Thermogravimetric analysis adsorption

Multiwall carbon nanotubes (MWCNTs) have been synthesized by catalytic chemical vapor deposition (CCVD) of ethylene on several mesoporous aluminosilicates impregnated with iron. The aluminosilicates were synthesized by sol-gel method optimizing the Si/Al ratios from 6 to 80. The catalysts are characterized by nitrogen adsorption, X-ray diffraction, 27A1 NMR, thermogravimetric analysis (TGA) and infrared. The MWCNTs are characterized by TGA and transmission and scanning electron microscope. 

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

The CeMCM-41 material studied had much higher quality than the corresponding MCM-41 sample synthesized under the same conditions. While both materials exhibited analogous adsorption properties with respect to nitrogen, their interaction with n-butylamine was different. Thermogravimetric analysis of w-butylamine thermodesorption showed that CeMCM-41 possessed medium and strong acid sites in contrast to the pure silica MCM-41, the acidity of which was negligible. Thus, incorporation of cerium to MCM-41 seems to improve its hydrothermal stability and enhance the adsorption and catalytic properties. 

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed in air at a heating rate of lOK/min. on a PTC-lOA thermogravimetric analyzer. The adsorption isotherms for vapor-phase water and ethanol were measured using the BET method. The saturation pressures, Pq, of water and ethanol at 299K are 758 mmHg. Prior to the adsorption experiments, the samples were dehydrated at 673K in air for 4 h. 

Although oxidation has been used to purify carbon materials, oxygen-carbon reactions have been shown to drastically alter physiochemical properties, such as wettability and adsorption characteristics. Moreover, oxidation can easily induce damage to carbon materials or even destroy the sample. This is of particular importance in the case of carbon nanostmctures. Thermogravimetric analysis (TGA), which measures changes of mass during oxidation processes, has been widely used to determine the purification conditions [22-24]. However, TGA does not provide information on what type of carbon is removed from the sample or to what extent nanostructures are damaged. 

The precursor and the calcined catalyst were characterized by various techniques such as nitrogen adsorption, mercury porosimetry, X-ray diffraction (XRD), atomic emission spectrometry by inductively coupled plasma (ICP), thermogravimetric analysis, and temperature-programmed reduction (TPR). More details about the catalyst preparation and characterization can be found in a previous work (22). 

The other posibility for characterizing structural properties of inorganic sorbents deals with the thermogravimetric analysis. By means of this analysis the pore size distribution, pore volume and specific surface area of adsorbents and catalysts which are fundamental adsorption characteristics may be obtained. 

The catalysts were characterized by N2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), temperature-programmed desorption of ammonia (NH3-TPD), X-ray diffraction (XRD), Raman spectroscopy, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). The procedures and experimental conditions have been detailed elsewhere [9]. 

The identity and crystalline purity of the bulk material are determined by PXRD, with the same diffraction pattern as the solvothermal reaction above. Solvent exchange in the pores is confirmed by thermogravimetric analysis and full evacuation is confirmed either by TGA (again, no weight loss until 420°C) or, more rigorously, by gas adsorption (N2,77K, Langmuir surface area of 3909 m2/g). 

The optimal calcination method for zeolite beta was established by thermogravimetric analysis using a PL-Thermal Sciences STA 1500 apparatus. Chemical compositions of the zeolites were determined by atomic absorption spectroscopy on a Varian AAIO spectrometer after dissolution of the samples in hydrofluoric acid. The structure was confirmed by x-ray diffraction on a Siemens D-5000 diffractometer and with infrared spectroscopy on a Mattson Instruments Galaxy 2000 spectrometer. Total surface area, micropore area and micropore volume of the samples were determined by argon adsorption on a Micromeritics ASAP 200M volumetric analyzer using standard techniques. Crystal diameters were determined by scanning electron microscopy. 

Adsorption of dibenzothiophene (DBT) over FAU zeolites exchanged with alkali cations has been studied. Cristallinity (by XRD and IR), exchange level (XRF) and basic properties (CO2 TPD) of different adsorbents used have been determined. The influence of Si/Al molar ratio and type of cation exchanged in the zeolite as well as the presence of toluene in feedstock mixture on DBT adsorption capacity and selectivity of adsorbent has been also determined. Thermogravimetric analysis showed a stronger DBT adsorption over X zeolites. 

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