(448f) MoVNbTeO for Chemical Looping - Oxidative Dehydrogenation of Ethane

Chemical looping (CL) is a concept that depends on conveying lattice oxygen, instead of gaseous oxygen, to a reaction by means of a metal oxide, termed, in this context, an oxygen carrier. This enables physical or temporal separation between the oxidation and reduction steps. Oxidation occurs when the oxygen carrier is contacted with air in the first reactor, while reduction takes place in the second reactor by reaction with a reducing agent. CL might be employed for the production of chemicals via selective oxidation, or oxidative dehydrogenation (ODH), reactions, which can render these reactions safer, more selective and more intensive. In addition, CL would result in reducing CO₂ and NO_x emissions. However, the key challenges to adopt CL for selective oxidations include quantifying the benefits and drawbacks of applying the concept, in addition to the development of a stable redox catalyst.

The present study investigates the potential of chemical looping ODH (CL-ODH) of ethane. A multimetallic catalyst, namely MoVNbTeO, was chosen as the primary catalyst for this study, given its high activity for ODH. The choice was confirmed by a wide catalyst screening, spanning other active metals and oxygen carriers. The activity of MoVNbTeO was optimised for CL by tuning preparation conditions, most importantly calcination regimes. XRD, TGA and SEM-EDS confirmed the improved crystal structure, high oxygen capacity and homogenous distribution of metals for the developed catalysts.

To further enhance ethylene yield, particulate oxygen carriers composed of bismuth oxides supported on ceria-zirconia were physically mixed with the catalyst. This class of oxygen carriers can selectively combust hydrogen in the presence of ethylene. The results showed that the presence of the oxygen carriers slightly improved conversion and CO₂ selectivity, without affecting overall ethylene yield.

Catalyst testing indicated that the developed catalyst can realise 50% ethylene yield, with 90% selectivity and 55% conversion at 450°C. This represents a significant improvement compared to CL-ODH catalysts described in the literature that can achieve similar yields only at temperatures as high as 850°C.