Authors:P. V. Surse, S. Wagholikar, S. Mayadevi, and S. Sivasanker
An examination of the kinetics of the alkylation of anisole with 1-hexene and 1-hexanol to produce alkylates over zeolite H-beta is presented. Anisole alkylation is found to occur by a set of parallel reactions when hexene is used as the alkylating agent. When hexyl alcohol is the alkylating agent, the reaction follows a multi-step parallel-series mechanism to form monoalkylates and dihexylether. With 1-hexene, a group of isomeric alkylates, viz., ortho-2-hexyl anisole (2-OHA), ortho-3-hexyl anisole (3-OHA), para-2-hexyl anisole (2-PHA), and para-3-hexyl anisole (3-PHA) was obtained. With hexanol, the olefin (hexene) and dihexyl ether were obtained additionally. The influence of process parameters like temperature, catalyst quantity, and alkylating agent on reaction behavior is reported.
La-modified ZrO2 with 10 mol% La was prepared by three different methods, namely co-precipitation, impregnation, and mechanical mixing and employed as cobalt catalyst supports. The use of La-modified ZrO2 prepared by mechanical mixing resulted in higher cobalt dispersion and higher CO hydrogenation activity than those supported on pure oxide (La2O3 and ZrO2) and La-modified ZrO2 obtained by the other methods. As revealed by XRD and TEM, an intimate contact and/or incorporation of La atoms in ZrO2 may occur on the La-modified ZrO2 prepared by co-precipitation and impregnation, which induced a stronger interaction between cobalt and the support. On the other hand, the presence of amorphous La2O3 in ZrO2 by mechanical mixing facilitated cobalt reducibility as shown by lower reduction temperature in the TPR profile.
Authors:Wang Zaihua, Li Xinjun, Song Wenji, Chen Jinfa, Li Tao, and Feng Ziping
A series of Ag-doped Ag–V/TiO2 catalysts with low vanadium loadings were prepared by one-step sol–gel methods and the effects of the Ag doping on the selective catalytic reduction (SCR) of NOx with NH3 were investigated. The catalytic activity of the catalysts increased about 20% by the addition of 1–3 wt% of Ag. The catalysts were characterized by XRD and H2-TPR. The results indicated that the V and Ag were well dispersed on the TiO2 support and the Ag doping inhibited the growth of TiO2 anatase crystallite and improved the oxidation ability of adsorption sites. The reduction temperature of vanadium oxide decreased and the activity for NH3-SCR enhanced. The doped Ag also had NH3-SCR activity, but it was very low. The durability of the catalysts was acceptable and the resistance to H2O was not very good. The effects of the calcination temperature and GHSV were also investigated; it was found that the optimal calcination temperature was 450 °C and the GHSV should not be higher than 48,000 h−1.
Nanocomposite thin films of TiO2/WO3 are prepared by the sol–gel method on glass substrates using a dip-coating technique. The initial precursors of composite sols are chloride salts of the respective metals dissolved in ethanol with the addition of hydrogen peroxide as a catalyst of the hydrolysis and sol stabilization. The WO3 content in the films is selected to be 5 or 10%. The film thickness is controlled by the number of coating cycles. The films are dried between the successive coatings and finally annealed at 520 °C in air for 2 h. The morphology and phase composition of the composite films is characterized by SEM/EDX and X-ray analysis. The photocatalytic action of the films is tested with respect to the degradation of malachite green in water solutions under UV and visible light irradiation. The composite films TiO2/WO3 with 10% of WO3 always exhibit a better photocatalytic activity than the pure TiO2 films even under strong visible light.
Authors:V. Udayakumar, S. Alexander, V. Gayathri, Shivakumaraiah, and B. Viswanathan
Hydrogenation of various nitroarenes by a polymer-supported palladium-imidazole complex at ambient conditions was investigated. The effect of various substituents upon the rate of hydrogenation of nitrobenzene was studied. The rate of para-substituted nitrobenzene hydrogenation was related to the corresponding Hammett substituent constant. The kinetics of hydrogenation and the reusability of the catalyst were also studied.
Tungsten promoted pure and sulfated ceria systems are employed as solid acid catalysts for the vapor phase cumene cracking reaction. The catalytic systems are prepared by the pseudo-template method. The results show the presence of both Lewis and Brønsted acid sites on the catalyst. Upon modification with tungsten oxide, an enhancement in the number of Lewis acid sites is observed. α-methyl styrene is the major product along with some dealkylated products. The influence of reaction conditions such as temperature, flow rate and time on stream on the conversion and selectivity is also investigated. Time on stream studies suggest deactivation of the catalysts presumably because of the coke formation on the acid sites.
