Structure Effects on Pyridine Hydrogenation over Pt(111) and Pt(100) Studied with Sum Frequency Generation Vibrational Spectroscopy

Sum frequency generation vibrational spectroscopy was applied in-situ during pyridine hydrogenation (10 Torr pyridine and 100 Torr hydrogen) over two well-defined platinum single crystals, Pt(100) and Pt(111). The surface reaction intermediates were clarified. Pyridine adsorbs to both crystals vertically, with in-tact aromatic ring. Over Pt(100) 1,4-dihydropyridine bound through the nitrogen was observed as a reaction intermediate, while over Pt(111) this was not detected. Upon heating the crystals from 300 to 350 K, the pyridine ring lies down flat on the catalyst surfaces. Over Pt(111) a tilted piperidine product is bound to the surface. Ring-cracking products were not observed over either surface.