The reaction rate and thermodynamic parameters in the reaction of phenylmagnesium bromide with phenyl tosylate in THF:toluene binary solvents and also in toluene were analyzed. The relative changes in the rate constants are strictly bound to changes in the equilibrium constant of complex formation between the sulfonate and the Grignard reagent by replacement of a donor THF molecule as well as the transfer rate of the carbanion to the sulfonate in the complex. These results provide another support for asynchronous SNa mechanism comprising a four-center transition state mechanism.
Theoretical analysis for the kinetics of heterogeneous enantioselective hydrogenation in the presence of binary modifier mixtures revealed conditions when not only nonlinear dependence of the enantiomeric excess on the composition of the modifier mixtures is observed, but maxima in ee are possible for mixtures compared with single modifiers. Experimental data on (E)-2,3-diphenylpropenoic acid hydrogenation over Pd were used to illustrate the applicability of the advanced model. The key features for a system to display such unusual behavior are associated with rate constants for steps involving one modifier being dependant on the concentration of the other one.
Authors:Dimitrinka Nikolova, Rumeana Edreva-Kardjieva, and Tatyana Grozeva
The effect of potassium additive on the catalytic activity of nickel–molybdenum alumina-supported systems has been studied by varying the molybdenum content within 5–18 mass% MoO3, reaction temperature from 180 to 400 (500)°C, and steam to gas ratio of 0.3, 0.7, and 1. It has been established that potassium reduces the activity of one-component Mo-containing samples, while, independent of molybdenum loading, nickel promotes activity within the whole temperature range studied and extends the temperature range of catalytic activity by about 70°C to lower reaction temperatures. A symbatic or additive, or antibatic catalytic behavior was observed with NiMo-containing samples depending on the atomic Ni/Mo ratio and temperature range. Potassium, being a third component in tri-component KNiMo-containing samples, enhances the water–gas shift (WGS) activity depending on the atomic K/(Ni + Mo) ratio. The activity approaches the equilibrium conversion degree in the interval of 320–500 °C. A decrease in the specific surface area of calcined and tested samples relative to the bare support shows close values indicating that the overall dispersion of the species is not changed during the catalytic test. Close examination indicated that the sample containing K2O, NiO, and MoO3 of 4.9, 2.5, and 12.7 mass%, respectively, was found to be the most suitable catalyst for water–gas shift reaction with sulfur containing feed since it attains equilibrium conversion even at 300 °C, and at a low steam to gas ratio of 0.3 atm. This catalyst demonstrates a stable and reproducible catalytic activity as inlet gas loading is increased.
Authors:Bao Agula, Qing-Fang Deng, Mei-Lin Jia, Yuping Liu, Bao Zhaorigetu, and Zhong-Yong Yuan
Mesoporous Ce0.8Zr0.2O2 oxides were prepared by a surfactant-assisted method of nanocrystalline particle assembly, and used as a support of nickel oxide nanocatalysts. The obtained mesoporous NiO/Ce0.8Zr0.2O2 nanocatalysts were characterized by XRD, N2 adsorption, TEM, H2-TPR and X-ray photoelectron spectroscopy techniques. The catalytic properties of the NiO/Ce0.8Zr0.2O2 nanocatalysts were evaluated by CO oxidation and toluene combustion. The results showed that the catalyst with 10 wt% NiO loading exhibited the highest catalytic activity for CO oxidation and toluene combustion.
Zirconia supported dodecaphosphotungstate and undecaphosphotungstate were successfully used as heterogeneous catalysts for the liquid-phase solvent-free oxidation of styrene. A detailed kinetic study was carried out in order to study the effect of removal of one addenda atom from the parent Keggin unit. The supported catalysts were also systematically characterized by various physicochemical techniques to show that the Keggin unit remains intact even after supporting on the support. Thermal studies also indicate that the supported catalysts are stable up to 450 °C. Maximum conversion with a single selective product was obtained after 30 h for the undecaphosphotungstate and after 20 h for dodecaphosphotungstate. The rate constants as well as the activation energy for the reaction were determined. From the values of activation energy derived from the Arrhenius plot, different thermodynamic parameters such as enthalpy and Gibbs free energy were also calculated. From the above studies, supported dodecaphosphotungstate was found to be more active as compared to undecaphosphotungstate.
