Lanthanum-doped zinc hydroxycarbonates for the catalytic disproportionation of hydrogen peroxide into singlet oxygen

Lanthanum-containing materials were obtained by coprecipitation of La3+ and Mg2+, Ca2+, or Zn2+ in the presence of sodium carbonate. All materials were tested in the disproportionation of hydrogen peroxide into singlet molecular oxygen (1O2). Whereas La supported on Mg or Ca hydroxycarbonate showed very low catalytic activity, La-doped zinc hydroxycarbonate was far more active, even without addition of a soluble base. This may be related to the high surface area and small crystal size of the Zn material and the high number of easily accessible basic sites. The catalytic performance of a series of La-containing Zn hydroxycarbonates with varying La/Zn ratios was strongly dependent on the composition; the highest catalytic activity was observed for materials having relatively small amounts of La. Structural characterization of the materials revealed that at low La content, the Zn–La coprecipitate can be considered a Zn hydroxycarbonate (hydrozincite) doped with a small amount of La. At higher La content, distinct La (hydroxy)carbonate phases are formed, which are less active in the disproportionation of H2O2. Filtrate tests demonstrated that the La-doped Zn hydroxycarbonate is a truly heterogeneous catalyst, allowing recycling of the catalyst. Finally, this material was used for the selective peroxidation of functionalized alkenes. After reduction of the hydroperoxides, the corresponding allylic alcohols were obtained in good chemical yield (>90%).