Studies of sulphated mixed oxides (ZrO2–SO4–La2O3) in the isomerization of n-hexane

Abstract

A series of mixed oxides (ZrO2–La2O3) was investigated to establish the effect of the source of the sulphate ion and the modification of sol–gel zirconia with La2O3. Supports were synthesized varying the content of La2O3 (2, 3, 5 and 10wt.%). Sample sulphation took place in situ, maintaining the amount at 20wt.% using concentrated H2SO4 and a 1M (NH4)2SO4 solution as the sulphating agents. These catalytic materials were characterized by: X-ray diffraction, nitrogen adsorption (BET), FTIR pyridine, 2-propanol dehydration, Scanning Electron Microscopy (SEM) and isomerization of n-hexane. The modification of sol–gel zirconia with La2O3 originated an increase in the surface area. When increasing the content of La2O3 (3, 5 and 10wt.%) a diminution of the surface area for samples sulphated with H2SO4 (CASLn) occurred. On the contrary, for samples sulphated with (NH4)2SO4 (CSALn) a not defined behavior was presented. In mixed oxides, the tetragonal phase was present which is characteristic of sulphated zirconia. By SEM, the morphology of the support can be perfectly observed showing the presence of clusters in each of them. It was observed that the crystallite size did not change when increasing the lanthanum content for the CASLn supports. According with the FTIR pyridine technique all the samples exhibited the presence of Brönsted and Lewis sites, and the support that achieved the highest acidity was the one containing 2wt.% of La2O3 (CASL2). It was determined that the effect of the sulphate agent generated more active catalysts in terms of conversion of n-hexane and it was also observed that La2O3 provided a higher catalytic selectivity toward isomerization products.