(294g) Layered Double Hydroxide Derived Manganese Promoted Pt Catalysts for Propane Dehdyrogenation

The catalytic conversion of propane to propylene via dehydrogenation reaction is one of the highly efficient and selective processes. Among the different types of catalysts used in industries, Pt-Sn/K-Al₂O₃ is still the most prominent catalysts. The major drawback of the catalysts is lower stability and metal sintering. Over the years, tremendous efforts have been made to prepare highly stable and sintering resistant catalysts Pt based catalysts for the dehydrogenation reaction. To this end, this study aim at promiting Pt with manganese supported on layered double hydroxide derived mixed oxides of MgO-Al₂O₃. The catalysts were synthesized using galvanic replacement (GR) method to obtain highly dispersed Pt and improve the interaction with support. A series of catalysts were tested at different temperature and reaction conditions. The catalysts were characterized using different techniques including TPR, XRD, XPS, H₂-chemisorption, pyridine FTIR, CO-DRIFTS, in-situ DRIFTS and HRTEM.

The characterization techniques revealed that the higher Pt dispersion and the formation of Pt-Mn were achieved with Pt to Mn ratio of 5 and the catalysts showed 28% conversion and 96% selectivity at 550 °C with stability test performed for 12 hours of reaction and negligible rate of deactivation with 2 % coke deposition. The HRTEM of spent catalysts showed no metal sintering as the particle size remained similar to the freshly reduced catalysts. The CO-DRIFTS analysis revealed the formation of Pt ensembles on the Pt-Mn nanoparticles and the particle size decreased with promotion on manganese on the support. The kinetics and mechanism studies were performed for the best performing catalysts by varying reactant partial pressure and reaction temperature. The activation energy of Pt-Mn/LDH catalysts was 30% lower as compared to the Pt/LDH which supports the higher selectivity Mn promoted catalysts. Overall, this study shows the promoting effect of Mn on Pt using a novel galvanic replacement method.