An in situ DRIFTS study of the deactivation and regeneration of sulfated zirconia

Changes in the surface structure of sulfated zirconia prepared by sol-gel m ethod were studied using nitrogen adsorption, XRD, TGA and in situ DRIFTS. These studies were performed following deactivation and regeneration of the catalyst. The physical properties of sulfated sol-gel zirconia were unchan ged as a result of reaction and catalyst regeneration. The isomerization of n-butane was used as a probe reaction. Both Bronsted and Lewis acid sites as determined using pyridine adsorption at 100 degrees C were observed on s ulfated zirconia. Only Lewis acid sites were observed on non-sulfated zirco nia. The ratio of Bronsted to Lewis acid sites was found to be strongly dep endent on catalyst pre-treatment temperature prior to reaction. The Bronste d to Lewis acid ratio was observed to decrease from a value of 0.466 to 0.1 27 following the removal of the catalytically active surface sulfur. The to tal catalyst acidity was observed to decrease only slightly following remov al of this surface sulfur species. An infrared band, centered at 1370 cm(-1 ), was observed for the catalytically active material. This band appeared f ollowing activation in N-2 at 375 degrees C and was assigned to S=O. A Bron sted/Lewis acid site ratio of approximately 0.5 was found to be optimum for the isomerization of n-butane. (C) 1998 Elsevier Science B.V. All rights r eserved.