CO2 SEPARATION AND HYDROGEN STORAGE PROPERTIES OF ZEOLITES FOR CLEAN ENERGY APPLICATIONS
Matthew R. Hudson1,2, Wendy L. Queen2, Craig M. Brown2, Dustin W. Fickel3, Raul F. Lobo3
1National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, MD 20899
2Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742
3Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, DE 19716
Zeolite materials are one class of porous materials that are currently being explored for the future applications in hydrogen fuel storage, and in the reduction of environmentally harmful nitrogen oxides (NOx) and carbon dioxide (CO2) from the combustion of fossil fuels. These byproduct gases have been linked to the greenhouse effect, acid rain, and ozone layer depletion. Copper cation-exchanged zeolite SSZ-13 presents an interesting opportunity to study the mechanism of interaction of adsorbate gases with the ion-exchange sites in zeolites as there is only one type of copper cation site, in contrast to many zeolites. Further, the potential for selective adsorption based on the small pore size in Cu-SSZ-13 lends to investigation of the separation properties of the zeolite based on the type of gas adsorbed. On a fundamental level, the interaction of hydrogen (H2) with cation-exchanged zeolites can provide critical information on the relative binding strengths to the zeolite host, as well as how the host framework changes as a function of the quantity of gas adsorbed. We present a multifaceted approach to the study of H2 and CO2 adsorption in Cu-SSZ-13. Powder neutron diffraction was employed to locate each of the site specific binding sites for H2/CO2 as neutron diffraction is a particularly useful tool for the investigation of in situ H2 adsorption allowing for the accurate determination of the location of the adsorbed H2 relative to the zeolite host. Additionally, inelastic neutron scattering spectroscopy was further used to probe the relative energies of the adsorption sites and low pressure gas adsorption measurements were completed to determine how the total uptake compared with that of other cation-exchanged zeolites and to the non-exchanged zeolite framework.