic value. Here, we describe the development and validation of the first cellular reporter to monitor human SHhC autoprocessing noninvasively in high-throughput compatible plates. The assay couples intracellular SHhC autoprocessing using endogenous cholesterol to the extracellular secretion of the bioluminescent nanoluciferase enzyme. We developed a WT SHhC reporter line for evaluating potential autoprocessing inhibitors by concentration response-dependent suppression of extracellular bioluminescence. Additionally, a conditional mutant SHhC (D46A) reporter line was developed for identifying potential autoprocessing activators by a concentration response-dependent gain of extracellular bioluminescence. The D46A mutation removes a conserved general base that is critical for the activation of the cholesterol substrate. Inducibility of the D46A reporter was established using a synthetic sterol, 2-α carboxy cholestanol, designed to bypass the defect through intramolecular general base catalysis. To facilitate direct nanoluciferase detection in the cell culture media of 1536-well plates, we designed a novel anionic phosphonylated coelenterazine, CLZ-2P, as the nanoluciferase substrate. This new reporter system offers a long-awaited resource for small molecule discovery for cancer and for developmental disorders where SHh ligand biosynthesis is dysregulated.

SUBSTITUTED AMINOCHALCONES AS STARTING COMPOUNDS FOR RECEIVING NEW 1,4-BENZODIAZEPINES DERIVATIVES

The aim of this work is the synthesis of a number of substituted E‑1-(2-amino‑5-R1-phenyl)-3-(4-R2-phenyl)prop‑2-en‑1-ones (2-aminochalcones) as precursors for obtaining new derivatives of 7-R1–5-[2-R2-phenylvinyl]-1,4-benzodiazepin‑2-ones. Starting 5-substituted 2-aminoacetophenones with bromo and nitro group were synthesized from 2-aminoacetophenone by bromination of the latter with N‑bromosuccinimide in acetonitrile and nitration of 2-acetaminoacetophenone with a nitrating mixture followed by removal of acetyl protection. 2-Aminochalcones were synthesized according to standard methods during the interaction of a number of 5-substituted 2-aminoacetophenones with para-substituted benzaldehydes under basic catalysis conditions. The target products turned out to be brightly colored compounds with low melting points, their isolation and purification did not cause any difficulties. According to the data of 1H NMR spectroscopy, all synthesized 2-aminochalcones were individual trans isomers, which was also confirmed by X‑ray structural analysis of one of the obtained 2-aminochalcones. A number of new substituted E‑1-(2-amino‑5R1-phenyl)-3-(4-R2-phenylprop‑2-en‑1-ones) were synthesized – compounds with amino and ketofunctions and are precursors for obtaining of a new series of 5-substituted 1,4-benzodiazepines with various arylvinyl groups. 2-aminoacetophenone, 2-amino‑5-bromoacetophenone, and 2-amino‑5-nitroacetophenone were selected as substrates for this series. The methyl groups of these acetophenones were condensed according to Claisen-Schmidt with parasubstituted benzaldehydes. Condensation was carried out under alkaline conditions in an aqueous solution. Yields of aminochalcones reached 60–85%. The methyl group of 2-aminoacetophenones smoothly reacted with aromatic aldehydes to form the corresponding 2-aminophenylchalcones. The structure of the obtained compounds was confirmed by mass spectrometry and 1H NMR spectroscopy. The structure of one of the chalcones was proved by X‑ray structural analysis. The obtained compounds can be used for the synthesis of 1,4-benzodiazepines with 5-arylvinyl substituents.

Base-catalyzed hydrolysis of spectinomycin in aqueous solutions: Kinetics and mechanisms

Hydrolysis plays an imperative role in the abiotic transformation process of antibiotics in aqueous solutions. However, little information is available on the hydrolysis process of spectinomycin (an aminocyclitol antibiotic). This study systematically investigated the spectinomycin hydrolysis kinetics and mechanisms under different pH via experiments and density functional theory (DFT) computation. Hydrolysis was first conducted in a pure water system under pH of 4.0–9.0 and temperature of 25 °C, 50 °C and 70 °C, respectively. Results showed that hydrolysis was highly dependent on pH and temperature. When pH > 6.0, spectinomycin hydrolysis was accelerated by the catalysis of OH−. Meanwhile, the hydrolysis rate increased with the elevation of temperature. Then, for the reference of the practical environment, the general base-catalyzed hydrolysis and mechanisms were studied under environmental pH 6.0–8.0 and 25 °C. DFT calculation demonstrated that base-catalyzed hydrolysis of spectinomycin could be more thermodynamically and kinetically favorable based on the lower Gibbs free energies of reaction and Gibbs free energies of activation. Further, instead of specific base catalysis (OH−), the general base catalysis (e.g., phosphate buffer) was also found to promote hydrolysis efficiency. The antibacterial activity and ecotoxicities of the hydrolysis product were analyzed to be lower than the precursor, thereby decreasing the environmental impact of spectinomycin.

