Transition metal oxides additivated with sulphate or phosphate as catalysts for the cracking of cumene and supports for sulphided nickel-tungsten hydrocracking catalysts Original Research Article

Oxides of zirconium, titanium, niobium, tin, and a mixed zirconium-tin oxide, additivated with sulphate, were prepared by the adsorption of sulphate from a sulphuric acid solution on the corresponding hydrous oxides, followed by calcination at 773 K. An oxide of niobium, additivated with phosphate, was also prepared by a similar procedure using phosphoric acid. The additivated oxides were characterized with respect to the total acidity by n-butylamine chemisorption using a gravimetric method. The acid site strength distribution was measured by titrating them with n-butylamine using Hammett indicators. The catalytic activities of the materials for the cracking of cumene were determined using a pulse method at 573 K. Nickel and tungsten were supported by the additivated oxides and the resulting catalysts were tested for the hydrocracking of cumene at 673 K and 3.1 MPa pressure, with carbon disulphide as a sulphiding agent. With the exception of the niobium samples, all oxides had their acid site density increased by the additivation. In all cases, except for the sulphated niobia, there was a marked shift in the acid site strength distribution towards the stronger and strongest sites (Ho≤−8,2), observed on the sulphated zirconia and phosphated niobia. These two samples also had activities, selectivities and stabilities, for the conversion of cumene, similar to those obtained with a zeolite containing sample, indicating the Brønsted nature of their acidic sites. Only sulphided nickel-tungsten, supported on sulphated zirconia and titania, and on phosphated niobia, displayed any significant activity in the hydrocracking of cumene at 673 K; but of these, only the phosphated niobia presented a good stability for this reaction. An activation effect, during the first few hours of the reaction, was observed with the catalysts supported by the sulphated titania sample, suggestive of the generation of Brønsted acid sites by a spill-over effect upon exposure to hydrogen.