Argon sorption

Table 1. Characterization of the pristine MCM-48 silica B and the host/guest compound B-Fe203 with respect to specific surface area, pore size and pore volume using various methods (BET-specific surface area Sbet, BJH-mode pore diameter dp(BJH), average pore diameter Dh = 4 Vpore/SBET- In addition argon sorption isotherms at 87 K for both materials were analyzed with respect to pore size (dp(SF)) and pore volume (Vp(SF)) by applying the Saito-Foley method.

Figure 5. Temperature dependence of sorption hysteresis for argon sorption on MCM-48 material A [dp,N (BJH) = 2.67 nm] and for comparison on controlled-pore glass [d n (BJH) = 15.7 nm], ...

The results for nitrogen, argon and krypton adsorption on pristine MCM-48 materials can be summarized as follows (i) Argon sorption isotherms at 87 K (T/Tc = 0.58, where Tc is the critical temperature of the bulk fluid) reveal for all MCM-48 silica phases used in this study pore condensation but no hysteresis at relative pressures p/po < 0.4. With increasing pore size... 

In a study of thermal stability and hydrogen sorption characteristics of a series of sorbent tablets composed of hydride-forming metals dispersed in polymers under a 50% hydrogen in argon atmosphere, it was found that tablets of 80% palladium in PTFE, and 80% of 1 5 atom lanthanum-nickel alloy in PTFE could not be used above 247° C because of explosive decomposition of the PTFE. 

Let us compare M-ZSM-5 zeolites with M = H+, Li+, Na, K+, Rb, Cs, AF+, on one hand, and organic electron donors of variable ionization potentials, on the other. Zeolite H-ZSM-5 generates cation-radicals from substrates with an oxidation potential of up to 1.65 V (Ramamurthy et al. 1991). The naphthalene sorption by Al-ZSM-5 zeolites calcified in an atmosphere of oxygen or argon leads to the appearance of two occluded particles—the naphthalene cation-radical and isolated electron. Both particles were fixed by ESR method. Back reaction between the oppositely charged particles proceeds in an extremely slow manner and both the signals persist over several weeks at room temperature (Moissette et al. 2003). 

In addition, the large pore volume, pore size flexibility, and structural variety of MCM-41 can be extensively used for the selective adsorption of a diversity of gases and liquids [39,40], An extremely high sorption capacity for benzene has been demonstrated [40], Widespread work has been carried out on the sorption properties of some adsorbates, such as nitrogen, argon, oxygen, water, benzene, cyclopentane, toluene, and carbon tetrachloride, as well as certain lower hydrocarbons and alcohols on MCM-41 [122],... 

Wacker J. F. (1989) Laboratory simulation of meteoritic noble gases III. Sorption of neon, argon, krypton, and xenon on carbon elemental fractionation. Geochim. Cosmochim. Acta 53, 1421-1433. 

The diffusivities obtained by Barrer and Brook (i) ranged from 5 X 10" cm /sec for sorption of argon in Li-mordenite to 5 X 10 for nitrogen in Ca-mordenite. A quantitative comparison of results for such different systems is not possible, but considering the relative effective sizes of the gas molecules and zeolite windows, the comparison with the present results is not unreasonable. 

P. Santikary and S. Yashonath, Molecular Dynamics Investigation of Sorption of Argon in NaCaA Zeolite, J. Chem. Soc. Faraday Trans. 88 (1992) 1063-1066 C. Fritzsche, R. Haberlandt, J. Kaerger, H. Pfeifer and K. Heinsinger, A MD Simulation on the Applicability of the Diffusion Equation for Molecules Adsorbed in a Zeolite, Chem. Phys. Lett. 198 (1992) 283-287. 

The study of Michot et al. [389] is an interesting attempt to determine where and how phenol adsorbs in activated carbons. These authors determined the uptake of phenol by a commercial activated carbon at pH 11.5 (i.e., under conditions of electrostatic repulsion) and concluded that ad.sorption of phenol on activated carbon is mainly controlled by the porous. structure of the adsorbent. They found a monotonic decrease in the ad.sorption of gas-phase argon with in-... 

Figure 4 Comparison of PSDs obtainedfor MCM-41 type adsorbents from nitrogen and argon porosimetry using DFT (left). The pore wall thickness of five different MCM adsorbents, found by combining results from XRD and sorption DFT measurements, is consistent in four of the five samples (right) [20].

Essential progress has been made recently in the area of molecular level modeling of capillary condensation. The methods of grand canonical Monte Carlo (GCMC) simulations [4], molecular dynamics (MD) [5], and density functional theory (DFT) [6] are capable of generating hysteresis loops for sorption of simple fluids in model pores. In our previous publications (see [7] and references therein), we have shown that the non-local density functional theory (NLDFT) with properly chosen parameters of fluid-fluid and fluid-solid intermolecular interactions quantitatively predicts desorption branches of hysteretic isotherms of nitrogen and argon on reference MCM-41 samples with pore channels narrower than 5 nm. 

Pore condensation and sorption hysteresis are of great importance for the characterization of porous media by the analysis of appropriate sorption isotherms (e.g., nitrogen, argon and... 

Here we present the first systematic study on the pore size- and temperature dependence of the sorption- and phase behavior of argon, krypton and nitrogen in the well defined, three-dimensional pore network of pristine mesoporous MCM-48 silica and MCM-48 silica/iron(III) oxide host-guest compounds. 

Results of systematic sorption studies of Nitrogen, Argon and Krypton at 77 K and 87 K on different pristine MCM-48 silica materials... 

Figure 4. Adsorption/desorption isotherms of argon at 77 K on the same MCM-48 silicas as in figure 3. In all cases pore condensation accompanied by sorption hysteresis is observed.

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