Effect of Glycine Addition on Physicochemical and Catalytic Properties of Mn, Mn–La and Mn–Ce Monolithic Catalysts Prepared by Solution Combustion Synthesis

Catalysts containing Mn, Mn–La and Mn–Ce oxides supported on ceramic honeycomb monoliths were prepared by excess-wet impregnation and solution combustion synthesis (SCS). In SCS, glycine was used as a fuel additive with variable concentration (fuel lean and fuel rich conditions). The catalysts were studied by BET, XRD, HRTEM, H2-TPR, and differential dissolution. Properties of the catalysts in the deep oxidation of butane were investigated. The best activity and stability were observed for the catalysts prepared by SCS under fuel rich conditions. Under these conditions, the active component is formed as highly dispersed particles of manganese oxides in the composition of simple and mixed oxides that are located in subsurface layers of the support. On the contrary, manganese oxides that are formed upon thermal treatment of the impregnation catalyst are located mostly in the bulk of the support. Reducing conditions of the SCS reaction lead to the formation of simple and mixed oxides where manganese is mostly in Mn3+ and Mn2+ oxidation states. The presence of reduced manganese species in the subsurface layers of support, which are accessible to reactants, provides high efficiency of SCS catalysts in the oxidation of butane.