Kinetics of Hydrogen Absorption in Palladium/Kieselguhr Materials at Constant Flows

The hydrogen absorption kinetic behaviour of the Palladium/kieselguhr (Pd/K) composite materials activated in the range of 0.1–1 sccm · g−1, 263∼293 K and 20–100 kPa was determined by the constant-flow method, to establish a new gas-solid reaction rate equation at constant flows and reveal kinetic regularity. The results indicate that the hydrogen absorption process at constant flows can be divided into three stages, with rate constants following kII < k < kIII. The nucleation and growth processes regulate all three stages of constantflow hydrogen absorption, and the corresponding kinetic rate equations are denoted as follows [−ln(1−ξ)]r = kt(rI = 2/5, rII = 1, rIII = 1/2), which it can be obtained that the changes of hydrogenation flows, temperature and initial hydrogen pressure have no effect on the hydrogen absorption kinetic regularity, but only on the hydrogen absorption rate. In the same hydrogen absorption stage, the hydrogen absorption rate increases with increasing hydrogenation flows and initial hydrogen pressure, and decreases with increasing temperature in the selected temperature range. The mechanism of hydrogen absorption reaction at different temperatures is the identical, the Arrhenius relationship is met between the reaction rate constants and temperatures, and the activation energies of the three stages are 12.9 kJ/mol, 36.5 kJ/mol and 9.0 kJ/mol respectively.