Effect of Mg substitution on LaTi1-xMgxO3+delta catalysts for improving the C2 selectivity of the oxidative coupling of methane

This study investigated the effect of the partial substitution of Ti by Mg on the La2Ti2O7 perovskite-type structure towards improvements in the selective results of OCM reactions. The LaTi1-xMgxO3+delta catalysts were prepared with x = 0, 0.25 and 0.50 according to a polymer complexing method. XPS analysis showed a surface reconstruction with Mg addition, increasing the formation of oxygen vacancies in the interface formed by La-O-Mg and with an Mg-enriched surface compared to bulk compositions. DRIFTS results presented spectra more restricted to mono- and bidentate carbonate bands with the Mg load increasing, which significantly influence the OCM reaction. Differences in the M-O bonding force were demonstrated by XPS, FTIR, and Raman analysis, which result in the change of the catalyst basicity with the Mg addition. The M-O bond force constants (k) were calculated and showed a linear correlation with C2 selectivity. The catalytic results showed that methane conversion and C2 selectivity increased as a function of the Mg amount. Changes in the reaction conditions confirmed that both CH4/O-2 feed ratio and reaction temperature are important parameters for the OCM reaction. The best catalytic reaction conditions were WHSV = 30 000 mL g(cat)(-1) h(-1), CH4/O-2 = 8 and T = 800 degrees C for LaTi0.5Mg0.5O3 (LTMO-50) catalyst, which achieved 51.4% C2 selectivity. The catalyst remained thermally stable under such conditions even after 24 h of reaction, which has proven the advantage of Mg substitution in this catalyst structure. (AU)