Improving Selectivity in 2-Butyne-1,4-diol Hydrogenation using Biogenic Pt Catalysts

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.