Search for: reaction-mechanism
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    On the energetics of NH3 adsorption and decomposition on Nb(100) surface: A UBI-QEP study

    , Article Reaction Kinetics and Catalysis Letters ; Volume 76, Issue 1 , 2002 , Pages 43-51 ; 01331736 (ISSN) Azizian, S ; Gobal, F ; Sharif University of Technology
    The energetics of the adsorption and decomposition of ammonia on Nb(100) surface was investigated by the method of unity bond index-quadratic exponential potential (UBI-QEP). The experimental as well as theoretically derived atomic heats of adsorption were used as the input data and the results were compared with the findings of local density functional theory (LDFT) and non-local density functional theory (NLDFT). The method was capable of correctly predicting the fragmentation of ammonia on 4-fold hollow sites on the surface of Nb(100) and magnitudes of the heats of adsorption and activation energies were more realistic  

    Clarification of penicillin G acylase reaction mechanism

    , Article Process Biochemistry ; Volume 36, Issue 11 , 2001 , Pages 1095-1101 ; 13595113 (ISSN) Kheirolomoom, A ; Ardjmand, M ; Fazelinia, H ; Zakeri, A ; Sharif University of Technology
    The kinetics of the enzymic reaction of penicillin G acylase from a mutant of Escherichia coli ATCC 11105 in forward and reverse directions were studied and the kinetic constants determined. Results show that the enzyme is inhibited by excess substrate, penicillin G (Pen G), and by both products. The non-competitive inhibition by 6-aminopenicillanic acid (6-APA) and competitive inhibition by phenylacetic acid were observed for the ordered uni bi deacylation reaction in the forward direction. The optimum pH value for the reverse acylation reaction was 5.7. The bi uni mechanism for the reverse reaction was investigated and the inhibitory effects of the substrates, 6-APA and phenyl acetic acid,... 

    Kinetic Modeling of Propane Dehydrogenation on Industrial Pt-Sn/γ-Al2O3 in Presence of Oxygenated Compounds

    , M.Sc. Thesis Sharif University of Technology Barghi, Bijan (Author) ; Khorasheh, Farhad (Supervisor)
    The study on the propane dehydrogenation process has been receiving significant attention due to the growing demand for propylene. The aim of this research is to develop an appropriate kinetic mechanism for dehydrogenation of propane over an industrial Pt–Sn/γ-Al2O3 catalyst in the presence of a very small amount of water. The reaction is carried out over the temperature range of 575 – 620 º C at atmospheric pressure. The results showed that a small amount of water and methanol can improve the performance of catalyst and also, increase the selectivity to COx. Addition the 0.5, 0.45, 0.3 water and 0.1, 0.05, 0.02 methanol are the optimum amount of these oxygenated compounds in order at... 

    Evaluation of Kinetics of Nickel Oxide Reduction by Carbon Dissolved in Molten Iron

    , M.Sc. Thesis Sharif University of Technology Naraghi, Mohammad (Author) ; Davami, Parviz (Supervisor) ; Halali, Mohammad (Supervisor)
    In this study, the recovery mechanism of nickel oxide by carbon dissolved in molten iron with the study of reaction kinetics were investigated. Nickel oxide pellets into molten iron containing graphite were added in the neutral atmosphere and the release of CO gas as a function of reaction time was measured until the end. The volume of gas produced at different times shows the number of moles of Ni metal was revived. Reaction by a) the following decomposition reaction under 1475 °C ; and b) carbon diffusion rate at temperatures over ° C1475 is controlled. The main reaction mechanism in order to a) decomposition of NiO; b) penetration of oxygen atoms in the melt, and c) reaction between... 

    Mechanism of nanostructured fluorapatite formation from CaO, CaF2 and P2O5 precursors by mechanochemical synthesis

    , Article Progress in Reaction Kinetics and Mechanism ; Volume 43, Issue 3-4 , 2018 , Pages 201-210 ; 14686783 (ISSN) Nikonam Mofrad,, R ; Sadrnezhaad, S. K ; Vahdati Khaki, J ; Sharif University of Technology
    Science Reviews 2000 Ltd  2018
    We determined the mechanism of mechanochemical synthesis of fluorapatite from CaO, CaF2 and P2O5 by characterisation of the intermediate compounds. We used atomic absorption spectroscopy, X-ray diffraction, field emission scanning electron microscopy, FTIR spectroscopy and transmission electron microscopy to find the transitional compounds. Investigation of the binary and ternary powder mixtures revealed the appearance of H3PO4, Ca(OH)2, Ca2P2O7 and CaCO3 as the intermediate compounds. At early stages of the milling, conversions of P2O5 to H3PO4 and CaO to Ca(OH)2 occurred in the wet atmosphere. Later, a combination of Ca(OH)2 and H3PO4 formed Ca2P2O7 while the unreacted CaO was converted to... 

