Effect of the addition of rare earths on the activity of alumina supported copper cobaltite in CO oxidation, CH_4 oxidationand NO decomposition

The effect of the addition of small amounts of rare earths （Ln=La, Ce, Nd and Gd） to alumina supported copper-cobalt spinel oxide on the catalysts efficiency in CO and CH4 oxidation and in NO decomposition was investigated. Samples of Ln/CuCo/AI catalyst were prepared and characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, atomic absorption spectroscopy （AAS）, scanning electron mieroscopy-energy dispersive spectroscopy （SEM-EDS）, H2-temperature-programmed reduc- tion （H2-TPR）, electron paramagnetic resonanee （EPR） spectroscopy and low temperature nitrogen adsorption, The results showed that the addition of rare earths changed the surface state of the alumina supported copper-cobalt spinel catalyst. As a result, partial re- duction of copper species was observed as well as migration of these species between the surface and the bulk. The Ln/CuCo/A1 catalysts behaved differently in oxidation and reduction processes. In oxidation processes where oxide structure was important, Ce/CuCo/A1 and Nd/CuCo/A1 were the most active catalysts. The catalyst Ce/CuCo/AI was the most active in the oxidation reactions because of the availability and favorable surface distribution of the redox couples Cu＋/Cu2＋ and Ce3＋/Ce4＋. In NO decompostion, Ln-modified catalysts significantly improved the selectivity of the process to N2.

Promotional effects of samarium on Co_3O_4 spinel for CO and CH_4 oxidation

A series of CO3O4 spinel catalysts modified by Sm were prepared by co-precipitation method and tested for CH4 and CO oxidation. The addition of a small amount of Sm into Co3O4 led to an improvement in the catalytic activity for both reactions. Co0.98Sm0. 02 and Co0.95Sm0.05, the two samples with Co/Sm molar ratio of 0.98/0.02 and 0.95/0.05 in sequence, showed the similar and the highest activity for CH4 oxidation, with CH4 complete conversion at 450 ℃. In contrast, Coo.90Smo l0 was the most active sample for CO oxidation, with CO complete conversion at 120 ℃. The catalysts were characterized by techniques of N2 adsor- tion-desorption with Brunauer-Emmett-Teller technique （N2-BET）, X-ray powder diffraction （XRD）, thermal gravity analy- sis-differential scanning calorimetry （TGA-DSC）, Hz temperature programmed reduction （H2-TPR） and X-ray photoelectron spec- troscopy analysis （XPS）. Compared with pure Co3O4, for CO1-xSmx catalysts with 0.02≤x≤0.10, the addition of a small amount of Sm resulted in the formation of spinel Co3O4 and amorphous SmCoO3, hence increasing the number of Co3＋ and the active surface oxygen species, which was responsible for the improvement of the activity. C00.95Sm0.05 catalyst showed not only high thermal stability and activity but also good reaction durability in the presence of 5% water vapor for CH4 oxidation.

Straw Application Altered CH_4 Emission,Concentration and ^(13)C-Isotopic Signature of Dissolved CH_4 in a Rice Field

CH4 emission and the concentration of dissolved CH4 in soil solution and floodwater in a rice field and their stable carbon isotopic signatures as affected by straw application were investigated in 2009 in a field experiment at Jurong, Jiangsu Province, China. Straw application increased CH4 emission and CH4 concentration in the soil solution and floodwater. A positive seasonal correlation was also observed in the variation between CH4 flux and CH4 concentration in soil solution. The seasonal total CH4 emission （51.6 g CH4 m^-2） in Treatment WS （straw applied） was about 168% higher than that in Treatment CK （without straw）. The emitted CH4 and CH4 in soil solution were initially relatively enriched, then depleted and finally enriched again in 13C in both treatments, while CH4 in floodwater became isotopically heavier. The carbon isotopic signature of emitted CH4 and CH4 in floodwater averaged around -62%o and -45%0 for both treatments, respectively, and was not significantly influenced by the application of straw. However, straw application caused the CH4 in soil solution to be significantly depleted in lac during the middle of the rice season, and the mean δ13C value was lower in WS （-57.5‰） than in CK （-49.9‰）. Calculation from the isotopic data showed that straw application increased the fraction of CH4 oxidized, causing no significant difference in the δ13C value of the emitted CH4 between the two treatments.

