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Reaction Kinetics, Mechanisms and Catalysis
Authors: Lixia Wang, Wanchun Zhu, Dafang Zheng, Xue Yu, Jing Cui, Mingjun Jia, Wenxiang Zhang, and Zhenlu Wang

Abstract  

The reaction of direct transformation of ethanol to ethyl acetate was investigated on reduced Cu/ZrO2 catalysts prepared by a co-precipitation procedure. The catalytic performances of these Cu–Zr mixed oxides were considerably influenced by changing the molar ratio of Cu to Zr. The highest selectivity to ethyl acetate was found over Cu/ZrO2(1) catalyst (molar ratio of Cu to Zr was 1). A variety of characterization techniques, such as N2 adsorption, XRD, XPS, TPR and NH3-TPD were carried out on the catalysts. The results revealed that the presence of a certain amount of Cu+ species may play very important role in improving the selectivity to ethyl acetate of the Cu/ZrO2 catalysts.

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Abstract  

The activity of solid niobic acid treated with sulfuric acid and with phosphoric acid was tested in the catalytic esterification of oleic acid and in transesterification of soybean oil with methanol. X-ray diffraction studies revealed niobic acid treated with sulfuric acid to be an amorphous solid, while niobic acid treated with phosphoric acid presented a crystalline phase, probably due to the formation of hydrogen niobium phosphate. Among the characterization methods employed here, XPS was particularly instrumental in showing that niobium dihydrogen phosphate and niobium hydrogen sulfate moieties are the acidic active sites responsible for the catalytic effect. The latter is more active according to ammonia TPD studies. Yields as high as 78% in the esterification of oleic acid with methanol and 40% in the transesterification of soybean oil catalyzed by NbSO4 were recorded.

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Abstract  

The reaction of urea with ZnO was investigated by FTIR and TPD. It was found that urea was thermally decomposed into isocyanic acid on ZnO, and the adsorbed isocyanic acid reacted with ZnO to form zinc isocyanate. Catalytic evaluation showed that ZnO had high activity towards urea methanolysis in a batch reactor, and zinc element and isocyanate were all detected in the product solution. Furthermore, the soluble zinc content was proportional to the DMC yield. Sample analyses suggested that the soluble zinc existed in the form of Zn(NCO)2(NH3)2, which originated from the reaction of ZnO with urea. It was the complex (not ZnO) that catalyzed the urea methanolysis. Based on these observations, a possible mechanism was suggested.

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Abstract  

A series of phosphorus modified Si-MCM-41 catalysts prepared via the impregnation method were used for the vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. The catalysts were characterized by XRD, N2 adsorption, FT-IR, and NH3-TPD. The results indicated that weak acid sites increased with P content, leading to enhanced catalytic activity. The catalyst with Si/P mol ratio of 25 showed best performance at 633 K. The conversion of cyclohexanone oxime and the selectivity for caprolactam were 92.7 and 64.2%, respectively. The P–OH groups are main active sites for the Beckmann rearrangement. Grafting acid hydroxyl groups to cover the Si–OH groups may be a good way to improve the selectivity for this reaction.

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-hydrotalcite oxides, usually assessed by temperature-programmed desorption (TPD) of carbon dioxide, is often invoked for explaining their catalytic activity in many reactions [ 6 – 8 ]. The drawback of such an approach is twofold: (i) it neglects any possible role of

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Journal of Thermal Analysis and Calorimetry
Authors: Luiz K. C. de Souza, Juliana J. R. Pardauil, José R. Zamian, Geraldo N. da Rocha Filho, and Carlos E. F. da Costa

mesoporous materials, using TPD-MS, GC–MS, and NMP to determine the effect of Al on the removal of surfactant molecules. They found that the trimethylamine formed at 150 °C in all the samples, agreeing with the results described above, and that at 300 °C, the

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.1016/0167-2738(93)90043-3 . 31. Jin , F , Li , Y . A FTIR and TPD examination of the distributive properties of acid sites on ZSM-5 zeolite with pyridine as a probe molecule . Cat Today . 2009 ; 145 : 101 – 107 . 10.1016/j.cattod.2008

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.01.045 . 22. Cicmanec , P , Bulánek , R , Frolich , K . 2011 . Thermodynamics of CO probe molecule adsorption on Cu–FER-zeolite comparison of TPD, FTIR, and microcalorimetry results . J Therm Anal Calorim . 105

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Journal of Thermal Analysis and Calorimetry
Authors: Kaia Tõnsuaadu, Kārlis Agris Gross, Liene Plūduma, and Mihkel Veiderma

. J Phys Chem C . 113 : 5478 – 5484 10.1021/jp900399c . 88. Yasukawa , A , Kandori , K , Ishikawa , T . 2003 . TPD-TG-MS study of carbonate calcium hydroxyapatite particles

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Abstract  

β-MCM41 composite molecular sieves were hydrothermally synthesized using NaOH treated β zeolite as precursors, and Pt/β-MCM41 bifunctional catalysts were prepared by impregnation. Hβ, desilicated Hβ by NaOH treatment (Dβ), and the physical mixture of Hβ and MCM41 (β+MCM41) were also used as control supports for bifunctional catalysts. All the catalysts were characterized by ICP, XRD, BET, nitrogen adsorption–desorption isotherm and NH3-TPD, and evaluated in the hydroisomerization of n-heptane using an atmospheric fixed bed flow reactor. Dβ, β+MCM41, or β-MCM41 supported Pt catalysts showed higher selectivity to isoheptanes than the counterpart Pt/Hβ did due to the presence of mesopores in addition to the zeolite micropores. Moreover, Pt/β-MCM41 was demonstrated to be a much more selective catalyst among them because the connection between mesopores and micropores accelerated the diffusion of larger molecules of isoheptanes. Under optimal conditions, Pt/β-MCM41 provided a very high selectivity to isomerization of 96.5%, coupled with a considerable high conversion of n-heptane of 56.0%.

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