Effect of support and second metal in catalytic in-situ generation of hydrogen peroxide by Pd-supported catalysts: application in the removal of organic pollutants by means of the Fenton process

A catalytic system for the generation of H₂O₂ from formic acid and oxygen at ambient conditions has been developed. Pd-supported catalysts (Pd/C, Pd/TiO₂ and Pd/Al₂O₃) have been tested, showing that for bulk purposes Pd/Al₂O₃ is more favourable while for in-situ applications Pd/TiO₂ seems to be preferable. However, when these catalysts were tested in the in-situ H₂O₂ generation for the oxidation of phenol by means of the Fenton process (in the presence of ferrous ion), Pd/TiO₂ did not demonstrate the expected results, whereas Pd/Al₂O₃ showed to be an efficient catalyst. Therefore, Pd/Al₂O₃ is offered as a good catalyst for Fenton's reactions with in-situ generated H₂O₂. In order to optimize the operating cost of the process, different initial concentrations of formic acid have been tested with Pd/Al₂O₃, and it has been seen that lowering the initial amount of formic acid favours the efficiency of the process. The effect of the addition of a second metallic (Pt, Au, Fe, Cu) active phase was studied. Concerning H₂O₂ generation, best results were obtained with a Pd-Au catalyst for bulk production (long time) while for in-situ application Pd-Fe showed interesting results. The Pd-Fe catalyst also performed similarly to the semi-heterogeneous Fenton system involving Pd/Al₂O₃ and ferrous ion in the degradation of phenol. Therefore, Pd-Fe catalyst offered an interesting prospect for making a full heterogeneous catalyst for Fenton reaction involving in-situ generation of H₂O₂