Mechanism and Kinetic Modeling of Hydrogenation in the Organic Getter/Palladium Catalyst/Activated Carbon Systems

Abstract

Experiments to measure the hydrogen uptake kinetics of DEB getter/Pd catalyst/activated carbon pellets have been performed under isothermal isobaric conditions. The extracted kinetics were then used to predict the performance of the getter pellets under different temperatures and pressures, including nonisobaric situations. For isothermal isobaric uptake at higher H2 pressure (666.6-2666.5 Pa), H2 solubility in the getter matrix is responsible for the uptake observed up to a 40-60% reacted fraction. Once the hydrogenated product becomes thicker, the diffusions of the reactants (atomic hydrogen and getter molecules) toward the reaction front become the rate limiting step. However, in a dynamic but very low H2 pressure, encountered in many vacuum electronic applications, the hydrogen spillover effect, over micrometer scale, becomes the dominant reaction mechanism. Despite such a complex dependence of the rate limiting mechanisms on the experimental environment, there is good agreement between kinetic prediction models and experiments. The investigation also reveals that the ultimate uptake capacity in the getter pellets scales inversely with the free volume of the vacuum vessel in which the DEB getter pellets are used, and that DEB getter pellets' performance greatly deteriorates during the final 10-15% capacity (as evidenced by the sharp bend in the slopes of the reacted fraction vs time curves at 85-90% reacted fraction).

Moisture outgassing from siloxane elastomers containing surface-treated-silica fillers

“…Further details on the methodology can be found elsewhere. 1,36 Once the kinetic parameters are estimated, the time for conversion (t n ) to reach a specific conversion level (α n ) at any isothermal temperature (T iso ) can be predicted as:…”

Concentrating Solar Power

“…158 Hydrogen getter materials include ZrCo 159,160 , 1,4diphenylbutadiyne (DPB) 161 and 1,4 bis(phenylethynyl)benzene (DEB). [162][163][164] Stronger understanding of hydrogen uptake mechanisms could lead to improved hydrogen getter performance in new materials, 165 and therefore higher performance and reliability in vacuum tube receivers.…”

Catalyst Surface Dispersion: Insights into Hydrogenation Kinetics and Mechanism

“…Therefore, unsaturated DEB molecules are expected to migrate toward the catalyst surface, ,, which enhances the hydrogenation rate. However, when the reaction is performed at low H 2 pressures (<2667 Pa), the consequent slower rate induces only low local temperature rise that is not sufficient for the DEB molecules to diffuse . In this study, although the initial pressure of each H 2 portion was 100 Torr (13332 Pa), the final H 2 pressure was as low as ∼2 Torr (267 Pa).…”

“…Moreover, since all the DEB-based composites in our study were subjected to the same hydrogenation conditions and characterized with the same composition (Table ), the potential effect of microscopic DEB mobility on the kinetics should be quite similar. Therefore, hydrogen atoms migration from the Pd catalyst surface to the DEB molecules (i.e., hydrogen spillover) becomes the dominant rate-determining reaction step …”