Empirical Correlation of Equilibrium Separation Factors in the Pd−H₂/D₂ System with Temperature and Composition

Abstract

The range of available data on separation factors (α) in the palladium−hydrogen/deuterium system has been extended in this study using a thermal conductivity detector. The thermal conductivity detector employed a matched pair of glass-coated bead thermistors to measure the gas-phase composition of hydrogen isotope mixtures. Separation factors (α) were measured in the β-phase, over the temperature (T) and hydrogen mole fraction (x H) ranges T = 175 K to 389 K and x H = 0.195 to 0.785, respectively. These data were correlated with temperature (T) and hydrogen mole fraction in the palladium (x H) by α = exp[−0.27 + B(x H)(1000/T)0.75] and B(x H) = 0.5155 − 0.0569x H − 0.12x H 2, where B(x H) is an empirical function relating the dependence of the separation factor on composition.

Hydrodechlorination reactions of 2-chloro-1,1,1,2-tetrafluoroethane and chloroethane in H2 and D2 on Pd catalysts

“…This experimental observation can be qualitatively explained by considering the equilibrium isotope effect and the kinetic isotope effect affecting steps (4) and (9) in Scheme 1, by which the products CF 3 CFH 2 and CF 3 CFHD are formed. The Pd surface has a higher "affinity" towards H 2 than to D 2 because of an equilibrium isotope effect [51,52] resulting in K H 2 > K D 2 in step 4. Additionally, for step 9, the C-H (or C-D) bond formation step will be affected by a kinetic isotope effect, since the zero point energy of C-H bond is 1.1 kJ mol −1 higher than a C-D bond [53].…”