Catalysts between Scylla and Charybdis: selective or active
Propylene production is an important bottleneck in the chemical industry because it cannot keep up with the demand. The older production methods, which rely on steam cracking and fluid catalytic cracking, are environmentally problematic to boot. Therefore an alternative production route is increasingly commonly used, where propane as a reactant is dehydrogenated to propylene over chromia catalysts.
Chromia is an effective catalyst for this reaction despite being plagued by low selectivity and quick deactivation. Due to the rapid accumulation of coke on the catalyst, the reaction is carried out in cycles with catalyst regeneration phases in-between. As the reaction takes place in an oxidative atmosphere, the oxygen atoms from the catalyst also participate actively.
In the study, we explained why the reaction does not proceed well on a fully reduced or fully oxidized catalyst. We demonstrated this difference by multilevel modelling, which included quantum chemical calculations of the catalyst and the reaction steps, and kinetic simulations. Only propylene is formed on the reduced catalyst, but the reaction is very slow (low activity). On an oxidized catalyst, the reaction is very fast, but most of propane is converted to carbon dioxide (low selectivity). We have shown that there exists an optimal level of the surface oxidation, where propylene production is fastest. This can be regulated with varying the oxidant pressure and with the selection of an appropriate oxidant (air, oxygen, N2O).
The research is a part of large European project Bizeolcat, where partners from France, Italy, the Netherlands, Norway, Spain, Sweden and Turkey also participate. The aim of the project is to develop efficient catalysts for the sustainable conversion of hydrocarbons.
The results were published in ACS Catalysis. The research was partly funded by the ARRS (core funding P2-0152) and the European Union (Bizeolcat project, Horizon 2020).
Authors: Matej Huš, Drejc Kopač, David Bajec and Blaž Likozar
Further information: matej.hus[at]ki.si