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The in situ combination of electrochemistry and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) has been used for the first time to investigate the surface structure sensitivity of asymmetric catalytic hydrogenation at single-crystal Pt electrodes. The adsorption and hydrogenation behavior of aqueous ethyl pyruvate (EP) at a range of modified and unmodified Pt{hkl} electrodes was measured both by cyclic voltammetry and by recording Raman spectra at hydrogen evolution potentials. Two primary surface intermediates were observed, including the previously reported half-hydrogenation state (HHS), formed by addition of a hydrogen atom to the keto carbonyl group, as well as a new species identified as intact chemisorbed EP bound in a μ2(C,O) configuration. The relative populations of these two species were sensitive to the Pt surface structure; whereas the μ2(C,O) EP adsorbate was dominant at pristine Pt{111} and Pt{100}, the HHS was only observed at these electrodes after the introduction of d...

The selectivity towards 1,4-butynediol hydrogenation of both a standard 5 wt % Pt on graphite supported catalyst and a biogenic Pt analogue is reported. In both cases, it is determined using cyclic voltammetry that step sites afford the greatest extent of hydrogenation and that deliberate blocking of such sites gives rise to significant selectivity in favor of the 1,4-butenediol product. For the 5 wt % Pt/graphite catalyst, irreversible adsorption of bismuth was used as the step site blocking agent. In the case of the biogenic Pt nanoparticles (NPs) synthesized within the bacterium Escherichia coli, residual molecular organic fragments, left over after chemical cleaning and subsequent separation from the bacterial support, were observed to have accumulated preferentially at defect sites. This phenomenon facilitated an increase in selectivity toward alkenic products of up to 1.4 during hydrogenation of the alkyne. When biogenic NPs of platinum supported upon bacterial biomass were also investigated, they too were found to be active and selective although selectivity toward 1,4-butenediol was optimized only after the particles were chemically cleaned and separated from the biomass. Bi-poisoned 5% Pt on graphite, although highly selective, gave half the reaction rate of the biogenic counterpart (20% and 45% conversion of starting material respectively after 2 h), but the latter exhibited less selectivity for butenediol (0.7 and 0.9 respectively). It is proposed therefore that such biogenic materials may potentially act in a similar manner to Lindlar-type catalysts, used extensively in organic synthesis for selective hydrogenation of alkynes, in which an additive partially poisons metal sites but without the associated hazards of toxic heavy metals such as lead being present.