Query: CH4

title: Selective visible light driven photocatalytic CO2 reduction to CH4 mediated by atomically thin CuIn5S8 layers
abstract: Due to the large number of possible products and their similar reduction potentials, a significant challenge in CO2 photoreduction is achieving selectivity to a single product while maintaining high conversion efficiency. Controlling the reaction intermediates that form on the catalyst surface through careful catalyst design is therefore crucial. Here, we prepare atomically thin layers of sulfur deficient CuIn5S8 that contain charge enriched Cu In dual sites, which are highly selective towards photocatalytic production of CH4 from CO2. We propose that the formation of a highly stable Cu C O In intermediate at the Cu In dual sites is the key feature determining selectivity. We suggest that this configuration not only lowers the overall activation energy barrier, but also converts the endoergic protonation step to an exoergic reaction process, thus changing the reaction pathway to form CH4 instead of CO. As a result, the CuIn5S8 single unit cell layers achieve near 100% selectivity for visible light driven CO2 reduction to CH4 over CO, with a rate of 8.7 mmol g 1 h 1.Many different molecules can form during photocatalytic reduction of CO2, so identifying catalyst structure product selectivity relationships is vital. Here, the authors find that sulfur deficient CuIn5S8 is highly selective to CH4 and suggest that the presence of Cu In binding sites is key to this behaviour.

title: Large contribution to inland water CO2 and CH4 emissions from very small ponds
abstract: Very small ponds have been omitted from greenhouse gas budgets. Estimates of CO2 and CH4 emissions from 427 lakes and ponds show that very small ponds account for 15% of CO2 and 40% of diffusive CH4 emissions, but 8.6% of lake and pond area. Inland waters are an important component of the global carbon cycle. Although they contribute to greenhouse gas emissions1,2,3,4,5, estimates of carbon processing in these waters are uncertain. The global extent of very small ponds, with surface areas of less than 0.001 km2, is particularly difficult to map, resulting in their exclusion from greenhouse gas budget estimates. Here we combine estimates of the lake and pond global size distribution, gas exchange rates, and measurements of carbon dioxide and methane concentrations from 427 lakes and ponds ranging in surface area from 2.5 m2 to 674 km2. We estimate that non running inland waters release 0.583 Pg C yr 1. Very small ponds comprise 8.6% of lakes and ponds by area globally, but account for 15.1% of CO2 emissions and 40.6% of diffusive CH4 emissions. In terms of CO2 equivalence, the ratio of CO2 to CH4 flux increases with surface area, from about 1.5 in very small ponds to about 19 in large lakes. The high fluxes from very small ponds probably result from shallow waters, high sediment and edge to water volume ratios, and frequent mixing. These attributes increase CO2 and CH4 supersaturation in the water and limit efficient methane oxidation. We conclude that very small ponds represent an important inland water carbon flux.

title: Effect of organic type and moisture on CO2/CH4 competitive adsorption in kerogen with implications for CO2 sequestration and enhanced CH4 recovery
abstract: Although research attentions for CO2 injection in gas bearing reservoirs have been drawn to CO2 sequestration with enhanced gas recovery (CS EGR) the microscopic competitive adsorption mechanism of methane (CH4) and carbon dioxide (CO2) considering the effect of organic type and moisture remains to be determined. In this work, we focus on the competitive adsorption behaviors of CH4 and CO2 on dry and moist realistic kerogen models of different organic types by performing combined molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. The effects of organic type and moisture content on kerogen pore structures, moisture distribution and interaction between CH4/CO2 and kerogen surfaces are discussed in details. Simulation results show that CO2/CH4 adsorption capacity and adsorption selectivity are in the order of kerogen IA