    Theoretical Determination of the Impedance Response of Some General Multi Step Electrode Processes

    , M.Sc. Thesis Sharif University of Technology Rash Seyedabadi, Hazhar (Author) ; Gobal, Fereydoon (Supervisor)
    Impedance measurement is one of the most efficient electrochemical methods to investigate the mechanism and kinetics of electrode reactions. This method can detect the steps of successive or parallel electron and mass transfer chemical reactions based on measuring the response time constant. The method of showing results, commonly known as Nyquist diagram,which is based on drawing real and imaginary components of the impedance, with respect to each other in different measurement frequencies, is very useful for determining the mechanism of electrode reactions and the kinetic measurements. The main objective of this thesis is totheoretically determine the impedance response of six... 

    Kinetic of Zinc Sulfide Roasting of

    , M.Sc. Thesis Sharif University of Technology Marzoughi, Omid (Author) ; Halali, Mohammad (Supervisor)
    In this study, the effect of two main parameters, time and temperature, were investigated in the roasting process of zinc sulfide of Bafgh’s mine, and kinetics and the mechanism of the roasting reaction were examined, too. The oxidation process was performed in a muffle furnace in the presence of the oxygen of air atmosphere. The raw powder material (with the particle size of 74-250 micron) was poured in Alumina crucibles. The roasting process was run in eight temperatures of 650, 700, 750, 800, 850, 900, 950 and 1000 ◦C. Oxidation percent was calculated in six times of 5, 10, 15, 30, 45 and 60 minutes. The experiments were designed in a way that the effect of each parameter could be... 

    Catalytic effect of copper oxide on H2S sensing properties of nanostructured WO3

    , Article Sensor Letters ; Volume 11, Issue 11 , 2013 , Pages 2015-2020 ; 1546198X (ISSN) Nowrouzi, R ; Razi, F ; Rahimi, F ; Zad, A. I ; Sharif University of Technology
    American Scientific Publishers  2013
    Cuprous oxide powder was added to WO3 sol as a catalyst and the composite sol was deposited on alumina substrates by spin coating process and annealing at 500 °C for 1 hour. Sensing properties of the pure and doped tungsten oxide samples to H2S gas were analyzed. WO 3-Cu2O (1%) samples showed good sensitivity towards 250 ppb of the gas at 100 °C and 1 ppm at room temperature (25 °C). Crystal structure, morphology and chemical composition of the sample were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX) analyses and X-ray photoelectron spectroscopy (XPS). Based on these data, possible reaction mechanisms of hydrogen sulfide over WO... 

    Effect of CO2 partial pressure on the thermal decomposition kinetics of zinc carbonate hydroxide

    , Article International Journal of Engineering, Transactions B: Applications ; Volume 24, Issue 3 , 2011 , Pages 263-268 ; 1728-144X (ISSN) Pishahang, M ; Halali, M ; Nobari, A. H ; Sharif University of Technology
    In this work, the effect of carbon dioxide partial pressure on the calcination kinetics of high purity zinc carbonate hydroxide has been studied. Non-isothermal analysis has been performed on samples at different CO 2 partial pressures by TGA and DTA. It has been found that the calcination behaviour of this material corresponds to the shrinking core model and the reaction mechanism is phase boundary controlled. The calcination reaction of zinc carbonate hydroxide starts at 240 °C. Increasing the carbon dioxide partial pressure can result in an increase in the reaction start temperature of up to 30°C. The activation energy for the reaction is calculated as 180 ± 5 kJ/mol at... 

    Synthesis of “L-cysteine–graphene oxide” hybrid by new methods and elucidation of its uptake properties for Hg(II) ion

    , Article Separation Science and Technology (Philadelphia) ; Volume 53, Issue 6 , 2018 , Pages 843-855 ; 01496395 (ISSN) Daneshmand, M ; Outokesh, M ; Akbari, A ; Kosari, M ; Tayyebi, A ; Sharif University of Technology
    Taylor and Francis Inc  2018
    This study introduces two new, simple, and scalable methods for synthesis of “cysteine–graphene oxide” hybrid, namely nucleophilic and covalent methods. Produced adsorbents could uptake 500 and 600 mg Hg2+/g, respectively, which are larger than capacities of most of the commercial adsorbents. By means of different instrumental techniques, chemical structures of the obtained graphene products were disclosed, and two pertinent mechanisms for their formations were suggested. Time for attaining uptake equilibrium for nucleophilic/covalent samples was 30 min/150 min, and kinetics was controlled by liquid film resistance/chemical reaction mechanisms, respectively. High selectivity and good... 

