Hydrogen Adsorption by the Spillover Mechanism on Carbon-Based Adsorbents: Capacity and Kinetic Studies Using Isotopic Tracer Reactions

We present results for hydrogen adsorption by spillover of hydrogen atoms from a metallic dissociation source to several carbon-based receptors, namely carbon synthesized from a molecular sieve template and a metal-organic framework. Hydrogen capacity enhancement by adsorption of hydrogen via the spillover phenomenon is reported for room temperature and from ambient pressure to 100 atm, where these materials are expected to find most widespread practical application.

We present kinetic response of such adsorbents for both hydrogen and deuterium. A unique feature of such studies is that desorption is consistently faster than adsorption at room temperature. Temperature programmed desorption studies were performed after sequential dosing of these species. Analysis of product distributions consistently yielded deuterium hydride, a strong indicator of spillover. The sequence of products was dependent on the dosing sequence, with HD always occupying an intermediate position.

We have further explored the difference in adsorption and desorption kinetics with HD in reverse reaction to form molecular hydrogen and deuterium. Based on these studies, we have found evidence that supports the theory of recombination of D atoms to form molecular deuterium, which prematurely desorbs from the carbon receptor and accounts for the apparent increase in reverse spillover kinetics.