Direct synthesis of H2O2 on model Pd surfaces

We experimental demonstrated that model catalysts in the form of ideal Pd surfaces, either single (100) and poly crystalline, are active for H2O2 direct synthesis at 15 degrees C and pressure in excess of 20 bars, in methanol. Activity scaled on the available surface is much larger than some of the best powder catalyst suggested so far (Pd-Au on sulphated zirconia). The surface with a long range order, i.e. single crystal Pd (100), was far more active that the corresponding polycristalline surface, suggesting an actual correlation between structure and reactivity, extremely relevant for performances. Prereduction treatments and corresponding X-ray photoelectron spectrocopy of the surfaces confirmed the presence of surface oxidized specie, whose structure appear to be related to the underlying Pd texture. These results, well validated, open new perspectives for an effective catalyst design, taking surface science speculations, based on either ultra high vacuum experiments in the gas phase and DFT calculations, closer to an experimental validation. This contribution goes well beyond the investigation of the H2O2 direct synthesis mechanism. (C) 2012 Elsevier B.V. All rights reserved.