CO 2 reduction via oxidative dehydrogenation and dry reforming of ethane over Fe 3 Ni 1 nanoparticles: The influence of the oxide support

The effect of the CO 2 :C 2 H 6 feed ratio, the relative Lewis acidity of reducible and unreducible catalytically active metal oxide supports with and without Fe 3 Ni 1 alloy nanoparticles on the activity, selectivity and stability for the CO 2 -mediated oxidative dehydrogenation of ethane (CO 2 -ODHE) is investigated. To circumvent the influence of the typically dissimilar textural properties of the supports in bulk form, overlayer oxide supports of V, Cr, Ga, Ti or Sm coated on a common gamma-Al 2 O 3 carrier were employed. Separately, (Ni 0.75 Fe 0.25 )Fe 2 O 4 precursor nanoparticles were synthesized via a nonaqueous surfactant-free method, sonication-deposited onto supports and reduced in situ into an Fe 3 Ni 1 alloy microstructure of bcc and fcc mixed phases captured with in situ XRD. When exposed to carbon dioxide at 255 degrees C, a selective re-oxidation of the bcc phase via CO 2 dissociation is observed, while the fcc phase stays stable and only partially re-oxidizes above 525 degrees C. Upon exposure to CO 2 -ODHE conditions, the initial activity of the bare supports increases with increasing acid site strength, but this activity is rapidly lost in case of the strongly acidic supports. Comparison of the C 2 H 4 and CO selectivity indicate direct dehydrogenation is preferred over the oxidative dehydrogenation pathway and is initially occurring in combination with some CO-forming routes, possibly the dry reforming of C 2 H 6 . This CO forming route is significant over the most acidic and reducible VO x @Al 2 O 3 support in the early stages of operation. The addition of the Fe 3 Ni alloy increases the conversions of both C 2 H 6 and CO 2 across all supports, with a notably stronger effect observed on CO 2 conversion especially over the highly acidic and reducible VO x @Al 2 O 3 and CrO x @Al 2 O 3 . As a result, the CO selectivity is increased due to ethane dry reforming activity over the latter supports while CO 2 -ODHE activity is observed over the supports with intermediate and weak acid sites.