Authors:K. Bachari, R. M. Guerroudj, and M. Lamouchi
reaction. These materials were characterized by N 2 adsorption measurements, X-ray diffraction (XRD), MET, temperature-programmed desorption (TPD) of pyridine and 71 Ga MAS-NMR spectroscopy.
Authors:Ping Chen, Jiqing Lu, Guanqun Xie, Lin Zhu, and Mengfei Luo
chromatograph with a thermal conductivity detector.
Ammonia temperature-programmed desorption (NH 3 -TPD) was conducted on a home-made apparatus. 50 mg of catalyst was loaded in a quartz tubular reactor (i.d. = 6 mm) prior to the measurement, and was
DSC and TG-DTA techniques were used to investigate micro-sized silver powder particles and the adsorption of ethyl cellulose
on these particles in a solution of ethyl acetate. The apparent specific heat of the silver particles was determined, and
the kinetics of temperature-programmed desorption (TPD) of these adsorbed silver particles was investigated. Results show
that the apparent specific heat and desorption kinetic parameters obtained by thermal analysis techniques could be used to
characterize certain physico-chemical properties of such a particulate system.
Authors:E. Alsdorf, M. Feist, H. Fichtner-Schmittler, H. Jerschkewitz, U. Lohse, and B. Parlitz
H, Li, Na, Cs, NH4, Mg and Al-ZSM 5 zeolites and H and NH4-mordenites were studied by DTA, X-ray diffraction, TPD and adsorption measurements. The stability relating to dealumination and structure destruction depends on the nature of the cation.
Authors:J. Goworek, Agnieszka Kierys, W. Gac, Anna Borówka, and R. Kusak
Thermal evacuation of a surfactant template from pure siliceous MCM-41 and MCM-41 containing aluminium in hydrogen flow was
investigated. Micelle templated MCM-41 were prepared using hexadecyltrimethylammonium bromide (CTAB). The products of thermal
surfactant degradation outside and inside pores were identified at various temperatures using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, gas chromatography coupled with mass spectrometer (GC-MS) and
temperature programmed desorption coupled with mass spectrometer (TPD-MS). The GC-MS and 13C MAS NMR results obtained from this study provide an insight into the mechanism of surfactant transformation during MCM-41
synthesis on molecular level.
Authors:Yanan Wang, Huanhui Chen, Guoqing Zhao, Min Liu, Xuewei Lang, and Zhirong Zhu
The aldol condensation of methyl acetate with formaldehyde to form methyl acrylate was studied in a continuous-flow reactor using a series of supported cesium basic catalysts with commercially available materials (ZSM-5, SiO2, and γ-Al2O3) as carriers prepared by vacuum impregnation. The catalysts were characterized by N2 adsorption-desorption, Fourier transform-infrared (FT-IR), X-ray diffraction (XRD), and temperature-programmed desorption of ammonia and carbon dioxide (NH3/CO2-TPD). The obtained results indicated that the selectivity of methyl acrylate was mainly influenced by the properties of supports. The formation of acetone is approximately proportional to the acidity of supports. The basicity of the catalysts was favorable to the formation of methyl acrylate according to the results of CO2-TPD. The hydrolysis of methyl acetate was inhibited over Cs-HT-SiO2 prepared by SiO2 after hydrothermal treatment. Furthermore, SiO2 with the large mesoporous volume is superior to other supports, which shows the best catalytic activity for the aldol condensation reaction. On the other hand, the catalytic performance of zeolite basic catalysts was strongly influenced by the effect of reactant diffusion. Internal diffusion resulted in the increase of conversion of methyl acetate with increasing specific surface area, while the conversion of methyl acetate decreased with increasing the weight hourly space velocity (WHSV) due to the external diffusion.
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: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: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. 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.