Optimization of Pt/WOx−ZrO2Catalysts for the Production of Reformulated Fuels by Isomerization−Cracking of Medium Length C8−C12Paraffins

Abstract

The effect of the temperature of calcination of the support on the structural properties of ZrO 2 and on the activity of the acid and metal functions of a Pt/WO x -ZrO 2 catalyst used in the isomerization—cracking of medium length paraffinic C 8 -C 12 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 H 2 Cl 6 Pt (1% Pt) and calcined in air at 500 °C. They were characterized by means of chemical analysis, XRD, N 2 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, H 2 /n-C 8 = 6), n-butane (350 °C, WHSV = 1, H 2 /n-C 4 = 6), and cyclohexane (300 °C, 1 atm, WHSV = 12.6, H 2 /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 Pt δ+ 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.