Comparison between Ni and Pt promoted SO 4 2) –ZrO 2 catalysts for n-octane hydroisomerization-cracking J.C. Yori, J.M. Grau, V.M. Benı´tez, C.R. Vera, C.L. Pieck, and J.M. Parera Instituto de Investigaciones en Cata ´lisis y Petroquı´mica, INCAPE (FIQ-UNL, CONICET), Santiago del Estero 2654, 3000 Santa Fe, Argentina Received 9 June 2004; accepted 2 November 2004 The production of C 4 –C 6 branched isoalkanes by isomerization-cracking of n-octane (300 °C, 0.1 MPa) using sulfated zirconia catalysts was studied. The effect of Ni addition on the activity and selectivity was compared to the effect of Pt. Pt enhanced the activity and stability of the catalysts. Ni mainly improved the selectivity to isoparaffins (maximum yield at 1% Ni). n-Octane conversion fully correlated with total acidity. Average and final stable conversion values were in comparison lower for Ni catalysts. This result was addressed to the lower metal activity of Ni and to the detrimental effect of sulfated zirconia on the reducibility of the metal. KEY WORDS: sulfated zirconia; hydroisomerization; hydrocracking; n-octane. 1. Introduction Hydrocracking has been practiced in modern oil refineries for the production of light fuels from heavy distillate and residua since 1959 when Chevron announced its Isocracking process. Hydroisomerization and hydrocracking cost-effectively convert medium- to heavyweight cuts into high-value streams, like gasoline and jet fuel, other middle distillates and lube oils. Waxy compounds, chiefly normal-paraffins, are however lar- gely unaffected and must be removed in a subsequent process in order to reduce the pour point. The conversion of long normal-paraffins into bran- ched ones boiling in the naphtha range (C 5 –C 7 ) by means of hydroisomerization-cracking has received growing attention in the last years [1–6]. Conversion of long paraffins has been studied mainly on Pt-doped ze- olites but lately the attention has been focused on the use of bifunctional superacid catalysts [7–11], composed of a zirconium oxide support surface promoted with sulfate or WO 3 . The metal function needed for hydro- genation/dehydrogenation is provided by a Group VIII metal, e.g. Pt. These catalysts conveniently provide high activity at low temperatures, thermodynamically favouring the conversion to isoparaffins. Sulfated zirconia (SO 4 2) –ZrO 2 ) has proved to be more active than tungsten–zirconia (WO 3 –ZrO 2 ) while the latter has proved to be more selective to hydroiso- merization products. In both catalysts the interaction between the metal function and the support is very strong and is seemingly related to the crystalline state of the zirconia support [12,13]. Pt is present both as zero- valent Pt 0 and as electron deficient Pt d+ . The use of Ni other than Pt in oxoanion promoted catalysts for hydroisomerization-cracking has been reported [9] but not studied thoroughly. Both Ni and SO 4 2) or WO 3 promoted ZrO 2 have been used in n- butane isomerization and ethylene dimerization [14–16]. The role of Ni in Ni/SO 4 2) –ZrO 2 catalysts for the hydroconversion of long paraffins is studied in this work and n-octane is used as model molecule. The perfor- mance of Ni/SO 4 2) –ZrO 2 catalysts is compared to that of Pt/SO 4 2) –ZrO 2 catalysts. 2. Experimental 2.1. Catalysts preparation Zirconium hydroxide, Zr(OH) 4 , was obtained by hydrolysis and precipitation of zirconium oxychloride (Strem, 99.9998%) [17]. To obtain zirconia, ZrO 2 , Zr(OH) 4 was calcined at 620 °C for 3 h in flowing air (10 mL min )1 ). A c-Al 2 O 3 support was obtained from Ketjen (CK300, 180 m 2 /g) and stabilized by calcination in flowing air (10 mL min )1 ) for 3 h at 450 °C. Sulfated zirconium hydroxide, was prepared by incipient wetness impregnation of Zr(OH) 4 with a vol- ume of H 2 SO 4 2 N equal to the pore volume plus a 10% excess (0.4 mL/g). The material was then dried at 120 °C overnight. Sulfated zirconia, SO 4 2) –ZrO 2 (SZ sample), was finally obtained by calcination in an air flow (10 mL min )1 ) at 620 °C for 3 h. c-Al 2 O 3 and SO 4 2) –ZrO 2 (all ground to 35–80 mesh) were impregnated by incipient wetness, using Ni(NO 3 ) 2 Æ 6H 2 O aqueous solutions. The concentration *To whom correspondence should be addressed. E-mail: jyori@fiqus.unl.edu.ar Catalysis Letters Vol. 100, Nos. 1–2, March 2005 (Ó 2005) 67 DOI: 10.1007/s10562-004-3087-8 1011-372X/05/0300–0067/0 Ó 2005 Springer Science+Business Media, Inc.