Theoretical evidence of the observed kinetic order dependence on temperature during the N2O decomposition over Fe-ZSM-5

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The efficiency of green hydrogen production via water splitting is typically hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Here we investigate the performance of various nickel nanoclusters, deposited via a binder-free gas-phase method, as OER catalysts on two distinct porous platforms: commercial gas diffusion layers (GDL) for electrocatalysis and mesoporous TiO 2 thin films for photoelectrocatalysis. For dark electrocatalysis on GDL, we find a non-linear relationship between ca

Controlling the temporal and kinetic statistics of excitons in semiconductor nanocrystals is important for understanding how multiexcitonic processes emerge in ultrafast excited‐state dynamics under low‐fluence conditions. Under conventional single‐pulse excitation, the Poissonian nature of exciton generation limits the manifestation of biexciton‐mediated processes in the observed kinetics at low fluence. Here, we demonstrate a sequential ultrafast excitation scheme in CsPbBr 3 nanocrystals that reshapes th

Xylose acetalization has emerged as a potent tool to extract this sugar from lignocellulosic biomass and for creating new biobased chemicals and materials. This article elucidates a generalized reaction network for xylose acetalization and reveals the role of aldehyde electrophilicity and ring strain in intermediate formation. Aldehydes with strong electrophilicity stabilize xylose as both furanose‐ and pyranose‐monoacetals, whereas weaker aldehydes favour xylofuranose acetalization due to the high ring str

A key challenge in metabolic engineering is to find and to improve biosynthetic pathways that lead to the cellular production of a given industrial, pharmaceutical or specialty chemical compound. In many cases, the enzymatic reactions required for bio-production have not been observed in nature and need to be designed from scratch. Computational approaches are essential to predict possible novel biotransformation and to find enzymes that can potentially catalyze the proposed reactions. In this work, we pres

Hybrid Car-Parrinello QM/MM calcns. are used to investigate the reaction mechanism of hydrolysis of a common b-lactam substrate (cefotaxime) by the monozinc b-lactamase from Bacillus cereus (BcII). The calcns. suggest a fundamental role for an active site water in the catalytic mechanism. This water mol. binds the zinc ion in the first step of the reaction, expanding the zinc coordination no. and providing a proton donor adequately oriented for the second step. The free energy barriers of the two reaction s

The reaction of half-sandwich complexes of ruthenium, rhodium, and iridium with amino-substituted 3-hydroxy-2-pyridone ligands in aqueous solution gives monomeric O,O'-chelate complexes. Upon addition of base, the complexes assemble to form trimeric metallamacrocycles, as evidenced by NMR spectroscopy and single-crystal X-ray analyses. The macrocycles are able to act as highly selective receptors for lithium ions. The binding constants depend on the nature of the half-sandwich complex. the ligand, and the p

Surface-active centers were detected in HZSM-5 with a low content of iron (

A novel liquid system has been developed to initiate the anionic polymerization of lactam-12. This system, containing both an activator and a catalyst, has the primary advantage over previous systems of permitting infinite storage of the reactant, and it avoids premixing of batches. The anionic species of the system were identified with matrix-assisted laser desorption/ionization time-of-flight measurements, and Fourier transforminfrared was used to measure the change in their concentrations during the poly

One-step hydroxylation of benzene to phenol by N2O has been performed over structured catalytic beds made of ZSM-5 coatings on stainless steel grids. The catalysts demonstrated high activity with a selectivity toward phenol formation of 98%. A detailed kinetic study was carried out with a variation in reactant concentrations, benzene/N2O ratio, and residence time. The results obtained suggest a surface reaction between benzene and nitrous oxide adsorbed on two different active sites.

