Oxidative dehydrogenation of n-butane on Cs doped nickel molybdate: Kinetics and mechanism

The oxidative dehydrogenation of n-butane over a highly selective catalyst (3% Cs doped alpha-NiMoO4) has been studied in order to understand the mechanism of the reaction. The catalyst characterization was carried out by BET, X-ray diffraction (XRD), coupled plasma spectroscopy (ICP), atomic absorption (AA), X-ray fluorescence (XRF), IR and X-ray photoelectron spectroscopy (XPS). All the results showed an atomic ratio of Mo/Ni = 1 and a cesium surface concentration of 3%. The kinetic tests were carried out between 773 and 833 K changing the contact time and the partial pressure of both butane and oxygen. Only dehydrogenation products (1-butene, 2-butenes (cis and trans) and butadiene) and CO and CO2 were observed under all experimental conditions. The experimental results can be correlated using a redox model. Two active sites were observed by CO2-TPD, which would be responsible for the formation of two different adsorbed intermediates of butane. It is proposed that in the more basic sites 1-butene would be formed which reacts partially to butadiene and in the less basic sites the formation of the 2-butene isomers would occur.