Nature of surface deposits on sulfated zirconia used as catalyst in the benzoylation of anisole

The benzoylation of anisole with benzoic anhydride over sulfated zirconia has been investigated, especially with regard to catalyst deactivation and regeneration. Calcined sulfated zirconia and spent catalysts have been characterized by BET analysts, C-H elemental analysis, DRIFTS, NH3-TPD, C-13-NMR and UV-Vis spectroscopy. In batch-mode experiments, a moderate deactivation attributed to the deposition of carbonaceous surface species has been observed. The surface deposits consist of benzoate species and strongly adsorbed molecules of anisole. A color change of the solid, observed immediately after the introduction of the catalyst into the reaction mixture, has been attributed to the protonation of the reaction products 2- and/or 4-methoxybenzophenone. The surface species formed may cover or modify surface acid sites and, in this way, reduce the accessibility of active centers. Removing the deposited and adsorbed species by calcination in air restores the initial activity of sulfated zirconia.