Hydroisomerization-cracking of n-octane on Pt/WO42--ZrO2 and Pt/SO42--ZrO2 -: Effect of Pt load on catalyst performance

The hydroconversion (isomerization-cracking) of n-octane was studied at 300 degreesC, 1.5 MPa, WHSV = 4 and H-2/nC(8) = 6 using oxoanion promoted zirconia with different Pt concentrations (0.1, 0.5 and Ilo) as catalysts. Tungstate was added to zirconia by impregnation with ammonium meta-tungstate or tungstic acid solutions and calcined at 800 degreesC. Sulfate was added by impregnation with 2N H2SO4 and calcined at 620 degreesC. Isooctanes are intermediate products that are cracked to C-3-C-5 alkanes with predominance of isoalkanes. Sulfate zirconia is the most active and selective catalyst to cracking products. The addition of 0.1% of Pt produces an increase in activity and stability, respect of the support without metal. However, the increase in Pt content (0.5 and 1.0%) produces a decrease in nC(8) conversion and in cracking products. The metallic properties of Pt are decreased by its strong interaction with the support, mainly with sulfate zirconia; at the same time, Pt decreases the acid cracking activity of the support. (C) 2001 Elsevier Science B.V. All rights reserved.