CO2 CH4 Research Articles

Experimental Study on Hydrate Structure Transition Using an In Situ High-Pressure Powder X-ray Diffractometer: Application in CO2 Capture

Clathrate (gas) hydrates as materials have received great interest due to their high-density gas storage potential and separation applications for their ability to preferentially separate a targeted component such as CO2 from waste streams. Among the three clathrate hydrate structures, only sH (structure H) hydrates require a large molecule such as neohexane (NH) or tert-butyl methyl ether (TBME) as well as a “help-gas” molecule such as methane (CH4) to form a stable structure. However, attempts to use CO2 as a help-gas came up with mixed results where it appeared that the sH hydrate formed was stable only at temperatures below the ice point, whereas the compound formed with CH4 was considerably more stable. sH hydrates have considerable potential for gas separation, for instance, of CH4–CO2 mixtures. Thus, in this work, several compositions were tested for their hydrate forming ability. The large cage guests tested were NH and TBME, the help-gas mixtures were a CO2-rich mixture (76% CO2 and 24% CH4), and a CO2 lean mixture (24% CO2 and 76% CH4). The phase behavior of hydrates formed from the various combinations was tested by measuring the endo- and exotherms associated with hydrate formation and decomposition in a high-pressure differential calorimeter. The different phases indicated from the DSC results were identified by employing an in situ high-pressure cell on a powder X-ray diffractometer. Powder patterns were recorded to identify the crystal phase arising from nucleation and possible re-crystallization events after annealing. It was confirmed that the CO2 lean mixture (24% CO2 and 76% CH4) forms structure H (sH) hydrate, while the CO2-rich mixture (76% CO2 and 24% CH4) forms structure I (sI) hydrate presenting a structure transition pattern across the gas mixtures investigated. Further, it was observed that the CO2 lean mixture, which forms sH hydrate, also starts as sI hydrate and gradually converts to the thermodynamically stable sH hydrate. This study, in essence, helps to understand the preference of CH4 and CO2 for three different types of cages in sH hydrates and presents a design framework for a suitable gas separation mechanism for this gas mixture of interest.

Influences of diffusion-limited transport in the crystals and initial water on the gaseous CO2 dynamic replacement in CH4 hydrate

CO2–CH4 dynamic replacement is a process of the CO2–CH4 replacement method. In this process, CO2 is injected into CH4 hydrate-bearing sediment continuously to recover CH4. The dynamic replacement process can be divided into the CO2 displacement stage and the subsequent dynamic replacement stage and is affected by the existence of initial water and diffusion-limited transport caused by the mixed hydrate layer. Effective fugacity is utilized to combine the thermodynamic model and kinetic model to investigate the effects of the above two factors on the CH4–CO2 dynamic replacement process. Initial water is assumed to distribute in the pore space. The CH4 hydrate decomposition due to the decrease of CH4 partial pressure in the gas phase during the CO2 displacement stage is considered. Our investigation results show that diffusion-limited transport is the main factor that restricts the replacement percent in the displacement stage, the effect of the existence of initial water on the replacement percent is more obvious than that of the diffusion-limited transport. CO2 storage efficiency is less than 10% during the entire dynamic replacement and is mainly affected by the existence of initial water rather than the diffusion-limited transport. The temperature increase is mainly due to newly formed hydrate. Finally, more CH4 hydrate is exploited near the outlet than that near the inlet. Therefore, the CH4–CO2 replacement method needs to be enhanced near the inlet. CO2 is mainly sequestrated in the CO2 hydrate formed through free water. CO2 sequestrated in the mixed hydrate is mainly distributed near the inlet, while the CO2 sequestrated in the CO2 hydrate is mainly distributed near the outlet.

