(87d) Catalytic Oxidation of Methyl Bromide Fumigation Emissions

Methyl bromide (MeBr) is widely used for quarantine and pre-shipment (QPS) chamber fumigations. Typically, spent MeBr is released to the atmosphere where it is recognized to be a potent ozone depleting compound. While most agricultural uses of MeBr have been banned in the U. S. for this environmental concern, MeBr as a QPS fumigant has been granted a critical-use exemption under the Montreal Protocol because it is the only fumigant proven to achieve insect pest control at probit 9 mortality levels ( > 99.9986%). Preservation of the current critical-use exemption in the face of continuing regulatory scrutiny will require methods to destroy or capture and reuse spent MeBr. One option for destroying organic vapors is combustion. The temperature of combustion can be greatly lowered by employing suitable nano-structured catalysts. A goal of this research is to design a catalytic system for the elimination of atmospheric emissions of methyl bromide following QPS fumigation. A number of catalysts have been synthesized by wet impregnation (e.g., Pd/CeO₂-Al₂O₃) and core-shell self-assembly (e.g., Pd@CeO₂- Al₂O₃) for testing and determination of products and their yields. The results of catalyst performance so far indicate that Pt/CeO₂-Al₂O₃ and Pd/CeO₂-Al₂O₃ nanoparticles give > 92 % and > 97 % conversion of methyl bromide, respectively, at 350^oC and are superior to the core-shell catalysts. Hydrobromic acid is a product and the reaction requires O₂ but not moisture, indicating catalyzed oxidation, not hydrolysis. Catalyst activity is unchanged after at least three cycles. The results show promise in regard to the use of low temperature oxidation for the effective treatment of QPS emissions of MeBr.