Exploring the Promotional Effects of K, Sr, and Mg on the Catalytic Stability of Red Mud for the Synthesis of Glycerol Carbonate from Renewable Glycerol

The focus of this study was to utilize red mud (RM), an aluminum industry waste, for the preparation of various catalysts for the synthesis of glycerol carbonate (GC) from glycerol (GL). A series of catalysts were prepared by doping potassium, strontium, and magnesium on the surface of RM, and their effect on the stability of RM based catalysts was examined. From preliminary studies, K-doped RM catalysts were found to have better activity as well as stability than the Sr- and Mg-doped RM catalysts for the transesterification of GL. The RK-30%-800 catalyst prepared by 30% K loading and calcination at 800 °C produced the highest activity and stability compared to other K-doped catalysts. The better activity of the RK-30% catalyst was due to the presence of the maximum surface concentration of active K₂O, which was confirmed from the XRD analysis. The surface concentration of K₂O contributed significantly to the increased basic properties of the catalyst, which was quite evident from the acid–base titration, CO₂-temperature programmed desorption (CO₂-TPD), and Hammett indicator test. A probable mechanism of the GL transesterification process by using the RK-30%-800 catalyst was proposed. Moreover, effect of the presence of impurities on the catalytic activity, the reaction kinetics, reusability study, and deactivation mechanism were studied in detail here.