The catalytic cracking of methane over nickel gauze is proposed as an attractive alternative for the prodn. of CO-free hydrogen. The catalyst deactivates due to intensive coke deposition. Therefore, the reactor was operated periodically with the reaction followed by the catalyst regeneration by burning of coke in oxidative atm. The optimal reaction performance was found to consist of reaction periods of 4 min followed by 4 min regeneration periods. [on SciFinder (R)]

The influence of cure temperature, composition and chemical structure on the morphology resulting from chemically induced phase separation has been investigated for different epoxy functionalized dendritic hyperbranched polymers blended with diglycydil bisphenol A and an aliphatic diamine. The cure temperature window chosen highlighted the influence of both the kinetics of phase separation and the thermodynamics of mixing on the final morphology. In relatively immiscible blends and at low cure temperatures,

The mechanism of the oxygen redn. reaction (orr) was studied in alk. media at La0.6Ca0.4CoO3-activated carbon electrodes in a channel flow cell (CFC). The electrodes were made by depositing a mixt. of the perovskite (La0.6Ca0.4CoO3) powder as the catalyst, Vulcan XC 72 as the carbon, and Triton X-100 as the binder on Ti substrates. The collection efficiency, N, of the double-electrode system in the CFC was evaluated in advance using the ferro-ferricyanide couple. The results obtained for the orr show that t

Metalation/trapping sequences applied to relatively inert, tert-alkyl substituted arenes tend to give poor yields unless the reagent is used in high concns. Under optimized conditions, even 1,4-bis(tert-butyl)benzene, 1,1,3,3-tetramethylindane and 1,1,2,2,3,3-hexamethylindane can be smoothly converted into derivs. Competition expts. enable the quant. assessment of tert-alkyl substituent effects on the metalation rates at arom. ortho, meta and para positions. Unlike alkyl groups, hetero elements generally ac

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The electrochemical promotion of heterogeneous catalytic reactions is a new development which draws the attention of the scientific community as much to fundamental research as to the possible direct applications of this phenomenon in automotive and in industrial catalysis. We have chosen to study the electrochemical promotion of the complete ethylene oxidation on metallic oxides catalysts. The principal oxides which we used has been the iridium oxide (IrO2) and iridium and titanium oxide mixtures (IrO2+TiO

Chem. ligation methods in combination with regioselective addressable templates have allowed the prepn. of well defined complex monomol. films tethered to gold surfaces. The supramol. monolayers exposed artificial recognition sites, here for monoclonal antibodies. SPR, FTIR spectroscopies, and TOF-SIMS were ideally suited surface sensitive techniques to enable the essential control of the individual reaction steps. The concept presented here for the functionalization of gold surfaces may be easily applied t

The oxidn. of CO on silica-supported hematite (Fe2O3) was studied by the step-response method in a tubular fixed-bed reactor at temps. 270-350 Deg. The oxidn. process appeared to proceed in two stages. First, oxygen atoms adsorbed on the surface of hematite react with gas phase CO according to an Eley-Rideal mechanism. Once that adsorbed oxygen has been consumed to some extent, surface oxygen from the lattice of iron oxide is removed in a second stage involving CO adsorption and CO reactive desorption steps

The fluorescence-excitation and fluorescence spectra as well as the fluorescence decay times were recorded for Hg atoms excited to the 61P1 state by synchrotron radiation in Ar, Kr, Xe, N2, and CH4 matrixes and in Ar matrixes with a low NH3 content. Sequential decays from the 61P1 to different 63PJ levels involve the intersystem crossing and intramultiplet relaxation, the dependence of the relaxation rate on the properties of the matrix being different for the 2 mechanisms. [on SciFinder (R)]

The addn. of a miscible org. solvent, which decreases the water concn. of the system, is considered as a means to reduce hydrolysis when transesterification is the desired reaction. This approach is illustrated by the study of a model reaction, the kinetically controlled transesterification of a racemic mixt. of phenylalanine Pr ester with 1,4-butanediol by chymotrypsin (EC 3.4.21.1) in the presence of the miscible org. solvent, DMSO. The results showed that no appreciable effect on the transesterification

We identified the nature of the chemical reaction between silver and the cleaved surface of BiCaSrCuO at room temperature as a Bi-Ag reaction with Bi segregation, accompanied by interaction with the Sr atoms. Our synchrotron-radiation photoemission spectra also reveal an interaction of the adatoms with the O atoms, not detected by previous studies.

Theoretical evidence of the observed kinetic order dependence on temperature during the N2O decomposition over Fe-ZSM-5

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