Variations of Stable Carbon Isotopes of CH4 Emission from Three Typical Rice Fields in China

Little is known about the stable carbon isotopes of methane （CH4） emitted （δ13CH4elnitted） from permanently flooded rice fields and double rice-cropping fields. The CH4 emission and corresponding （δ13CH4emitted under various field managements （mulching, water regime, tillage, and nitrogen （N） fertilization） were simultaneously measured in three typical Chinese rice fields, a permanently flooded rice field in Ziyang City, Sichuan Province, Southwest China, a double-rice cropping field in Yingtan City, Jiangxi Province, Southeast China, and a rice-wheat rotation field in Jurong City, Jiangsu Province, East China, from 2010 to 2012. Results showed different seasonal variations of δ13CH4emitted among the three fields during the rice-growing season. The values of （δ13CH4emitted were negatively correlated with corresponding CH4 emissions in seasonal variation and mean, indicating the importance of CH4 production, oxidation, and transport associated with isotopic fractionation effects to the δ13CH4emitted. Seasonal variations of δ13CH4emltted were slightly impacted by mulching cultivation, tillage, and N application, but highly controlled by drainage. Meanwhile, tillage, N application, and especially mulching cultivation had important effects on seasonal mean CH4 emissions and corresponding δ13CH4emitted with low emissions accompanied by high values of δ13CH4emitted. Seasonal mean values of （δ13CH4emitted from the three fields were similar, mostly ranging from -60‰ to -50‰ which are well in agreement with previously published data. These demonstrated that seasonal variations of （δ13CH4emitted mainly depended on the changes in CH4 emission from rice fields and further indicated the important effects of methanogenic pathways, CH4 oxidation, and CH4 transport associated with isotope fractionation effects influenced by field managements on δ13CH4emitted.

Reforming of CH_4 with CO_2 over Co/Mg–Al oxide catalyst

A series of Co/Mg-Al oxide samples, CoMgAl-x （x = （Mg ＋ Co）]AI molar ratio of 1-5）, were prepared by the self-combustion method followed by H2 reduction. The catalytic performance and stability of the samples were studied in dry reforming ofCH4. XRD and H2-TPR characterization results showed that the reduced CoMgAl-x samples mainly consisted of solid solution and spinel phases with cobalt particles. The spinel phases contained COB04 and ConMgl-nAl204 （0 〈 n 〈 1 ） varying with the （Mg ＋ Co）/AI ratio, The effect of （Mg ＋ Co）/A1 molar ratio on the catalytic behavior was investigated in detail and CoMgAI-3 exhibited the highest catalytic activity and stability among the catalysts studied.

Effect of Structural Properties of Mesoporous Co3O4 Catalysts on Methane Combustion

Highly ordered 2D and 3D-Co3O4 catalysts were prepared using SBA-15 and KIT-6 as templates. Na- no-Co304 catalyst was obtained by calcination of cobalt nitrate as a comparison. The BET surface area of nano- CO304, 2D-Co3O4 and 3D-Co3O4 catalysts was 16.2, 63.9 and 75.1 mE/g, respectively. All the catalysts were tested for the total combustion of methane and their catalytic performance was in the order of 3D-Co3O4（T90=355℃）〉 2D-CoaO4（T90=383℃）〉nano-Co3O4（T90=455℃）. It was also found that the order of the areal specific reaction rates for the combustion of methane followed the same order of total activity. The characterization result demonstrates that enhanced catalytic performance of methane of the 2D-Co3O4 and 3D-Co3O4 catalysts is due to their pronounced reducibility and abundant active Co3O4 species, which was caused by the preferential exposure of {220} crystal planes in 3D-Co3O4 and 2D-Co3O4 catalysts compared to the nano-Co3O4.

Methanogenesis and Methanotrophy in Soil: A Review

Global warming, as a result of an increase in the mean temperature of the planet, might lead to catastrophic events for humanity. This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases （GHG） concentration. Water vapor, carbon dioxide （CO2）, methane （CH4） and nitrous oxide （N20） are the most important GHG, and human activities, such as industry, livestock and agriculture, contribute to the production of these gases. Methane, at an atmospheric concentration of 1.7 gmol tool-1 currently, is responsible for 16% of the global warming due to its relatively high global warming potential. Soils play an important role in the CH4 cycle as methanotrophy （oxidation of CH4） and methanogenesis （production of CH4） take place in them. Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG. The current knowledge of methanogenesis and methanotrophy in soils, anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.