Adsorbate Bonding and Selectivity in Partial Oxidation

Catalytic oxidative dehydrogenation ofn-butane

“…For example, the idea that nucleophilic oxygen species are able to perform selective oxidations is supported by the findings of constant activity and selectivity even after cutting gas-phase oxygen feed (3). By contrast, oxides that tend to adsorb ionic-oxygen species produce essentially carbon oxides (83). Bielanski and Haber's theory is generally accepted.…”

“…Thermodynamic calculations point out that M}R intermediates are more stable than M}O}R intermediates. The longer surface residence time of the M}R complexes, coupled to lack of fast selective reaction pathways, favors irreversible oxidation to CO x (72,83). Haber also points to the existence of defects in the catalyst structure as a selectivity determining factor, since they are intimately related to the different adsorbed-oxygen species on the catalyst surface (equilibrium 3) (74).…”

AnOperandoRaman, IR, and TPSR Spectroscopic Investigation of the Selective Oxidation of Propylene to Acrolein over a Model Supported Vanadium Oxide Monolayer Catalyst

“…The nature of the oxygen species (bulk lattice atomic O*, surface atomic O*, surface molecular O 2 *) involved in selective propylene oxidation has also been a contentious issue in the literature. ,,,– It has been demonstrated with the aid of gas phase molecular 18 O 2 that bulk lattice oxygen is involved in the surface intermediate oxidation step at elevated reaction temperatures ,, and the role of gaseous O 2 is to reoxidize the reduced catalyst sites . The reaction between the surface allyl intermediate with chemisorbed molecular O 2 * to form a surface hydroperoxide intermediate (H 2 CCHCH 2 OO*) that decomposes to acrolein and water has also been proposed. , Other studies have proposed that surface atomic O* rather than surface molecular O 2 * is the active form of oxygen on the catalyst .…”

“…Consequently, supported metal oxide catalysts represent model catalytic systems for obtaining fundamental insights about the nature of the catalytic active sites and the surface reaction intermediates. Only a limited number of propylene oxidation studies with supported metal oxide catalysts have been undertaken to date (supported MoO 3 /SiO 2 , V 2 O 5 /SiO 2 and V 2 O 5 /TiO 2 catalysts) and, unfortunately, these studies primarily yielded nonacrolein products (propylene oxide, acetone and combustion) under the chosen experimental conditions. – …”

“…Only a limited number of propylene oxidation studies with supported metal oxide catalysts have been undertaken to date (supported MoO 3 /SiO 2 , V 2 O 5 /SiO 2 and V 2 O 5 /TiO 2 catalysts) and, unfortunately, these studies primarily yielded nonacrolein products (propylene oxide, acetone and combustion) under the chosen experimental conditions. [26][27][28][29][30][31] The selective oxidation of propylene to acrolein over model supported V 2 O 5 /Nb 2 O 5 catalysts was recently reported by the current authors with the aid of in situ Raman, in situ IR and C 3 H 6 -temperature programmed surface reaction (TPSR) spectroscopy studies. 30 The most abundant surface reaction intermediate (MARI) during propylene oxidation was found to be surface allyl (H 2 CCHCH 2 *).…”