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. 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.