Catalytic activity of bulk and supported sulfated zirconia

Abstract

SummaryTo assess whether Lewis acid sites are present on zirconium sulfate, we prepared water-free bulk zirconium sulfate. Furthermore, a water-free silica-supported zirconium sulfate catalyst was prepared by deposition-precipitation of zirconia on silica and subsequent gas-phase reaction with SO 3 . The activity of these catalysts was compared with that of two conventionally prepared sulfated zirconia catalysts.The different catalysts were extensively characterized. XPS indicated that the conventionally prepared sulfated zirconia catalysts contained sulfuric acid. The activity of the catalysts was determined with the gas-phase trans-alkylation of diethylbenzene with benzene and the solvent-free liquid-phase addition of acetic acid to camphene.Both water-free zirconium sulfate catalysts did not exhibit a significant activity; Lewis acid sites are therefore not active in these sulfated zirconia catalysts. Upon exposure to water vapor the initially water-free catalysts were active. The stability of the conventional sulfated zirconia catalysts appeared to be determined in the gas-phase by the volatilization of sulfuric acid. As a result, a highly porous catalyst was more effective than a catalyst based on zirconia of a relatively low porosity. With liquidphase reactions extraction of sulfuric acid proceeds leading to an acid liquid, which is catalytically active also after separation of the solid catalyst from the reaction mixture.

Sulfation Mechanism and Catalytic Behavior of Manganese Oxide in the Oxidation of Methanethiol

“…Although XPS and DRIFTS evidenced the presence of sulfur species at the catalyst surface, samples characterized after reaction at 150 and 180 °C exhibited no modification of their XRD diffraction patterns. On these samples, the position of the S 2p3/2 peak was centered around 168.4 eV and was inferior to the binding energy of the reference manganese sulfate sample (168.8 eV) but can nonetheless be assigned to adsorbed sulfate species (most likely in the form of adsorbed sulfuric acid-like species) . The new band centered around 1230 cm -1 observed in the DRIFTS spectrum after reaction at 150 °C was also assigned to hydrated sulfate species.…”

“…However, a modification of the sulfate state was noticed because the S 2p 3/ 2 peak position was shifted from 168.3 to 168.8 eV with increasing temperature. Dijs et al have observed a higher binding energy of S 2p 3/2 for bulk Zr(SO 4 ) 2 (170 eV) than for adsorbed sulfuric acid on zirconium hydroxide (168.3 eV). The 168.8-eV position corresponds well to the value measured on the manganese sulfate sample, whereas the lower BE position around 168.3 eV would be better assigned to adsorbed “sulfuric acid-like” species.…”

“…On these samples, the position of the S 2p3/2 peak was centered around 168.4 eV and was inferior to the binding energy of the reference manganese sulfate sample (168.8 eV) but can nonetheless be assigned to adsorbed sulfate species (most likely in the form of adsorbed sulfuric acid-like species). 40 The new band centered around 1230 cm -1 observed in the DRIFTS spectrum after reaction at 150 °C was also assigned to hydrated sulfate species. Furthermore, a slight reduction of the manganese oxidation state was evidenced by XPS and potentiometric analysis on the same samples.…”