Molybdate-exchanged layered double hydroxides for the catalytic disproportionation of hydrogen peroxide into singlet oxygen:: Evaluation and improvements of 1O2 generation by combined chemiluminescence and trapping experiments

The generation of singlet molecular oxygen (O-1(2)) from H2O2 catalyzed by molybdate-exchanged layered double hydroxides (Mo-LDHs) was studied by chemiluminescence (CL) and chemical trapping (CT) experiments. In the first part, the utility of chemiluminescence spectroscopy to quantify the amount of O-1(2) produced in heterogeneous media was evaluated by comparison with O-1(2) yields determined in homogeneous solutions of sodium molybdate. On the other hand, the O-1(2) yields determined by CL spectroscopy were compared with those obtained via chemical trapping of O-1(2) with P-citronellol as an olefinic substrate. Advantages and limitations of CL spectroscopy for the determination of O-2 yields in heterogeneous media are discussed. CL spectroscopy allows the rapid screening of heterogeneous catalysts for the generation of O-1(2). On the other hand, the spectroscopic technique only yields the total amount of O-1(2) and provides no information on the availability of the produced (1)(2) for reaction with olefinic substrates. In the second part, CL and CT experiments were used to determine optimized conditions for the generation Of O-1(2) from Mo-LDHs. Compositional parameters of the catalyst and reaction conditions were varied. A Mo-LDH catalyst possessing a low Mg/Al molar ratio and a low Mo loading was identified as the optimum catalyst in terms of activity and efficiency. Methanol and N,N-dimethylformamide are the optimum solvents. (c) 2005 Elsevier B.V. All rights reserved.