Ni-Nb-O mixed oxides as highly active and selective catalysts for ethene production via ethane oxidative dehydrogenation. Part II: Mechanistic aspects and kinetic modeling

摘要: Abstract In this work, transient and SSITKA experiments with isotopic 18 O 2 were conducted to study the nature of oxygen species participating in reaction ethane oxidative dehydrogenation ethylene obtain insight mechanistic aspects ODH over Ni-based catalysts. The was performed on NiO, a typical total oxidation catalyst, bulk Ni–Nb–O mixed-oxide catalyst (Ni 0.85 Nb 0.15 ) developed previously [E. Heracleous, A.A. Lemonidou, J. Catal., press], very efficient material (46% ethene yield at 400 °C). results revealed that both materials, proceeds via Mars–van Krevelen-type mechanism, participation lattice anions. However, exchange measurements showed different distribution two materials. prevalent formation cross-labelled NiO indicates dissociation is fast step process, leading large concentration intermediate electrophilic surface, active for ethane. Larger amounts doubly exchanged observed indicating doping makes diffusion process suppresses oxidizing species. Kinetic modeling Ni by combined genetic algorithm nonlinear regression techniques confirmed above, since superior model based redox parallel-consecutive network types sites: type I, responsible overoxidation reaction, II, direct CO . kinetic able successfully predict catalytic performance considerably experimental conditions than (high temperature conversion levels).