Nanowire Morphology of Mono- and Bidoped α-MnO₂ Catalysts for Remarkable Enhancement in Soot Oxidation

Abstract

In the present work, nanowire morphologies of α-MnO, cobalt monodoped α-MnO, Cu and Co bidoped α-MnO, and Ni and Co bidoped α-MnO samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H-TPR), and oxygen-temperature-programmed desorption (O-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO nanowires showed a remarkable improvement in soot oxidation performance, with its T (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combustion activation energy for the Cu and Co bidoped MnO nanowires is 121 kJ/mol. The increased oxygen vacancies, greater number of active sites, facile redox behavior, and strong synergistic interaction were the key factors for the excellent catalytic activity. The longevity of Cu and Co bidoped α-MnO nanowires was analyzed, and it was found that the Cu/Co bidoped α-MnO nanowires were highly stable after five successive cycles and showed an insignificant decrease in soot oxidation activity. Furthermore, the HR-TEM analysis of a spent catalyst after five cycles indicated that the (310) crystal plane of α-MnO interacts with the soot particles; therefore, we can assume that more-reactive exposed surfaces positively affect the reaction of soot oxidation. Thus, the Cu and Co bidoped α-MnO nanowires provide promise as a highly effective alternative to precious metal based automotive catalysts.

Nanocrystalline CeO2−δ coated β-MnO2 nanorods with enhanced oxygen transfer property

“…3a) in CeO 2-δ @β-MnO 2 were found to be 642.0 and 653.8 eV, respectively. The two peaks with binding energies of 641.9 eV and 643.6 eV in the deconvolution of Mn 2p 3/2 can be attributed to Mn 3+ and Mn 4+ , respectively, which are in good agreement with those reported for MnO 2 , [35][36][37] indicating the oxidation states of Mn species are Mn 3+ and Mn 4+…”

Experimental and Theoretical Investigation of the Effect of Oxygen Vacancies on the Electronic Structure and Pseudocapacitance of MnO2

“…Recently, numerous researchers have focused on MnO 2 ‐based composites or the doping of MnO 2 with metals (e.g., Al, Zn, Ce, Co and Fe) to improve their intrinsic conductivity . For example, Cakici et al.…”

“…Recently,n umerous researchers have focused on MnO 2based composites or the doping of MnO 2 with metals (e.g.,A l, Zn, Ce, Co and Fe) to improve their intrinsic conductivity. [23][24][25][26][27][28][29] For example, Cakici et al prepared ac arbon fiberf abric/corallike MnO 2 nanostructure by using ag reen hydrothermal method,w hich displayed ac apacitance of 467 Fg À1 at 1Ag À1 . [30] Zhou and co-workers reported Al-doped a-MnO 2 , which showed enhancede lectrochemical performance owing Defect engineering is an effective way to modulate the intrinsic physicochemical properties of materials.…”

Enhancement of soot oxidation activity of manganese oxide (Mn2O3) through doping by the formation of Mn1.9M0.1O3–δ (M = Co, Cu, and Ni)

“…Our earlier work reported on the synthesis of iron‐doped Mn 2 O 3 catalysts (Mn 2− x Fe x O 3 : x = 0.05 to 0.2) for the application of low‐temperature soot oxidation and achieved a T 50 (temperature at 50% soot conversion) of 400°C because of the formation of an increased amount of active oxygen species upon doping . Jampaiah et al fabricated mono‐doped and bi‐doped α‐MnO 2 nanowires and reported that strong redox behavior, number of active sites, surface adsorbed oxygen species, and active crystalline planes of Co and Cu Bi‐doped α‐MnO 2 nanowires were responsible for their highest catalytic soot oxidation activity . However, Mn 2 O 3 doped with other active transition metals for the application in soot oxidation has not been studied and reported in the literature so far.…”

“…23 Jampaiah et al fabricated mono-doped and bi-doped α-MnO 2 nanowires and reported that strong redox behavior, number of active sites, surface adsorbed oxygen species, and active crystalline planes of Co and Cu Bi-doped α-MnO 2 nanowires were responsible for their highest catalytic soot oxidation activity. 24 However, Mn 2 O 3 doped with other active transition metals for the application in soot oxidation has not been studied and reported in the literature so far.…”