    Mechanical characteristics of cement paste in the presence of carbon nanotubes and silica oxide nanoparticles: An experimental study

    , Article Materials ; Volume 14, Issue 6 , 2021 ; 19961944 (ISSN) Karakouzian, M ; Farhangi, V ; Farani, M. R ; Joshaghani, A ; Zadehmohamad, M ; Ahmadzadeh, M ; Sharif University of Technology
    MDPI AG  2021
    Considering the remarkable characteristics of nanomaterials, previous research studies investigated the effects of incorporating different types of these materials on improving the concrete properties. However, further studies are required to evaluate the complementary hybridization and synergistic influence of nanomaterials. In this research, the combined effect of adding nano silica particles (NS) and multi-walled carbon nanotubes (MWCNT) on enhancing both the compressive and flexural strengths of the cement paste was investigated. Moreover, the morphology of the interface between cement paste and aggregates was studied by scanning electron microscopy (SEM). The mixtures were prepared... 

    Experimental Study of Formaldehyde Decomposition Using a Plasma - Catalyst Hybrid Reactor as a Potential Voc Removal Technique

    , M.Sc. Thesis Sharif University of Technology Nemati Tamar, Amin (Author) ; Hamzeh Louyan, Tayyebeh (Supervisor) ; Khani, Mohammad Reza (Supervisor)
    Volatile organic compounds (VOCs) has harmful environmental and health effects and appropriate processes are needed to remove them from industrial and indoor environments. In this study, formaldehyde as one of the most toxic VOCs was investigated. Various methods have been developed to remove formaldehyde, however due to the to their low removal efficiencies, secondary pollution, and low energy efficiency, development of alternative methods will be beneficial. In recent years, the use of a combination of non-thermal plasma and catalyst technologies, called plasma-catalytic hybrid reactors, has provided significant results in the fields of chemical synthesis and removal of pollutants. In the... 

    Kinetics and reaction mechanism of isothermal oxidation of Iranian ilmenite concentrate powder

    , Article Journal of Thermal Analysis and Calorimetry ; Volume 112, Issue 2 , 2013 , Pages 781-789 ; 13886150 (ISSN) Mozammel, M ; Sadrnezhaad, S. K ; Khoshnevisan, A ; Youzbashizadeh, H ; Sharif University of Technology
    Thermal oxidation of commercial ilmenite concentrate from Kahnouj titanium mines, Iran, at 500-950 C was investigated for the first time. Fractional conversion was calculated from mass change of the samples during oxidation. Maximum FeO to Fe2O3 conversion of 98.63 % occurred at 900 C after 120 min. Curve fit trials together with SEM line scan results indicated constant-size shrinking core model as the closest kinetic mechanism of the oxidation process. Below 750 C, chemical reaction with activation energy of 80.65 kJ mol-1 and between 775 and 950 C, ash diffusion with activation energy of 53.50 kJ mol-1 were the prevailing mechanisms. X-ray diffraction patterns approved presence of... 

    A study on the kinetics of gold nanowire electrodeposition in polycarbonate templates

    , Article Journal of Electroanalytical Chemistry ; Volume 645, Issue 1 , June , 2010 , Pages 28-34 ; 15726657 (ISSN) Soleimany, L ; Dolati, A ; Ghorbani, M ; Sharif University of Technology
    Electrodeposition of gold nanowires is carried out in cyanide solution in polycarbonate templates with pore diameter of 80 nm. Electrochemical methods are utilized to characterize the gold electrodeposition and to obtain the nucleation and growth mechanism. The analysis of cyclic voltammograms shows that the electrodeposition of gold nanowires takes place under diffusion control. Current transients reveal that nucleation mechanism is instantaneous with a three-dimensional growth process. The transition-time measurements show that the gold elecrodeposition occurs as one-electron valence involved in the reaction mechanism. Charge transfer coefficient is also found to be 0.67 ± 0.01. The value... 

    The free radical scavenging activity of lespedezacoumestan toward ˙OH radical: a quantum chemical and computational kinetics study

    , Article Journal of Physical Organic Chemistry ; Volume 31, Issue 2 , February , 2018 ; 08943230 (ISSN) Bayat, A ; Fattahi, A ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    The free radical activity of lespedezacoumestan was investigated toward hydroxyl (˙OH) radical in polar and nonpolar media using density functional theory. Four reaction mechanisms including radical adduct formation, hydrogen atom transfer, sequential single electron-proton transfer (SET-PT), and sequential proton loss electron transfer were considered. The rate constants and branching ratio for all possible sites of reaction were calculated and reported for the first time. According to the obtained results, lespedezacoumestan reacts faster with ˙OH radical in aqueous solution than in nonpolar media. Also, lespedezacoumestan is an excellent ˙OH radical scavenger regardless of the environment... 

