Low Temperature Hydrocarbon Storage on Zeolite Beta: Effects of Precious Metal Loading, Si/Al Ratio, and Multicomponent Hydrocarbon Feed

Ryan  Zelinsky, University of Virginia

The characteristics of zeolite beta as a hydrocarbon trap were studied using a multicomponent hydrocarbon feed. The adsorption-desorption behavior effects of various precious metal loadings, Si/Al ratio, and competing adsorbents are presented in this work. Dodecane was selected to represent long chain n-hydrocarbons while ethylene was used to represent short chain olefins. Adsorption experiments, followed by temperature programmed oxidation (TPO) experiments were performed over H/BEA, Pt/BEA, and Pd/BEA. In addition, cold start experiments were performed over mixtures of H/BEA and Pt/Al₂O₃, demonstrating the effects of layering and mixing catalysts on hydrocarbon trap efficiency. Dodecane uptake was similar over zeolite beta with and without precious metal, while ethylene uptake was higher over Pd/BEA. Hydrocarbon desorption temperature was found to be coupled with the hydrocarbon oxidation properties of the catalyst when precious metals were present. Using various levels of ethylene uptake, we found that desorption temperature increased with increasing ethylene uptake, while oxidation activity decreased. For H/BEA, increased dodecane uptake was observed for a higher Si/Al ratio catalyst. During cold start tests, a layered geometry on a monolith was found to more effectively trap and convert hydrocarbons than a physical mixture of the two catalysts. The results of this work serve to highlight the effects of different hydrocarbon trap materials and help streamline future research efforts.