Effects of copper on the activity of sulfated zirconia catalysts for n-pentane isomerization Original Research Article

A sample of sulfated zirconia (SZ) containing 2.5% S and 2.7% Cu after calcination in air at 650°C/1 h and reduction in flowing hydrogen at 250°C/5 h gives 53.1 wt.% n-pentane conversion with 98% i-pentane (2-methylbutane) selectivity at 150°C. Isomerization activity depends on the calcination temperature used to activate the catalyst and on the metal promoter present. Copper promoter has been found to produce more active SZs than Ag, Fe, Mn or Fe–Mn combinations.The reduced Cu-SZ catalyst has a low surface area and pore volume (PV) of 43 m2/g and 0.047 ml/g, respectively. Microcalorimetry experiments with ammonia have indicated that the reduced catalyst contains a moderate acidity sorbing only 179 μmol NH3/g. In addition, initial heats are low, <120 kJ/mol and as ammonia coverage increases, a small (43 μmol NH3/g) population of sites with strength in the 100–150 kJ/mol range, appears. Thus, neither porosity nor acid site strength or density (as determined by microcalorimetry experiments) control n-pentane conversion at the conditions used in this study. The oxidized Cu-SZ is inactive and gains its isomerization activity only after reduction in H2. It has been proposed that the function of the Cu0 in the reduced catalyst is to remove oxygens from the zirconia support to form CuO and oxygen-deficient Zr atoms capable of initiating the isomerization reactions of n-pentane at 150°C.