Abstract
The effect of MFI zeolite morphology (2D-nanosheets vs conventional 3D structure) on ethanol dehydration was probed by FTIR operando spectroscopy. Simultaneous examination of turnover rates and Bronsted acid sites coverage under different reaction conditions allowed determining activation energies for monomolecular and bimolecular dehydration pathways, as well as thermodynamic parameters (Delta H-ads and Delta S-ads) for the adsorption of the most abundant surface species (i.e., ethanol monomers and dimers).
The catalytic results showed smaller first-order activation energy (E-first) for 2D-MFI (E-first = 16 +/- 4 kJ mor(-1)) nanosheets vs 3D-MFI (E-first = 41 +/- 1 kJ mol(-1)) and similar zero-order activation energies (E-zero) for both 2D-(E-zero = 117 +/- 4 kJ mol(-1)) and 3D-MFI (E-zero = 124 +/- 1 kJ mol(-1)). Correlating the kinetic and thermodynamic parameters revealed that the different in stabilization of adsorbed ethanol monomers and dimers is the origin behind the differences in the intrinsic activities of 2D- and 3D-MFI zeolites which is refected in the corresponding zero-order activation entropies (Delta S-zero(double dagger)).