Physisorption and Chemisorption of Linear Alkenes in Zeolites: A Combined QM-Pot(MP2//B3LYP:GULP)–Statistical Thermodynamics Study

Abstract

Physisorption and chemisorption of C2–C8 linear alkenes in H–FAU, H–BEA, H–MOR, and H–ZSM-5 have been quantified up to 800 K by combining QM-Pot(MP2//B3LYP:GULP) with statistical thermodynamics calculations. The influence of the zeolite topology and the alkene CC double bond position on the alkene sorption thermodynamics is addressed on the basis of linear variations of sorption enthalpies and entropies as a function of the carbon number. The physisorption strength and entropy losses increase in the order H–FAU < H–BEA < H–MOR < H–ZSM-5. Higher physisorption strength is computed for 2-alkenes (H–MOR) and 2-, 3-, and 4-alkenes (H–ZSM-5) as compared with 1-alkenes. Protonation of physisorbed alkenes leads to significantly more stable alkoxides. In contrast to the physisorption, higher chemisorption strength does not lead to larger chemisorption entropy losses. Also, the intrinsic stability of the alkoxides, i.e., relative to gas phase H2 and graphite, only depends on the carbon number and not on the detailed alkoxide structure in H–FAU, H–BEA, and H–MOR. In the narrower pores of H–ZSM-5, the 3- and 4-alkoxides are however more stable than the 2-alkoxides.

One step-synthesis of highly dispersed iron species into silica for propylene epoxidation with dioxygen

“…These energy values are of the same order as those reported for alkene adsorption on different Al-zeolites [67]. Interaction energies between ferrosilicate cluster and the adsorbates (O 2 and C 3 H 6 ) are quite similar, suggesting that both species interact with the surface to similar extents.…”

“…4, (Fig. 7), as suggested by Nguyen et al for alkene adsorption on Al-zeolites [67]. Different multiplicities of the adsorbate-cluster complexes were studied as this can be important in the case of iron containing species [68,69].…”

“…7). This configuration has been studied previously [67] and is in accordance with a precursor for the production of coke due to acid cracking reaction of the hydrocarbon. For this geometry, the most energetically stable cluster complex is the one where M=6 for both, the complex and the cluster.…”

On the stability and nature of adsorbed pentene in Brønsted acid zeolite H-ZSM-5 at 323 K

“…1 [11][12][13][14]. A first state corresponds to a free alkene in the cages of the zeolite, which undergoes only a weak van der Waals (vdW) interaction with the walls of the zeolite.…”

“…A more bound state corresponds to the p-complex, where a specific non-bonded interaction between the p-electrons of the double bond and the Brønsted acid site occurs. Finally the p-complex may be protonated leading to the formation of a chemisorbed species [11][12][13][14]. The nature of the resulting intermediate is still debated.…”