Nanocrystalline anatase TiO2 has been successfully synthesized using TiCl4 and O2 as precursors by atmospheric cold plasmas generated by dielectric barrier discharges (DBD) without extra heating or thermal treatment. For the TiO2 powders synthesized by DBD plasma at an energy density of 5.9 k J۰ L-1, XRD and TEM analyses revealed that the nanocrystallite size is about 10–15 nm. Only a single crystalline structure of anatase was observed performing XRD, HRTEM and SAED measurements. It was found that the particle size decreased with increasing the discharge power, and that the chlorine contamination dramatically decreased when using high discharge power levels.

At atmospheric pressure and room temperature, dielectric barrier discharge induced plasma oxidation for achieving supported TiO2 photocatalysts derived from TiCl4 adsorbed onto γ-Al2O3 pellets was studied. The supported TiO2/γ-Al2O3 photocatalysts prepared by a cyclic ‘adsorption–discharge’ approach, without requirement of heat treatment, exhibit high activity in the photocatalytic degradation reaction of formaldehyde. The mass spectra and optical emission spectra during O2/Ar discharge for oxidizing the adsorbed-state TiCl4 were measured. The mechanism for the TiO2 formation from adsorbed-state TiCl4 by plasma oxidation was discussed.

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.

The oxidative dehydrogenation of ethane to ethylene and acetylene with carbon dioxide at ambient temperature and atmospheric pressure by pulse corona plasma over various catalysts has been investigated. The products included C2H4, C2H2 and syngas (H2 and CO). The conversion of ethane and distribution of products depend on the catalyst used, the C2H6/CO2 feed ratio, the energy density of plasma, etc. The rare earth metal oxides catalyst such as La2O3/γ-Al2O3 and CeO2/γ-Al2O3 enhance the conversion of ethane and the yield of ethylene and acetylene. The sequence of ethane conversion and yield of ethylene and acetylene is from CeO2/γ-Al2O3 to La2O3/γ-Al2O3. The metal catalyst Pd/γ-Al2O3 exhibits high ethylene selectivity. The optimum C2H6/CO2 ratio in the feed for oxidative dehydrogenation of ethane under plasma catalytic conditions is 1/1. The conversion of ethane and the yield of ethylene and acetylene increase with increasing of the energy density of plasma. © 2003 Elsevier B.V. All rights reserved.

A new bimetallic catalyst (Ag–Co/CeO2) was studied for simultaneously catalytic removal of NO and CO in the absence or presence of O2. CeO2 prepared by homogeneous precipitation method was optimized as supports for the active components. The addition of Ag on CeO2 greatly improved the catalytic activities in the lower temperature regions (≤300ºC), and the introduction of Co on CeO2 increased the activities at higher temperatures (≥250ºC). The bimetallic Ag–Co/CeO2 catalyst combined the advantages of the corresponding individual metal supported catalysts and showed superior activity due to the synergetic effect. The effect of support, temperature, loading amount, GHSV and oxygen on catalysis was investigated. NO and CO could be completely removed in the temperature range of 200–600ºC at a very high space velocity of 120 000 h-1. No deactivation was observed over 4% Ag–0.4% Co/CeO2 catalyst even after 50 h test. © 2006 Elsevier B.V. All rights reserved.

A process for a high yield of aromatics and co-produced hydrogen from the oxygen-free conversion of methane using a two-stage plasma-followed-by-catalyst (PFC) reactor at atmospheric pressure and low temperature is reported. Pure methane and a methane and hydrogen mixture as the feed gas for the two-stage PFC process were investigated, respectively. Using the methane and hydrogen mixture as the feed gas into the two-stage PFC reactor, Ni/HZSM-5 catalysts keep stable catalytic activity for a much longer on-stream time than that using pure methane as the feed gas. The maximum aromatic yield may be achieved using low Ni-loading Ni/HZSM-5 catalysts and at a suitable catalyst temperature.

Formaldehyde (HCHO) is a typical air pollutant capable of causing serious health disorders in human beings. This work reports plasma-catalytic oxidation of formaldehyde in gas streams via dielectric barrier discharges over Ag/CeO2 pellets at atmospheric pressure and 70◦C. With a feed gas mixture of 276 ppm HCHO, 21.0% O2, 1.0% H2O in N2, ～99% of formaldehyde can be effectively destructed with an 86% oxidative conversion into CO2 at GHSV of 16500 h−1 and input discharge energy density of 108 J l−1. At the same experimental conditions, the conversion percentages of HCHO to CO2 from pure plasma-induced oxidation (discharges over fused silica pellets) and from pure catalytic oxidation over Ag/CeO2 (without discharges) are 6% and 33% only. The above results and the CO plasma-catalytic oxidation experiments imply that the plasma-generated short-lived gas phase radicals, such as O and HO2, play important roles in the catalytic redox circles of Ag/CeO2 to oxidize HCHO and CO to CO2.

Methane conversion to C2 hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C2 products. Pulsed spark discharges gives the highest acetylene yield (54%) and H2 yield (51%) with 69% of methane conversion in a pure methane system and at 10 SCCM of flow rate and 12 Wof discharge power. In the two DBD processes, ethane is the major C2 products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H2 formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18–69%), 14–25, 35–65 and 10–17 eV/molecule; in pulsed streamer discharges (methane conversion 19–41%), 17–21, 38–59, and 12–19 eV/molecule; in pulsed DBD (methane conversion 6–13%), 38–57, 137–227 and 47–75 eV/molecule; in AC DBD (methane conversion 5–8%), 116–175, 446–637, and 151–205 eV/molecule, respectively. The immersion of the γ-Al2O3 pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C2 yield. © 2004 Elsevier B.V. All rights reserved.