Pd/FeAlPO-5 zeolites with different Pd loading were prepared and characterized by N2 physisorption, XRD and H2-TPR. The results indicate that Pd addition has little influence on the textural structure of FeAlPO-5 zeolites. The TPR profiles of zeolites show the peak temperatures related with the reduction of Fe(III) and subsurface Pd species decrease with the increase of Pd content, suggesting the existence of interactions between Fe and Pd. The Pd/FeAlPO-5 catalysts were tested in the catalytic reduction of N2O with methane and show a better low-temperature activity in comparison with FeAlPO-5. The improved activity of Pd/FeAlPO-5 can be ascribed to the synergic effect between noble metal and iron species.
Authors:Zhiqiang Wang, Zhanwei Bu, Tiegang Ren, Tingting Cao, and Lirong Yang
The mechanism of the cycloaddition of CO2 with propylene oxide to afford propylene carbonate catalyzed by a highly active trans-dichlorotetrapyridineruthenium [trans-Ru(py)4Cl2] complex and tetrabutylammonium chloride (TBAC) has been studied by means of electrospray ionization mass spectrometry (ESI–MS), structural characterization of trans-Ru(py)4Cl2, catalyst activity tests and so on. Further experiments demonstrated that the tributylamine formed in situ was involved in the catalysis and that addition of butyl chloride to re-convert the tributylamine into TBAC resulted in the inhibition of the reaction. The mechanistic study explains the reported early experimental observations well and provides a clear profile for the cycloaddition of carbon dioxide with propylene oxide using trans-Ru(py)4Cl2 as catalyst. The mechanism also fully explains the role of the TBAC by providing a role for the in situ generated tributylamine in activating the carbon dioxide.
Authors:Ekkachai Kanchanatip, Nurak Grisdanurak, Raumporn Thongruang, and Arthit Neramittagapong
V-TiO2 and C60/V-TiO2 photocatalysts were synthesized by titanium(IV) isopropoxide using a chelation sol–gel and impregnation method. All catalysts were calcined at 450 °C for 5 h, which resulted in them being in the anatase phase. The catalysts were characterized by thermogravimetric analysis and differential thermal analysis (TGA–DTA), X-ray diffractometry (XRD), UV–vis diffuse reflectance (UV–DR) spectra, Brunauer–Emmett–Teller (BET) surface area analyses, photoluminescence (PL) spectra, and zeta potential, and tested for their paraquat photodegradation ability under visible light. An insignificant decrease in surface area was observed in the modified catalysts. The modified photocatalysts exhibited higher visible light responses, ranking them as follows: 1C60/1 V-TiO2 > 1 V-TiO2 > TiO2 (composition in wt%). 1wt% C60/1wt% V-TiO2 performed higher activity than 1wt% V-TiO2. The kinetics of paraquat photocatalytic degradation was expressed by the Langmuir–Hinshelwood (LH) model with a rate constant of 0.171 mg/L min−1.
Authors:Pingbo Zhang, Lianxiang Kang, Caiyun Shu, and Mingming Fan
The catalytic performance of the microporous Hβ sieve supported K2CO3 catalyst for the synthesis of dipropyl carbonates (DPC) by transesterification of dimethyl carbonate (DMC) with propyl alcohol was investigated at atmospheric pressure, and the optimized reaction conditions were acquired. The catalyst of Hβ with 28% K2CO3-loading performed best, giving 94.4% conversion of DMC and 58.7% selectivity to DPC. An optimum reactant molar ratio n(propyl alcohol)/n(DMC) existed for catalytic activity, which was about 3/1. The optimum reaction time was 10 h and the suitable reaction temperature was about 363 K considering various factors. The XRD results indicated that the structure of Hβ was gradually deformed with the increase in the K2CO3 loading. From nitrogen physisorption, it could be concluded that the improvement of the catalytic activities with the optimized K2CO3-loading about 28% can be ascribed to both enough active sites and preferable surface area and bigger pore diameter. There was no significant difference between the IR spectrums of K2CO3/Hβ catalyst before and after a 10 h reaction, which was consistent with that K2CO3/Hβ catalyst had excellent utility for repeated use. The possible mechanism of the transesterification reaction was also discussed.