Adsorption of Glycerol at Brønsted Sites in Mordenite: a Density Functional Theory Study

Adsorption of various glycerol conformations at Brønsted sites in mordenite is studied by the density functional theory. It is shown that the adsorption energy depends on the initial conformation of the glycerol molecule and ranges from –44.0 kcal/mol (ββ conformation) to –64.7 kcal/mol (αγ conformation). In some cases, the glycerol molecule switches its conformation as a result of nanoconfinement. It is shown that the most energetically favorable adsorption of glycerol on mordenite proceeds via the primary OH group. High adsorption energy is due to the proton transfer from the zeolite Brønsted site to glycerol as a result of the hydrogen bond formation and also due to the formation of up to four additional hydrogen bonds with oxygen atoms of the zeolite framework. As a result, the backbone of the adsorbed molecule deforms, which fact should affect the course of chemical reactions involving glycerol.