Design of Solid Base Catalysts from the Steal-Slag Materials

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The blast furnace slag (BFS) resulting from iron-making processes, can be considered as a low-cost and abundant precursor for preparing layered double hydroxide (LDH) compounds. Here it has been demonstrated that a Ca-based LDH compound (hydrocalumite) synthesized from waste BFS through facile two-step procedures and its derivatives work as useful heterogeneous base catalysts for multiple chemical reactions including the Knoevenagel condensation, oxidation of alkylaromatics with O2, transesterification, and cycloaddition reaction of epoxides with atmospheric CO2. Structures were verified by using XRD and thermogravimetric analysis. The surface basicity and coordination geometry of the active metal specieswere investigated by CO2-temperature programmed desorption (TPD) and X-rayabsorption fine structure (XAFS) measurements. These characterization revealed that the slag-derived impurity elements, such as Fe, Ti, and Mn, effectively act eitheras active sites or as catalyst promoters in particular reactions and that the kind of guest counter anion (Cl- or NO3-) also plays a key role for achieving high catalytic efficiencies. It is believed that the slag-made hydrocalumite can replace existing LDH catalysts as a low-cost alternative and contribute to sustainable chemical processes.