Full coupling of CO2–CH4 transport and sorption with solid deformation in gas shale enhances natural gas recovery and geological CO2 storage capacity

A thermodynamically rigorous constitutive model is used to describe the full coupling among the nonlinear processes of transport, sorption, and solid deformation in organic shale where the pore fluid is the binary mixture of carbon dioxide and methane. The constitutive model is utilized in a numerical solution that simulates injection of carbon dioxide in shale before producing carbon dioxide and methane from the same. The solution considers advection and diffusion as viable mechanisms of pore fluid transport where the latter comprises molecular, Knudsen, and surface diffusion in ultralow permeability shale. Results indicate that gas adsorption would be the main storage mechanism of sequestration in shale which may comprise up to 70% of the stored CO2 mass. A third of this storage capacity could be due to the geomechanical effects. Therefore, complete or partial exclusion of the coupling between sorption and solid phase deformation from the solution would result in underestimation of carbon dioxide storage capacity and natural gas recovery factor of the rock. Surface diffusion, sorption-induced deformation, as well as strain-induced changes in gas sorption capacities, are all conducive to both outcomes. Sensitivity analysis shows that the solution results are most sensitive to changes in adsorption capacities, followed by initial permeability, Young's modulus, Poisson's ratio, surface diffusivities, and initial pore radius.

Methane Emissions from Wetlands in China and Their Climate Feedbacks in the 21st Century.

Wetlands are large sinks of carbon dioxide (CO2) and sources of methane (CH4). Both fluxes can be altered by wetland management (e.g., restoration), leading to changes in the climate system. Here, we use multiple models to assess CH4 emissions and CO2 sequestration from the wetlands in China and the impacts on climate under three climate scenarios and four wetland management scenarios with various levels of wetland restoration in the 21st century. We find that wetland restoration leads to increased CH4 emissions with a national total of 0.32-11.31 Tg yr-1. These emissions induce an additional radiative forcing of 0.0005-0.0075 W m-2 yr-1 and global annual mean air temperature rise of 0.0003-0.0053 °C yr-1, across all future climate and management scenarios. However, wetland restoration also resulted in net CO2 sequestration, leading to a combined net greenhouse gas sink in all climate management scenarios, except in the highest restoration level combined with the hottest climate scenario. The highest climate cooling was achieved under medium restoration, with the climate scenario consistent with the Paris agreement target of below 2 °C, with a cumulative global warming potential of -3.2 Pg CO2-eq (2020-2100). Wetland restoration in the Qinghai-Tibet Plateau offers the greatest cooling effect.

Microbial iron reduction and greenhouse gas production in response to organic matter amendment and temperature increase of periglacial sediments, Bolterdalen, Svalbard

ABSTRACT Arctic permafrost soils store substantial reserves of organic matter (OM) from which microbial transformation contributes significantly to greenhouse gas emissions of CH4 and CO2. However, many younger sediments exposed by glacier retreat and sea level change in fjord landscapes lack significant organic carbon resources, so their capacity to promote greenhouse gas emissions is unclear. We therefore studied the effects of increased temperatures (4°C and 21°C) and OM on rates of Fe(III) reduction, CO2 production, and methanogenesis in three different Holocene sedimentary units from a single site within the former marine limit of Adventdalen, Svalbard. Higher temperature and OM addition generally stimulated CH4 production and CO2 production and an increase in Bacteria and Archaea abundance in all units, whereas an equal stimulation of Fe(II) production by OM amendment and an increase in temperature to 21°C was only observed in a diamicton. We observed an accumulation of Fe(II) in beach and delta deposits as well but saw no stimulating effect of additional OM or increased temperature. Interestingly, we observed a small but significant production of CH4 in all units despite the presence of large reservoirs of Fe(III), sulfate, and nitrate, indicating either the availability of substrates that are primarily used by methanogens or a tight physical coupling between fermentation and methanogenesis by direct electron transfer. Our study clearly illustrates a significant challenge that comes with the large heterogeneity on a narrow spatial scale that one encounters when studying soils that have complex histories.

Synthesis of Chalcones Derivatives and Their Biological Activities: A Review

Chalcone derivatives are considered valuable species because they possess a ketoethylenic moiety, CO–CH=CH–. Due to the presence of a reactive α,β-unsaturated carbonyl group, chalcones and their derivatives possess a wide spectrum of antiproliferative, antifungal, antibacterial, antiviral, antileishmanial, and antimalarial pharmacological properties. Recent developments in heterocyclic chemistry have led to the synthesis of chalcone derivatives, which had been biologically investigated toward certain disease targets. The major aspect of this review is to present the most recent synthesis of chalcones bearing N, O, and/or S heterocycles, revealing their biological potential during the past decade (2010–2021). Based on a review of the literature, many chalcone–heterocycle hybrids appear to exhibit promise as future drug candidates owing to their similar or superior activities compared to those of the standards. Thus, this review may prove to be beneficial for the development and design of new potent therapeutic drugs based on previously developed strategies.

