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 (1O2) 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 1O2 produced in heterogeneous media was evaluated by comparison with 1O2 yields determined in homogeneous solutions of sodium molybdate. On the other hand, the 1O2 yields determined by CL spectroscopy were compared with those obtained via chemical trapping of 1O2 with β-citronellol as an olefinic substrate. Advantages and limitations of CL spectroscopy for the determination of 1O2 yields in heterogeneous media are discussed. CL spectroscopy allows the rapid screening of heterogeneous catalysts for the generation of 1O2. On the other hand, the spectroscopic technique only yields the total amount of 1O2 and provides no information on the availability of the produced 1O2 for reaction with olefinic substrates. In the second part, CL and CT experiments were used to determine optimized conditions for the generation of 1O2 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.