Emission of organic carbon, elemental carbon and water-soluble ions from crop straw burning under flaming and smoldering conditions

Emissions from major agricultural residues were measured using a self-designed combustion system. Emission factors （EFs） of organic carbon （OC）, elemental carbon （EC）, and water-soluble ions （WSIs） （K＋, NH4＋, Na＋, Mg2＋, Ca2＋, Cl-, NO3-, SO42–） in smoke from wheat and rice straw were measured under flaming and smoldering conditions. The OC1/TC （total carbon） was highest （45.8% flaming, 57.7% smoldering） among carbon fractions. The mean EFs for OC （EFOC） and EC （EFEC） were 9.2 ± 3.9 and 2.2 ± 0.7 g/kg for wheat straw and 6.4 ± 1.9 and 1.1 ± 0.3 g/kg for rice straw under flaming conditions, while they were 40.8 ± 5.6 and 5.8 ± 1.0 g/kg and 37.6 ± 6.3 and 5.0 ± 1.4 g/kg under smoldering conditions, respectively. Higher EC ratios were observed in particulate matter （PM） mass under flaming conditions. The OC and EC for the two combustion patterns were significantly correlated （p 〈 0.01, R = 0.95 for wheat straw; p 〈 0.01, R = 0.97 for rice straw）, and a higher positive correlation between OC3 and EC was observed under both combustion conditions. WSIs emitted from flaming smoke were dominated by Cl- and K＋, which contributed 3.4% and 2.4% of the PM mass for rice straw and 2.2% and 1.0% for wheat straw, respectively. The EFs of Cl- and K＋ were 0.73 ± 0.16 and 0.51 ± 0.14 g/kg for wheat straw and 0.25 ± 0.15 and 0.12 ± 0.05 g/kg for rice straw under flaming conditions, while they were 0.42 ± 0.28 and 0.12 ± 0.06 g/kg and 0.30 ± 0.27 and 0.05 ± 0.03 g/kg under smoldering conditions, respectively. Na＋, Mg2＋, and NH4＋ were vital components in PM, comprising from 0.8% （smoldering） to 3.1% （flaming） of the mass. Strong correlations of Cl- with K＋, NH4＋, and Na＋ ions were observed in rice straw and the calculated diagnostic ratios of OC/EC, K＋/Na＋ and Cl-/Na＋ could be useful to distinguishing crop straw burning from other sources of atmospheric pollution.

Preparation of 3D micro/nanostructured CeO2： Influence of organic/inorganic acids

CeO2 is an important porous material with a wide range of applications in the abatement of volatile organic compounds （VOCs）. In this paper, we prepared a series of novel three-dimensional （3D） micro/nanostructured CeO2 materials via a solvothermal method. Organic acid-assisted synthesis and inorganic acid post-treatment were used to adjust the Ce02 microstructures. The size of the 3D micro/nanostructures could be controlled in the range from 180nm to 1.5 μm and the surface morphology changed from rough to smooth with the use of different organic acids. The CeO2 synthesized with acetic acid featured a hierarchical porosity and showed good performance for toluene catalytic combustion： a T50 of 187 ℃ and a T90 of 195 ℃. Moreover, the crystallite size, textural properties, and surface chemical states could be tuned by inorganic acid modification. After treatment with HNO3, the modified CeO2 materials exhibited improved catalytic activity, with a T50 of-175 ℃ and a T90 of -187 ℃. We concluded that the toluene combustion activity is related to the porosity and the amount of surface active oxygen of the CeO2. Both these features can be tuned by the co-work of organic and inorganic acids.

Catalytic oxidation of carbon monoxide, toluene, and ethyl acetate over the xPd/OMS-2 catalysts： Effect of Pd loading

The Pd catalyst supported on cryptomelanetype manganese oxide octahedral molecular sieve （OMS- 2） were prepared. The effect of Pd loading on the catalytic oxidation of carbon monoxide, toluene, and ethyl acetate over xPd/OMS-2 has been investigated. The results show that the Pd loading plays an important role on the physicochemical properties of the xPd/OMS-2 catalysts which outperform the Pd-free counterpart with the 0.5Pd/ OMS-2 catalyst being the best. The temperature for 50% conversion was 25, 240 and 160 ℃, and the temperature for 90% conversion was 55,285 and 200 ℃ for oxidation of CO, toluene, and ethyl acetate, respectively. The low- temperature reducibility and high oxygen mobility ofxPd/ OMS-2 are the factors contributable to the excellent catalytic performance of 0.5Pd/OMS-2.

Cu–Mn–Ce ternary mixed-oxide catalysts for catalytic combustion of toluene

Cu-Mn, Cu-Mn-Ce, and Cu-Ce mixed-oxide catalysts were prepared by a citric acid sol-gel method and then characterized by XRD, BET, H_2-TPR and XPS analyses. Their catalytic properties were investigated in the toluene combustion reaction. Results showed that the Cu-Mn-Ce ternary mixed-oxide catalyst with 1：2：4 mole ratios had the highest catalytic activity, and 99% toluene conversion was achieved at temperatures below 220°C. In the Cu-Mn-Ce catalyst, a portion of Cu and Mn species entered into the Ce O2 fluorite lattice, which led to the formation of a ceria-based solid solution. Excess Cu and Mn oxides existed on the surface of the ceria-based solid solution. The coexistence of Cu-Mn mixed oxides and the ceria-based solid solution resulted in a better synergetic interaction than the Cu-Mn and Cu-Ce catalysts, which promoted catalyst reducibility, increased oxygen mobility, and enhanced the formation of abundant active oxygen species.