At ambient temperature and pressure. C2H2 and H2 are the dominating products from pure methane conversion under corona discharge (PCD). When the energy density of 194-1788 kJ/mol was applied, 7%-30% of C2H2 yield and 6%-35% of H2 yield per pass have been obtained. These resuits are higher than the maximum thermodynamic yield of H2H2 (5.1%) and H2 (3.8%) at 100 kPa and 1100 K, respectively. Thereby, pulsed corona discharge is a very effective tool for “beyond-thermal-equilibrium” conversion of methane of C2H2 and H2 at ambient temperature and pressure. In the PCD energy density range of 339-822 kJ/mol, the carbon distribution of the methane conversion products is found to be: C2H2 86%-89%, C2H6 4%-6%, C2H4 4%-6%, C3～2%, C4～1%. Through comparison of the product from pure methane, ethane and ethylene conversion at the same discharge conditions, it can be concluded that three pathways may be responsible for the C2H2 formation via CH, radicals produced from the collisions of CH4 molecules with energized electrons in the PCD plasma: (i) C2H2 is formed directly from free radical reactions, (ii) C2H2 is formed through the dehydrogenation of C2H2, which is formed via free radical reactions primarily, and (iii) C2H6 is the primary product and then dehydrogenates to C2H4 (secondary product) and followed by C2H4 dehydrogenation to C2H2.

A pretreatment-transient reaction product analysis method was applied to study the reactions and average composition of the possible surface intermediate species in selective catalytic reduction with ethylene of NOx over Co-ZSM-5. The reactions of the surface species, formed by the pretreatment of Co-ZSM-5 in a NO/C2H4/O2 mixture at 275◦C, with the NO/O2 flow produced much more N2 than that with the individual NO or O2 flow. The similarity of N2/COx/H2O product distribution generated from the above surface species-NO/O2 reactions and that from the normal NO/C2H4/O2 flow reactions implies that the surface species NCaObHc formed in the three-component pretreatment process is very likely the primary intermediate surface species generated during the real flow reactions. The in situ FT-IR (DRIFT) spectroscopy measurements of the surface species support the above conclusion.

This article reports observations of significant synergistic effects between dielectric barrier discharge (DBD) plasmas and Cu-ZSM-5 catalysts for C2H4 selective reduction of NOx at 250◦C in the presence of excess oxygen by using a one-stage plasma-over-catalyst (POC) reactor. With a reactant gas mixture of 530 ppm NO, 650 ppm C2H4, 5.8% O2 in N2, GHSV=12 000 h−1 and input discharge energy density of 155 J L−1, the pure catalytic, pure plasma-induced (discharges over fused silica pellets) and plasma-catalytic (in the POC reactor) NOx conversion percentages are 39%, 1.5% and 79%, respectively. A moderate plasma enhancement of NOx reduction by C2H4 was also observed in a two-stage plasma-followed-by-catalyst (PFC) reactor consisting of a discharge stage filled by fused silica pellets and a Cu-ZSM-5 catalyst stage.

Formaldehyde is a major indoor air pollutant and can cause serious health disorders in residents. This work reports the removal of formaldehyde from gas streams via alumina-pellet-filled dielectric barrier discharge plasmas at atmospheric pressure and 70°C. With a feed gas mixture of 140 ppm HCHO, 21.0% O2, 1.0% H2O in N2, 92% of formaldehyde can be effectively destructed at GHSV (gas flow volume per hour per discharge volume) of 16 500 h−1 and Ein = 108 J l−1. An increase in the specific surface area of the alumina pellets enhances the HCHO removal, and this indicates that the adsorbed HCHO species may have a lower C–H bond breakage energy. Based on an examination of the influence of gas composition on the removal efficiency, the primary destruction pathways, besides the reactions initiated by discharge-generated radicals, such as O, H, OH and HO2, may include the consecutive dissociations of HCHO molecules and HCO radicals through their collisions with vibrationally- and electronically-excited metastable N2 species. The increase of O2 content in the inlet gas stream is able to diminish the CO production and to promote the formation of CO2 via O-atom or HO2-radical involved reactions.

A novel process consisting of a pulsed streamer discharge over Ni/HZSM-5 catalysts for an oxygen-free conversion of methane to aromatics is reported here. This plasma-over-catalyst process shows a significant synergetic effect on promoting methane conversion to aromatic products and high stability. Using this process at atmospheric pressure and a temperature of 573 K, significant amounts of aromatics have been obtained.