Stochastic and dimensional analysis of high-pressure hydrogen adsorption via spillover on carbon supported catalyst

Carbon metal synergy in the form of hydrogen spillover can significantly increase the uptake of a carbon-based hydrogen storage material. The fundamental processes involved in hydrogen spillover are: adsorption of active hydrogen species, desorption of hydrogen species as molecular hydrogen, and surface diffusion of hydrogen species. The rates of these processes are suggested to be system dependent and it is not fully clear whether or when the hydrogen spillover process is a function of metal dispersion, metal particle size, metal loading, and metal-carbon interface. The hypothesis that hydrogen surface coverage will be determined by the competing rates of desorption vs. surface diffusion lends itself to a dimensional analysis of the spillover process. The dimensional analysis, combined with a kinetic Monte Carlo model, studied the effect of hydrogen pressure; relative activation energies of the processes involved; active metal and carbon surface area; and length of metal-support interface. These theoretically-grounded models facilitated optimization of hydrogen storage materials beyond a "trial and error" approach. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).