Energetic Characterization of Faujasite Zeolites Using a Sensor Gas Calorimeter

Abstract

In addition to the adsorption mechanism, the heat released during exothermic adsorption influences the chemical reactions that follow during heterogeneous catalysis. Both steps depend on the structure and surface chemistry of the catalyst. An example of a typical catalyst is the faujasite zeolite. For faujasite zeolites, the influence of the Si/Al ratio and the number of Na+ and Ca2+ cations on the heat of adsorption was therefore investigated in a systematic study. A comparison between a NaX (Sodium type X faujasite) and a NaY (Sodium type Y faujasite) zeolite reveals that a higher Si/Al ratio and therefore a smaller number of the cations in faujasite zeolites leads to lower loadings and heats. The exchange of Na+ cations for Ca2+ cations also has an influence on the adsorption process. Loadings and heats first decrease slightly at a low degree of exchange and increase significantly with higher calcium contents. If stronger interactions are required for heterogeneous catalysis, then the CaNaX zeolites must have a degree of exchange above 53%. The energetic contributions show that the highest-quality adsorption sites III and III’ make a contribution to the load-dependent heat of adsorption, which is about 1.4 times (site III) and about 1.8 times (site III’) larger than that of adsorption site II.

Influence of Temperature on the Binary Adsorption of Ethane and Ethene on FAU Zeolites

“…The order of this distribution is supported by X-ray diffraction (XRD) data and results from the consideration to minimize repulsive cation-cation interactions and to create the smallest possible distance between cations and the oxygen atoms of the zeolite framework. Additional evidence for Kulprathipanjas’s distribution was found by Mauer et al, who analyzed methane adsorption on zeolite NaX and on a systematic series of calcium-exchanged materials by volumetric and calorimetric measurements.…”

“…Framework topography of the FAU structure with framework cations I–III′. Adapted with permission from ref . Copyright 2021 by the authors.…”

“…Nevertheless, it should be noted that the zeolite framework also contributes to the interaction. 21 Since both adsorptives have a smaller molecular diameter than the pore diameter of the zeolites (0.74 nm), steric hindrance to the supercage can be excluded.…”

Investigation of the Adsorption of Hydrogen Sulfide on Faujasite Zeolites Focusing on the Influence of Cations

“…Mauer et al examined the influence of the type and number of cations on the adsorption of methane on FAU zeolites. The measured adsorption isotherms and enthalpies indicate a significant influence of the occupied cation positions and cation type on the strength of interactions . Frising and Leflaive studied the occupation of cation positions in detail and prepared a comprehensive review paper on the cation distribution in X- and Y-FAU zeolites.…”

“…The measured adsorption isotherms and enthalpies indicate a significant influence of the occupied cation positions and cation type on the strength of interactions. 17 Frising and Leflaive studied the occupation of cation positions in detail and prepared a comprehensive review paper on the cation distribution in X- and Y-FAU zeolites. The authors compiled studies on FAU zeolites including the cations Na + , Li + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ as well as other cations.…”