| Ethylene oxide (EO) is produced by the partial oxidation of ethylene with atomic oxygen on supported Ag/alpha-Al2O 3 catalysts. Recent work has shed light on the mechanism of ethylene epoxidation. With knowledge of the mechanism, exploration of silver alloys was conducted in an effort to develop a catalyst with enhanced selectivity to EO. DFT-based computational studies were conducted and showed that a copper-silver alloy surface should be more selective to EO than pure silver. The results of the computational studies were validated by reactor studies. The reactor data clearly showed that supported Cu-Ag bimetallic catalysts were more selective to EO than supported silver catalysts over a wide range of ethylene and oxygen feed pressures and stoichiometries. In addition to being more selective to EO, the Cu-Ag bimetallic catalysts were also more active.; 3,4-Epoxy-1-butene (EpB) dosed onto the Ag(110) surface at 300 K ring-opens to form a stable surface oxametallacycle. Upon heating the surface, this oxametallacycle undergoes 1,2- and 1,4-ring closure reactions to form EpB and 2,5-DHF, respectively, identifying a heterogeneous reaction pathway for the formation of 2,5-DHF via EpB isomerization on silver. In an attempt to bridge the gap between UHV and applied catalysis, studies were conducted involving the scale-up of results obtained under UHV conditions to a heterogeneous process involving a supported silver catalyst. Reactor studies showed that 2,5-DHF could be formed directly from EpB on supported silver catalysts with low selectivity. The activity of the catalyst was limited, however, due to the build-up of an EpB-derived surface oligomer. It was found that running the reaction with an oxygen co-feed improved the process by preventing deactivation, allowing for stable activity, while also increasing the selectivity to the desired product, 2,5-DHF. In addition, the Cu-Ag bimetallic catalysts developed for selective ethylene epoxidation were also evaluated for the EpB isomerization process. It was found that the bimetallic catalysts were more active and selective to 2,5-DHF than pure silver catalysts, a result analogous to that observed for ethylene epoxidation.; These studies demonstrate the translation of fundamental experimental and theoretical results into advances in catalysis. |
