Experimental and theoretical investigation of Ce/Ti-doped LaMnO3 catalysts effect on catalytic oxidation rarefied CH4 for natural gas engine

Abstract

To mitigate the high greenhouse effect caused by methane emissions of natural gas engines, this study employed the citric acid complexation method to synthesize Ce/Ti-doped LaMnO₃ perovskite catalysts. Firstly, the properties of perovskite catalysts were investigated through several characterization techniques and activity evaluations. Secondly, density functional theory (DFT) calculations were performed to study the effects of Ce/Ti doping on perovskite unit cell properties and methane adsorption characteristics. Results indicate that Ce/Ti doping is conducive to enhancing the magnetic properties and attractive forces between particles, thereby improving the crystallinity and specific surface area of catalyst. Additionally, it enhances the oxygen migration rate, promotes the formation of low-temperature reduction active components and reduces the reduction temperature for the catalysts. When Ce/Ti are co-doped, the ratios of the surface-active elements Mn⁴⁺/Mn³⁺ and O⁻/O²⁻ on the catalyst reach their maximum values of 1.56 and 1.53, respectively. The co-doping also leads to the formation of alkaline sites such as Mn-O and Ti-O metal pairs, which facilitate the dehydrogenation oxidation of methane. Ce/Ti-co-doped LaMnO₃ perovskite exhibits the optimal low-temperature oxidation activity towards methane, with an ignition temperature reduced to 269 °C and complete methane conversion at 479 °C. Ce/Ti doping enhances the adsorption behavior of methane on catalyst surface, with the adsorption energy of −5.4361eV. Meanwhile, Ce/Ti doping results in a significant transfer of electrons from H₁ atoms of methane to Mn atoms and increases the charge directivity of the surface-active atoms of catalysts, and in turn, it leads to higher catalytic performance and structural stability.