scholarly journals Aromatization of light naphtha fractions on zeolites: 2. Model of catalyst deactivation

2004 ◽  
Vol 58 (3) ◽  
pp. 104-108 ◽  
Author(s):  
Nikolaj Ostrovski ◽  
Svetlana Rovenskaja ◽  
Genadij Echevski
Keyword(s):  
Rate Constants ◽  
Catalyst Deactivation ◽  
Activation Energies ◽  
Modeling And Optimization ◽  
Light Naphtha ◽  
Deactivation Rate ◽  
Deactivation Kinetics

A model of catalyst deactivation in the "Zeoforming" process was developed. The deactivation rate constants and activation energies were estimated. The role of adsorbed oligomers in the reaction and the deactivation kinetics were examined. The model is intended for further modeling and optimization of the process.

scholarly journals Aromatization of light naphtha fractions on zeolites 1: Kinetic model

2003 ◽  
Vol 57 (9) ◽  
pp. 399-403 ◽  
Author(s):  
Svetlana Rovenskaja ◽  
Nikolaj Ostrovski
Keyword(s):  
Experimental Data ◽  
Kinetic Model ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Scheme ◽  
Activation Energies ◽  
Modeling And Optimization ◽  
Light Naphtha ◽  
Reaction Rate Constants

On the basis of analyzing kinetic experimental data performed in laboratory integral reactors a lumping kinetic model of the "Zeoforming" process was developed. A reaction scheme of the lumped components was proposed, that was adapted to the technological requirements. The reaction rate constants and activation energies were estimated, that are valid for certain feed compositions. The model is intended for further modeling and optimization of the process.

Kinetics of esterification of monoisopropylphenols with phosphoryl trichloride

1989 ◽  
Vol 54 (5) ◽  
pp. 1311-1317
Author(s):  
Miroslav Magura ◽  
Ján Vojtko ◽  
Ján Ilavský
Keyword(s):  
Liquid Phase ◽  
Rate Constants ◽  
Reaction Rates ◽  
Activation Energies ◽  
The Individual ◽  
Kinetics Of

The kinetics of liquid-phase isothermal esterification of POCl3 with 2-isopropylphenol and 4-isopropylphenol have been studied within the temperature intervals of 110 to 130 and 90 to 110 °C, respectively. The rate constants and activation energies of the individual steps of this three-step reaction have been calculated from the values measured. The reaction rates of the two isomers markedly differ: at 110 °C 4-isopropylphenol reacts faster by the factors of about 7 and 20 for k1 and k3, respectively. This finding can be utilized in preparation of mixed triaryl phosphates, since the alkylation mixture after reaction of phenol with propene contains an excess of 2-isopropylphenol over 4-isopropylphenol.

scholarly journals The Role of H2C2O4 and Na2CO3 as Precipitating Agents on The Physichochemical Properties and Photocatalytic Activity of Bismuth Oxide

2020 ◽  
Vol 18 (1) ◽  
pp. 129-137
Author(s):  
Yayuk Astuti ◽  
Rizka Andianingrum ◽  
Abdul Haris ◽  
Adi Darmawan ◽  
Keyword(s):  
Photocatalytic Activity ◽  
Methyl Orange ◽  
Physicochemical Properties ◽  
Bismuth Oxide ◽  
Rate Constants ◽  
Degradation Rate ◽  
Precipitation Method ◽  
Methyl Orange Degradation ◽  
Methyl Orange Dye

AbstractSynthesis of bismuth oxide synthesis through the precipitation method using H2C2O4 and Na2CO3 precipitating agents, identification of physicochemical properties and its photocatalysis activity for methyl orange degradation were conducted. The bismuth oxide synthesis was undertaken by dissolving Bi(NO3)3.5H2O in HNO3, then added precipitating agents to form precipitate. The results showed that bismuth oxide produced by H2C2O4 precipitating agent was a yellow powder containing a mixture of α-Bi2O3 (monoclinic) and β-Bi2O3 (tetragonal), porous with size of 28-85 μm. Meanwhile, the use of Na2CO3 as precipitating agent resulted in bismuth oxide consisting of α-Bi2O3 and β-Bi2O3 and Bi2O4, irregular shape without pore being 40-115 μm in size. Bismuth oxide synthesized with H2C2O4 precipitating agent showed higher photocatalytic activity compared to bismuth oxide synthesized using Na2CO3 on degrading methyl orange dye with degradation rate constants of 2.35x10-5 s-1 for H2C2O4 and 1.81x10-5 s-1 for Na2CO3.

scholarly journals Deciphering the role of quantum dot size in the ultrafast charge carrier dynamics at the perovskite–quantum dot interface

