Different amounts of silver were successfully incorporated into cryptomelane-type manganese oxide (K-OMS-2) via a one-step hydrothermal method for application in the catalytic combustion of benzene. Silver incorporation could promote the benzene oxidation performance of the catalysts. The silver doping effect was addressed in terms of the relationship between structure and activity. The prepared catalysts were characterized by ICP-OES, BET, XRD, Raman, FE-SEM, TEM, XPS, XAFS, H2-TPR and CO-TPD. The best precursor Mn/Ag mole ratio was 40. The resulting K/Ag-OMS-40 catalyst exhibited the highest activity in terms of benzene combustion and good tolerance to chlorine poisoning, all of which make it a promising candidate as an alternative to noble metal supported catalysts. All catalysts after silver incorporation maintained the structural integrity of the cryptomelane structure but with decreased crystalline size, which significantly increased the surface area and number of defects of the catalyst. The silver species, mostly in the form of Ag+, were well dispersed and partially replaced K+ in the tunnels of cryptomelane. K/Ag-OMS-40 had the largest surface area, the smallest nanorods and most abundant Mn octahedral defects. The large number of active oxygen species derived from the high Mn3+ content and Ag-O-Mn bridge bonds appeared to play critical roles in VOC decomposition.
TEM/HRTEM/Mapping images of the K/Ag-OMS-x catalysts, (A) TEM: K-OMS-2, (B) TEM: K-Ag-OMS-40, (C) HRTEM:K-OMS-2, (D) HRTEM:K/Ag-OMS-40, (E) HAADF-STEM image, (F) Mn-element mapping, (G) O-element mapping, (H) Ag-element mapping for K/Ag-OMS-40.