The effect of the density difference between supercritical CO2 and supercritical CH4 on their adsorption capacities: An experimental study on anthracite in the Qinshui Basin

Deep unmineable coals are considered as economic and effective geological media for CO2 storage and CO2 enhanced coalbed methane (CO2-ECBM) recovery is the key technology to realize CO2 geological sequestration in coals. Anthracite samples were collected from the Qinshui Basin and subjected to mercury intrusion porosimetry, low-pressure CO2 adsorption, and high-pressure CH4/CO2 isothermal adsorption experiments. The average number of layers of adsorbed molecules (ANLAM) and the CH4/CO2 absolute adsorption amounts and their ratio at experimental temperatures and pressures were calculated. Based on a comparison of the density of supercritical CO2 and supercritical CH4, it is proposed that the higher adsorption capacity of supercritical CO2 over supercritical CH4 is the result of their density differences at the same temperature. Lastly, the optimal depth for CO2-ECBM in the Qinshui Basin is recommended. The results show that: (1) the adsorption capacity and the ANLAM of CO2 are about twice that of CH4 on SH-3 anthracite. The effect of pressure on the CO2/CH4 absolute adsorption ratio decreases with the increase of pressure and tends to be consistent. (2) A parameter (the density ratio between gas free and adsorbed phase (DRFA)) is proposed to assess the absolute adsorption amount according to the supercritical CO2/CH4 attributes. The DRFA of CO2 and CH4 both show a highly positive correlation with their absolute adsorption amounts, and therefore, the higher DRFA of CO2 is the significant cause of its higher adsorption capacity over CH4 under the same temperature and pressure. (3) CO2 adsorption on coal shows micropore filling with multilayer adsorption in the macro-mesopore, while methane exhibits monolayer surface coverage. (4) Based on the ideal CO2/CH4 competitive adsorption ratio, CO2 storage capacity, and permeability variation with depth, it is recommended that the optimal depth for CO2-ECBM in the Qinshui Basin ranges from 1000 m to 1500 m.

Variations in terms of CO2 capture and CH4 recovery during replacement processes in gas hydrate reservoirs, associated to the “memory effect”

The replacement of methane molecules, contained within natural hydrates reservoirs, with a theoretical equal number of carbon dioxide molecules, represents a promising opportunity for the near future. However, the maximum theoretical efficiency was proved to be approximately equal to 75% and, in the real applications, it is drastically lower. This article focused the attention on the possible reasons of such difference and found in the memory effect one of them. Firstly, the formation process of pure CH 4 and CO 2 hydrates was performed and thermodynamically characterized; then, the replacement process was realized on a system excluding memory and on a system including it. In the first situation, the theoretical efficiency was reached, while, in presence of memory effect, the results were drastically less effective, both in terms of methane recovery and in terms of carbon dioxide storage . When the system did not retain memory of previous formation processes, the quantity of CO 2 captured ranged from 73.97 to 75.05 vol% and the quantity of methane released was approximately equal to the one of CO 2 captured. Conversely, in presence of memory effect, the percentage of CO 2 captured dropped to 26 vol% and the quantity of methane release was still lower (24.97–26.03 vol%). • The influence of memory effect on the CO 2 /CH 4 replacement process was studied. • The memory effect was confirmed to be a kinetic promoter for hydrates formation. • The memory of previous CH 4 hydrates formation lowered the replacement efficiency. • Both the quantity of CH 4 released and CO 2 stored drastically decreased. • In absence of memory, the percentage of CO 2 storage reached the theoretical value.

Evaluating the recovery potential of CH4 by injecting CO2 mixture into marine hydrate-bearing reservoirs with a new multi-gas hydrate simulator

