An investigative study of surface interaction and reaction on (2x1)platinum(110).

摘要

While investigating surface interaction and reaction on (2 x 1)Pt(110), two new methods are developed that can be extended to studies on other surfaces. First, by combining electron energy loss spectroscopy (EELS) and ab initio quantum mechanical computation, monomeric behavior, intermolecular interaction, and surface-adsorbate interaction of H2O/H3O + on (2 x 1)Pt(110) are studied. It is found that each H3O + is directly hydrogen bonded to approximately 2 H2O monomers. About 25% of all oxygen containing species are H3O+, giving the adsorbed layer a pH of --1.1.;The same methods are used on H + CH3OH on (2 x 1)Pt(110). EELS spectra (both on and off spectral axis) suggest methoxonium (CH3OH2+) formation. Ab initio calculations confirm this suggestion. This is the first time a carbocation is observed on a metal surface. Since methoxonium is a reactive intermediate for acid catalyzed methanol dehydration, this study also opens a way for the study of acid-base reactions on metal surfaces in the future.;The second method developed is the ultraviolet high resolution electron energy loss spectroscopy (UV/HREELS). This method enables collection of electronic transition of adsorbed species for the first time. Combined with conventional EELS, identification of adsorbed species becomes more direct, and surface-adsorbate interaction is clarified. Using both EELS and UV/HREELS to study benzene on (2 x 1)Pt(110), it is found that chemisorbed benzene is in the form of a cyclohexadiene, most likely the conjugated 1,3 cyclohexadiene. Meanwhile, condensed benzene retains its identity. UV/HREELS spectra of condensed benzene are almost identical to UV spectra of gas phase benzene, both in peak location and shape. This shows that UV/HREELS can produce high quality spectra. Indeed, it is to surface analysis as UVS is to gas phase studies.;Investigation of CO on (2 x 1)Pt(110) using both EELS and UV/HREELS shows that electronic transitions are shifted compared to those of gas phase. Careful analysis reveals that these shifts are caused by sigma-donation and pi-back donation between CO and the surface, confirming the Blyholder model, which has been a topic of debate since its conception in 1967.