Immobilization of Candida Rugosa lipase on Ca/Kit-6 used as bifunctional biocatalysts for the transesterification of coconut oil to biodiesel

Immobilization of Candida Rugosa lipase (CRL) on Ca doped Kit-6 solid was investigated via the adsorption method. Effects of the experimental parameters, such as pH value, temperature, time, and Ca content on the adsorption of CRL on Ca/Kit-6 were studied. In the Ca doped Ca/Kit-6 materials, Ca2+ coexisted in two environments: Ca2+ in CaO nanoparticles and in Ca-O-Si in the framework of Kit-6. There existed three kind of oxygen species: (1) lattice oxygen in CaO and SiO2; (2) Oxygen in structural defects; and (3) non-stoichiometric surface oxygen in OH form. The 0.5Ca/Kit-6 showed the most CRL immobilization capacity and stability under the optimal adsorption condition, which was correlated with its greater amount of basicity resulting from its more non-stoichiometric surface oxygen and oxygen in structural defects as well as more Ca2+ incorporation in the Kit-6 framework. In the production of biodiesel via transesterification of coconut oil, the catalysts showed better catalytic performance under weak basic than acidic condition. Under the optimal reaction conditions (40 °C, pH 7.5, 200 rpm, oil to methanol ratio 1:3 with stepwise addition of methanol, and 0.1 g of CRL/0.5Ca/Kit-6), the coconut oil conversion and biodiesel yield catalyzed with CRL/0.5Ca/Kit-6 was 95 and 98%, respectively. 10wt% water in the reaction mixture promoted the coconut oil transesterification to biodiesel. The CRL/0.5Ca/Kit-6 catalyst possessed bifunctional roles of the enzymatic catalysis role from immobilized CRL and the basic catalysis role from CaO doping. The CRL adsorption modes, water influence and the reaction mechanism of coconut oil transesterification were discussed.

One-pot non-covalent heterogenization and aromatization of poly(ionic liquids) for metal-/cocatalyst-free and atmospheric CO2 conversion

The intensification of Lewis acidity/basicity of a given heterogeneous catalyst at a molecular level is an advanced approach for boosting CO2 activation and conversion under extremely mild conditions, which, yet remains a great challenge. This work proposes a one-pot strategy for heterogenization and aromatization of homopolymerized ionic liquids (HpolyILs) through dynamic imine assembly with aromatic spacers for boosting CO2 conversion into cyclic carbonates. The aromatization of HpolyILs can be controllably achieved at room temperature, and has been proven to enhance the Lewis acidity of C-2 proton on imidazolium IL for promoting ring-opening of epoxides and facilitate CO2 bending synchronously. The resultant dynamic covalent polyILs exhibit superior catalytic activity and outstanding recyclability for a variety of epoxides under extremely mild conditions (1 atm, 50–90 ºC) without metal/co-catalyst consumption. This work offers a feasible to scale-up approach for tailor-made designing high-efficiency heterogeneous catalysts for CO2 utilization, guiding the precise regulation of acid-base catalysis.

Advances in Catalytic Depolymerization of Lignin

AbstractThe depletion of traditional fossil energy sources and increasing environmental concerns have sparked continued interest in the development and utilisation of renewable energy sources. Lignin is a renewable resource with an abundant aromatic ring structure and low price. However, the complex structure and low reactivity of lignin limit the development of its application. The depolymerization of lignin is considered to be an effective solution to this dilemma. The catalytic depolymerization of lignin allows the preparation of value‐added fine chemicals, such as monophenols and high‐grade biofuels, partially replacing some products based on petroleum resources. In order to produce biofuels and value‐added chemicals on a large scale through lignin depolymerization, it is necessary to develop efficient catalysts and mature catalytic systems. This review provides an overview of recent advances in catalytic depolymerization of lignin, both in terms of biocatalytic and chemical methods, respectively. Biocatalytic methods depolymerize lignin through the action of fungi, bacteria and enzymes. Chemical methods for depolymerization of lignin include pyrolysis, acid catalysis, base catalysis, oxidative catalysis, hydrogenolysis, photocatalysis, and electrocatalysis. In addition, through a detailed discussion of catalyst types, reaction mechanisms and product properties, we summarise the current opportunities and challenges for the catalytic conversion of lignin and provide an outlook on future developments in this field.