The conventional exploitation technologies (depressurization, thermal stimulation, and chemical inhibitor injection) of natural gas hydrate (NGH) are easy to induce environmental and geological problems. An alternative way of NGH exploitation using CO2 replacement method is the most promising technology, because it offers a dual purpose of CH4 safe recovery and CO2 sequestration in a form of hydrate. To evaluate the recovery potential of CH4 by injecting CO2 mixture into a marine hydrate-bearing reservoir, a simulator capable of modeling the behaviors of multi-gas hydrate-bearing geologic systems was newly developed. The simulator was applied to evaluate the recovery efficiency of CH4 by injecting CO2 mixture into a marine hydrate-bearing reservoir at SH2 site in the South China Sea. The simulated results suggest that by performing the similar operational procedures used in the Iġnik Sikumi #1 field trial, the recovery efficiency of CH4 by injecting CO2 mixture reaches about 6.95%, and the storage ratio of CO2 is about 0.3. The results of sensitivity analysis show that decreasing the concentration of CO2 in the mixtures can improve the recovery efficiency of CH4, but simultaneously reduce the storage ratio of CO2. The higher initial saturation of free water reduces the recovery efficiency of CH4, while increases the storage ratio of CO2. This work is significant to the safe exploitation of NGH and to the climate change mitigation through sequestering CO2 in the geological formation.

Experimental study on the effect of decomposition induction on the replacement process of CO2[sbnd]CH4 hydrate in hydrate-bearing sediments below the freezing point

The replacement technique of CH4 by CO2 is a promising strategy for natural gas hydrate exploitation, which has been regarded as a win-win situation for simultaneously achieving CO2 storage and CH4 recovery in permafrost region. How to improve the replacement efficiency is a fundamental issue related to the natural gas hydrate exploitation in permafrost region. In this work, the replacement process of CO2CH4 hydrate was carried out in the ice-sand mixture system and the replacement characteristics were further illustrated through experiment. The influence of different decomposition induction on the replacement process CO2CH4 hydrate was deeply analyzed, especially for the decompression driving force (ΔP) and thermal driving force (ΔT). The results showed that the ΔP has a significant inductive effect on the replacement process of CO2CH4 hydrate in porous media below the freezing point. The replacement efficiency attained 12.25% under condition of decomposition induction driven by ΔP with -0.1 MPa, which was raised 3.09% in comparison. However, the larger ΔP didn't mean that it was more favorable to the replacement process of CO2CH4 hydrate, and there was an optimal value in the experiment. Furthermore, an additional thermal drive (ΔT) is beneficial to the replacement efficiency of CH4 hydrate and the sequestration efficiency of CO2. It greatly improved the CH4 recovery and CO2 sequestration ratio during the replacement process of CO2CH4 hydrate. The replacement efficiency attained 20.34% under condition of depressurization drive combined with thermal drive. It was worth noting that the contribution of thermal drive (ΔT) was different on CH4 recovery and CO2 sequestration. There was an optimal value for the enhancement on the replacement process of CO2CH4 hydrate. These results are of significance for providing a theoretical guidance for natural gas hydrate exploitation in permafrost regions.

Reduction of Enteric Methane Emissions in Heifers Fed Tropical Grass-Based Rations Supplemented with Palm Oil

Vegetable oils have been shown to reduce enteric methane (CH4) production by up to 20%. However, when the level of incorporation exceeds the threshold of 70 g/kg DM, dry matter intake (DMI) and nutrient digestibility may be reduced. The objective of this study was to determine the effects of the incorporation of three levels of palm oil (PO) on enteric CH4 emissions, rumen fermentation and apparent digestibility in heifers fed low-quality grass. Four rumen-cannulated heifers (Bos taurus × Bos indicus) were randomly assigned to four treatments: control (CON) and three increasing PO levels: 20, 40 and 60 g/kg in a 4 × 4 Latin square design with four periods of 22 days (14 days of adaptation to the ration), 5 days of feces and rumen fluid sampling (day 18, 4 h postprandial) and the last 3 days for measurements of CH4 in respiration chambers. With the exception of CP (p = 0.04), starch (p = 0.002) and EE (p < 0.001), the intake of nutrients was not affected by the inclusion of PO (p > 0.05). The apparent digestibility (AD) of nutrients was not affected by the inclusion of PO (p > 0.05), except for starch, which reduced its AD as the PO level was increased (p < 0.05). The gross energy intake was higher in PO-containing rations (p = 0.001), on the other hand, the digestible energy intake was similar between treatments (p > 0.05). In situ ruminal digestion kinetics and the potential degradability remained unchanged (p > 0.05), however, the effective degradability decreased with the inclusion of PO in the rations (p < 0.05). The ruminal pH and molar proportions of acetic, isovaleric and valeric acid were not different between treatments (p > 0.05). The ruminal concentration of propionic acid increased as the PO level increased, reaching its highest molar proportion with 60 g/kg PO (p < 0.05), however, the acetic/propionic ratio and the molar proportions of butyric acid and isobutyric acid decreased as the PO level increased (p < 0.05). The total daily CH4 production was lower in diets containing 20, 40 and 60 g/kg PO compared to the CON diet (p < 0.001). The production of CH4 per kg DMI and DOMI was greater (p < 0.05) for the CON diet compared to all three rations containing PO. The emission intensity, Ym, energy lost as CH4, emission factor (EF) and kg CO2 eq/year were reduced as an effect of the inclusion of PO (p < 0.05). Based on the results obtained, it is concluded that the incorporation of PO in cattle rations has the potential to reduce enteric methane emissions by 4% for every 10 g/kg PO in the ration, without affecting DMI, apparent digestibility or the consumption of digestible nutrient fractions.