2020 ◽  
Vol 8 (42) ◽  
pp. 14834-14844
Author(s):  
Piotr Piatkowski ◽  
Sofia Masi ◽  
Pavel Galar ◽  
Mario Gutiérrez ◽  
Thi Tuyen Ngo ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Charge Carrier ◽  
Rate Constants ◽  
Transient Absorption ◽  
Carrier Dynamics ◽  
Carrier Transfer ◽  
Charge Carrier Dynamics ◽  
Conduction Bands

Charge-carrier transfer (CT) from the perovskite host to PbS QDs were studied using fs-transient absorption and THz techniques. The CT rate constants increase with the size of QDs due to a change in the position of valence and conduction bands in PbS QDs.

Role of activation energies of individual phases in two-phase range on constitutive equation of Zr–2.5Nb–0.5Cu alloy

2017 ◽  
Vol 27 (1) ◽  
pp. 172-183 ◽  
Author(s):  
K.K. SAXENA ◽  
S.K. JHA ◽  
V. PANCHOLI ◽  
G.P. CHAUDHARI ◽  
D. SRIVASTAVA ◽  
...  
Keyword(s):  
Constitutive Equation ◽  
Activation Energies ◽  
Two Phase ◽  
Phase Range

scholarly journals Insights on the mechanisms of Ca2+ regulation of connexin26 hemichannels revealed by human pathogenic mutations (D50N/Y)

2013 ◽  
Vol 142 (1) ◽  
pp. 23-35 ◽  
Author(s):  
William Lopez ◽  
Jorge Gonzalez ◽  
Yu Liu ◽  
Andrew L. Harris ◽  
Jorge E. Contreras
Keyword(s):  
Essential Role ◽  
Negative Charge ◽  
Salt Bridge ◽  
Cysteine Residue ◽  
Wild Type ◽  
Closed State ◽  
Large Size ◽  
Deactivation Kinetics ◽  
Connexin Hemichannel

Because of the large size and modest selectivity of the connexin hemichannel aqueous pore, hemichannel opening must be highly regulated to maintain cell viability. At normal resting potentials, this regulation is achieved predominantly by the physiological extracellular Ca2+ concentration, which drastically reduces hemichannel activity. Here, we characterize the Ca2+ regulation of channels formed by wild-type human connexin26 (hCx26) and its human mutations, D50N/Y, that cause aberrant hemichannel opening and result in deafness and skin disorders. We found that in hCx26 wild-type channels, deactivation kinetics are accelerated as a function of Ca2+ concentration, indicating that Ca2+ facilitates transition to, and stabilizes, the closed state of the hemichannels. The D50N/Y mutant hemichannels show lower apparent affinities for Ca2+-induced closing than wild-type channels and have more rapid deactivation kinetics, which are Ca2+ insensitive. These results suggest that D50 plays a role in (a) stabilizing the open state in the absence of Ca2+, and (b) facilitating closing and stabilization of the closed state in the presence of Ca2+. To explore the role of a negatively charged residue at position 50 in regulation by Ca2+, this position was substituted with a cysteine residue, which was then modified with a negatively charged methanethiosulfonate reagent, sodium (2-sulfanoethyl) methanethiosulfonate (MTSES)−. D50C mutant hemichannels display properties similar to those of D50N/Y mutants. Recovery of the negative charge with chemical modification by MTSES− restores the wild-type Ca2+ regulation of the channels. These results confirm the essential role of a negative charge at position 50 for Ca2+ regulation. Additionally, charge-swapping mutagenesis studies suggest involvement of a salt bridge interaction between D50 and K61 in the adjacent connexin subunit in stabilizing the open state in low extracellular Ca2+. Mutant cycle analysis supports a Ca2+-sensitive interaction between these two residues in the open state of the channel. We propose that disruption of this interaction by extracellular Ca2+ destabilizes the open state and facilitates hemichannel closing. Our data provide a mechanistic understanding of how mutations at position 50 that cause human diseases are linked to dysfunction of hemichannel gating by external Ca2+.

scholarly journals Things go better with coke: the beneficial role of carbonaceous deposits in heterogeneous catalysis

2016 ◽  
Vol 6 (2) ◽  
pp. 363-378 ◽  
Author(s):  
C. H. Collett ◽  
J. McGregor
Keyword(s):  
Heterogeneous Catalysis ◽  
Heterogeneous Catalysts ◽  
Catalyst Deactivation ◽  
Catalytic Performance ◽  
Fischer Tropsch ◽  
Carbonaceous Deposits ◽  
Beneficial Role ◽  
Catalytic Processes

Carbonaceous deposits on heterogeneous catalysts are traditionally associated with catalyst deactivation. However, they can play a beneficial role in many catalytic processes, e.g. dehydrogenation, hydrogenation, alkylation, isomerisation, Fischer–Tropsch, MTO etc. This review highlights the role and mechanism by which coke deposits can enhance catalytic performance.

