Optimization of Pt/WO3-ZrO2 catalysts for the production of reformulated fuels by isomerization-cracking of medium length C8-C12 paraffins

JAVIER M. GRAU; CARLOS R. VERA; VIVIANA M. BENÍTEZ; JUAN C. YORI

ENERGY & FUELS (PRINT)

American Chemical Society

Año: 2008 vol. 22 p. 1680 - 1686

0887-0624

The effect of the temperature of calcination of the support on the structural properties of ZrO2 and on the activity of the acid and metal functions of a Pt/WOx-ZrO2 catalyst used in the isomerization-cracking of medium length paraffinic C8-C12 cuts was studied. n-Octane was used as model molecule. The calcination temperature was varied in order to change the metal/acid balance and to increase the yield of the reaction to isoparaffins of high octane number. Four supports were prepared by impregnating Zr(OH)4 with ammonium metatungstate (15% W) and then they were calcined at 500, 600, 700, and 800 °C. These supports were then impregnated with H2Cl6Pt (1% Pt) and calcined in air at 500 °C. They were characterized by means of chemical analysis, XRD, N2 adsorption, pyridine TPD, hydrogen chemisorption, temperature-programmed reduction, and infrared spectroscopy of adsorbed CO. The catalytic activity of the catalysts was evaluated with the test reactions of n-octane (300 °C, 1 atm, WHSV ) 1, H2/n-C8 ) 6), n-butane (350 °C, WHSV ) 1, H2/n-C4 ) 6), and cyclohexane (300 °C, 1 atm, WHSV ) 12.6, H2/CH ) 1.4). The results reveal a strong influence of the calcination temperature on the final metal/acid balance of the catalysts. At 5 min time on stream, all catalysts produce a RON gain of 55 points. In general, the higher the calcination temperature the higher the promoting action of W for generating strong acid sites and the higher the concentration of Ptä+ of the metal function. The highest liquid yield and isoparaffin yield were obtained with the sample calcined at 700 °C. The sample calcined at 800 °C had the highest cracking activity and the maximum yield of isobutane and propane.2 and on the activity of the acid and metal functions of a Pt/WOx-ZrO2 catalyst used in the isomerization-cracking of medium length paraffinic C8-C12 cuts was studied. n-Octane was used as model molecule. The calcination temperature was varied in order to change the metal/acid balance and to increase the yield of the reaction to isoparaffins of high octane number. Four supports were prepared by impregnating Zr(OH)4 with ammonium metatungstate (15% W) and then they were calcined at 500, 600, 700, and 800 °C. These supports were then impregnated with H2Cl6Pt (1% Pt) and calcined in air at 500 °C. They were characterized by means of chemical analysis, XRD, N2 adsorption, pyridine TPD, hydrogen chemisorption, temperature-programmed reduction, and infrared spectroscopy of adsorbed CO. The catalytic activity of the catalysts was evaluated with the test reactions of n-octane (300 °C, 1 atm, WHSV ) 1, H2/n-C8 ) 6), n-butane (350 °C, WHSV ) 1, H2/n-C4 ) 6), and cyclohexane (300 °C, 1 atm, WHSV ) 12.6, H2/CH ) 1.4). The results reveal a strong influence of the calcination temperature on the final metal/acid balance of the catalysts. At 5 min time on stream, all catalysts produce a RON gain of 55 points. In general, the higher the calcination temperature the higher the promoting action of W for generating strong acid sites and the higher the concentration of Ptä+ of the metal function. The highest liquid yield and isoparaffin yield were obtained with the sample calcined at 700 °C. The sample calcined at 800 °C had the highest cracking activity and the maximum yield of isobutane and propane.