Partial oxidation of alkenes by a membrane catalyst utilizing fuel cell reactions

Abstract

Partial oxidation of ethylene with a gas-cell system were studied at 353 K. The gas-cell structure was [ C 2 H 4, H 2 O|(Pd- black+ VGCF)- anode|H 3 PO 4 /silica– wool|cathode|O 2] (VGCF: vapor growing carbon fiber). Addition of NO to O 2 stream at the cathode dramatically enhanced the oxidation rate of ethylene to MeCHO more than 10 times with high selectivities >95%. The enhancement of the formation rate of MeCHO was due to the acceleration of the electrochemical oxidation rate of Pd 0 to Pd 2+ at the anode by a strong oxidant of NO 2 produced from O 2 and NO. NO 2 was electrochemically reduced to H 2O and NO that functioned as a mediator over the graphite-cathode. When a membrane of carbon matrix holding H 3PO 4 was chosen instead of H 3PO 4/silica–wool, both H + and e − could conduct from anode to cathode side through the H 3PO 4/carbon matrix, self-short circuiting condition. The oxidation of C 2H 4 could perform with the self-shorted cell reactor excluded electric parts. Several carbon matrices were tested for the oxidation by the self-shorted cell and the suitable one was a sheet of (VGCF+AC+PTFE) (AC: active carbon) prepared by the hot-press method. This self-shorted gas-cell was more active than the cell system. In the case of propene oxidation, acetone was selectively produced with the self-shorted cell. Kinetic studies were carried out to get information for reaction mechanism of the alkene oxidation. The self-shorted cell works as a new type of membrane catalytic system for the oxidation of alkene [alkene|oxidation catalyst|mixed conductor of H + and e −|reduction catalyst|oxidant]. This membrane catalyst also functioned as a hydrogen permeation membrane.