Desorption experiments adsorption

SEM and" SEM-EDX analyses have been used in order to observe how and where the new material forms on the alumina support. XRD and MASNMR studies have been performed for its identification. Porous characteristics of the composite material have been explored using N2 adsorption-desorption experiments (Micromeritics ASAP 2000M)... 

As stated above, when probes with specific adsorption characteristics are used, additional chemical information can be extracted from adsorption-desorption experiments. Temperature-programmed desorption (TPD) in particular is often employed to obtain information about specific sites in catalysts [55,56], The temperature at which desorption occurs indicates the strength of adsorption, whereas either the amount of gas consumed in the uptake or the amount of desorption upon heating attests to the concentration of the surface sites. The most common molecules used in TPD are NH3 and C02, which probe acidic and basic sites, respectively, but experiments with pyridine, Oz, H2, CO, H20, and other molecules are often performed as well [57-59], As an example, the ammonia... 

Analogous methanol adsorption/desorption experiments conducted with the supported manganese pyrophosphate catalyst gave the following results 1) A single desorption peak centered at lOO C is observed (Figure 8). 2) Mass spectral analysis indicates the... 

Fig. 10. Evaluation of kinetic parameters for the DOC model—HC adsorption/desorption (reaction R7 in Table II). Comparison of the measured and simulated outlet Ci0H22 concentrations in the course of the adsorption/desorption experiment. Synthetic gas mixture, other gases 6% C02, 6% H20, N2 balance, SV = 30,000 h 1 (Kryl et al., 2005). Reprinted with permission from Ind. Eng. Chem. Res. 44, 9524, 2005 American Chemical Society.

Examples of light-off experiments for CO and 22 are given in Fig. 11 together with the results of the ID model using global DOC kinetics. In the case of decane, the adsorption has to be considered with the kinetic parameters already evaluated from the adsorption/desorption experiments... 

A cycle of repeated adsorption-desorption experiments is currently under way. It aims to determine the long-term operational characteristics of adsorbents and the stability of adsorption/structural properties. The results already obtained appear to be quite promising the properties of adsorbents are comparable with those shown by the adsorbents synthesized in a two-step procedure with TEOS as a silica precursor. 

Experiments were then performed to preadsorb the various forms of oxygen on an iron oxide surface. These were then followed by the butene adsorption-desorption experiments to determine the amounts of the two types of oxidation sites. Typical results are shown in Table V (6). The amounts of oxidation products are independent of the presence of preadsorbed oxygen. In fact, even the thermally desorbed isomers are not affected by the preadsorbed oxygen. This absence of effect of the preadsorbed oxygen was observed also in pulse experiments. It was found that the amounts of butadiene, C02, and butene isomers formed from a butene pulse passing over the catalyst at 100,200, or 300°C are independent of preadsorbed oxygen (6). 

Effect of Preadsorbed Oxygen on the Oxidation of cis-2-Butene in Adsorption-Desorption Experiments -6... 

Fig. 7. The fraction of butadiene and C02 precursosr left adsorbed on a-Fe203 and y-Fe203 as a function of desorption temperature in a butene adsorption experiment. Filled circles are for adsorption-desorption experiments without oxygen, open circles are for those in which the desorption process was interrupted for passage of an oxygen pulse over the catalyst at the indicated temperatures. From Ref. 18, reprinted with permission from Academic Press.

Figure 1 gives a schematic overview of the whole adsorption equipment. With this apparatus adsorption/desorption experiments can be carried out up to 500 bar pressure at water bath temperatures. The equipment consists of three main sections a high pressure pump, the water... 

Prior to each TPD-TGA experiment, the samples were exposed to between 10 and 15 Torr of 2-propanol or 2-propanamine for approximately 5 min at 295K. This exposure was sufficient to fill a substantial fraction of the zeolite pore volume of each sample. Desorption measurements were performed following evacuation of the samples for 1 to 20 hrs to remove some of the weakly adsorbed species. While the evacuation time did affect the amount of weakly adsorbed species observed in TPD at lower temperatures, it had no affect on the well-defined, stoichiometric complexes observed in this study. Following an adsorption-desorption experiment, the sample... 

Permeation experiments are often complemented by adsorption measurements, which can help to explain the permeation mechanism observed. To this end, temperature-programmed adsorption/desorption experiments are employed, based on weight measurements (thermobalance), or on continuous gas analysis. It is important to ensure that the initial state of the membrane in adsorption experiments is reproducible, i.e., there is no unwanted material previously adsorbed on the membrane. 

The crystallinities were determined by XRD (Phillips PW1830 spectrometer, CuK< radiation) in reference to the parent TEA-beta sample. Textural properties were determined by nitrogen adsorpticm at 77 K in a Mictomeritics ASAP 2400. Before experiments, the samples were treated in vacuum at 573 K for three hours. The acidity of the samples was measured by IR spectroscopy combined with pyridine adsorption/desorption experiments on a Nicolet 710 FTIR Spectrometer equipped with data station. The solid state Si and A1 NMR spectra were collected by using a Varian spectrometer, VXR-300 FT NMR, at 7.05 T and equipped with a Varian CP-MAS probe. A 38% ethanolic solution of acetylacetone (ACAC) was used for impregnation of the samples before Al NMR analyses in order to complex all the EFAL including the NMR "invisible" species. The XPS data were collected by a VG-Scientific Escalab MKII spectrometer operated with a MgKa x-ray source. 

