PMoA/MCM-41 catalyzed aza-Michael reaction: special effects of mesoporous nanoreactor on chemical equilibrium and reaction rate through surface energy transformation

2015 ◽  
Vol 39 (8) ◽  
pp. 5916-5919 ◽  
Author(s):  
Kui Fan ◽  
Yonghai Hui ◽  
Xinmei Hu ◽  
Wei Shi ◽  
Haixia Pang ◽  
...  
Keyword(s):  
Surface Energy ◽  
Chemical Equilibrium ◽  
Reaction Rate ◽  
Michael Reaction ◽  
Energy Transformation ◽  
Special Effects ◽  
Mcm 41

Nanoreactors as catalysts can affect not only speed but also the chemical equilibrium of the reaction under investigation.

scholarly journals Aeration / Stripping of n-Butyl Mercaptan in aqueous environment

2013 ◽  
Vol 8 (2) ◽  
pp. 103-112
Keyword(s):  
Experimental Data ◽  
Water Quality ◽  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Chemical Equilibrium ◽  
Reaction Rate ◽  
Reaction Parameter ◽  
Ph Values ◽  
Neutral Compound

Μany applications in water quality management have a common key water quality parameter, dissolved oxygen, resulting to the critical role of aeration. On the other hand, in municipal and industrial wastewater, especially where aeration is applied, the presence of volatile organic compounds (VOCs) causes several concerns including a direct threat to humans, partly due to their emission from treatment tanks. pH, temperature and Henry’s Law govern VOCs’ speciation and consequently their emission characteristics. Limited data and simplifications of available mass-transfer models pose obstacles to a realistic approach, especially in the presence of a chemical equilibrium, for example in the case of mercaptans. In the present study the importance of oxygen transfer and stripping of a VOC (n-butyl mercaptan) on aeration’s overall effectiveness are examined separately. Clean water oxygenation and stripping of mercaptan to an inert gas (nitrogen) were studied aiming to consider mass transfer aspects and to investigate the influence of chemical equilibrium between ionic and neutral form of the target compound in neutral and alkaline solutions. Using appropriate mass transfer relationships (dynamic method), experimental data were analyzed for the determination of overall mass transfer coefficient ( kOL,O2α ) of oxygen. Correlating kOL,O2 α with the corresponding mass transfer coefficient of n-butyl mercaptan in neutral solutions (calculated according the model proposed by Matter-Muller et al. [1]), a value of ratio βy of 0.566 is found, close to the reported values of other VOCs with similar values of Henry’s constant. At alkaline pH however the conventional simplified model fails to predict realistic values of mass-transfer coefficients. A coupled differential algebraic equation system, based on mass balances, taking into account dissociation of the compound to be stripped and assuming chemical non-equilibrium conditions during stripping, was developed. Reaction parameter k2 was calculated with non-linear least-squares analysis. The model predicts satisfactorily the experimental data and it provides a useful tool for the semibatch stripper design in situations where a reversible reaction is involved. At pH values below 8.5 mercaptan concentration falls exponentially whereas above 10.5 it tends to linearity. The bubble equilibrates and mercaptan transferred depends upon solubility and not diffusivity. Especially after depletion of initial neutral compound, transport depends upon neutral/ionic form speciation. The effectiveness of stripping n-butyl mercaptan, at a given pH, is mainly determined by a proportionality constant considered as “fugacity capacity” (removal effect on the process) and by a reversible reaction rate constant k2 (kinetic effect on the process). The ‘’fugacity capacity” is determined by hydrophobicity (i.e. low solubility and high limiting activity coefficient) rather than pure-component volatility (i.e. vapor pressure or boiling point). High limiting activity coefficient promotes mercaptan emission due to established vapor-liquid equilibrium, while the low reaction parameter k2, controls neutral compound quantity. At high pH, where ionic form predominates, experimental data showed that stripping was almost independent of the gas flow rate applied. A strong sensitivity of the model to uncertainty of γ∞ was found: γ∞ controls emission rate and through this the dynamic variations of neutral/ionic concentration profiles whereas reaction rate law parameter k2 controls the neutral/ionic transformation and it is the crucial quantity which governs the process at high pH values.

