Adsorption and Desorption of a Model Hydrocarbon Mixture Over HY Zeolite Under Dry and Wet Conditions

Abstract

International audienceAdsorption behavior of a hydrocarbon mixture (propene, toluene, decane) mimicking Diesel cold-start was investigated under dry and wet conditions for commercial HY zeolites with a Si/Al ratio ranging from 2.5 to 100. Textural and structural characterizations were carried out using N-2 adsorption at 77 K and X-ray diffraction. In situ FTIR spectroscopy of adsorbed pyridine was exploited to probe acidic sites. The methodology used in this study consisted of adsorption phase at 35 degrees C with several kinds of mixtures followed by a Temperature-Programmed Desorption (TPD) at 10 degrees C/min. At high Si/Al ratio, a competitive thermodynamic adsorption between toluene and decane was demonstrated. To the opposite, propene is substantially not adsorbed whatever the Si/Al ratio of the zeolite. By decreasing the Si/Al ratio, the presence of large amounts of acidic sites enhances adsorption of unsaturated hydrocarbons. Water adsorption was found to be detrimental for HC storage due to hydrophilic nature

Zeolite Beta Doped with La, Fe, and Pd as a Hydrocarbon Trap

“…The XPS results (see Figure 2) show that the addition of Fe, and especially La, resulted in lowering of the Pd oxidation state. As the oxygen in the zeolite framework is mostly associated with Lewis acid sites [10][11][12][18][19][20]. The lower oxidation state of the Pd might indicate a lower number of Lewis acid sites, which could be an explanation for the lower desorption quantities observed in the toluene-TPD in Figure 8.…”

“…These results contradict the results from the propene-TPD experiments, where the addition of Pd resulted in lower storage capacity of propene in dry conditions. We suggest that the reason for this difference is that the phenyl ring of toluene can also adsorb Lewis acid sites [10][11][12][18][19][20], such as Pd, while propene preferentially interacts with Brønsted acid sites through hydrogen bonding with the π electrons in the C=C bond [17]. Some desorption peaks also appear at higher temperatures in Figure 5.…”

“…These results are interesting and are the exact opposite of the corresponding findings for propene adsorption, where water completely blocks the adsorption capacity of the hydrocarbon. The results suggest that the Lewis acid storage sites are less affected by the presence of water since propene mainly adsorbs on Brønsted acid sites [17], whereas toluene can adsorb on Lewis acid sites [10][11][12][18][19][20]. Figure 6.…”

“…Toluene; however, is proposed to interact with both the Brønsted and Lewis acid sites. Negatively charged oxygen in the zeolite structure interacts with the methyl group in toluene, while the Lewis and Brønsted acid sites interact with the phenyl ring [10][11][12][18][19][20].…”

Influence of structural, textural and chemical parameters of silver zeolites on the retention of methyl iodide

“…This will slow down the diffusion of CH 3 I. In our previous works dealing about multiple-hydrocarbon adsorption by different zeolitic structures, we have shown that adsorbed amounts and breakthrough profiles were not only influenced by the chemical nature of the adsorbates but also by the pore connectivity and topology [17,40,41]. Finally, the presence of sodium in fauajsite zeolites appears also to adversely affect the filtering efficiency by inducing a change in the distribution or speciation of silver species (as stated in the characterization part).…”