High Initial Activity Research Articles

Immobilization of catalase on chitosan and amino acid- modified chitosan beads

Bovine liver catalase was covalently immobilized onto amino acid-modified chitosan beads. The beads were characterized with SEM, FTIR, TGA and the effects of immobilization on optimum pH and temperature, thermostability, reusability were evaluated. Immobilized catalase showed the maximal enzyme activity at pH 7.0 at 30°C. The kinetic parameters, Km and Vmax, for immobilized catalase on alanine–chitosan beads and lysine–chitosan beads were estimated to be 25.67 mM, 27 mM and 201.39 μmol H2O2/min, 197.50 μmol H2O2/min, respectively. The activity of the immobilized catalase on Ala–CB and Lys–CB retained 40% of its high initial activity after 100 times of reuse.

Preparation and Characterization of BaTiO<SUB>3</SUB>-BaAl<SUB>2</SUB>O4-Al<SUB>2</SUB>O<SUB>3</SUB> Composite Support and Catalytic Performance of Its Nickel-Based Catalyst for CO<SUB>2</SUB> Reforming of Methane

Nickel-based catalyst supported on BaTiO3 possesses higher initial activity for carbon dioxide reforming of methane. However, the specific surface area of the BaTiO3 support is too small, and this restricts its application as a catalyst support. A BaTiO3-BaAl2O4-Al2O3 composite support was prepared by the sol-gel method using hexadecyltrimethylammonium bromide as the structure template. The Ba-TiO3-BaAl2O4-Al2O3 composite was characterized by X-ray diffraction, infrared spectroscopy, N2 adsorption-desorption, transmission electron microscopy, and H2 temperature-programmed reduction. The catalytic performance of the Ni/BaTiO3-BaAl2O4-Al2O3 catalyst was investigated by CO2 reforming of CH4. The results showed that the BaTiO3-BaAl2O4-Al2O3 composite support owns a porous texture and high specific surface area, the BaTiO3 and BaAl2O4 phases, whose crystalline size is in the range of 20–50 nm, exist on the inside and outside surface of the composite support in the form of crystalline particles. The size of micropores of the composite support is 10–20 nm, The presence of both BaTiO3 and BaAl2O4 phases on the surface of the composite support weakens the strong interaction between the nickel species and γ-Al2O3 of the Ni/BaTiO3-BaAl2O4-Al2O3 catalyst, and the possibility of the formation of NiAl2O4 spinel is decreased. The Ni/BaTiO3-BaAl2O4-Al2O3 catalyst with 17.33% Ba content shows the highest activity and excellent stability for CH4 reforming with CO2 to synthesis gas.

Functional nanostructured catalysts based on the niobates to the dry methane reforming and ethylene homologation reactions

Catalytic activity and selectivity of niobate-based nanostructured materials were investigated. Dry methane reforming (DMR) and ethylene homologation reaction (EHR) were selected as test reactions. KSr2Nb5O15,Sr2NaNb5O15 and NaSr2(NiNb4)O15−δ niobate powders were prepared by the high energy ball milling method and calcined in a reductor atmosphere. N2 adsorption isotherms, X-ray diffraction and infrared spectroscopy characterization was performed. Hydrogen pretreated niobates showed from low to moderate catalytic initial activity in DMR’s test, nevertheless the materials were deactivated rapidly and the kinetic parameters associated to deactivation were estimated. Otherwise, non-treated catalysts showed a high initial activity in EHR’s test and KSr2Nb5O15 catalyst requires 24h to the total deactivation with a high selectivity to form propylene. A reaction mechanism to the propylene formation is discussed.

Graphene ribbon-supported Pd nanoparticles as highly durable, efficient electrocatalysts for formic acid oxidation

Graphene ribbon-supported Pd nanoparticles (Pd/GR) have been prepared by a simple, clean process in aqueous medium, involving only a Pd precursor and graphene ribbon (GR) as both a reducing agent and a catalyst support. A high density of Pd nanoparticles with a small average particle size (∼2.8±0.8nm) could be successfully deposited on graphene ribbons. The as-obtained Pd/GR electrocatalysts show increased electrochemical surface area and significantly enhanced catalytic activity for formic acid oxidation reaction (FAOR) compared to the conventional Pd/C electrocatalysts in terms of peak current density (1.4Amg−1 vs. 0.79Amg−1) and peak potential (−0.15V shift). Both the good dispersion and the relatively small particle size of the Pd nanoparticles on graphene ribbon and the synergetic effect between Pd and GR lead to high initial catalytic activity for FAOR. More importantly, a dramatic enhancement in durability is found with Pd/GR for FAOR due to the strong interaction between Pd and GR.

