Controlled synthesis of tunnel-structured MnO2 through hydrothermal transformation of δ-MnO2 and their catalytic combustion of dimethyl ether

Synthesis of tunnel-structured MnO2 with one-dimensional morphologies (alpha-MnO2 nanowires and beta-MnO2 nanorods) is reported, which is based on the hydrothermal transformation of layer-structured MnO2 with two-dimensional morphology (delta-MnO2 nanosheets) via altering the reaction conditions readily. The types of the anions (SO42- and Cl-) in the acid solution play critical roles in determining the crystalline structures of the final products. Both of the MnO2 samples were characterized by means of XRD, Raman, FESEM, TEM, BET, XPS and H-2-TPR techniques. Owning to its more abundant surface adsorbed oxygen species, stronger reducibility, larger specific surface area and lower Mn-O bond strength, the alpha-MnO2 nanowires showed enhanced catalytic performance in the dimethyl ether catalytic combustion (T-10 = 200 degrees C and T-90 = 274 degrees C at WHSV = 30,000 ml g(-1) h(-1)), which was much higher than the beta-MnO2 nanorods.