Authors:M. Marečić, F. Jović, V. Kosar, and V. Tomašić
This work deals with the photocatalytic oxidation of toluene at room temperature and atmospheric pressure in the gas phase. The differential equations of the reactor model are solved numerically with simultaneous estimation of the model parameters. Estimation of the kinetic data is performed using a modified differential method of data analysis and a Nelder–Mead method of nonlinear optimization for parameter estimation. The reaction is performed in an annular photoreactor using UVA black light blue fluorescent lamp. The experiments are carried out at different total flow rates of the reaction feed (20–160 cm3 min−1), two different inlet concentrations of toluene (2.67 and 5.24 g m−3) and at constant relative humidity (25%). A good agreement between the experimental data and theoretical predictions is obtained, supporting the applicability of the proposed models to describe the investigated process performed in laboratory annular photoreactor.
Authors:Kun Hong Hu, Yong Kui Cai, Guo Quan Shao, and Xian Lu Cui
A MoS2/AlOOH composite was synthesized by calcining the reaction product of Na2MoO4, Na2S, HCl and basic Al2O3. The obtained composite was characterized using thermal analysis, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, high-resolution transmission electron microscopy, ultraviolet–visible spectroscopy and infrared spectroscopy. The degradation reaction of methyl orange was used to evaluate the photocatalytic properties of the composite. The results showed that alumina existed in the form of AlOOH with the deposited nano-MoS2 on the surface. The composite contained an intensive absorption between 380 and 450 nm and presented excellent photocatalytic properties. In addition, the composite still retained a high catalytic activity after repeatedly used for three times. The catalytic activity of the composite was influenced by the initial concentration of methyl orange, the amount of the catalyst, the pH value, and the temperature. The composite was a promising photocatalyst for the removal of organic chemicals from wastewater.
Authors:Fanpeng Shang, Shujie Wu, Jingqi Guan, Jianrui Sun, Heng Liu, Chunhua Wang, and Qiubin Kan
Two samples of aminopropyl-functionalized silica (APS) have been prepared by grafting an organosilane precursor 3-aminopropyl-triethoxysilane onto the SBA-15 in ethanol or toluene. Aminopropyl-functionalized silica-E (sample grafted in ethanol) and APS-T (sample grafted in toluene) were evaluated in carbon–carbon bond forming reactions such as the Knoevenagel condensation and the Claisen–Schmidt condensation. It has been found that the sample grafted in ethanol displayed better catalytic properties than the sample grafted in toluene. The surface silanol groups, which were proven to be more numerous in samples grafted in ethanol compared to those grafted in toluene, were found to be responsible for the enhanced catalytic activity in carbon–carbon bond forming reactions.
Authors:Ling Tao, Gui-Sheng Li, Shuang-Feng Yin, Qiang Ou-Yang, Sheng-Lian Luo, Xiao-Ping Zhou, and Chak-Tong Au
Described in this paper are the synthesis, characterization and catalytic application of H-ZSM-5 zeolites for the conversion of CH3Br into aromatics. The H-ZSM-5 zeolites were fabricated by hydrothermal crystallization using n-butylamine (BTA) as a template and characterized by XRD, SEM and NH3-TPD techniques. The effects of batch SiO2/Al2O3 ratio, alkalinity, NaCl/Al2O3 ratio, seed crystals, and crystallization time on the yield, structure/texture and catalytic performance were systematically studied. Adopting the optimum sol (SiO2/Al2O3 = 70, BTA/SiO2 = 0.2847, Na2O/SiO2 = 0.1237, H2O/SiO2 = 37.4, NaCl/Al2O3 = 60, and seed/SiO2 = 5 wt%) and under the most preferable crystallization conditions of 100 °C/24 h–170 °C/24 h, H-ZSM-5 zeolites of high crystallinity and small size (300–700 nm) were obtained. Good catalytic performance was observed over the H-ZSM-5 zeolites (aromatic yield up to 44.2%). However, unlike the modification of large commercial HZSM-5, the use of MoO3 or PbO as modifying agents for the small-size H-ZSM-5 zeolites results in a decline of catalytic performance. The relationship between the structure and the catalytic efficiency of as-synthesized H-ZSM-5 samples were investigated. It was found that with crystallinity enhancement and/or decline in crystal size, there is improvement of catalytic performance.
Authors:Changlin Yu, Caifeng Fan, Xiangjie Meng, Kai Yang, Fangfang Cao, and Xin Li
A novel Ag/BiOBr composite catalyst has been synthesized by a solution combination with photodeposited method. The as-synthesized catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–Vis diffuse reflectance spectra. The photocatalytic reaction tests in the degradation of the dyes of acid orange II, rhodamine B and methyl orange showed that the deposition of optimal amount of 1–2 wt% Ag could bring about a big increase in the activity under visible light irradiation. The high photocatalytic performance could be attributed to the strong visible light absorption and low recombination rate of the e−/h+ pairs resulted in by the presence of metal silver nanoparticles.