Oxidative dehydrogenation of i-butane over nanostructured silica-supported NiMoO_4 catalysts with low content of active phase

摘要

NiMoO_4 silica-supported samples (6.5% w/w) were prepared by coprecipitation technique.In order to study the influence of the surface area of the support material,silicas with different surface areas have been used:Durosil (60 m~2/g) and Sipernat 22 (190 m~2/g) from Degussa and silica prepared in the laboratory (590 m~2/g).Nanosized grains of beta-NiMoO_4 phase were obtained for all the prepared samples.The crystallinity of the active phase (mixed oxide) depends on the nature of the support material.The laboratory-made silica allowed reaching the highest degree of nanocrystallinity (observed by TEM) for the active phase.Results from TPR and ITR show that the sample reducibility depends on the size and crystallinity of the dispersed active phase.All the prepared samples were more reducible than the unsupported NiMoO_4 sample due to the presence of beta-phase instead alpha-NiMoO_4 phase.In the tested conditions the sample prepared using the silica with the highest surface area displays the highest i-butane conversion,the highest i-butene selectivity and the lowest selectivity towards deep oxidation products.