Optimization of Pt/WO_x−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 ZrO2 and on the activity of the acid and metal functions of a Pt/WO x −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 Ptδ+ 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.

Bulk and surface characterization and isomerization activity of Pt/WO4 2−/ZrO2 catalysts of different preparations

“…It has been reported elsewhere [20,23] that the highest activity of Pt/WO 4 2-/ ZrO 2 catalysts is reached when tungstated zirconia is calcined at 700°C prior to Pt deposition. However, according to Hino and Arata [21], the most active bifunctional catalysts are obtained after the calcination of tungstated zirconia at 800 and 850°C.…”

“…Tungstated zirconia based catalysts for the isomerization of heavier paraffins are of particular interest [6,[14][15][16][17][18][19][20]. They exhibit catalytic activity slightly lower than that of sulfated zirconia based catalysts, but have greater isomerization selectivity [2,3,21].…”

“…The conventional procedure of catalyst preparation includes the impregnation of amorphous hydrated zirconium oxide with aqueous solutions containing WO 4 2-ions followed by drying and high temperature calcination [20,[22][23][24][25][26][27]. Finally, Pt is introduced to the catalysts to enhance the activity and suppress catalyst deactivation.…”

Catalysis in the Upgrading of Fischer–Tropsch Syncrude

“…This test confirmed the high activity and stability of the bi-promoted (WO 3 and SO 2 À 4 ) Pt on zirconia catalyst, producing an isomerate with the highest molar ratio of branched C 4 -C 7 to total branched products. 509 The acidity of the bi-promoted catalyst could be regulated by the amount of WO 3 in the catalyst. In addition to the Brønsted-toLewis acid ratio, the calcination temperature also had a pronounced effect on the final metal-to-acid site balance of the catalysts.…”

Textural properties and crystalline structure of tungstated zirconia, a catalyst for isomerization of lower alkanes

“…The problem of designing catalysts for the low temperature isomerization of hydrocarbon fractions including long chain alkanes has stirred considerable attention to acid catalyst systems based on zirconia modified with tungstate anions [2,5,[8][9][10][11][12]. It has been shown that their catalytic properties depend on the method of preparation of the hydroxide precursor, the amount of anions, the method of their introduc tion into the catalyst, calcination temperature, and other preparation conditions [2,8,9,12,13].…”