Influence of alkali and alkaline earth metals on catalytic epoxidation of propene
Propylene oxide (PO) is a key component for the production of propylene glycol, its ethers and polyether polyols. Most of PO currently in use is obtained through processes that produce a lot of waste (are not environmentally friendly), or are found to be cost inefficient (use of expensive oxidants like hydrogen peroxide). These drawbacks have driven research into direct gas-phase epoxidation of propylene using molecular oxygen.
We examined the mechanism by which alkali metals, added to the CuOx/SiO2 catalyst, affect the selectivity of the catalytic reaction. In the conducted research work we employed several operando spectroscopic techniques (XANES, UV/Vis DRS).
We have shown that doping with alkali metals (Na+ and K+) modulates the nucleophilic character of oxygen in [Cu-O-Cu]x species, which decreases its reactivity with the allylic hydrogen in the propylene molecule and steers the selectivity towards the epoxidation reaction. During doping with alkaline earth metals (Ca2+), this effect was found to be negligible due to the higher amount of hydroxyl groups that remain attached to the catalyst surface. Using the operando XANES technique, we clearly demonstrated that the modification with alkali and alkaline earth metals significantly changes the dynamics of the catalyst reduction. The results of this research deepen our understanding of modulating catalyst activity and selectivity, and enable a more targeted synthesis of catalysts.
The article was published in the journal Applied Catalysis B: Environmental. The authors are: Janvit Teržan, Petar Djinović, Gregor Žerjav and Albin Pintar from the National Institute of Chemistry, Janez Zavašnik from the Institute Jožef Stefan/Max Planck Institute, Iztok Arčon from the University of Nova Gorica and Matjaž Spreitzer from the Institute Jožef Stefan.