New Insight into the Electrocatalytic Hydrogenation of Model Unsaturated Organic Compounds

摘要

We present new results on the influence of C6H6 ads on the Hupp and anion adsorption on the Pt(111) electrode in aq. HCIO_4. The Pt(111) electrode is modified by an overlayer of C_6H_6 ads by its cycling in the 0.05-0.80 V potential range in aq. HCIO4 + 1 mM C_6H_6. The C_6H_(6 ads) overlayer significantly changes the Hupp and anion adsorption, and CV profiles show a sharp cathodic peak and an asymmetric anodic one in the 0.05-0.80 V potential range. The C_6H_(6 ad), layer blocks the perchlorate adsorption but facilitates the adsorption of one ML of Hupp which is embedded in the Pt(111) surface. Cycling of Pt(111) in the 0.40-1.25 V potential range in C6H6free aq. HCIO_4 results in complete oxidation of C_6H_(6 ad), to CO_2, which supports the notion that the overlayer of C_6H_(6ads) lies on the Pt(111) surface. Repetitive cycling of the C_6H_6nodified Pt(111) in C_6H_(6-free) aq. HClO_4 from 0.05 to 0.80 V results in a partial desorption of C_6H_6 and in a partial recovery of the CV profile characteristic of an unmodified Pt(111). The presence of an overlayer of C_6H_(6 ads) modifies the Pt(111)-H_(UPD) attractive interactions. The behavior described above in aq. HC10_4 is the same as in aq. H_2 SO_4. The behaviour of the Pt(110) and Pt(100) electrodes is somewhat similar to that of the Pt(111) electrode in H_2SO_4 but the strength of the bond between C_6 H_(6 ads), and the-Pt surface differs with the Miller index, increasing in the order Pt( 111), Pt(110), Pt(100). Hupp does not hydrogenate benzene on Pt(hkl) electrodes in aqueous acid.