Low temperature catalytic combustion of chlorobenzene over cobalt based mixed oxides derived from layered double hydroxides

Cobalt based mixed oxides were synthesized by a thermal treatment of layered double hydroxides (LDHs) with molar ratio of Co/M = 3 (M = Al, Fe, Cr) and characterized by various techniques such as XRD, N-2 sorption, H-2-TPR, O-2-TPD, NH3-TPD-MS and so on. The results indicated that the mixed oxides derived from LDHs possessed high specific surface area and uniform morphology. Meanwhile, the elements in the mixed oxides were homogenously dispersed. The addition of a second metal (Al, Fe or Cr) enhanced not only the acidity but also the basicity, moreover, Fe and Cr notably improved the reducibility at low temperature and the oxygen mobility of pristine Co3O4. The results of chlorobenzene catalytic combustion showed the addition of Cr or Fe promoted the apparent activity of pristine Co3O4 at low temperature and suppressed the formation of polychlorinated by-products. Among mixed oxides, CoCr catalyst possessed the highest activity and more obvious inhibition of dichlorobenzene formation, which was ascribed to its high redox ability, superior acidity and rapid removal of adsorbed inorganic chlorine species in the form of Cl-2. In addition, the CoCr catalyst showed high catalytic stability.