Influence of temperature and space velocity on the MTO reaction over nano sheet-like SAPO-34 catalyst and the theoretical calculation

Nano sheet-like silicoaluminophosphate molecular sieve SAPO-34 was synthesized under hydrothermal conditions by using tetraethylammonium hydroxide as the template. The catalytic performances of methanol-to- olefin (MTO) reactions over nano SAPO-34 catalysts under different temperatures and weight hourly space velocity (WHSV) were systematically studied. The catalytic temperature and WHSV can affect both the catalytic lifetime and the selectivity of ethylene and propylene. The lifetime of catalyst decreased with the increase of catalytic temperature and WHSV. In addition, the ratio between ethylene and propylene enhanced with the increase of catalytic temperature, but decreased with the increase of WHSV. Density functional theory (DFT) calculations demonstrated that the energy barrier of producing ethylene is higher than that of propylene. According to the variation of Gibbs free energy along with temperature, the increase of temperature is more advantageous to the generation of ethylene.