Sr2TiO4 Prepared Using Mechanochemical Activation: Influence of the Initial Compounds' Nature on Formation, Structural and Catalytic Properties in Oxidative Coupling of Methane

Methane oxidative coupling (OCM) is considered a potential direct route to produce C-2 hydrocarbons. Layered perovskite-like Sr2TiO4 is a promising OCM catalyst. Mechanochemical activation (MA) is known to be an environmentally friendly method for perovskite synthesis. Sr2TiO4 were synthesized using MA of the mixtures containing SrCO3 or SrO and TiO2 or TiO(OH)(2) and annealing at 900 and 1100 degrees C. XRD and FT-IRS showed that MA leads to the starting component disordering and formation of SrTiO3 only for SrO being pronounced when using TiO(OH)(2). After annealing at 900 degrees C, Sr2TiO4 was mainly produced from the mixtures of SrCO3 or SrO and TiO(OH)(2). The single-phase Sr2TiO4 was only obtained from MA products containing SrCO3 after calcination at 1100 degrees C. The surface enrichment with Sr was observed by XPS for all samples annealed at 1100 degrees C depending on the MA product composition. The OCM activity of the samples correlated with the surface Sr concentration and the ratio of the surface oxygen amount in SrO and perovskite (O-o/O-p). The maximal CH4 conversion and C-2 yield (25.6 and 15.5% at 900 degrees C, respectively), and the high long-term stability were observed for the sample obtained from (SrCO3 + TiO2), showing the specific surface morphology and optimal values of the surface Sr concentration and O-o/O-p ratio.