title: Isolation of Cu Atoms in Pd Lattice: Forming Highly Selective Sites for Photocatalytic Conversion of CO2 to CH4.
abstract: Photocatalytic conversion of CO2 to CH4, a carbon neutral fuel, represents an appealing approach to remedy the current energy and environmental crisis; however, it suffers from the large production of CO and H2 by side reactions. The design of catalytic sites for CO2 adsorption and activation holds the key to address this grand challenge. In this Article, we develop highly selective sites for photocatalytic conversion of CO2 to CH4 by isolating Cu atoms in Pd lattice. According to our synchrotron radiation characterizations and theoretical simulations, the isolation of Cu atoms in Pd lattice can play dual roles in the enhancement of CO2 to CH4 conversion: (1) providing the paired Cu Pd sites for the enhanced CO2 adsorption and the suppressed H2 evolution; and (2) elevating the d band center of Cu sites for the improved CO2 activation. As a result, the Pd7Cu1 TiO2 photocatalyst achieves the high selectivity of 96% for CH4 production with a rate of 19.6 mmol gcat 1 h 1. This work provides fresh insights into the catalytic site design for selective photocatalytic CO2 conversion, and highlights the importance of catalyst lattice engineering at atomic precision to catalytic performance.

title: One Step Reforming of CO2 and CH4 into High Value Liquid Chemicals and Fuels at Room Temperature by Plasma Driven Catalysis
abstract: The conversion of CO2 with CH4 into liquid fuels and chemicals in a single step catalytic process that bypasses the production of syngas remains a challenge. In this study, liquid fuels and chemicals (e.g. acetic acid, methanol, ethanol, and formaldehyde) were synthesized in a one step process from CO2 and CH4 at room temperature (30 degC) and atmospheric pressure for the first time by using a novel plasma reactor with a water electrode. The total selectivity to oxygenates was approximately 50 60 with acetic acid being the major component at 40.2 selectivity, the highest value reported for acetic acid thus far. Interestingly, the direct plasma synthesis of acetic acid from CH4 and CO2 is an ideal reaction with 100 atom economy, but it is almost impossible by thermal catalysis owing to the significant thermodynamic barrier. The combination of plasma and catalyst in this process shows great potential for manipulating the distribution of liquid chemical products in a given process.

title: Selective photocatalytic reduction of CO2 into CH4 over Pt Cu2O TiO2 nanocrystals: The interaction between Pt and Cu2O cocatalysts
abstract: Photocatalytic reduction of CO2 with water is one of the most popular and challenging technologies to produce renewable energy. In this paper, Pt and Cu2O nanoparticles (NPs) were deposited on the surface of anatase TiO2 nanocrystals, and their effects on the photocatalytic performance of TiO2 were thoroughly studied. Based on experimental results, Pt tended to promote the production of CH4 and H2. However, Cu2O suppressed H2 production and exhibited lower CH4 selectivity than that of Pt. Furthermore, when Pt and Cu2O were co deposited on TiO2 crystals, H2 production was inhibited and CO2 was selectively converted into CH4. From characterization, we found that Pt could not only capture photogenerated electrons and but also increase the electrons density on the catalyst, which were beneficial for selective CH4 formation. In addition, co deposited Cu2O enhanced the CO2 chemisorption on TiO2 while inhibited that of water, resulting in enhancement of CO2 reduction and lower H2 production. On account of the above mentioned contribution of Pt and Cu2O NPs, Pt Cu2O/TiO2 catalyst showed high CH4 selectivity towards all products from reductive reaction.

