Improving the catalytic performance of LaNiO3 perovskite by manganese substitution via ultrasonic spray pyrolysis for dry reforming of methane

Dry reforming of methane is an attractive process because it uses two important greenhouse gases, CO2 for CH4, to produce valuable syngas. However, Ni-based catalysts are prone to a high carbon deposition in the dry reforming process. Mesoporous LaNi1-xMnxO3 perovskite (with x between 0 and 1) were synthesized by ultrasonic spray pyrolysis method. The substitution of Mn in the perovskite structure increased the specific surface area (from 7.2 for LaNiO3 to 22.4 for LaNi0.4Mn0.6O3), the pore size and pore volume. Temperature programmed reduction showed a lower reduction tendency of Mn-substituted samples, suggesting high structural stability. O2temperature-programmed desorption showed significantly higher oxygen mobility as the result of partial Mn substitution. The Mn substitution improved the catalytic activity and stability, where LaNi0.6Mn0.4O3 achieved the highest conversion and remained relatively unchanged in the time on stream tests. The Mn substituted catalysts substantially decreased the carbon deposition and changed its form from whiskers to amorphous type. The XPS analysis suggests this change is due to the reversible transformation of Mn4+ and Mn3+, resulting in higher oxygen mobility. Microstructural characterization of the used catalyst revealed a lower sintering tendency for the Mn substituted catalysts than LaNiO3. Results suggest that Mn substitution significantly changed the catalytic mechanisms, where LaNiO3 removes carbon by forming La2O2CO3 intermediate, but the stable Mn substituted perovskite with high oxygen mobility and capacity removes the carbon through a cyclic redox mechanism.