Optimization of Mn‐Mg‐Al Mixed Oxides Composition on their Activity towards the Total Oxidation of Aromatic and Oxygenated VOCs

This study examines the influence of the Mn/Mg ratio on the physicochemical properties and catalytic activity of Mn_xMg_6-xAl₂-O catalysts. H₂-TPR results demonstrate that as Mn-content in the material increases, so does the reducibility of manganese species. Thus, for the total oxidation of ethanol and toluene, better catalytic performance is observed for the rich Mn-based materials.

Abstract

A series of mixed oxides (Mn-Mg-Al) is prepared by coprecipitation via a hydrotalcite route with different manganese ratios. Structural, textural, and redox properties are studied by XRD, N₂-sorption, H₂-TPR, and XPS techniques. Mn_xMg_6-xAl₂-O mixed oxides (with 0≤x≤6) are tested in the total oxidation of ethanol and toluene, two probe molecules representing respectively oxygenated and aromatic VOCs. Catalysts with higher manganese contents have shown the best catalytic performance for the oxidation of both ethanol and toluene. The surface activity of the materials is mainly related to the presence of manganese species in three different oxidation states (+II, +III, and +IV) in the bulk and on the material's surface. Since high Mn-content catalysts showed similar physicochemical properties and catalytic activity, Mn₄Mg₂-O is selected as the optimal composition of these materials. Furthermore, its aging test is compared to that of noble metal-based commercial catalysts (Pd/γ-Al₂O₃).

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