Authors:V. Rac, Vesna Rakić, S Gajinov, Vera Dondur, and Aline Auroux
In this work, room temperature interaction of n-hexane with HZSM-5 (Si/Al=20) and ion-exchanged
samples containing one (CuZSM-5, FeZSM-5 and MnZSM-5) or two transition-metal
cations (Fe,CuZSM-5; Cu,MnZSM-5 and Fe,MnZSM-5) was studied by microcalorimetry
and TPD methods. Both differential heats and the amounts of n-hexane
adsorbed per one unit cell were quantitatively determined. Higher heats of
adsorption and higher amounts of adsorbed gas were found for ion-exchanged
samples than for HZSM-5. The experiments of n-hexane
adsorption on hydrated samples were also performed. The amounts of n-hexane
adsorbed on hydrated ZSM-5 were lower in comparison with dehydrated samples,
while the energies of interaction were similar.
Authors:F. Villiéras, L. Michot, G. Gérard, J. Cases, and W. Rudzinski
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.
Authors:Lixia Wang, Wanchun Zhu, Dafang Zheng, Xue Yu, Jing Cui, Mingjun Jia, Wenxiang Zhang, and Zhenlu Wang
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.
Authors:Mendelssolm de Pietre, Luiz Almeida, Richard Landers, Rita Vinhas, and Fernando Luna
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.
Authors:Hui Wang, Mouhua Wang, Wenbo Zhao, Wei Wei, and Yuhan Sun
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.
Authors:Jinbo Ni, Min Wu, Zhaohui Yang, Changfei Bu, and Qin He
SO42−/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). SO42−/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.
Authors:F. Cavani, G. Centi, F. Trifirò, and G. Poli
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.
Authors:S. Aukkaravittayapun, C. Thanachayanont, T. Theapsiri, W. Veerasai, Y. Sawada, T. Kondo, S. Tokiwa, and T. Nishide
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+),
16(O+), 17(OH+ or NH3+),
18(H2O+ or NH4+),
19(F+), 20(HF+), 28(CO+
or N2+), 32(O2+),
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.
Authors:I. Ferino, R. Monaci, E. Rombi, and V. Solinas
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.
Authors:J. A. Navio, M. Macias, A. Justo, and C. Real
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.