Electrochemical behaviour of Mn3+/Mn2+, Co3+/Co2+ and Ce4+/Ce4+ redox mediators in methanesulfonic acid

The redox behaviour of Mn³⁺/Mn²⁺, Co³⁺/Co²⁺ and Ce⁴⁺/Ce³⁺ mediators commonly used in indirect oxidation of organic compounds were evaluated in methane sulfonic acid on a glassy carbon working electrode employing cyclic voltammetry. Manganic methanesulfonate exhibits higher instability in dilute methanesulfonic acid. The solid MnO₂ formed during disproportionation on the glassy carbon electrode further affects the reproducibility. Cobaltic methanesulfonate formation occurs only at oxygen evolution region rendering the overall oxidation process less efficient. Ceric methane sulfonate formation is highly efficient over a wide acid concentration range. Ceric methanesulfonate can also be employed over a wide temperature range to oxidize different aromatic compounds.     

Partial Oxidation of Methane to Syngas over Calcined Ni–Mg/Al Layered Double Hydroxides

The catalytic partial oxidation of CH₄ to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH₄ into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl₂O₄ spinel phase had a positive effect on the stability of the catalyst.     

Methane Transport Capacity of Rice Plants. II. Variations Among Different Rice Cultivars and Relationship with Morphological Characteristics

Of the total methane (CH4) emitted from a rice field during the growing season 60–90% is emitted through the rice plants. We determined the methane transport capacity (MTC) of rice plants at different physiological growth stages using an automatic measuring system under greenhouse conditions. A total of 12 cultivars (10 inbred varieties and 2 hybrids) were studied in sets of two experiments and was distinguished into three groups according to the patterns of MTC development. MTC is generally increasing from seedling stage to panicle initiation (PI), but differs in the development from PI to maturity. While the hybrid showed a gradual increase in MTC, the inbred cultivars showed either minor changes in MTC or a drastic decrease from flowering to maturity. Among tall cultivars, Dular showed the highest MTC, followed by B40; the lowest MTC was found in Intan. High-yielding dwarf cultivars showed MTC in the descending order of IR72 > IR52 > IR64 > PSBRc 20. New plant type cultivars showed very low MTC with IR65600 exhibiting the smallest MTC at PI, flowering, and maturity. Hybrids (Magat and APHR 2) showed the largest MTC that continued to increased with plant growth. The MTC patterns were attributed to growth parameters and the development of morphological characteristics of the aerenchyma. These results suggest that in tall, dwarf, and NPT cultivars, increase in root or aboveground biomass during initial growth determines a corresponding increase in MTC. Once aerenchyma has fully developed, further increase in plant biomass would not influence MTC. However, in the case of hybrids, a positive relationship of MTC with root + shoot biomass (r = 0.672, p 0.05) and a total plant biomass including grain (r = 0.849, p 0.01) indicate continuous development of aerenchyma with plant growth, resulting in enhanced MTC. In all cultivars, tiller number, but not height, was linearly related to MTC, indicating that the number of outlets/channels rather than plant size/biomass determines the transport of CH₄. These results clearly demonstrate that rice cultivars differ significantly in MTC. Therefore, the use of high-yielding cultivars with low MTC (for example, PSBRc 20, IR65598, and IR65600) could be an economically feasible, environmentally sound, and promising approach to mitigate CH₄ emissions from rice fields.     

氧泵型催化膜反应器中甲烷氧化偶联反应(Ⅰ)——氧泵型催化膜的制备及其反应性能

本文采用1％Sr/La_2O_3-Ag-YSZ氧泵型催化膜反应器进行了甲烷氧化偶联反应研究。比较了不同制备方法的催化膜的反应性能,结果发现浸涂法(Ag-YSZ管随旋转轴转动涂制)制备的膜性能最佳。研究了操作条件对甲烷氧化偶联反应的影响。研究证明,传递氧与气相氧同时进料是一种较好的反应方式。结果表明,利用该反应器不仅可以简化分离过程,而且还可得到更高的C_2烃选择性。     