From the adsorption/desorption experiments (Fig. 3) it appears that butene adsorbs irreversibly on FER in the relevant temperature range for butene isomerization. Since the heat of adsorption of butenes in silicon-rich FER is estimated to be 10 kcal/mol, desorption should be facilitated at about 350°C. The low rate of desorption at 350°C proves, therefore, that butenes have reacted to higher molecular weight material, presumably oligomers, inside the pores of FER. 

Nitrogen adsorption/desorption experiments have been performed with silanised silica samples using n-alkyldimethylchlorosilanes with varying chain lengths (Fig. 3.16). 

An investigation of the mechanism of the charcoal catalysed reaction (10.17) reveals that the reaction proceeds via a strongly absorbed intermediate, identified as chloromethyl chloroformate, CHjC10C(0)Cl [1765]. This compound is found to form rapidly above 100 C in co-adsorption/desorption experiments, and decomposes rapidly above 170 C without significant desorption [1765], to give the final products, CH Clj and COj. The... 

The IR spectra were obtained with a Bruker IFS 48 spectrometer. The catalyst powders, as self-supporting pellets, were placed in an infrared cell allowing adsorption-desorption experiments to be carried out in situ. Prior to the adsorption of toluene, the cell was evacuated (1.0x10 Torr) at room temperature. 

Acetone, 81, 82, 100, 102, 181, 321 Acetone-propane binary system, 123 Acid-base complex, 102 Acrylate-ethylene copolymer, 194 Activated carbon, regeneration, 158-169 Adamson, A. W., 347 Adsorbent regeneration, 168 Adsorption/desorption experiments, 161, 163 Adsorption equilibria, 166, 169 AIChE Journal, 135 Aida, T., 325 Alachlor... 

To investigate the acid properties of these materials, adsorption/desorption experiments with pyridine as the probe molecule were carried out. FT-IR spectra of samples were recorded after adsorption of pyridine and desorption at increasing temperatures. The acid strength is subdivided into i) very weak, i.e., acid sites able to retain pyridine only after evacuation at 21°C, ii) weak, i.e., acid sites able to retain pyridine after evacuation at 100°C, and iii) medium, i.e., acid sites able to retain pyridine after evacuation up to 200°C. The results are reported in Table 3. 

In this study, we reported the preparation of mesoporous Ti02 materials via the sol-gel method involving a co-assembly of titanium (IV) isopropoxide and mainly neutral soluble starch CTMACl is used only for comparative reason. Ethanol and cyclohexane were used as solvents. The effect of key parameters, including surfactant removal process either by washing and/or by calcination and the solvent nature are discussed. Ti02 samples were characterized by means of N2 adsorption-desorption experiments, X-ray Diffraction analysis, UV-vis spectrophotometer. Scanning Electron Microscopy and Atomic Force Microscopy. 

Specific surface area of C5 polyol-boehmite is also much higher (343 m. g" ) than those of C4 polyol-boehmite (168 m. g ) or even of reference boehmite (144 m. g" ) according to the decrease of particle size previously described. In table 1, these specific surface area values measured from Na adsorption/desorption experiment (Sbet) are compared to geometric specific surface area calculated from particle morphological data (Sga,). Sbet values are slightly lower than Sgeo values probably due to particle aggregation. 

The system of differential equations which describe the mass balance of the adsorption-desorption experiments of our case study are the following ... 

Overall, the two-sink model provided a reasonable description of the mass balance of the adsorption-desorption experiments performed and reproducible parameter estimates. However, the reported results have given evidence that the reproducibility of parameter estimates for adsorption of a compound on chamber walls may critically depend on residues of the compound in the sinks from earlier experiments. It highlighted the very long time needed to attain equilibrium between the vapor phase and the adsorbed phase and vice versa. This effect was particularly pronounced for adsorption on chamber walls. The chamber sink, compared with the adsorption on three test materials, showed that, in general, the former will introduce only a minor or negligible bias in the measurement of the latter, provided that a sufficiently large surface of the test material is used. 

MgO ex-hydroxide (MgO-h) was prepared by thermal decomposition of the parent Mg(OH)2 under vacuum conditions directly inside the IR chamber. The hydroxide was slowly decomposed in vacuo at ca. 523 K and finally outgassed at 1123 K. This procedure gives MgO with high specific surface area (SSAbet= 200 m -g ) which is assumed to be completely dehydroxylated, as no OH stretching vibration bands were observed in the background IR spectrum. IR spectra of the adsorption of H2 at room temperature were obtained by a Bruker IPS 48 instrument the resolution was 4 cm . The IR chamber, linked to a vacuum pump, allowed both the thermal pretreatment and the adsorption-desorption experiments to be performed in situ . The spectra are reported in absorbance, the background spectrum of the MgO san le before H2 absorption being subtracted. 

The IR and EPR sample cells are connected to an appropriate high vacuum pumping rack. It allows thermal activation of the sample at less than 10" mbar and adsorption/ desorption experiments with diverse gases. For the IR experiments small quantities of MgO powder (20-30 mg) were pressed into selfsupporting pellets. The pressure applied was less than 10 bar and did not initiate any change of the specific surface area. For the EPR experiments similar amounts of the MgO sample batch, also used for IR spectroscopy, were filled in EPR tubes. 

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