Promoted catalytic oxidation of benzene over Mn-Ni solid solutions: Effect of metal oxygen bond parameters

Abstract

In this work, Mn-Ni solid solutions were obtained by doping Ni into MnOx via solution combustion synthesis and the resulting catalysts were then applied to benzene oxidation. Various characterizations revealed that Ni doping changed the metal oxygen bond parameters, such as coordination numbers (CNs) and bond length. Both Mn-O and Ni-O bonds in Mn-Ni solid solutions exerted reduced CNs, while the bond length of Mn-O bonds was extended, making the oxygen species more chemically reactive., which further improved physicochemical properties (such as reducibility, oxygen mobility, surface active oxygen species etc.) and catalytic performance. Remarkably, the solid solutions with a Mn/Ni molar ratio of 4:1 (named Mn4Ni1) showed Mn-O and Ni-O bonds with lower CNs and longer bond lengths, which enhanced the activity and mobility of oxygen species, reducibility and chemisorption capacity of benzene. Therefore, Mn4Ni1 demonstrated optimal benzene oxidation activity and showed the lowest T90 (192 °C). The potential reaction mechanism was proposed according to the analysis results of C6H6-TPSR and in-situ FTIR. Furthermore, promoted oxidation of benzene and phenolate species on Mn4Ni1 could inhibit accumulation of intermediates and avoid catalyst poisoning and deactivation. This strategy shed light to the design of catalysts in environmental catalysis and thermal catalysis.