16 Imaging Regional Differences in Beta-2 Adrenergic Receptor Function at The Cellular Level

A common feature of stress cardiomyopathy is contractile impairment of the left ventricular (LV) apical myocardium, although sympathetic effectors are elevated. We investigated the responsiveness of murine cardiomyocytes (CMs) from different LV regions to beta-2 adrenergic (beta2AR) stimulation. Although, initially positively inotropic, beta2AR may become negatively inotropic via biassed-agonism. The apical myocardium may express more beta2ARs as it’s relatively reliant on inotropic support from circulating adrenaline. High initial beta2AR-cAMP activation may initiate stimulus trafficking to beta2AR-Gi signalling. Contractile response to beta2AR stimulation (1µM Isoprenaline with 300nM CGP20712A) was measured by video microscopy. Whole-cell cAMP production after beta2AR stimulation was measured by FRET-based cAMP sensors. Apical CMs (ApCMs) significantly increased their initial contractility following beta2AR stimulation compared to Basal CMs (BCMs) from rats (ApCM 2.28 fold ±0.12 n=10 vs. BCM 1.32 fold ±0.06 n=8 p

Highly flexible self-standing film electrode composed of mesoporous rutile TiO2/C nanofibers for lithium-ion batteries

There is increasing interest in flexible, safe, high-power thin-film lithium-ion batteries which can be applied to various modern devices. Although TiO2 in rutile phase is highly attractive as an anode material of lithium-ion batteries for its high thermal stability and theoretical capacity of 336mAhg−1 and low price, its inflexibility and sluggish lithium intercalation kinetics of bulk phase strongly limit its practical application for particular in thin-film electrode. Here we show a simple way to prepare highly flexible self-standing thin-film electrodes composed of mesoporous rutile TiO2/C nanofibers with low carbon content (<15wt.%) by electrospinning technique with outstanding electrochemical performance, which can be applied directly as electrodes of lithium-ion batteries without the further use of any additive and binder. The atmosphere during calcination plays a critical role in determining the flexible nature of thin film and particle size of TiO2 in as-fabricated nanofibers. Big size (10cm×4cm), flexible thin film is obtained after heat treatment under 10%H2–Ar at 900°C for 3h. After optimization, the diameter of fibers can reach as small as ∼110nm, and the as-prepared rutile TiO2 films show high initial electrochemical activity with the first discharge capacity as high as 388mAhg−1. What is more, very stable reversible capacities of ∼122, 92, and 70mAhg−1 are achieved respectively at 1, 5 and 10C rates with negligible decay rate within 100 cycling times.

Structure-activity relation of Re nanoparticles

By combining density functional theory and thermodynamic considerations we determined the equilibrium shape of Re particles in contact with O${}_{2}$ and N${}_{2}$ environments. At low and intermediate coverages oxygen adsorption has a minor influence on the particle shape, while nitrogen adsorption leads to the stabilization of spherically shaped polyhedra with a large contribution from atomically rough faces. At very high coverages of O and N particles are perfect prisms consisting of low-index faces. By comparing these results with the experimental data for the activity of different Re surfaces we propose that the experimentally measured high initial activity of polycrystalline Re for ammonia synthesis might be due to the N-induced formation of high-index faces with a high density of low-coordinated atoms (roughening). Moreover, the measured decrease in the activity of polycrystalline Re at saturation coverage might be because of the N-induced formation of close-packed faces (smoothing). Our calculations suggest that adsorbate-induced roughening or smoothing of catalytic particles on the atomic scale is capable of controlling the activity of the catalysts.

Stable Vapor-phase Catalytic Conversion of Pinacolone into 2,3-Dimethyl-1,3-butadiene

Abstract In the vapor-phase synthesis of 2,3-dimethyl-1,3-butadiene from pinacolone over modified alumina catalysts, it was found that alumina modified with transition metals such as Co stabilized the conversion of pinacolone and produced 2,3-dimethyl-1,3-butadiene selectively under hydrogen flow conditions, whereas the catalytic activity of pure alumina was seriously deteriorated irrespective of its high initial activity.

Polymerization of Ethylene over rac-Et(1-indenyl)2ZrCl2/MAO Catalyst Supported on Pseudo-Inverse Opal Silica Particles

The polymerization of ethylene with rac-Et(1-indenyl)2ZrCl2/MAO catalyst supported on ultraporous and spherical pseudo-inverse opal silica (PIOS) particles with unique morphology is reported. The novel silica particles with an inverse opal-like structure provide wide-open pore and surface structures favorable for the catalyst deposition and monomer access with minimal intraparticle diffusion resistance. The metallocene catalyst supported on the PIOS support exhibited very high initial catalyst activity and longer catalyst lifetime compared with conventional silica-supported catalysts. The experimental data that show the effects of support geometry on the catalytic activity, catalyst particle fragmentation, polymer particle morphology, and polymer molecular weight distribution in ethylene polymerization are presented.