Enhanced performance of LaFeO3 oxygen carriers by NiO for chemical looping partial oxidation of methane

Partially oxidizing methane into syngas via a two step chemical looping scheme is a promising option for methane transformation. However, providing the optimum lattice oxygen to selectively produce syngas represents the major challenge for the development of oxygen carrier materials in chemical looping processes. In this work, a NiO-modified LaFeO3 (x wt% Ni/LaFeO3, x = 0, 3, 5, 7, 9, 11) oxygen carrier is proposed to enhance the activity of lattice oxygen for chemical looping partial oxidation of methane. The results show that the methane conversion rate of 5 wt% Ni/LaFeO3 is increased by 25% compared to that of unmodified LaFeO3. It is worth noting that the methane conversion and product selectivity mainly depend on the Ni loading, and 5 wt% Ni/LaFeO3 oxygen carriers has higher CH4 conversion (95.2%) and CO selectivity (85.1%). The results demonstrate that it is feasible to active the lattice oxygen of LaFeO3 perovskite oxygen carriers by surface modification of NiO, which ultimately influences their reaction performance in chemical looping partial oxidation of methane (CL-POM) processes.

Precise Modulation of Triple‐Phase Boundaries towards a Highly Functional Exsolved Catalyst for Dry Reforming of Methane under a Dilution‐Free System

AbstractDry reforming of methane (DRM) has been emerging as a viable solution to achieving carbon neutrality enhanced by the Paris Agreement as it converts the greenhouse gases of CO2 and CH4 into industrially useful syngas. However, there have been limited studies on the DRM catalyst under mild operating conditions with a high dilution gas ratio due to their deactivation from carbon coking and metal sintering. Herein, we apply the triple‐phase boundary (TPB) concept to DRM catalyst via exsolution phenomenon that can secure elongated TPB by controlling the Fe‐doping ratio in perovskite oxide. Remarkably, the exsolved catalyst with prolongated TPB shows exceptional CO2 and CH4 conversion rates of 95.9 % and 91.6 %, respectively, stable for 1000 hours under a dilution‐free system. DFT calculations confirm that the Lewis acid of support and Lewis base of metal at the TPB promote the adsorption of reactants, resulting in lowering the overall CO2 dissociation and CH4 dehydrogenation energy.

Review on Carbon Dioxide Replacement of Natural Gas Hydrate: Research Progress and Perspectives

Natural gas hydrate (NGH) is a new energy with great potential that has the advantages of large reserves and high energy density and has become the key exploitation target of many countries in the world. Compared with traditional exploitation methods, such as the heat injection method and the depressurization method, the CO2 replacement method can meet the demand of NGH exploitation and achieve the geological storage of CO2 at the same time, which has more advantages in environmental protection. This paper summarizes the feasibility study of this method, including thermodynamics, kinetics, and mechanical stability of reservoirs, and discusses the replacement mechanism of different types of hydrate; then it summarizes the research progress of improving the replacement efficiency and puts forward corresponding suggestions for the existing problems. The relevant conclusions are as follows: (1) The replacement reaction is feasible in terms of thermodynamics and kinetics, but the mechanical stability of the reservoir is uncertain during actual exploitation. (2) The contact position between CO2 molecules and CH4 hydrates is the main replacement position. The fugacity difference between different guest molecules dominates the replacement reaction and is affected by the mass transfer capacity. (3) At present, there is no consensus on whether the CH4 hydrate will dissociate during the replacement reaction. (4) sII and sH hydrates will undergo structural transformation during the replacement reaction and eventually become sI mixed hydrates. (5) Different phase CO2 and different guest molecules have different replacement efficiencies for CH4.

