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 supported TiO2/γ-A12O3 photocatalyst has been prepared by γ-Al2O3 pellet-filled dielectric barrier discharges induced plasma CVD at atmospheric pressure and room temperature. The TiO2/γ-A12O3 photocatalyst exhibits higher photocatalytic activity than Degussa P25, and much higher photocatalytic activity than that prepared by thermal CVD.

At normal temperature and pressure, pulse corona plasma was used as a new method for the dehydrogenative coupling of methane in the absence of oxygen. The effects of voltage polarity and input energy on the dehydrogenative coupling of methane were investigated. The parameter “energy efficiency” was introduced to examine the coupling of the input energy and the dehydrogenative coupling of methane. The experimental results show that positive corona gives higher energy efficiency than negative corona. When the positive corona was chosen, C2 yield per pass was 31.6% and acetylene yield per pass was 30.1% with 44.6% methane conversion at an input energy density of 1788kJ/mol and a pulse repetition frequency of 66Hz. The function of input energy density towards methane conversion may be expressed as a formula of –ln (1-X) = k (P/F). In the range of input energy employed, C2 yield is proportional to input energy density, but energy efficiency drops off with increasing input energy density.

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.