Hydroxylation of Phenol over Ti-MCM-41 and TS-1

1995 ◽  
Vol 60 (3) ◽  
pp. 451-456 ◽  
Author(s):  
Kornelia Kulawik ◽  
Günter Schulz-Ekloff ◽  
Jiří Rathouský ◽  
Arnošt Zukal ◽  
Jiří Had
Keyword(s):  
Hydrogen Peroxide ◽  
Reaction Rate ◽  
Hydroxylation Of Phenol ◽  
Oxidation Of Phenol ◽  
Mcm 41

In the oxidation of phenol by hydrogen peroxide over titanium containing MCM-41 materials, practically only para isomers are formed. The exclusive para selectivity is proposed to be due to the different strength of adsorption for the para and ortho isomers influencing the overall reaction rate or the faster polymerization of the ortho product. The former mechanism is more probable.

scholarly journals Investigation of chemical equilibrium kinetics by the electromigration method

2003 ◽  
Vol 91 (5) ◽  
Author(s):  
G. A. Bozhikov ◽  
P. I. Ivanov ◽  
G. D. Bontchev ◽  
O. D. Maslov ◽  
M. V. Milanov ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Complex Formation ◽  
Stability Constant ◽  
Chemical Equilibrium ◽  
Reaction Rate ◽  
Reaction Rates ◽  
Reaction Rate Constant ◽  
Diethylenetriaminepentaacetic Acid ◽  
Zone Electrophoresis ◽  
Chemical Reaction Rates

SummaryThe measurement of the chemical reaction rates for complex formation as well as hydrolysis type reactions by the method of horizontal zone electrophoresis is outlined. The correlation between chemical equilibrium kinetics and electrodiffusion processes in a constant d.c. electric field is described. In model electromigration experiments the reaction rate constant of the formation a complex by Hf(IV) and diethylenetriaminepentaacetic acid (DTPA) is determined. The electrophoretic mobility, diffusion coefficient and stability constant of the [HfDTPA]

scholarly journals The nature of the interplay among components of pedagogical content knowledge in reaction rate and chemical equilibrium topics of novice and experienced chemistry teachers

2018 ◽  
Vol 19 (1) ◽  
pp. 80-105 ◽  
Author(s):  
Fatma Nur Akın ◽  
Esen Uzuntiryaki-Kondakci
Keyword(s):  
Pedagogical Content Knowledge ◽  
Content Knowledge ◽  
Chemical Equilibrium ◽  
Reaction Rate ◽  
Novice Teacher ◽  
Experienced Teachers ◽  
Instructional Materials ◽  
Chemistry Teachers ◽  
Pedagogical Content ◽  
Depth Analysis

We examined the interactions among pedagogical content knowledge (PCK) components of novice and experienced chemistry teachers in teaching reaction rate and chemical equilibrium topics in this qualitative multiple-case design study. For this aim, three chemistry teachers who had different levels of teaching experience in chemistry teaching were selected through a process of purposeful sampling. Multiple types of data were gathered through more than two months. In order to collect and triangulate data, a card-sorting activity, a Content Representation (CoRe) tool, semi-structured interviews, observation of instruction, and field notes were utilized. Data were analyzed through three approaches: in-depth analysis of explicit PCK, the enumerative approach, and constant comparative methods. The results revealed eight characteristics of the interactions of the PCK components: (a) the novice teacher's orientations towards science, in contrast to the experienced teachers’, were more broad and non-specific, which impeded the interactions among the components, (b) the interplay of the PCK components was idiosyncratic and topic specific, (c) the novice teacher's PCK maps were fragmented while the experienced teachers’ PCK maps were integrated, (d) the experienced teachers, in contrast to the novice teacher, interacted more than two PCK components in most of their teaching fragments, (e) knowledge of learner, knowledge of curriculum and knowledge of instructional strategies were central in the interplays of all teacher maps, (f) the experienced teachers were more successful than the novice teacher in translating their knowledge into practice in terms of the integration among PCK components, (g) teacher self-efficacy appeared to play a role in their use of PCK components and constructing interactions among them, and (h) all teachers taught the same topics with similar lesson plans and the same instructional materials; however, they differed in terms of how they connect the PCK components. Implications and suggestions for teacher education and science education research are presented.

scholarly journals EVALUATING OF PRE-SERVICE SCIENCE TEACHERS’ UNDERSTANDING OF GENERAL CHEMISTRY CONCEPTS BY USING TWO TIER DIAGNOSTIC TEST

