A DFT study on Zr-SBA-15 catalyzed conversion of ethanol to 1,3-butadiene

Density functional theory (DFT) calculations have been used to elucidate the influence of the surface properties of Zr-SBA-15 on the conversion of ethanol to 1,3-butadiene at the molecular level. To identify the critical reactive intermediates of ethanol catalysis to catalytically form 1,3-butadiene on the Zr-SBA-15 surface, the model of Zr-SBA-15 was first built. The overall enthalpy energy surface was explored for the highly-debated reaction mechanisms, including Toussaint's aldol condensation mechanism and Fripiat's Prins mechanism. It was found that ethanol dehydration to form ethylene possessed a lower energy barrier than dehydrogenation to yield acetaldehyde, which means they are competing reactive pathways. C–C bond coupling to form acetaldol (3-hydroxybutanal) proceeds with a 2.15 eV forward reaction barrier. Direct reaction of ethylene and acetaldehyde proceeds with a free energy barrier of 2.90 eV suggesting that Prins condensation hardly occurs. The results here provide a first glimpse into the overall mechanism of 1,3-butadiene formation on Zr-SBA-15 reactive sites in light of the variety of proposed mechanistic pathways mostly based on conventional homogenous organic chemistry reactions.