Direct CH Research Articles

Effect of cattle diet and manure storage conditions on carbon dioxide, methane and nitrous oxide emissions from tie-stall barns and stored solid manure

The diversity of beef cattle production systems in terms of diet, manure management and building design results in variation in greenhouse gas (GHG) emissions and the opportunities to reduce them. Within this context, we studied the effect of the varying proportions of concentrate (37–85% of DM) in the diet of Belgian Blue heifers on CH 4 and N 2O emissions from a tie-stall system (barn and solid manure storage). Trials were conducted over two consecutive periods in which manure was stored mainly in winter and spring. Increasing the proportions of concentrate in the diet reduced the GHG (CH 4 + N 2O) emissions from the barns from 8.5 ± 1.6 to 1.9 ± 0.4 kg CO 2 eq/kg live-weight gain, but had not significant influence on the emissions from the stored solid manure. Seasonal variation in gas emissions was observed, with lower emissions from stored solid manure in winter than in spring (159 ± 25 and 314 ± 49 mg CO 2, 0.14 ± 0.02 and 2.47 ± 0.78 mg CH 4, and <0.01 and 0.24 ± 0.09 mg N 2O/kg of fresh manure stored/d of storage, respectively), indicating that manure storage in the warmer season should be avoided. The GHG (CH 4 + N 2O) emissions from stored solid manure, however, were less than 11% of the total emissions (barns + manure storage). The emphasis in these systems should therefore be on modelling and reducing direct CH 4 emissions from cattle but feed production impact should also be included. The GHG emissions were validated using nutrient (C, K, P and ash) balances including CO 2 and CH 4 emissions for the C balance.

Effect of B and Sn on Ni catalysts supported on pure- and on WO3/MoO3-modified zirconias for direct CH4 conversion to H2

Methane cracking for hydrogen production was studied over monometallic/bimetallic Ni catalysts supported on pure or WO3/MoO3-modified zirconias. The catalysts were reduced easily with methane at 773K, indicating that regeneration studies can be performed without using hydrogen. Ni–B and Ni–Sn bimetallic catalysts presented different behaviors when exposed to methane at 773K. The former, because of its low thermal stability, behaved as a well dispersed phase with small nickel crystallites, while the latter behaved as a bimetallic catalyst. For all catalysts, except for Ni–Sn, the metallic particles, after 8h of methane exposure at 773K, were mostly concentrated at the tip of the carbon filaments, whereas zirconia surface was found to be free from these filaments. Additionally, our results suggest that the presence of Sn does not improve catalytic performance for hydrogen production by methane cracking, considering the catalytic systems under study. Rather, adding Sn seems to inhibit access to Ni sites, which are necessary for the C–H bond activation of methane and then for the nucleation of carbon species.

A subtle interplay of C–H hydrogen bonds in complexation of anions of varied dimensionality by a nitro functionalized tripodal podand

The structural aspects of binding of halides (1 and 2), nitrate (3), perchlorate (4), trifluoroacetate (5) and hexafluorosilicate (6) with the protonated tripodal podand L are examined crystallographically. Anion binding with multiple receptor units is attributable entirely to the (NH)+⋯anion and multiple C–H⋯anion hydrogen bonding interactions in all six complexes. Protonation at the apical nitrogen and presence of nitro functionality renders the methylene and aryl hydrogen sufficiently acidic for their active participation in moderate to weak CH⋯anion interactions are noteworthy. All supramolecular networks of complexes 1–6 are guided by various non-convalent interactions, especially directional CH⋯Onitro hydrogen bonds and π-stacking interactions.