Modification of LaFe1-xCoxO3 oxygen carrier by Silicalite-1 for chemical looping coupled with the reduction of CO2

A series of LaFe1−xCoxO3/w%S-1 are used as oxygen carriers in chemical looping reforming of CH4 coupled with the reduction of CO2 process to produce syngas and CO. In this work, the effect of Co doping and Silicalite-1 content on the performance of oxygen carriers can be obtained from reactivity tests. Among LaFe1−xCoxO3 samples, excellent reactivity is achieved over LaFe0.8Co0.2O3 and LaFe0.9Co0.1O3. It is found that the introduction of Silicalite-1 can greatly improve the reactivity and stability of the chemical looping process, which can be attributed to that the existence of Silicalite-1 inhibits the agglomeration of the perovskite particles. Among the LaFe1−xCoxO3/w%S-1 samples with different Silicalite-1 content, LaFe0.9Co0.1O3/10%S-1 and LaFe0.8Co0.2O3/10%S-1 show higher CH4 conversion and CO selectivity in the CH4 oxidation reaction, while only quite smaller amount of carbon deposits formed on the surface of the oxygen carriers. After 20 redox cycles, LaFe0.8Co0.2O3/10%S-1 still shows excellent reactivity and high resistance to carbon deposition.

Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms.

The rate constant for the self-reaction of the acetonyl peroxy radicals, CH3C(O)CH2O2, has been determined using laser photolysis/continuous wave cavity ring down spectroscopy (cw-CRDS). CH3C(O)CH2O2 radicals have been generated from the reaction of Cl atoms with CH3C(O)CH3, and the concentration time profiles of four radicals (HO2, CH3O2, CH3C(O)O2, and CH3C(O)CH2O2) have been determined by cw-CRDS in the near-infrared. The rate constant for the self-reaction was found to be k = (5.4 ± 1.4) × 10-12 cm3 s-1, in good agreement with a recently published value (Zuraski, K., et al. J. Phys. Chem. A 2020, 124, 8128); however, the branching ratio for the radical path was found to be ϕ1b = (0.6 ± 0.1), which is well above the recently published value (0.33 ± 0.13). The influence of a fast reaction of Cl atoms with the CH3C(O)CH2O2 radical became evident under some conditions; therefore, this reaction has been investigated in separate experiments. Through the simultaneous fitting of all four radical profiles to a complex mechanism, a very fast rate constant of k = (1.35 ± 0.8) × 10-10 cm3 s-1 was found, and experimental results could be reproduced only if Cl atoms would partially react through H-atom abstraction to form the Criegee intermediate with a branching fraction of ϕCriegee = (0.55 ± 0.1). Modeling the HO2 concentration-time profiles was possible only if a subsequent reaction of the Criegee intermediate with CH3C(O)CH3 was included in the mechanism leading to HO2 formation with a rate constant of k = (4.5 ± 2.0) × 10-14 cm3 s-1.

Methane and Carbon Dioxide Fluxes in a Temperate Tidal Salt Marsh: Comparisons Between Plot and Ecosystem Measurements

AbstractTidal wetlands are comprised of complex interdependent pathways where measurements of carbon exchange are often scale dependent. Common data collection methods (i.e., chambers and eddy covariance) are inherently constrained to different spatial and temporal scales which could generate biased information for applications of carbon accounting, identifying functional relationships and predicting future responses to climate change. Consequently, it is needed to systematically evaluate measurements derived from multiple approaches to identify differences and how techniques complement each other to reconcile interpretations. To accomplish this, we tested ecosystem‐scale eddy covariance with plot‐scale chamber measurements within a temperate salt marsh. We found good agreement (R2 = 0.71–0.95) when comparing measurements of CH4 emissions and CO2 exchange but this agreement was dependent upon canopy phenology with discrepancies mainly arising during senescence and dormancy phenophases. The environmental drivers for CH4 and CO2 fluxes were mostly preserved across different measurement techniques, but the number of drivers increases while their individual strength decreases at the ecosystem scale. Empirical upscaling models parameterized with chamber measurements overestimated annual net ecosystem exchange (NEE; 108%) and gross primary production (GPP; 12%) while underestimating ecosystem respiration (Reco; 14%) and CH4 emissions (69%) compared to eddy covariance measurements. Our results suggest that the environmental complexity of CH4 and CO2 fluxes in salt marshes may be underestimated by chamber‐based measurements, and highlights how different techniques are complementary while considering limitations at each level of measurement.

