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Abstract  

Controlled-rate thermodesorption (CRTD) spectra are obtained by adjusting the heating rate in such a way that the rate of desorption can be constant. A quantitative analysis of the obtained spectra is presented, based on application of the statistical rate theory of interfacial transport (SRTIT) to describe both adsorption and desorption kinetics. The SRTIT approach relates the rates of adsorption and desorption to the chemical potentials of the adsorbate in the gaseous and in the adsorbed phases. This quantitative analysis of the CRTD spectra yields the condensation approximation for the actual adsorption energy distribution. For the purpose of illustration, an analysis is made of water desorption from a synthetic apatite mineral under CRTD and classical TPD conditions. The influence of the adsorption and desorption rates is also discussed.

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Abstract  

SO4 2−/TiO2–MxOy (M = Zr, Ce, La) were prepared by the precipitation-impregnation method and characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), and temperature-programmed desorption (NH3-TPD). Catalytic activities were evaluated in the acetalization of 1,3-propanediol (1,3-PD) with acetaldehyde and hydrolysis of 2-methyl-1,3-dioxane (2MD). SO4 2−/TiO2–ZrO2 (STZ) exhibited the best catalytic activity both in the acetalization and hydrolysis. With the molar ratio of Zr4+/Ti4+ = 1:4, the highest yields were 96.45% in 3 h and 93.68% of 2MD hydrolyzed in 18 h, in contrast to the yields lower than 60% by using other superacids. These results are consistent with the strongest acidity of the superacid containing Zr4+ among prepared superacids containing other cations.

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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 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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Abstract  

Temperature-programmed desorption (TPD) of water was applied to characterize short-time dealuminated HZSM-5 zeolites. Using a regularization method, distribution functions of the effective desorption energy of water were calculated. The results clearly show that during dealumination a new adsorption site is formed which can be attributed to non-framework or transient aluminium species. The highest concentration of these sites was observed for a dealumination time of 25-30 min. NO adsorption studies support this result. Furthermore, it could be concluded that the heterogeneity and the average acid strength of the remaining Si-OH-Al groups of the dealuminated samples do not change compared to the Si-OH-Al groups of the parent HZSM-5 zeolite.

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The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO4·1/2H2O→(VO)2P2O7+2 H2O for VOHPO4·1/2H2O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different P∶V atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different P∶V ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.

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The thermal decomposition of sodium nitrite or nitrate pre-adsorbed upon TiO2 surfaces has been investigated by employing several techniques as infrared spectroscopy (IR) and temperature programmed desorption in conjunction with mass spectrometry analysis (TPD-MS) to study the features observed during these thermal decompositions. Differential thermal analysis (DTA) in combination with X-ray diffraction analysis (XRD) were used to investigate the possibility of a solid state chemical reaction between the solid products originated from the thermal decomposition of the pre-adsorbed species and the TiO2. On the basis of our results, various characteristic features of these thermal decomposition reactions will be discussed.

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Journal of Thermal Analysis and Calorimetry
Authors: S. Aukkaravittayapun, C. Thanachayanont, T. Theapsiri, W. Veerasai, Y. Sawada, T. Kondo, S. Tokiwa, and T. Nishide

Abstract  

Fluorine-doped tin dioxide (FTO) films were deposited on silicon wafers by inverted pyrosol technique using solutions with different doping concentration (F/Sn=0.00, 0.12, 0.75 and 2.50). The physical and electrical properties of the deposited films were analyzed by SEM, XRF, resistivity measurement by four-point-probe method and Hall coefficient measurement by van der Pauw method. The electrical properties showed that the FTO film deposited using the solution with F/Sn=0.75 gave a lowest resistivity of 3.210–4 ohm cm. The FTO films were analyzed by temperature programmed desorption (TPD). Evolved gases from the heated specimens were detected using a quadruple mass analyzer for mass fragments m/z, 1(H+), 2(H2 +), 12(C+), 14(N+), 15(CH3 +), 16(O+), 17(OH+ or NH3 +), 18(H2O+ or NH4 +), 19(F+), 20(HF+), 28(CO+ or N2 +), 32(O2 +), 37(NH4F+), 44(CO2 +), 120(Sn+), 136(SnO+) and 152(SnO2 +). The majority of evolved gases from all FTO films were water vapor, carbon monoxide and carbon dioxide. Fluorine (m/z 19) was detected only in doped films and its intensity was very strong for highly-doped films at temperature above 400C.

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Abstract  

Interaction between 1-methylnaphthalene and alkali-metal X and Y zeolites has been investigated using TPD. All spectra show only a single peak, the temperature of which changes with the nature and amount of the alkali-metal cation and the Si/Al ratio of the faujasite. A correlation between peak temperature and average charge of structural oxygen atoms of the zeolite is shown. On the basis of the atomic charge distribution in the 1-methylnaphthalene molecule, it is, suggested that adsorption is initiated by interaction between the alkali-metal cation and the carbon atom of the methyl group. Simultaneously, an interaction involving hydrogens atoms of the aromatic rings and structural oxygen atoms of the zeolite occurs, except for X samples containing high amounts of large alkali-metal cations.

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