Fast NMDA Receptor–Mediated Synaptic Currents in Neurons From Mice Lacking the ε2 (NR2B) Subunit

2000 ◽  
Vol 83 (1) ◽  
pp. 616-620 ◽  
Author(s):  
Kenneth R. Tovar ◽  
Kathleen Sprouffske ◽  
Gary L. Westbrook
Keyword(s):  
Nmda Receptor ◽  
Hippocampal Neurons ◽  
Postsynaptic Membrane ◽  
Synaptic Activity ◽  
Wild Type ◽  
Nmda Receptor Subunit ◽  
Deactivation Kinetics ◽  
Low Concentrations ◽  
Specific Antagonist

The N-methyl-d-aspartate (NMDA) receptor has been implicated in the formation of synaptic connections. To investigate the role of the ε2 (NR2B) NMDA receptor subunit, which is prominently expressed during early development, we used neurons from mice lacking this subunit. Although ε2−/− mice die soon after birth, we examined whether NMDA receptor targeting to the postsynaptic membrane was dependent on the ε2 subunit by rescuing hippocampal neurons from these mice and studying them in autaptic cultures. In voltage-clamp recordings, excitatory postsynaptic currents (EPSCs) from ε2−/− neurons expressed an NMDA receptor–mediated EPSC that was apparent as soon as synaptic activity developed. However, compared with wild-type neurons, NMDA receptor–mediated EPSC deactivation kinetics were much faster and were less sensitive to glycine, but were blocked by Mg2+ or AP5. Whole cell currents from ε2−/− neurons were also more sensitive to block by low concentrations of Zn2+ and much less sensitive to the ε2-specific antagonist ifenprodil than wild-type currents. The rapid NMDA receptor–mediated EPSC deactivation kinetics and the pharmacological profile from ε2−/−neurons are consistent with the expression of ζ1/ε1 diheteromeric receptors in excitatory hippocampal neurons from mice lacking the ε2 subunit. Thus ε1 can substitute for the ε2 subunit at synapses and ε2 is not required for targeting of NMDA receptors to the postsynaptic membrane.

scholarly journals Phosphate has dual roles in cross-bridge kinetics in rabbit psoas single myofibrils

2021 ◽  
Vol 153 (3) ◽  
Author(s):  
Masataka Kawai ◽  
Robert Stehle ◽  
Gabriele Pfitzer ◽  
Bogdan Iorga
Keyword(s):  
Rate Constants ◽  
Striated Muscle ◽  
Intrinsic Rate ◽  
Isometric Tension ◽  
Force Generation ◽  
Skinned Fibers ◽  
Sinusoidal Analysis ◽  
Rabbit Psoas ◽  
Cross Bridge

In this study, we aimed to study the role of inorganic phosphate (Pi) in the production of oscillatory work and cross-bridge (CB) kinetics of striated muscle. We applied small-amplitude sinusoidal length oscillations to rabbit psoas single myofibrils and muscle fibers, and the resulting force responses were analyzed during maximal Ca2+ activation (pCa 4.65) at 15°C. Three exponential processes, A, B, and C, were identified from the tension transients, which were studied as functions of Pi concentration ([Pi]). In myofibrils, we found that process C, corresponding to phase 2 of step analysis during isometric contraction, is almost a perfect single exponential function compared with skinned fibers, which exhibit distributed rate constants, as described previously. The [Pi] dependence of the apparent rate constants 2πb and 2πc, and that of isometric tension, was studied to characterize the force generation and Pi release steps in the CB cycle, as well as the inhibitory effect of Pi. In contrast to skinned fibers, Pi does not accumulate in the core of myofibrils, allowing sinusoidal analysis to be performed nearly at [Pi] = 0. Process B disappeared as [Pi] approached 0 mM in myofibrils, indicating the significance of the role of Pi rebinding to CBs in the production of oscillatory work (process B). Our results also suggest that Pi competitively inhibits ATP binding to CBs, with an inhibitory dissociation constant of ∼2.6 mM. Finally, we found that the sinusoidal waveform of tension is mostly distorted by second harmonics and that this distortion is closely correlated with production of oscillatory work, indicating that the mechanism of generating force is intrinsically nonlinear. A nonlinear force generation mechanism suggests that the length-dependent intrinsic rate constant is asymmetric upon stretch and release and that there may be a ratchet mechanism involved in the CB cycle.

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