Controlling activity and selectivity of bare ZrO2 in non-oxidative propane dehydrogenation

A detailed study was carried out on the factors affecting the activity and, particularly, selectivity of bare ZrO2 in the non-oxidative propane dehydrogenation (PDH) to propene. To this end, a series of ZrO2 samples differing in their redox and acidic properties, morphology and phase composition were synthesized by precipitation, sol-gel, glycine-nitrate combustion, template, digestion and calcination methods as well as through controlled thermal decomposition of zirconium oxonitrate. The ability of ZrO2 to release its lattice oxygen in reducing atmosphere was identified as the main factor affecting PDH activity and propene selectivity. This is due to the fact that so generated surface zirconium cations (Zr-cus) with lower coordination than their regular counterparts show higher activity for propene formation. As the latter sites strongly contribute to coke formation, the selectivity to this undesired product can be hindered through improving the ability of ZrO2 to generate Zr-cus sites under reducing conditions.