Enantioselective, Decarboxylative (3+2)-Cycloaddition of Azomethine Ylides and Chromone-3-Carboxylic Acids.

Herein, we describe the synthesis of a variety of chiral hybrid pyrrolidine-chromanone polycyclic derivatives. A convenient (3+2)-annulation of azomethine ylides with chromone-3-carboxylic acid realized under Brønsted base catalysis produced highly functionalized products in high yields with good stereoselectivities through asymmetric, intermolecular, and decarboxylative (3+2)-cyclization.

Asymmetric and switchable divergent multicomponent reactions involving distinct alkynes via palladium catalysis

Asymmetric multicomponent reactions represent an efficient and economic strategy for the construction of complicated structures, and those involving two different alkynes have been rarely explored, probably due to the challenges in sequence control and chemo-, regio-, and stereoselectivity. Here, we disclosed an asymmetric multicomponent cascade vinylogous addition/Sonogashira reaction between 1,3-enynes, N -sulfonylimines, and terminal alkynes catalyzed by Pd(0), which consecutively served as a π-Lewis base catalyst and a traditional coupling catalyst. High selectivity has been achieved; moreover, the cascade reaction with a switchable hydroamination process was realized in a one-pot or stepwise manner by slightly tuning the catalytic conditions, thus furnishing enantioenriched N -heterocycles with an exocyclic double bond in either E or Z configuration stereodivergently. This work provided rapid access to a full set of stereoisomers possessing a stereogenic center and a trisubstituted double bond, and it could arouse more interest in palladium catalysis and asymmetric multicomponent reaction. • An asymmetric palladium-catalyzed reaction involving two alkynes is developed • Switchable stereodivergent synthesis of enantioenriched N -heterocycles is realized • Wide functional groups are tolerated With the advantages of simplicity, efficiency, and atom economy, the asymmetric multicomponent reaction provides easy access to structurally diverse products from independently tunable starting materials. We developed an asymmetric multicomponent process between 1,3-enynes, N -sulfonylimines, and terminal alkynes via π-Lewis base catalysis of Pd(0), which showed a broad substrate scope and was even compatible with the late-stage modification of acetylene-embedding drugs. Moreover, a domino or a sequential hydroamination reaction led to a full set of stereoisomers of N -heterocycles with an exocyclic double bond and a stereogenic center by simply tuning the catalytic conditions. The cascade reaction involving different alkynes—which proceeded in a strictly ordered fashion to furnish densely functionalized products with stereodiversity in high chemo-, regio-, and stereoselectivity—might have more applications in synthetic chemistry. A Pd-catalyzed asymmetric multicomponent reaction between 1,3-enynes, N -sulfonylimines, and terminal alkynes is reported, proceeding in a cascade vinylogous addition and Sonogashira coupling sequence with high chemo-, regio-, and stereoselectivity. A tandem hydroamination process to access N -heterocycles with a switchable Z - or E -exocyclic double bond can be further realized by simply tuning the catalytic conditions.

Scaling Catalytic Contributions of Small Self-Cleaving Ribozymes.

Nucleolytic ribozymes utilize general acid-base catalysis to perform phosphodiester cleavage. In most ribozyme classes, a conserved active site guanosine is positioned to act as general base, thereby activating the 2'-OH group to attack the scissile phosphate (γ-catalysis). Here, we present an atomic mutagenesis study for the pistol ribozyme class. Strikingly, "general base knockout" by replacement of the guanine N1 atom by carbon results in only 2.7-fold decreased rate. Therefore, the common view that γ-catalysis critically depends on the N1 moiety becomes challenged. For pistol ribozymes we found that γ-catalysis is subordinate in overall catalysis, made up by two other catalytic factors (α and δ). Our approach allows scaling of the different catalytic contributions (α, β, γ, δ) with unprecedented precision and paves the way for a thorough mechanistic understanding of nucleolytic ribozymes with active site guanines.

Scaling Catalytic Contributions of Small Self-Cleaving Ribozymes.

Nucleolytic ribozymes utilize general acid-base catalysis to perform phosphodiester cleavage. In most ribozyme classes, a conserved active site guanosine is positioned to act as general base, thereby activating the 2'-OH group to attack the scissile phosphate (γ-catalysis). Here, we present an atomic mutagenesis study for the pistol ribozyme class. Strikingly, "general base knockout" by replacement of the guanine N1 atom by carbon results in only 2.7-fold decreased rate. Therefore, the common view that γ-catalysis critically depends on the N1 moiety becomes challenged. For pistol ribozymes we found that γ-catalysis is subordinate in overall catalysis, made up by two other catalytic factors (α and δ). Our approach allows scaling of the different catalytic contributions (α, β, γ, δ) with unprecedented precision and paves the way for a thorough mechanistic understanding of nucleolytic ribozymes with active site guanines.

