Platinum (410), a face with unusual activity for the breaking of N-O and C-O bonds

Abstract

Banholzer et al., Surface Sci. 128 (1983) 176, suggested that ideas, analogous to those proposed by Woodward and Hoffmann for reactions in organic systems might be useful in identifying especially promising catalysts structures for further study. This work shows that Pt(410) has sites with the right orbital symmetry to break NO and CO bonds. Recently X-ray photoemission spectroscopy (XPS), temperature programed desorption (TPD), auger electron spectroscopy (AES), and reflection adsorption infrared spectroscopy (RAIRS) studies were done to see if these sites do indeed have unusual properties for N-O and C-O bond breaking. XPS showed that NO dissociates upon adsorption on Pt(410) at room temperature. RAIRS indicates that there is however, a small fraction (≈ 20%) of the NO which molecularly adsorbs. TPD indicates that more than 90% of the NO which adsorbs dissociates before it desorbs. By comparison, the next most active face considered previously shows negligible dissociation at room temperature, and only 50% dissociation upon heating. Surprisingly however, nitrogen and oxygen bond energies inferred from flash desorption peak temperatures are lower on Pt(410), than on other less active faces (Pt(100), Pt(110)). CO was found to adsorb molecularly at room temperature. However, heating the layer to 500 K results in changes in the XPS spectra that are consistent with dissociation. No other platinum surface studied previously shows similar behavior. RAIRS indicates that initially the CO adsorbs in a linearly bound state. However, readsorption on a partially dissociated layer results in the formation of bridge bound CO. Clearly, then Pt(410) is unusually active. These results show that simple orbital symmetry arguments can be used to explain the relative activity of single crystal planes, and identify planes with potential for enhanced activity for study.