    Mechanism of photocatalytic reduction of CO2 by Ag3PO4(111)/g-C3N4 nanocomposite: a first-principles study

    , Article Journal of Physical Chemistry C ; Volume 123, Issue 36 , 2019 , Pages 22191-22201 ; 19327447 (ISSN) Tafreshi, S. S ; Moshfegh, A. Z ; De Leeuw, N. H ; Sharif University of Technology
    American Chemical Society  2019
    Density functional theory (DFT) calculations have been performed to investigate the electronic structure and photocatalytic activity of a hybrid Ag3PO4(111)/g-C3N4 structure. Due to Ag(d) and O(p) states forming the upper part of the valence band and C(p), N(p), and Ag(s) the lower part of the conduction band, the band gap of the hybrid material is reduced from 2.75 eV for Ag3PO4(111) and 3.13 eV for monolayer of g-C3N4 to about 2.52 eV, enhancing the photocatalytic activity of the Ag3PO4(111) surface and g-C3N4 sheet in the visible region. We have also investigated possible reaction pathways for photocatalytic CO2 reduction on the Ag3PO4(111)/g-C3N4 nanocomposite to determine the most... 

    New insight into reaction mechanisms of TiCl4 for the synthesis of TiO2 nanoparticles in H2O-assisted atmospheric-pressure CVS process

    , Article Materials Science and Engineering B: Solid-State Materials for Advanced Technology ; Volume 264 , 2021 ; 09215107 (ISSN) Rahiminezhad Soltani, M ; Saberyan, K ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2021
    Crystalline anatase TiO2 nanoparticles were synthesized in the gas phase using an H2O-assisted atmospheric-pressure CVS process. Simultaneous oxidation/hydrolysis of TiCl4 in the H2O-assisted APCVS process demonstrates the feasibility of facile fabrication and the designed synthesis of TiO2 nanoparticles in atmospheric pressure. Kinetics and thermodynamics studies of TiCl4 reactions in the gas phase illustrated oxidation or hydrolysis domination theoretically and were confirmed by experimental runs. Effects of H2O/O2 ratio on the reactions mechanisms, phase formation, size characteristics, morphology, and purity of TiO2 nanoparticles were experimentally studied using various analytical... 

    Analysis and characterization of phase evolution of nanosized BaTiO 3 powder synthesized through a chemically modified sol-gel process

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 43, Issue 11 , November , 2012 , Pages 4414-4426 ; 10735623 (ISSN) Ashiri, R ; Sharif University of Technology
    In the current research, a cost-effective and modified method with a high degree of reproducibility was proposed for the preparation of fine nanoscale and high-purity BaTiO3. In contrast to the other established methods, in this research, carbonate-free BaTiO3 nanopowders were prepared at a lower temperature and in a shorter time span. To reach an in-depth understanding of the scientific basis of the proposed process, an in-detail analysis was carried out for characterization of nanoscale BaTiO3 particles via differential thermal analysis (DTA)/thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and... 

    An innovative, highly stable Ag/ZIF-67@GO nanocomposite with exceptional peroxymonosulfate (PMS) activation efficacy, for the destruction of chemical and microbiological contaminants under visible light

    , Article Journal of Hazardous Materials ; Volume 413 , 2021 ; 03043894 (ISSN) Kohantorabi, M ; Giannakis, S ; Moussavi, G ; Bensimon, M ; Gholami, M. R ; Pulgarin, C ; Sharif University of Technology
    Elsevier B.V  2021
    In this work, Ag nanoparticles were loaded on ZIF-67 covered by graphene oxide (Ag/ZIF-67@GO), and its catalytic performance was studied for the heterogeneous activation of peroxymonosulfate (PMS) under visible-light. The catalyst surface morphology and structure were analyzed by FT-IR, XRD, XPS, DRS, FE-SEM, EDX, TEM, BET, ICP-AES and TGA analysis. The efficacy of PMS activation by the Ag/ZIF-67@GO under visible light was assessed by phenol degradation and E. coli inactivation. Phenol was completely degraded within 30 min by HO•, SO4•− and O2•− generated through the photocatalytic PMS activation. In addition, total E. coli inactivation was attained in 15 min that confirmed the highly...