Mutations affecting the activity of the cyclodextrin glucanotransferase of Paenibacillus pabuli US132: insights into the low hydrolytic activity of cyclodextrin glucanotransferases

The cyclodextrin glucanotransferase from Paenibacillus pabuli US132 (US132 CGTase) was engineered using a rational approach in an attempt to provide it with anti-staling properties comparable to those of the commercial maltogenic amylase (Novamyl). The study aimed to concurrently decrease the cyclization activity and increase the hydrolytic activity of US132 CGTase. A five-residue loop (PAGFS) was inserted, alone or with the substitution of essential residues for cyclization (G180, L194 and Y195), mimicking the case of Novamyl. The findings indicate that, unlike the case of the CGTase of Thermoanerobacterium thermosulfurigenes strain EM1 whose initial high hydrolytic activity was exceptional, these mutations completely abolished the cyclization and hydrolytic activities of the US132 CGTase. This suggests that those mutations are not able to convert conventional CGTases, whose hydrolytic activities are very weak, into hydrolases. Accordingly, and for the first time, a structural barrier at subsite −3 was advanced as an influential factor which might explain the low hydrolytic activity of conventional CGTases.

Binding of piano‐stool Ru(II) complexes to DNA; QM/MM study

Ru(II) "piano-stool" complexes belong to group of biologically active metallocomplexes with promising anticancer activity. In this study, we investigate the reaction mechanism of [(η(6)-benzene)Ru(II)(en)(H(2)O)](2+) (en = ethylenediamine) complex binding to DNA by hybrid QM/MM computational techniques. The reaction when the Ru(II) complex is coordinated on N7-guanine from major groove is explored. Two reaction pathways, direct binding to N7 position and two-step mechanism passing through O6 position, are considered. It was found that the reaction is exothermic and the direct binding process is preferred kinetically. In analogy to cisplatin, we also explored the possibility of intrastrand cross-link formation where the Ru(II) complex makes a bridge between two adjacent guanines. Two different pathways were found, leading to a final structure with released benzene ligand. This process is exothermic; however, one pathway is blocked by relatively high initial activation barrier. Geometries, energies, and electronic properties analyzed by atoms in molecules and natural population analysis methods are discussed.

Modeling of phosphorus deactivation in polysilicon for simulation of memory process in nanometer era

In this study, experiments were performed to investigate phosphorus deactivation in polysilicon and a deactivation model was proposed to improve the simulation of nanometer memory devices. Decay of carrier concentration was observed during low-temperature annealing in polysilicon films formed by different methods. However, the decay rate decreased with time and the carrier concentration almost saturated after long-term annealing. The grain size of polysilicon did not significantly affect the decay of carrier concentration. A clustering model was proposed to simulate the deactivation. The model assumes that the cluster formation rate dominates the dependence of the deactivation process on temperature. Direct reactions between neighboring phosphorus atoms was suggested to explain the rapid deactivation with a high initial activation level. The impact of deactivation on the electrostatics of memory devices was demonstrated by simulation using the proposed clustering model.

Fluorinated Solvents in Methyltrioxorhenium‐Catalyzed Olefin Epoxidations

AbstractEpoxidations with methyltrioxorhenium(VII) (MTO) as catalyst precursor and additives are examined in fluorinated solvents under various conditions. These fluorinated solvents have a strong influence on the 1H NMR, 13C NMR, and 17O NMR spectroscopic data of the catalyst precursor, apparently contributing significantly to the catalytic activity of such systems. Accordingly, the highest turnover frequencies (TOF) obtained with MTO‐containing systems have been determined, reaching up to 39000 h–1. Despite the high initial activity, such systems show a pronounced sensitivity to water leading also to faster catalyst decomposition. The high activity as well as the high sensitivity of the catalyst may be due to its solvent‐enhanced higher Lewis acidity, leading to quantitative epoxide yields only when quite stable epoxides are the end products and very high amounts of Lewis base additives are applied.