Ni-Ir/MgAl2O4 for balanced carbon deposition-elimination in methane dry reforming

In this issue of Chem Catalysis, Zhao and co-workers developed a Ni-Ir/MgAl2O4 alloy catalyst offering comparable rates of CH4 dissociation and CO2 activation to avoid carbon deposition, a major undesired side reaction in methane dry reforming.

Characterization and mitigation option of greenhouse gas emissions from lactating Holstein dairy cows in East China

BackgroundThis study investigated greenhouse gas (GHG) emission characteristics of lactating Holstein dairy cows in East China and provided a basis for formulating GHG emission reduction measures. GreenFeed system was used to measure the amount of methane (CH4) and carbon dioxide (CO2) emitted by the cows through respiration. Data from a commercial cow farm were used to observe the effects of parity, body weight, milk yield, and milk component yield on CH4 and CO2 emissions.ResultsMean herd responses throughout the study were as follows: 111 cows completed all experimental processes, while 42 cows were rejected because they were sick or had not visited the GreenFeed system 20 times. On average, lactating days of cows was 138 ± 19.04 d, metabolic weight was 136.5 ± 9.5 kg, parity was 2.8 ± 1.0, dry matter intake (DMI) was 23.1 ± 2.6 kg/d, and milk yield was 38.1 ± 6.9 kg/d. The GreenFeed system revealed that CH4 production (expressed in CO2 equivalent, CO2-eq) was found to be 8304 g/d, {mathrm{CH}}_{4left({mathrm{CO}}_2-mathrm{eq}right)} /DMI was 359 g/kg, {mathrm{CH}}_{4left({mathrm{CO}}_2-mathrm{eq}right)} /energy-corrected milk (ECM) was 229.5 g/kg, total CO2 production (CH4 production plus CO2 production) was 19,201 g/d, total CO2/DMI was 831 g/kg, and total CO2/ECM was 531 g/kg. The parity and metabolic weight of cows had no significant effect on total CO2 emissions (P > 0.05). Cows with high milk yield, milk fat yield, milk protein yield, and total milk solids yield produced more total CO2 (P < 0.05), but their total CO2 production per kg of ECM was low (P < 0.05). The total CO2/ECM of the medium and high milk yield groups was 17% and 27% lower than that of the low milk yield group, respectively.ConclusionsThe parity and body condition had no effect on total CO2 emissions, while the total CO2/ECM was negatively correlated with milk yield, milk fat yield, milk protein yield, and total milk solids yield in lactating Holstein dairy cows. Measurement of total CO2 emissions of dairy cows in the Chinese production system will help establish regional or national GHG inventories and develop mitigation approaches to dairy production regimes.

Effect of No-Tillage Management on Soil Organic Matter and Net Greenhouse Gas Fluxes in a Rice-Oilseed Rape Cropping System

No-tillage (NT) management is considered a leading approach for sustaining crop production and improving soil and environmental quality. Based on a long-term no-tillage experiment in a rice–oilseed rape cropping system, we examined differences in soil organic matter (SOM), soil microbial carbon (C) and nitrogen (N) content, and methane (CH4) and carbon dioxide (CO2) fluxes between NT and conventional tillage (CT) management. SOM under NT was 21.0 g kg–1, and a significant difference was detected between 2004 and 2016. SOM increased under NT and CT by averages of 0.60 and 0.32 g kg–1 year–1, respectively. Soil microbial C and N content were higher under CT than under NT. However, soil C:N ratios under NT were 17.4 and 9.7% higher than the CT, respectively, whereas soil microbial C:N ratios under NT were on average 9.47 and 9.70% higher. In addition, about 70% of CO2 net uptake and over 99% of net CH4 emissions occurred during the rice season in May–September in the rice–oilseed rape cropping system. Annual cumulative CH4 and daytime net ecosystem CO2 exchange (NEE) under NT was 1813.9 g CO2 equiv. m–2, 10.8% higher than that under CT. Our results suggest that a higher soil microbial C:N ratio and NEE (CH4 and daytime CO2) could contribute to increasing SOM/C in the surface soil under NT management.