Hydrogen-Deuterium Equilibration Reaction over Platinum Supported on Polyamide-6

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Abstract
Catalysis by platinum supported on polyamide-6 was examined for the H2-D2 equilibration reaction at 0 °C in the pressure range of 5–20 Torr (1 Torr=133.3 Pa). Three kinds of polyamides with different molecular weights were prepared as support; the concentration of platinum varied from 0.5 to 2.7 wt%. With preadsorption of hydrogen at 0 °C, the rate of the reaction was found to increase up to 10 times as high as the original level. The rate km (HD molecule s−1Pt atom−1) showed a maximum, depending on surface area of the polyamides used, in the range 0.8–1.0 wt% of Pt content and its dependence on total pressure is represented by km=K1P⁄(1+K2√‾P)2 irrespective of Pt content. No significant isotope effect was observed at 0 °C. It was found that a linear relationship exists between the enhancement of km and the amount of hydrogen preadsorbed, indicating an important role of the preadsorbed hydrogen in activation of the catalysts. In contrast to km, the turn-over frequency kt (HD molecule s−1 site−1) was nearly independent of Pt concentration. The exchange reaction is explained in terms of the Bonhoeffer-Farkas mechanism. XPS spectra provided the evidence for the presence of Pt(II) complexes on the surface. The structure of active sites is discussed.