Effects of Catalytic Site Position on the Performance and Lifetime of Carbon Nanotubes Supported Cobalt Fischer-Tropsch Synthesis Nano Catalyst

The effects of confinement in carbon nanotubes on the performance and lifetime of carbon nanotubes (CNT) supported cobalt Fischer–Tropsch (FT) catalysts are reported. A method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes. TEM analyses revealed that about 80-85% of cobalt oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Deposition of cobalt oxide inside the nanotube pores decreased the average size of the cobalt oxide particles from 16.6 to 7.2 nm and shifted the reduction peak temperature of cobalt oxide species to lower temperatures (from 330 to 318oC, and 446 to 428oC) and improved the reducibility of the catalyst by 7%. The catalysts were assessed in terms of their activity, selectivity and lifetime in a fixed-bed micro reactor. The catalyst with catalytic sites inside the pores showed 30.5% higher initial activity than the catalyst with catalytic sites outside the pores. Also, the catalyst with cobalt particles inside the pores exhibited higher selectivity to heavier hydrocarbons (79.5% vs. 76.2% C5 + selectivity). Deposition of cobalt particles on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced 50.4% deactivation within a period of 20 days due to catalytic sites sintering. It is concluded that encapsulation of the catalytic metal nanoparticles inside the nanotubes prevents the catalytic site agglomeration. Keywords: Fischer-Tropsch, cobalt nano particles, Carbon nanotubes, Confinement, Activity, Selectivity, Deactivation

Highly Dispersed and Active ReOx on Alumina-Modified SBA-15 Silica for 2-Butanol Dehydration

SBA-15 silica supported rhenium catalysts were synthesized using solution-based atomic layer deposition method, and their activity and stability were studied in the acid-catalyzed 2-butanol dehydration. We find that ReOx/SBA-15 exhibited an extremely high initial activity but a fast deactivation for 2-butanol dehydration at 90–105 °C. Fast deactivation was likely due to the sintering, sublimation, and reduction of rhenia as confirmed by TEM, elemental analysis, and in situ UV–vis (DRS) measurements. To overcome these issues, ReOx/AlOx/SBA-15 catalysts with significantly improved stability were prepared by first modifying the surface identity of SBA-15 with alumina followed by dispersion of rhenia using atomic layer deposition. The AlOx phase stabilizes the dispersion of small and uniform rhenia clusters (<2 nm) as as confirmed by TEM, STEM, and UV–vis (DRS) characterizations. Additional 27Al MAS NMR characterization revealed that modification of the SBA-15 surface with alumina introduces a strong interact...

Palladium Catalysts for Fatty Acid Deoxygenation: Influence of the Support and Fatty Acid Chain Length on Decarboxylation Kinetics

Supported metal catalysts containing 5 wt% Pd on silica, alumina, and activated carbon were evaluated for liquid-phase deoxygenation of stearic (octadecanoic), lauric (dodecanoic), and capric (decanoic) acids under 5 % H2 at 300 °C and 15 atm. On-line quadrupole mass spectrometry (QMS) was used to measure CO + CO2 yield, CO2 selectivity, H2 consumption, and initial decarboxylation rate. Post-reaction analysis of liquid products by gas chromatography was used to determine n-alkane yields. The Pd/C catalyst was highly active and selective for stearic acid (SA) decarboxylation under these conditions. In contrast, SA deoxygenation over Pd/SiO2 occurred primarily via decarbonylation and at a much slower rate. Pd/Al2O3 exhibited high initial SA decarboxylation activity but deactivated under the test conditions. Similar CO2 selectivity patterns among the catalysts were observed for deoxygenation of lauric and capric acids; however, the initial decarboxylation rates tended to be lower for these substrates. The influence of alkyl chain length on deoxygenation kinetics was investigated for a homologous series of C10–C18 fatty acids using the Pd/C catalyst. As fatty acid carbon number decreases, reaction time and H2 consumption increase, and CO2 selectivity and initial decarboxylation rate decrease. The increase in initial decarboxylation rates for longer chain fatty acids is attributed to their greater propensity for adsorption on the activated carbon support.

Hydrogen production via sulfur-based thermochemical cycles: Part 3: Durability and post-characterization of silicon carbide honeycomb substrates coated with metal oxide-based candidate catalysts for the sulfuric acid decomposition step

