TRANSITION-METAL OXIDES ADDITIVATED WITH SULFATE OR PHOSPHATE AS CATALYSTS FOR THE CRACKING OF CUMENE AND SUPPORTS FOR SULFIDED NICKEL-TUNGSTEN HYDROCRACKING CATALYSTS
Acb. Dossantos et al., TRANSITION-METAL OXIDES ADDITIVATED WITH SULFATE OR PHOSPHATE AS CATALYSTS FOR THE CRACKING OF CUMENE AND SUPPORTS FOR SULFIDED NICKEL-TUNGSTEN HYDROCRACKING CATALYSTS, Applied catalysis. A, General, 153(1-2), 1997, pp. 83-101
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 o
xides, followed by calcination at 773 K. An oxide of niobium, additiva
ted with phosphate, was also prepared by a similar procedure using pho
sphoric acid. The additivated oxides were characterized with respect t
o 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 activit
ies of the materials for the cracking of cumene were determined using
a pulse method at 573 K. Nickel and tungsten were supported by the add
itivated oxides and the resulting catalysts were tested for the hydroc
racking of cumene at 673 K and 3.1 MPa pressure, with carbon disulphid
e as a sulphiding agent. With the exception of the niobium samples, al
l 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 strong
est sites (H-0 less than or equal to-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 Bro
nsted nature of their acidic sites. Only sulphided nickel-tungsten, su
pported on sulphated zirconia and titania, and on phosphated niobia, d
isplayed any significant activity in the hydrocracking of cumene at 67
3 K; but of these, only the phosphated niobia presented a good stabili
ty for this reaction. An activation effect, during the first few hours
of the reaction, was observed with the catalysts supported by the sul
phated titania sample, suggestive of the generation of Bronsted acid s
ites by a spill-over effect upon exposure to hydrogen.