HYDROFORMYLATION OF ETHYLENE VIA SPONTANEOUS CELL REACTIONS IN THE GAS-PHASE

A new method for the hydroformylation of ethylene using a gas cell com posed of (C2H4, CO, cathode \H3PO4 aq.\ anode(Pt-black), H-2) has been examined at ca. 373 K and atmospheric pressure. Among many cathode el ectrocatalysts tested, H2PtCl6 showed the highest selectivity and high activity for the formation of C2H5CHO. However, H2PtCl6 did not catal yze the reaction at all under a gas mixture of C2H4, CO, and H-2. H2Pt Cl6 was specifically active for the electrocatalytic hydroformylation by separating H-2 from C2H4 and CO with a H3PO4-electrolyte membrane. The addition of Na3PO4 to the cathode enhanced the rate of C2H5CHO for mation as well as the selectivity. The cell reaction does not require electrical energy input but takes place spontaneously and most efficie ntly under short-circuit conditions. The results from kinetic and elec trochemical studies have suggested that the catalytic active species i s the Pt2+-chloride supported on the host graphite. A stronger coordin ation of CO compared to those of C2H4 and hydride reduces both the hyd rogenation and hydroformylation of C2H4. Therefore, a low partial pres sure of CO and higher partial pressures of C2H4 and H-2 are recommende d for the conversion of C2H4. The optimum temperature for the hydrofor mylation was 373 K. The results of transition response experiments hav e suggested a rapid reversible coordination of C2H4 but a slow convers ion of the precursor of C2H5CHO on the Pt2+ sites. A tentative reactio n mechanism assuming the formations of ethyl-carbonyl, ethyl-carbonyl hydride and acyl-carbonyl Pt complexes has been proposed on the bases of the results in this work. (C) 1997 Academic Press