Shuiliang Yao

Enhanced oxidation of naphthalene using plasma activation of TiO2/diatomite catalyst

Non-thermal plasma technology has great potential in reducing polycyclic aromatic hydrocarbons (PAHs) emission. But in plasma-alone process, various undesired by-products are produced, which causes secondary pollutions. Here, a dielectric barrier discharge (DBD) reactor has been developed for the oxidation of naphthalene over a TiO2/diatomite catalyst at low temperature. In comparison to plasma-alone process, the combination of plasma and TiO2/diatomite catalyst significantly enhanced naphthalene conversion (up to 40%) and COx selectivity (up to 92%), and substantially reduced the formation of aerosol (up to 90%) and secondary volatile organic compounds (up to near 100%). The mechanistic study suggested that the presence of the TiO2/diatomite catalyst intensified the electron energy in the DBD. Meantime, the energized electrons generated in the discharge activated TiO2, while the presence of ozone enhanced the activity of the TiO2/diatomite catalyst. This plasma-catalyst interaction led to the synergetic effect resulting from the combination of plasma and TiO2/diatomite catalyst, consequently enhanced the oxidation of naphthalene. Importantly, we have demonstrated the effectiveness of plasma to activate the photocatalyst for the deep oxidation of PAH without external heating, which is potentially valuable in the development of cost-effective gas cleaning process for the removal of PAHs in vehicle applications during cold start conditions.

Plasma-catalyst hybrid reactor with CeO 2 /γ-Al 2 O 3 for benzene decomposition with synergetic effect and nano particle by-product reduction

A dielectric barrier discharge (DBD) catalyst hybrid reactor with CeO2/γ-Al2O3 catalyst balls was investigated for benzene decomposition at atmospheric pressure and 30 °C. At an energy density of 37-40 J/L, benzene decomposition was as high as 92.5% when using the hybrid reactor with 5.0wt%CeO2/γ-Al2O3; while it was 10%-20% when using a normal DBD reactor without a catalyst. Benzene decomposition using the hybrid reactor was almost the same as that using an O3 catalyst reactor with the same CeO2/γ-Al2O3 catalyst, indicating that O3 plays a key role in the benzene decomposition. Fourier transform infrared spectroscopy analysis showed that O3 adsorption on CeO2/γ-Al2O3 promotes the production of adsorbed O2- and O22‒, which contribute benzene decomposition over heterogeneous catalysts. Nano particles as by-products (phenol and 1,4-benzoquinone) from benzene decomposition can be significantly reduced using the CeO2/γ-Al2O3 catalyst. H2O inhibits benzene decomposition; however, it improves CO2 selectivity. The deactivated CeO2/γ-Al2O3 catalyst can be regenerated by performing discharges at 100 °C and 192-204 J/L. The decomposition mechanism of benzene over CeO2/γ-Al2O3 catalyst was proposed.

Naphthalene Decomposition by Dielectric Barrier Discharges at Atmospheric Pressure

Naphthalene decomposition in O₂/N₂ gas mixture with different O₂ concentrations has been studied in a dielectric barrier discharge reactor at atmospheric pressure. O₂ played an important role in the decomposition of naphthalene, especially in the selectivities of CO and CO₂. There was an optimal naphthalene decomposition rate at an O₂ concentration of about 3%. The CO_x selectivity increased up to 83.3% gradually with the O₂ concentration increasing from 1% to 20%. Nanoparticles were found in the gas samples, concentrations of which can be reduced greatly through raising the O₂ concentration. The decomposition byproducts of naphthalene were obviously different under different O₂ concentrations. Some nitrogenous compounds reduced but some oxygenous compounds increased with increasing O₂ concentration. The mechanism of naphthalene decomposition was proposed as that naphthalene was first initiated by dehydrogenation and oxidation, and then followed by deep oxidation to CO and CO₂.

Mechanism of Decane Decomposition in a Pulsed Dielectric Barrier Discharge Reactor

Decane decomposition in Ar, N2, and O2/N2 gases was investigated using a pulsed dielectric barrier discharge reactor. The mechanism of decomposition was discussed on the basis of the products detected by gas chromatograph (GC) and GC-mass spectrometer techniques. Decane decomposition in Ar was initiated by dehydrogenation to form decane radicals, which were then dehydrogenated to yield decenes, lighter hydrocarbons. When O2 was present in the discharge space, decane radicals were oxidized to decanone, CO, and CO2. The oxidation mechanism of decane radicals to CO and CO2 was suggested due to the radical oxidation by O atoms and OH radicals. Nanoparticles were found in a size range of 5.5-160 nm. The sizes of the nanoparticles were different with the gas components due to the difference in the produced radicals in the discharge space. We proposed that the oxidation and nitridation of the decane led to the formation of the nanoparticles.

Promotion of graphitic carbon oxidation via stimulating CO2 desorption by calcium carbonate

Carbon oxidation has two stages, the first is the formation of surface oxides and the second is the gasification of the surface oxides to CO2. Calcium carbonate (CaCO3) was used to catalyze the gasification of the surface oxides. The catalytic effect of on graphite oxidation and its catalytic mechanism were studied by using thermogravimetric technique and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that characteristic temperature (T50) of graphite oxidation with CaCO3 was 946 K, 113 K lower than that of graphite only. DRIFTS analysis results show that surface oxides (adsorbed CO2 and carbonate CO32-) were formed on the graphite surface at a temperature above 473 K, carbonate products on graphite surface disappeared when CaCO3 was present; formation of CO32- on CaCO3 surface was confirmed, this CO32- may be more easily gasified into gaseous CO2. The kinetic analysis results showed that CaCO3 promoted graphite oxidation has an activation energy of 74.3 kJ mol-1, far lower than that of graphite (148 kJ mol-1).