Reaction of CO, CH2O, CH3OH on Zn-Modified Pt(111) Surfaces

In order to provide insight into how alloying Pt with Zn affects its reactivity for the steam reforming of methanol (SRM), the adsorption and reaction of CO, CH2O, and CH3OH on Zn-modified Pt(111) surfaces was investigated using a combination of X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS), and temperature-programmed desorption (TPD). The reactivity of PtZn near surface alloys were found to be similar to that of Pt(111) and have relatively low activity for methanol decomposition. In contrast, on Zn-modified Pt(111) surfaces where the Zn was present only as adatoms, methanol adsorbs dissociatively to form methoxide groups bound to both Pt and Zn sites. The Pt-bound methoxides are stable up to similar to 450 K at which point they undergo dehydrogenation to produce H-2 and CO, while those adsorbed on Zn sites undergo partial dehydrogenation at 300 K to produce formaldehyde which desorbs intact. These differences in the reactivity of the two types of surfaces studied suggest that Zn adatoms may play a role as active sites for the SRM reaction which is in agreement with studies of high surface area PtZn catalysts that indicate that excess surface Zn is required to obtain high selectivity to CO2 and H-2.