Study On Abatement Of Unregulated Emissions Of Alternative Fuel Vehicles Over Oms-2 Catalysts

The development of renewable fuels is the strategic layout of energy and environment field. Bioethanol and biodiesel, the two main products of alternative fuels made from biomass, have been widely applied as the fuels in automobiles. The use of biofuel in automobiles results in a statistically significant increase in emissions of ethanol, acetaldehyde and formaldehyde. In addition, alcohol and aldehyde are quite resistant to decomposition by Pt/Rh based three-way catalysts. Therefore, more efficient catalysts for the reduction of alcohol and aldehyde emissions are needed. In this work, OMS-2 catalysts were prepared by refluxing method and they were characterized by BET, XRD and XPS methods. The activities of OMS-2 catalysts were investigated in detail under the simulated emission conditions of alternative fuel vehicles. Furthermore, the influences of the catalyst structure on alcohol and aldehyde oxidation and the mechanism of ethanol oxidation were investigated based on the activity tests and catalyst characterizations. The main results were summarized as follows:OMS-2 catalysts demonstrated good reactivity towards alcohol and aldehyde oxidation. The total oxidation of ethanol, acetaldehyde and formaldehyde were achieved at 140°C, 160°C and 120°C, respectively. OMS-2 catalysts were found to possess excellent hydrophobicity and the suppression effect of water vapor on catalytic activities was reversible. However, sulfur dioxide strongly influenced the bonding of the Mn-O lattice of the catalyst through chemical reaction with Mn-O bond to form manganese sulfate, resulting in a slow but irreversible catalyst deactivation.The prepared OMS-2 catalysts were essentially the same as the pattern of synthetic cryptomelane and displayed fibrous morphologies with diameters between 10 and 30 nm. OMS-2 catalysts demonstrated strong Lewis acidity. However, the modification in catalyst acidity had no promotion effect on catalytic activities. Lattice oxygen played an important role in alcohol and aldehyde oxidation on OMS-2 catalysts. Facile accessibility and a high concentration of lattice oxygen benefited the oxidation process. Mn-O bond of OMS-2 catalysts was a vital parameter that determined the catalytic performance for alcohol and aldehyde oxidation. Weaker Mn-O bond resulted in more lattice defects and labile lattice oxygen and, hence, better performance.Acetaldehyde and formaldehyde, the intermediates of ethanol oxidation on OMS-2 catalysts, were directly oxidized to carbon dioxide, not via acetic acid. The reaction process seemed to involve: adsorption of ethanol on Lewis acid sites forming ethoxide species; hydrogen abstraction by lattice oxygen ions and reduction of Lewis acid sites; and a reoxidation process at Lewis acid sites by oxygen donors and the replenishment of lattice oxygen vacancies to complete the catalytic cycle.