Mechanism of Epoxidation of Propylene with H2/O2 Mixtures

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

PROPOSAL NUMBER: 0651238 PRINCIPAL INVESTIGATOR: Oyama, S. Ted INSTITUTION: Virginia Polytechnic Institute and State University Scientific Merit. The epoxidation reaction of propylene with gas-phase hydrogen and oxygen mixtures is of considerable importance as a possible replacement for current processes employing hydrogen peroxide or organic peroxides. Although the reaction is of commercial significance, the mechanism by which it operates has not been clarified, and a deeper understanding will lead to improved catalysts. Existing catalysts consists of nano-sized gold particles dispersed on a titanosilicate support. The oxidant mixture of oxygen and hydrogen is believed to form hydrogen peroxide on the gold particles, which then migrates to titanium centers to form hydroperoxides, which are responsible for the epoxidation reaction. We plan to study this catalytic system using several in situ techniques, including ultraviolet-visible (UV-vis) absorption spectroscopy, laser Raman spectroscopy (LRS), Fourier transform infrared spectroscopy (FTIR), and extended and near-edge x-ray absorption spectroscopy (EXAFS, XANES) to study the structure and function of working catalysts so as to obtain insight on the mechanism by which they operate. The studies will be supported by ab initio Hartree-Fock calculations to describe active sites and adsorbates. Study of the catalysts at reaction conditions using in situ UV-vis and LRS will give information about the hydroperoxide adsorbed intermediate and the nature of the ratedetermining step (rds). FTIR will probe the nature of adsorbed organic moieties. The adsorbed intermediates will be studied using transient techniques to determine whether they respond to perturbations at a rate consistent with the overall rate of reaction, and thus, to establish whether they are reactive participants or merely spectators. In situ EXAFS will be used to study the coordination of the Ti centers, and in situ XANES will probe the oxidation state of the gold at reaction conditions. The best reported catalyst is gold supported on the microporous zeolite TS-1. Work will be carried out to improve the catalyst by creating mesoporous structures with TS-1 building blocks. The mesoporosity will give the reactants better access to the active sites, while the microporosity will protect the sites from deactivation by adsorption of products of reaction. The effect of the particle size of the gold will be studied by varying the pH of deposition. The catalysts will also be studied in a membrane reactor to allow the safe mixing of the hydrogen and oxygen components. The separate feed of these reactants will allow the use of concentrations within the explosive regime, without the danger of detonation. The higher levels of hydrogen and oxygen should lead to higher rates. Broader Impact. The proposed project has broad aspects of benefit to society. First, the research will not only advance understanding of the epoxidation reaction, but will also develop general techniques for use in other systems to study catalysts in their working state. Second, the project has a strong international component, as part of the research will involve use of facilities at a National Institute in Japan (Advanced Industrial Science and Technology-AIST). Funds for living costs for the PI and students have already been approved from the Institute. Third, the project will have an emphasis in the training and education of minority and women students. In the past our laboratory has successfully recruited members from underrepresented groups and this will be continued. Fourth, a substantive collaboration will be initiated with a faculty member from a local undergraduate school (Radford Univ.) to promote personal growth of the individual, as well as to stimulate the participation of students from that school in higher education.