Interrogating the chemical mechanism for carbon dioxide (CO2) reactivity in aqueous tertiary amine solutions: Can a simple parallel hydration reaction mechanism work?

AbstractIn this study, the kinetics of CO2 absorption into tertiary amine methyldiethanolamine (MDEA) was studied intensively using both experimental and theoretical approaches. The experimental work measured the kinetics of CO2(aq) react with MDEA over a range of concentrations including dilute (0.5–10.0 mM) and concentrated (0.5–2.5 M) solutions via stopped‐flow spectrophotometric at 25.0°C. The resulting kinetic data has been theoretically evaluated using three chemical reaction mechanism variants including the complete base catalysis mechanism, the simplified base catalysis mechanism, and the parallel CO2 hydration mechanism. Results showed that the simplified base catalysis mechanism in the absence of the kinetic pathways for CO2 via hydroxide and water is insufficient to predict the measured kinetic data while the complete base catalysis mechanism and parallel hydration mechanisms can accurately predict the kinetics of CO2 absorption into MDEA solutions. In particular, the experimental data of reversibility of the hydration reactions at low pH was in poor agreement with the simplified model predicted results. Given the simplicity of the parallel hydration mechanism with no requirement for determination of rate constants of the base catalysis reaction unlike the complete base catalysis mechanism, the parallel hydration mechanism can be considered the simplest and preferred mechanism describing the reaction between tertiary amine MDEA and CO2. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Mechanistic insights on base-DMSO mediated aerobic oxidation of (hetero)benzylic C-H bonds

Aerobic oxidation of (hetero)benzylic C-H bonds to ketone products always relies on radical process initiated by transition-metal catalysis. Using inorganic bases, here we report an efficient transition-metal-free strategy, which is enabled by DMSO as both the high-polar solvent and the effective reductant. The ionic mechanism was suggested for this reaction, and a high yield of ketones was obtained by choosing the alkalinity-matched inorganic base with the acidity of (hetero)benzylic C-H bonds. Via kinetic experiments, a mixed mechanism with two reaction pathways was suggested for the generation of ketones, one of which involved the reduction of peroxide intermediates toward alcohols intermediates by DMSO, while the dehydration of peroxide intermediates lead to the direct formation of ketones in the other pathway. These findings not only provide a greener approach for ketones production from (hetero)benzylic oxidation, but also encourage the possible strategy to generate alcohols under inorganic base catalysis.

Synergy of physical and chemical constraints for stable lithium-sulfur batteries

Lithium-sulfur battery is an appealing battery system, but it also suffers from the shuttle effect of lithium polysulfide (LiPS) and an unstable cycling life. Physical constraints to polysulfide via coating and chemical constraints from Lewis Acid-Based catalysis are considered as two promising solutions to achieve improvements. Herein, we design a porous polypyrrole-coated cobalt-rich bimetallic oxide (CoFe2O4 @PPy) via a simple method. It endows the cathode with abundant pore structure and adsorption/catalytic sites (N/O and Fe/Co), which can alleviate the polysulfide shuttle phenomenon and protect from sulfur lost. Because of an important synergy between physical and chemical constraints applied to LiPS, CoFe2O4 @PPy/S composite cathode shows excellent performance with a low capacity decay rate of 0.035 % per cycle after 300 cycles at 1 C.

Comparison of the properties of silica aerogel doped with two different laser dyes: Crystal violet and Rhodamine B

In this paper, silica aerogel was doped with two laser dyes, Crystal violet and Rhodamine B, dissolved in ethanol. All samples were prepared in two different ways, with different concentrations and compared with non-doped prepared aerogel. The first way is the modification after the samples are converted to gel. The second way, the modification procedure, starts by adding the modified solution to the sol. TEOS was used as a precursor in two-step acid-base catalysis, and the silanol group trimethylchlorosilane + n-hexane was used as a surface modification. Fourier-transform infrared spectroscopy, field emission scanning electron microscope, X-ray diffraction, nitrogen adsorption-desorption isotherm, and contact angle measurements compared the characterization and structural properties of the two dyes. Results indicate that crystal violet gives better than Rhodamine B, as the contact angle measurement was 153°, total pour volume was 1.066 cm3/gm and the surface area was more significant than 970 m2/gm. While for Rhodamine B, the maximum contact angle was 146°, and the largest surface area was 899 m2/gm. And total pour volume was 1.6 cm3/gm.