Low Temperature Production of Formaldehyde from Carbon Dioxide and Ethane by Plasma-Assisted Catalysis in a Ferroelectrically Moderated Dielectric Barrier Discharge Reactor

Plasma-assisted catalysis of the reaction between CO 2 and C 2 H 6 in a single-pass, ferroelectrically moderated dielectric barrier discharge reactor has been studied at near ambient temperature as a function of physicochemical and electrical reaction variables. The presence of small amounts of a vanadia/alumina catalyst dispersed on the BaTiO 3 ferroelectric markedly enhanced the production of formaldehyde, the focus of this work. A maximum HCOH selectivity of 11.4% (defined with respect to the number of ethane carbon atoms consumed) at ∼100% ethane conversion was achieved, the other products being CO, H 2 O, H 2, CH 4 and a small amount of C 3 H 8 . N 2 O was also an effective partial oxidant (HCOH selectivity 8.9%) whereas use of O 2 led to complete combustion, behavior that may be rationalized in terms of the electron impact excitation cross sections of the three oxidants. Control experiments with the coproducts CH 4 and C 3 H 8 showed that these species were not intermediates in HCOH formation from C 2 H 6 . Analysis of reactor performance as a function of discharge characteristics revealed that formaldehyde formation was strongly favored at low frequencies where the zero-current fraction of the duty cycle was greatest, the implication being that plasma processes also acted to destroy previously formed products. A tentative reaction mechanism is proposed that accounts for the broad features of formaldehyde production.