This work is a follow-up of previous efforts reported on the synthesis of various single and mixed oxide materials and their evaluation as catalysts for the sulfuric acid dissociation reaction for the production of SO2 and O2. The current work concerns the comparative assessment of Fe2O3, CuO, Cu–Fe, Fe–Cr, Cu–Al and Cu–Fe–Al mixed oxides coated as catalysts on silicon carbide monolithic honeycomb structures, with respect to sulfuric acid decomposition reaction conditions for 100h at 850°C and ambient pressure, as well as their ex-situ characterization after such operation. The exposure conditions are representative to a potential future real application. The exposure time, although of relatively short-term, is adequate to extract safe conclusions on the stability and therefore to a large extent also on the suitability of the candidate oxide-based catalysts. All catalytic systems tested exhibited high SO3 conversions reaching or exceeding 70%, for space velocities in the range of 5–35h−1. For some of the samples, the relatively high initial activity decreased by about 5–10 percentage points in the course of the 100h testing, reaching stable mean values. It was concluded that Fe2O3, CuO and Fe–Cr mixed oxide retained their chemical and structural stability after exposure to reaction conditions, while the other three mixed oxides studied suffered from significant phase decomposition phenomena. Based on the fact that the initial catalytic activity of the Fe–Cr mixed oxide, as identified in a previous comparative study among several materials, was found higher than the ones of Fe2O3 and CuO and relatively close to the one of the highly active but costly Pt/Al2O3 catalyst, the particular mixed oxide is considered a promising catalyst for the SO3 dissociation reaction.

Open-field arena boundary is a primary object of exploration for Drosophila.

Drosophila adults, when placed into a novel open-field arena, initially exhibit an elevated level of activity followed by a reduced stable level of spontaneous activity and spend a majority of time near the arena edge, executing motions along the walls. In order to determine the environmental features that are responsible for the initial high activity and wall-following behavior exhibited during exploration, we examined wild-type and visually impaired mutants in arenas with different vertical surfaces. These experiments support the conclusion that the wall-following behavior of Drosophila is best characterized by a preference for the arena boundary, and not thigmotaxis or centrophobicity. In circular arenas, Drosophila mostly move in trajectories with low turn angles. Since the boundary preference could derive from highly linear trajectories, we further developed a simulation program to model the effects of turn angle on the boundary preference. In an hourglass-shaped arena with convex-angled walls that forced a straight versus wall-following choice, the simulation with constrained turn angles predicted general movement across a central gap, whereas Drosophila tend to follow the wall. Hence, low turn angled movement does not drive the boundary preference. Lastly, visually impaired Drosophila demonstrate a defect in attenuation of the elevated initial activity. Interestingly, the visually impaired w1118 activity decay defect can be rescued by increasing the contrast of the arena's edge, suggesting that the activity decay relies on visual detection of the boundary. The arena boundary is, therefore, a primary object of exploration for Drosophila.

Immobilization of lipase B from Candida antarctica on porous styrene–divinylbenzene beads improves butyl acetate synthesis

A new biocatalyst of lipase B from Candida antarctica (MCI-CALB) immobilized on styrene-divinylbenzene beads (MCI GEL CHP20P) was compared with the commercial Novozym 435 (immobilized lipase) in terms of their performances as biocatalysts for the esterification of acetic acid and n-butanol. The effects of experimental conditions on reaction rates differed for each biocatalyst, showing different optimal values for water content, temperature, and substrate molar ratio. MCI-CALB could be used at higher acid concentrations, up to 0.5 M, while Novozym 435 became inactivated at these acid concentrations. Although Novozym 435 exhibited 30% higher initial activity than MCI-CALB for the butyl acetate synthesis, the reaction course was much more linear using the new preparation, meaning that the MCI-CALB allows for higher productivities per cycle. Both preparations produced around 90% of yield conversions after only 2 h of reaction, using 10% (mass fraction) of enzyme. However, the main advantage of the new biocatalyst was the superior performance during reuse. While Novozym 435 was fully inactivated after only two batches, MCI-CALB could be reused for six consecutive cycles without any washings and keeping around 70% of its initial activity. It is proposed that this effect is due to the higher hydrophobicity of the new support, which does not retain water or acid in the enzyme environment. MCI-CALB has shown to be a very promising biocatalyst for the esterification of small-molecule acids and alcohols.

Support effects on the oxidation of ethanol at Pt nanoparticles

The effects of metal oxide supports on ethanol oxidation have been investigated by drop coating Pt nanoparticles onto glassy carbon electrodes coated with thin layers of ruthenium oxide, tin oxide, a mixed Ru+Sn oxide, and onto an indium–tin oxide (ITO) electrode. All four oxide supports exhibited significant co-catalytic effects, with their effectiveness at low potentials increasing in the order Ru oxide<ITO<Ru+Sn oxide<Sn oxide. However, at higher potentials (e.g. 0.4V vs. SCE) currents were higher for Pt supported on Ru oxide or Ru+Sn oxide than on Sn oxide, revealing mechanistic differences between the roles of Ru and Sn oxide. Although Sn oxide produced very high initial activities, ITO and Ru+Sn oxide provided more stable performances.