2016 ◽  
Vol 15 (1) ◽  
pp. 79-96
Author(s):  
Ayfer Mutlu ◽  
Burçin Acar Şeşen
Keyword(s):  
Diagnostic Test ◽  
Science Teachers ◽  
Rate Constant ◽  
Chemical Equilibrium ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Service Science ◽  
Alternative Conceptions ◽  
Conservation Of Energy ◽  
Acids And Bases

This research aimed at evaluating pre-service science teachers’ understanding of the subject matters such as “thermochemistry, chemical kinetics, chemical equilibrium, acids and bases and electrochemistry”. For this purpose, a two-tier diagnostic test consisting of 44 items (α = 0.84) related to the aforementioned concepts was developed by the researchers. This test was applied on to the first, second, and third year pre-service science teachers in Hasan Ali Yucel Education Faculty, Istanbul University. The results showed that the pre-service science teachers had alternative conceptions about endothermic-exothermic reactions, conservation of energy, reaction enthalpy, calorimeters; rate of reaction, reaction rate constant, effects of some factors on reaction rate and reaction rate constant; effects of some factors on equilibrium, equilibrium dynamics, Le Chatelier Principle; equivalence point, end point, indicators, buffers, titrations, neutralization, strength and properties of acids and bases, pH; effects of concentrations on cell potential, metal electrodes, localization of anode and cathode, plating, galvanization. Key words: acids and bases, alternative conception, chemical equilibrium, chemical kinetic, electrochemistry, thermochemistry, two tier diagnostic test.

Immobilization of cationic zinc(II) complexes of phthalocyanine and unsymmetrical porphyrazine in mesoporous MCM-41 silica, and photo-catalytic activity of the composites

2006 ◽  
Vol 10 (10) ◽  
pp. 1212-1218 ◽  
Author(s):  
Kuninobu Kasuga ◽  
Makoto Imai ◽  
Hiroyuki Irie ◽  
Hidekazu Tanaka ◽  
Takashi Ikeue ◽  
...  
Keyword(s):  
Reaction Rate ◽  
Pore Diameter ◽  
Nitrogen Adsorption ◽  
Initial Reaction Rate ◽  
Initial Reaction ◽  
Photo Catalytic Activity ◽  
Surface Areas ◽  
Specific Surface Areas ◽  
Nitrogen Adsorption Isotherms ◽  
Mcm 41

Cationic 2,9,16,23-tetrakis(3- N , N , N -trimethylaminoethyloxy)phthalocyaninatozinc(II) and 20,21-bis(4- N , N , N -trimethylaminophenyl)-4,5,9,10,14,15-hexakis(4-t-butylphenyl)porphyrazinatozinc(II) were immobilized in MCM-41 silica by the use of an electrostatic interaction with the deprotonated silanol groups of MCM-41. From nitrogen adsorption isotherms, specific surface areas were estimated as 1031 and 702 m2.g−1 for MCM-41 and the composite of 2,9,16,23-tetrakis(3- N , N , N -trimethylaminoethyloxy)phthalocyaninatozinc(II), respectively. From pore-size distribution curves, the maximum pore diameter of MCM-41 and the composite were also estimated as 3.24 and 3.10 nm, respectively. These results revealed that 2,9,16,23-tetrakis(3- N , N , N -trimethylaminoethyloxy)phthalocyaninatozinc(II) was immobilized in the mesopores of MCM-41. While 2,9,16,23-tetrakis(3- N , N , N -trimethylaminoethyloxy)phthalocyaninatozinc(II) formed a dimer with increase in the amount of the complex in the composite, 20,21-bis(4- N , N , N -trimethylaminophenyl)-4,5,9,10,14,15-hexakis(4-t-butylphenyl)porphyrazinatozinc(II) only slightly formed a dimer in the composite, due to steric hindrance of its peripheral substituents. 1,3-diphenylisobenzofuran was photo-oxidized using the composites as the sensitizer in aerated acetonitrile. The reaction proceeded with singlet dioxygen generated by visible-light irradiation of the sensitizers. While the initial reaction rate with the composite of 20,21-bis(4- N , N , N -trimethylaminophenyl)-4,5,9,10,14,15-hexakis(4-t-butylphenyl)porphyrazinatozinc(II) increased in proportion to the increase in the amount of the complex, the initial reaction rate with the composite of 2,9,16,23-tetrakis(3- N , N , N -trimethylaminoethyloxy)phthalocyaninatozinc(II) at first increased, but subsequently decreased due to the formation of the photo-inactive dimer.

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