Sulfated Zirconia Nanoparticles Synthesized in Reverse Microemulsions:  Preparation and Catalytic Properties

Abstract

Microemulsion-derived sulfated zirconia was prepared by addition of zirconium butylate to mixtures of aqueous H2SO4, nonionic surfactants, and heptane as the oil phase and subsequent drying and calcination at 873 K. The resulting catalysts have surface areas ranging from 40 up to 175 m 2 g -1 depending on the microemulsion composition and show a high activity in n-butane isomerization (4.7 × 10 -7 mol s -1 g -1 , TOS ) 60 min) comparable to that of other commercially available catalysts. The size of the inverse micelles in the microemulsion can be used to tailor the properties of the catalyst in a wide range. In situ X-ray diffraction studies demonstrate significant differences in the crystallization kinetics of materials derived from low and high water/surfactant ratios (Rw). Transmission electron microscope investigations show that a higher degree of crystallite agglomeration and sintering is responsible for lower surface areas of high R w derived zirconias. According to thermogravimetric studies coupled with mass spectrometry, the lower activity of low Rw derived materials is due to a lower degree of sulfate incorporation. The parameters in the synthesis procedure which affect the activity of the catalyst are systematically studied, and the advantages and limitations of the microemulsion method are discussed.

The Balance Between Reactivity and Stability of Modified Oxide Surfaces Illustrated by the Behavior of Sulfated Zirconia Catalysts

“…The first two weight losses and the observation of first water and then SO 2 and O 2 in the effluent stream in the TGA-MS experiments on calcined samples are well documented in the literature [69]. Reported temperatures for water loss are around 373383 K [69,71], consistent with our observation of 370 K. Sulfate is reported to decompose between 873 and 1123 K [71], with the observed value of 1080 K fitting well within this range. It has been proposed that SO 2 and O 2 are not directly released from the sample but form through decomposition of evolving SO 3 [66].…”

“…Althues and Kaskel [71] reported that TG-MS data indicated the decomposition of bulk sulfate groups between 973 and 1273 K; the gas phase products were not discussed in detail. Fărcaşiu et al [72] proposed the presence of internal sulfate ions in the zirconia matrix on the basis of X-ray photoelectron spectra.…”

Nanocatalysts for Rearrangement Reactions

“…Recently, Althues and Kaskel have demonstrated that microemulsion-derived sulfated zirconia NPs, with surface areas up to 175 m 2 g −1 , present a higher activity in n-butane isomerization compared to conventional sulfated zirconia (4.7 × 10 −7 vs 3.1 × 10 −7 mol s −1 g −1 at 300 • C). 105 The same reaction was also explored using nanoparticles of sulfated zirconia anchored to different inorganic supports such as TiO 2 or MCM-41 mesoporous silica. [106][107][108][109][110] Interestingly, in the course of these studies, a remarkable promotional effect of Al 2 O 3 on the catalytic behaviour of this solid acid catalyst was disclosed, allowing to improve the n-butane conversion up to six times compared to that of the corresponding unpromoted catalyst (selectivities up to 94% toward iso-butane could be reached).…”

Investigation of factors influencing catalytic activity for n-butane isomerization in the presence of hydrogen on Al-promoted sulfated zirconia

“…Generally, a larger surface area is required to reach a higher catalytic activity. Since conventional sulfated zirconia has a relatively small surface area, many methods have been attempted to improve its surface area [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]. For example, sulfated zirconia was supported on silica materials and alumina materials with high surface area [30][31][32][33][34][35][36].…”