title: Agricultural peatland restoration: effects of land use change on greenhouse gas (CO2 and CH4) fluxes in the Sacramento San Joaquin Delta.
abstract: Agricultural drainage of organic soils has resulted in vast soil subsidence and contributed to increased atmospheric carbon dioxide (CO2) concentrations. The Sacramento San Joaquin Delta in California was drained over a century ago for agriculture and human settlement and has since experienced subsidence rates that are among the highest in the world. It is recognized that drained agriculture in the Delta is unsustainable in the long term, and to help reverse subsidence and capture carbon (C) there is an interest in restoring drained agricultural land use types to flooded conditions. However, flooding may increase methane (CH4) emissions. We conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land use types (a rice paddy and two restored wetlands) to assess the impact of drained to flooded land use change on CO2 and CH4 fluxes in the Delta. We found that the drained sites were net C and greenhouse gas (GHG) sources, releasing up to 341 g C m( 2) yr( 1) as CO2 and 11.4 g C m( 2) yr( 1) as CH4. Conversely, the restored wetlands were net sinks of atmospheric CO2, sequestering up to 397 g C m( 2) yr( 1) However, they were large sources of CH4, with emissions ranging from 39 to 53 g C m( 2) yr( 1) In terms of the full GHG budget, the restored wetlands could be either GHG sources or sinks. Although the rice paddy was a small atmospheric CO2 sink, when considering harvest and CH4 emissions, it acted as both a C and GHG source. Annual photosynthesis was similar between sites, but flooding at the restored sites inhibited ecosystem respiration, making them net CO2 sinks. This study suggests that converting drained agricultural peat soils to flooded land use types can help reduce or reverse soil subsidence and reduce GHG emissions.

title: Reticular Synthesis of HKUST like tbo MOFs with Enhanced CH4 Storage.
abstract: Successful implementation of reticular chemistry using a judiciously designed rigid octatopic carboxylate organic linker allowed the construction of expanded HKUST 1 like tbo MOF series with intrinsic strong CH4 adsorption sites. The Cu analogue displayed a concomitant enhancement of the gravimetric and volumetric surface area with the highest reported CH4 uptake among the tbo family, comparable to the best performing metal organic frameworks (MOFs) for CH4 storage. The corresponding gravimetric (BET) and volumetric surface areas of 3971 m(2) g( 1) and 2363 m(2) cm( 3) represent an increase of 115% and 47% respectively, in comparison to the corresponding values for the prototypical HKUST 1 (tbo MOF 1) and are 42% and 20% higher than that of tbo MOF 2. High pressure methane adsorption isotherms revealed a high total gravimetric and volumetric CH4 uptakes, reaching 372 cm(3) (STP) g( 1) and 221 cm(3) (STP) cm( 3) respectively, at 85 bar and 298 K. The corresponding working capacities between 5 and 80 bar were found to be 294 cm(3) (STP) g( 1) and 175 cm(3) (STP) cm( 3) and are placed among the best performing MOFs for CH4 storage particularly at relatively low temperature. To gain insight on the mechanism accounting for the resultant enhanced CH4 storage capacity, molecular simulation study was performed and revealed the presence of very strong CH4 adsorption sites near the organic linker with similar adsorption energetics as the open metal sites. The present findings support the potential of tbo MOFs based on the supermolecular building layer (SBL) approach as an ideal platform to further enhance the CH4 storage capacity via expansion and functionalization of the quadrangular pillars.

title: Spatio temporal variability of lake CH4 fluxes and its influence on annual whole lake emission estimates
abstract: Lakes are major sources of methane (CH4) to the atmosphere that contribute significantly to the global budget. Recent studies have shown that diffusive fluxes, ebullition and surface water CH4 conc

title: Adsorption Equilibrium of CO2 and CH4 and Their Mixture on Sichuan Basin Shale
abstract: Adsorption equilibrium isotherms of CO2, CH4, and mixtures of CO2/CH4 on shale sampled from Nanchuan, southeastern Sichuan Basin, were measured at 278, 298, and 318 K by an accurate gravimetric method. The adsorption equilibrium data of CO2 and CH4 were fitted using both the virial model and the Brunauer Emmett Teller (BET) model, and the isotherms of CO2/CH4 mixtures were fitted by an extended BET model. On the basis of adsorption data, the adsorption selectivity factors for CO2 over CH4 (aCO2/CH4) and thermodynamic parameters were estimated. Nanchuan shale was characterized with a high total organic carbon (TOC) having inorganic minerals and wide pore size distribution ranges. The adsorption heat, negative Gibbs free energy change, and negative surface potential of CO2 are larger than those of CH4, and the entropy loss of CO2 is larger than that of CH4, suggesting that adsorbed CO2 is in a more highly ordered arrangement than CH4 on shale. aCO2/CH4 values at different temperatures are all larger than 2.5.