Datensatz

Zusammenfassung

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 PtO_x. 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.