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.

Strong mass signals of H2− and D2− ions have been observed from low-pressure dielectric barrier discharge hydrogen and deuterium plasmas via molecular beam mass spectrometry. The observed H2−/H− and D2−/D− ratios (～0.35–0.4) are over five orders of magnitude higher than those observed by other techniques. The kinetic energy of H2− and D2− ions sampled from the plasmas was determined to be widely distributed, from a few eV to >100 eV, giving lifetimes greater than ∼40 μs for H2− and ∼55 μs for D2− . The highest vibrotational excitation of neutral H2 species in the plasma was determined to be about J = 0, v = 5 or J = 19, v = 0 via threshold ionization mass spectrometry. The possible pumping mechanisms for generating H2− with further high J, required by the current high-rotation model, have been proposed. Similar to the lifetime of D2− determined recently by another group, the H2− lifetime observed in this work is about two orders of magnitude longer than that predicted by the current theoretical model. To explain these experimental observations regarding the meta-stability of long-livedH2− andD2− ions, the improved current high-rotation model or other new models, including the possible existence of some long-lived electronically excited states of H2−/D2−, need to be developed.

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.

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.