Metal-zeolite catalysts for the removal of pharmaceutical pollutants in water by catalytic ozonation

Catalytic ozonation of salicylic acid (SA), as model pharmaceutical pollutant, at room temperature was studied in an aqueous phase using mono- (Pd, Cu) and bimetallic (Pd-Cu, Cu-Pd) zeolite catalysts prepared by the ion exchange method, using different zeolite structures: FAU (USY) and MFI (ZSM5). All metal-zeolite catalysts positively affected SA degradation in comparison with the parent zeolites, except for PdCu-HUSY. The mineralization degree was improved in the presence of the heterogeneous catalysts, regardless of the zeolite used. Nevertheless, the catalysts based on different zeolite structures presented distinct performances during SA oxidation, with those based on HUSY zeolite showing lower activity, which indicated that the physicochemical properties of the zeolite structures are very important. Wide-ranging, the catalytic oxidation of SA with ozone on zeolite-based catalysts was found to be affected by a combination of the acidic properties of zeolites and the chemical composition at the surface. The evolution of oxalic acid as a by-product in SA oxidation, as well as its degradation by catalytic ozonation, were also studied. Reutilization runs revealed that the zeolite-based catalysts were very stable.