Authors:Rita Sattler, W.-D. Einicke, and B. Hunger
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.
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:Ping Liu, Xingguang Zhang, Yue Yao, and Jun Wang
Alkaline earth metal (Mg, Ca, Sr and Ba) ions were exchanged into Hβ zeolite, which were used as the supports to load the
noble metal Pt to prepare bifunctional catalysts for hydroisomerization of n-heptane. The catalysts were characterized by ICP, XRD, BET, NH3-TPD, H2-TPR and H2-chemisorption techniques, and evaluated in an atmospheric fixed bed reactor. The catalysts promoted by the alkaline earth
metals are revealed to present much higher selectivity to isomerization than the counterpart Pt/Hβ. Moreover, the Ba-bearing
catalyst loaded with 0.4 wt% Pt and 5:1 molar ratio of Ba to Pt gives a very high selectivity to iso-heptanes 95.4% with a
considerable high conversion of n-heptane 61.7%. The promotion effect of alkaline earth metals is briefly discussed in relation to characterization data.
Authors:Dongshun Zhang, Rijie Wang, Xiaoxia Yang, and Wensheng Yao
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.
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: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.
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%.
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.