Methanol Steam Reforming over Indium-Promoted Pt/Al₂O₃ Catalyst: Nature of the Active Surface

The surface state of the Pt/In2O3/Al2O3 catalyst coated onto a microchannel stainless steel reactor was investigated under working conditions using synchrotron-based ambient pressure photoelectron (APPES) and X-ray absorption near-edge structure (XANES) spectroscopies, combined with online mass spectrometry. The surface of the fresh catalyst consists of metallic Pt, In2O3, and Al2O3. Reduction under 0.2 mbar of H2 at 250°C leads to surface enhancement of Pt and partial reduction of In2O3, while Al2O3 remains unchanged. Reoxidation in O2 atmosphere stimulates surface segregation of In2O3 over Pt, accompanied by partial oxidation of Pt to PtOx. Based on these results a dynamic, gas-phase-dependent surface state is demonstrated. Under methanol steam reforming conditions, the surface state rapidly adapts under the reaction stream regardless of the pretreatment. However, correlation of gas phase with spectroscopic results under working conditions pointed out the beneficial effect of surface indium to reduce the CO selectivity. Finally, evidence of a distorted symmetry of Al sites on Pt/In2O3/Al2O3 catalyst compared to that of γ-Al2O3 is given. The findings obtained in the present study are of fundamental significance in understanding the relation between the surface state and the catalytic performance of a functional methanol reforming catalyst