Exploring microemulsion-prepared lanthanum catalysts for natural gas valorisation

Abstract

Microemulsions were used to develop a catalyst with high selectivity towards ethylene and ethane while maintaining considerable methane (CH4) conversion. The use of this technique to produce lanthanum nanoparticles was studied under different conditions. Temperature was shown to have the most significant effect on the final material properties providing a minimum crystallite size at 25°C. The morphology observed for all the samples was flake or needle like materials containing nanocrystallites. To obtain the catalytically active materials a thermal treatment was needed and this was studied using in situ X-ray diffraction (XRD). This analysis demonstrated that the materials exhibited significant changes in phase and crystallite size when submitted to thermal treatment and these were shown to be difficult to control, meaning that the microemulsion synthesis method is a challenging route to produce La nanoparticles in a reproducible manner. The materials were tested for oxidative coupling of methane (OCM) and no correlation could be observed between the ‘as synthesised’ crystallite size and activity. However, the presence of La carbonates in the materials produced was deemed to be crucial to ensure an adequate OCM activity.