Preparation and NO x -assisted soot oxidation activity of a CuO–CeO 2 mixed oxide catalyst

Synergistic Effects of Multicomponents Produce Outstanding Soot Oxidation Activity in a Cs/Co/MnOx Catalyst

The control of soot emission from diesel vehicles is of extraordinary importance to the environment, and catalytic removal of soot is a highly effective and clean method. Here, we report a novel, non-noble metal catalyst for application in the catalytic combustion of soot with superb activity and resistance to H₂O and SO₂. MnO_x oxide was prepared via a hydrothermal method, and then, Cs and Co were loaded on MnO_x by impregnation. The 5%Cs/1%Co/MnO_x catalyst displayed excellent catalytic activity with values of T₁₀ (332 °C), T₅₀ (371 °C), and T₉₀ (415 °C) under loose contact. The as-prepared catalysts were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (TPR), O₂ temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). The results suggest that, after the introduction of Cs and Co into the MnO_x oxide, more NO₂ molecules take part in soot oxidation, exhibiting higher NO₂ utilization efficiency; this is due to the synergistic effects of multiple components (Cs, Co, and Mn) promoting the generation of more surface-active oxygen and then accelerating the reaction between NO₂ and soot. This study provides significant insights into the development of high-efficiency catalysts for soot oxidation, and the developed 5%Cs/1%Co/MnO_x catalyst is a promising candidate for application in diesel particulate filters.

Effect of Cu(NO3)2 and Cu(CH3COO)2 Activating Additives on Combustion Characteristics of Anthracite and Its Semi-Coke

The process of anthracite and its semi-coke combustion in the presence of 5 wt.% (in terms of dry salt) additives of copper salts Cu(NO3)2 and Cu(CH3COO)2 was studied. The activating additives were introduced by an incipient wetness procedure. The ignition and combustion parameters for coal samples were examined in the combustion chamber at the heating medium temperatures (Tg) of 600–800 °C. The composition of the gaseous combustion products was controlled using an on-line gas analyzer. The fuel modification with copper salts was found to reduce the ignition delay time on average, along with a drop in the minimum ignition temperature Tmin by 138–277 °C. With an increase in Tg temperature, a significant reduction in the ignition delay time for the anthracite and semi-coke samples (by a factor of 6.7) was observed. The maximum difference in the ignition delay time between the original and modified samples of anthracite (ΔTi = 5.5 s) and semi-coke (ΔTi = 5.4 s) was recorded at a Tg temperature of 600 °C in the case of Cu(CH3COO)2. The emergence of micro-explosions was detected at an early stage of combustion via high-speed video imaging for samples modified by copper acetate. According to the on-line gas analysis data, the addition of copper salts permits one to reduce the volume of CO formed by 40% on average, providing complete oxidation of the fuel to CO2. It was shown that the introduction of additives promoted the reduction in the NOx emissions during the combustion of the anthracite and semi-coke samples.

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

In the present work, nanowire morphologies of α-MnO₂, cobalt monodoped α-MnO₂, Cu and Co bidoped α-MnO₂, and Ni and Co bidoped α-MnO₂ 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), N₂ sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H₂-TPR), and oxygen-temperature-programmed desorption (O₂-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO₂ nanowires showed a remarkable improvement in soot oxidation performance, with its T₅₀ (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 MnO₂ 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-MnO₂ nanowires was analyzed, and it was found that the Cu/Co bidoped α-MnO₂ 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-MnO₂ 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-MnO₂ nanowires provide promise as a highly effective alternative to precious metal based automotive catalysts.