Catalytic activity and some related spectral features of yttria-stabilised sulfated zirconia

Cubic sulfated zirconia (c-SZ) was prepared by sulfating phase-stabilised c-ZrO2, and its properties are compared with those of tetragonal (t-SZ) and monoclinic (m-SZ) systems. ZrO2 crystalline phases have been identified by XRD and, far more efficiently, by Raman spectroscopy. c-SZ exhibits better catalytic activity (n-butane isomerization at 423 K) than t-SZ, whereas m-SZ is virtually inactive. The better activity of c-SZ is not ascribable to changes of surface functionalities, but probably derives from a better stabilization of the high symmetry crystalline form (i.e., from a more favourable distribution of surface sulfates among regular and defective crystal terminations).