Linear surface adsorption-desorption

Examples with the linear surface adsorption-desorption... 

In the case of the full 2D problem with linear surface adsorption-desorption reactions (1), (2), (131) and (132), we present two tests. 

Linear surface adsorption-desorption reactions. Case A2 with the times of flow t — 100, 211 and 350 s... 

Table 5 Full linear surface adsorption-desorption problem parameter values at the Case A2 diffusive transport with surface reaction...

Figure 3 Comparison between the volume concentrations (1/H) c dz and for the linear surface adsorption-desorption reactions, Case A2, obtained using our effective problem (eff), average of the section of the concentration from the original problem (pbreeB) and the concentration coming from the simple average (moy) at time, t = 100 s.

TPD Temperature programmed desorption After pre-adsorption of gases on a surface, the desorption and/or reaction products are measured while the temperature Increases linearly with time. Coverages, kinetic parameters, reaction mechanism... 

Parsons-Zobel plot for NaF solutions was linear (Table 12). The value of Cf"0,determined by the extrapolation of the Cl, Q1 curve to Cjl = 0 and corrected by the value of /pz, has been obtained (Cf 0 - 0.32 F m 2). Adsorption studies of (C l at a polished pc-Pb show splitting of the adsorption-desorption peaks, which can be explained by the energetic inhomogeneity of the surface. The difference between Ea=Q values of various Pb faces has been estimated to be on the order of50-60 mV.604... 

For this estimate, values for the surface diffusion coefficient (D) and the surface exchange coefficient (i) in eq 2 were obtained by linearizing Mitterdorfer s rate expressions for surface transport and adsorption/desorption (ref 84) and re-expressing in terms of the driving forces in eq 2. 

The nitrogen adsorption-desorption isotherms were obtained at 77K by AutoSorb-1 -C (Quantachrome). Prior to measurement, the samples were outgassed at 300°C for 3 h. The specific surface areas of the samples were determined from the linear portion of the BET plots. Pore size distribution was calculated from the desorption branch of N2 desorption isotherm using the conventional Barrett-Joyner-Halenda (BJH) method, as suggested by Tanev and Vlaev [15], because the desorption branch can provide more information about the degree of blocking than the adsorption branch. 

Both types of molecular sieves, MCM-36 and MCM-41, demonstrate large BET surface area and high static sorption capacity (see Table 2). Considerable qualitative differences are observed in N2 isotherms, which are shown in Figure 3. The nitrogen isotherm for MCM-41, prepared with cetyltrimethylammonium cation, is type IV [9] and shows the characteristic reversible steep capillary condensation at p/p0 = -0.4 corresponding to the pore opening -40 A [1]. MCM-36 also shows the type IV isotherm with almost linear and reversible uptake increase up to - p/p0 = 0.5, followed by a hysteresis loop. This profile of adsorption/desorption is typical for layered materials with slit-like porosity generated between layers [9],... 

The studies of Ertl and co-workers showed that the reason for self-oscillations [142, 145, 185-187] and hysteresis effects [143] in CO oxidation over Pt(100) in high vacuum ( 10 4 Torr) is the existence of spatio-temporal waves of the reversible surface phase transition hex - (1 x 1). The mathematical model [188] suggests that in each of the phases an adsorption mechanism with various parameters of CO and 02 adsorption/desorption and their interaction is realized, and the phase transition is modelled by a semi-empirical method via the introduction of discontinuous non-linearity. Later, an imitation model based on the stochastic automat was used [189] to study the qualitative characteristics for the dynamic behaviour of the surface. 

The aim of this work is to test and to compare the performances of various nitrogen adsorption-desorption isotherms analysis methods. These models were applied to model samples obtained by mechanically mixing two micro- and mesoporous solids respectively in perfectly known proportions. The relevant morphological characteristics of the porous texture of the mixtures, such as the specific surface and volume, are physically additive. A criterion that allows determining the reliability of the analysis methods tested is thus to check the linearity of the relation between a given parameter and the weight percentage of the pure solids. 

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