The effect of several parameters on catalytic denitrification of water by the use of H₂ in the presence of O₂ over metal supported catalysts

The present paper involves a detailed study of the selective catalytic reduction of nitrates in aqueous mediums by the use of H₂ in the presence of O₂ over monometallic and bimetallic supported catalysts. In this study, an attempt has been made to improve the denitrification efficiency (X_NO3⁻, S_N2) of several catalysts by regulating some experimental parameters that are involved in the process. Therefore, the effects of the type of reactor (semi-batch reactor vs continuous flow reactor), the nature of the active phase (Pd, Cu, and Pd-Cu) and the particle size of γ-Al₂O₃ spheres (particle diameter = 1.8 mm and 3 mm) on catalytic activity and reaction selectivity, as well as the adsorption capacity of γ-Al₂O₃ spheres for nitrates, were examined. As the review indicates, most of the research has so far been conducted on batch or semi-batch reactors. This study successfully demonstrates the benefits of using a continuous flow reactor in terms of catalytic activity (X_NO3⁻, %) and reaction selectivity (S_N2, %). Another important aspect of this study is the crucial role of bimetallic Pd-Cu clusters for the prevention of NH₄⁺ formation. Moreover, the use of 1.8 mm diameter γ-Al₂O₃ spheres as a support was proved to significantly enhance the catalytic performance of bimetallic Pd-Cu catalysts towards nitrate reduction compared to 3 mm diameter γ-Al₂O₃ spheres. This difference may be attributed to mass (NO₃⁻, OH⁻) transfer effects (external mass transfer phenomena).