Catalytic Combustion of Methane over Rare Earth Stannate Pyrochlore

Well-defined Ln₂Sn₂O₇ powders (Ln = La, Sm and Gd) with a phase-pure pyrochlore structure were synthesized by hydrothermal reaction. The catalytic activities of Ln₂Sn₂O₇ powders for methane combustion were measured. Methane oxidation started at 500 °C and increased with oxidation temperature. Catalytic methane combustion is strongly influenced by the presence of oxygen vacancies that form by breaking Sn–O lattice bonds as the temperature increases. Addition of manganese to the rare earth pyrochlores improved methane oxidation activity. Manganese-doped samarium stannate pyrochlore (Sm₂Sn_1.8Mn_0.2O₇) shows highest the catalytic activity. Light-off and complete oxidation temperatures were measured at about 400 and 650 °C, respectively.     

我国甲烷氯化物产品成本核算规程的探讨

从核算规程修改的原理、原则及内容等方面对甲烷氯化物产品成本核算规程的修改、规范和完善情况进行了介绍。     

甲烷单加氧酶模型化合物的合成及性能测试

设计、合成了一个新的甲烷单加氧酶(MMO)模型化合物[Fe2(Ⅲ,Ⅲ)L(μ-OAc)2]·PF6,其中L为2,6-二{[(2-羟基-5-叔丁基-苄基)(吡啶-2-甲基)-氨基]-甲基}-4-甲基苯酚。与以往的模型体系[Fe2(Ⅱ,Ⅲ)(bpmp)(μ-OAc)2]·(BPh4)2相比,新模型增加了2个酚配体、2个叔丁基。这些基团的引入提高了中心金属Fe的价态,并增加了配体的电子云密度从而调节了Fe的氧化还原电位。该模型进一步缩小了人工模型体系与甲烷单加氧活性中心(MMOH)的差异。通过红外(IR)、电喷雾电离质谱(ESI-MS)、核磁共振NMR(gCOSY、gHMBC、gHSQC)及电化学对新配体及络合物进行了表征和测试。     

Scientific basis for establishing country greenhouse gas estimates for rice-based agriculture: An Indian case study

A comprehensive scientific assessment of CH₄ budget estimation for Indian rice paddies, based on a decade of measurements in India, is presented. Indian paddy cultivation areas contain soils that have low to medium levels of soil organic carbon. The average seasonally integrated CH₄ flux (E _sif) values calculated from these measurements were 15.3 ± 2.6 g m^–2 for continuously flooded (CF), 6.9 ± 4.3 g m^–2 for intermittently flooded (IF) single aeration (SA) and 2.2 ± 1.5 g m^–2 for IF multiple aeration (MA) rice ecosystems. For CF and IF (MA) rice ecosystems having high soil organic carbon, without organic amendments, the CH₄ flux (E _sif) may be increased by 1.7 times relative to low soil organic carbon, whereas it may enhance by 5.3 for CF if amended organically. Organic amendment and high soil organic carbon paddy areas do not alter the methane budget estimates for India (3.6±1.4 TgY^–1) much, due to their small paddy harvested area. Methane estimated using average emission factors (E _sif) for all paddy water regimes, which include harvested areas having soils with high organic carbon and organic amendments, may give a budget of 5 TgY^–1 for India.     

Adsorption properties of oxygen and methane on Ga-ZSM-5; the origin of the selectivity of NOx reduction using methane

The adsorption properties of oxygen and methane on Ga-ZSM-5 and Cu-ZSM-5 catalysts were examined by a TPD method to clarify the extraordinary selectivity of HC-SCR using methane on Ga-ZSM-5. It was observed that Ga-ZSM-5 did not adsorb oxygen but adsorbed methane dissociatively, while on Cu-ZSM-5 oxygen was dissociatively adsorbed and reacted with adsorbed ethylene.     

Reforming of methane with carbon dioxide over supported bimetallic catalysts containing Ni and noble metal: I. Characterization and activity of SiO2 supported Ni–Rh catalysts

Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70 nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800 m²/g), large pore volume (∼5 cm³/g), and an average pore diameter in the mesoporous regime (∼25 nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53 g CO per g-cat per hour. The catalysts were selective for the C₁₀₊ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C₉–C₁₅ hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support.