Photochemistry of methyl bromide on the α-Cr 2O 3(0001) surface

The photochemical properties of the Cr-terminated α-Cr 2O 3(0001) surface were explored using methyl bromide (CH 3Br) as a probe molecule. CH 3Br adsorbed and desorbed molecularly from the Cr-terminated α-Cr 2O 3(0001) surface without detectable thermal decomposition. Temperature programmed desorption (TPD) revealed a CH 3Br desorption state at 240 K for coverages up to 0.5 ML, followed by more weakly bound molecules desorbing at 175 K for coverages up to 1 ML. Multilayer exposures led to desorption at ~ 130 K. The CH 3Br sticking coefficient was unity at 105 K for coverages up to monolayer saturation, but decreased as the multilayer formed. In contrast, pre-oxidation of the surface (using an oxygen plasma source) led to capping of surface Cr 3+ sites and near complete removal of CH 3Br TPD states above 150 K. The photochemistry of chemisorbed CH 3Br was explored on the Cr-terminated surface using post-irradiation TPD and photon stimulated desorption (PSD). Irradiation of adsorbed CH 3Br with broad band light from a Hg arc lamp resulted in both photodesorption and photodecomposition of the parent molecule at a combined cross section of ~ 10 − 22 cm 2. Photodissociation of the CH 3–Br bond was evidenced by both CH 3 detected in PSD and Br atoms left on the surface. Use of a 385 nm cut-off filter effectively shut down the photodissociation pathway but not the parent molecule photodesorption process. From these observations it is inferred that d-to-d transitions in α-Cr 2O 3, occurring at photon energies < 3 eV, do not significantly promote photodecomposition of adsorbed CH 3Br. It is unclear to what extent band-to-band versus direct CH 3Br photolysis play in CH 3–Br bond dissociation initiated by more energetic photons.

Low Oxygen Tension and Synthetic Nanogratings Improve the Uniformity and Stemness of Human Mesenchymal Stem Cell Layer

A free-standing, robust cell sheet comprising aligned human mesenchymal stem cells (hMSCs) offers many interesting opportunities for tissue reconstruction. As a first step toward this goal, a confluent, uniform hMSC layer with a high degree of alignment and stemness maintenance needs to be created. Hypothesizing that topographical cue and a physiologically relevant low-oxygen condition could promote the formation of such an hMSC layer, we studied the culture of hMSCs on synthetic nanogratings (350 nm width and 700 nm pitch) and either under 2 or 20% O(2). Culturing hMSCs on the nanogratings highly aligned the cells, but it tended to create patchy layers and accentuate the hMSC differentiation. The 2% O(2) improved the alignment and uniformity of hMSCs, and reduced their differentiation. Over a 14-day culture period, hMSCs in 2% O(2) showed uniform connexon distribution, secreted abundant extracellular matrix (ECM) proteins, and displayed a high progenicity. After 21-day culture on nanogratings, hMSCs exposed to 2% O(2) maintained a higher viability and differentiation capacity. This study established that a 2% O(2) culture condition could restrict the differentiation of hMSCs cultured on nanopatterns, thereby setting the foundation to fabricate a uniformly aligned hMSC sheet for different regenerative medicine applications.

Catalytic partial oxidation of methane over SrTiO3 with oxygen-permeable membrane reactor

The catalytic partial oxidation of methane to syngas over perovskite SrTiO 3 was studied with Ce 0.8 Sm 0.2 O 2− δ −La 0.8 Sr 0.2 CrO 3− δ dual-phase composite membrane reactor. The catalytic performance strongly depends on both reaction temperature and CH 4 feed rate. Approximately 74% CO and 75% H 2 selectivity at 17% CH 4 conversion can be achieved under the optimized membrane reactor operating conditions at 950 °C and CH 4 feed rate of 20 ml min −1 . The reaction routes were explored by a comparative study with conventional fixed-bed reactor, suggesting a direct CH 4 partial oxidation route below 750 °C and obvious CO 2 and steam reforming activities above 800 °C.

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

The reaction of the ground state methylidyne radical CH (X(2)Pi) with pyrrole (C(4)H(5)N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 363 K, at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr(3)) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C(5)H(5)N) is identified as the product of the reaction and resolved from (79)Br atoms, and the result is consistent with CH addition to pyrrole followed by H-elimination. The photoionization efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C(5)H(4)DN and identified as deuterated pyridine (d-pyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as gas-phase combustion processes, are discussed.

Hydrothermal methane fluxes from the soil at Pantelleria island (Italy)

Chemical and isotopic analyses of the main gas manifestations of the island of Pantelleria (Italy) were used to gain insight on the origin of the released methane. Results indicate that the most probable origin is through abiogenic reactions within the hydrothermal system. Methane and CO 2 flux measurements from the soils were made with the accumulation chamber method in an area of about 0.015 km 2 within the main fumarolic area of the island (Favara Grande). The 23 measurements range from − 34 to 3550 mg m −2 d − 1 for CH 4 and from 0.6 to 379 g m − 2 d − 1 for CO 2. The relationships between CH 4 and CO 2 fluxes and the CH 4/CO 2 ratios in the gases collected between the depths of 25 and 100 cm provide evidence for methanotrophic processes within the soils. Methane output for the surveyed area was calculated to be 2.5 t a − 1 and extrapolated to about 5–10 t a − 1 for the entire volcanic/hydrothermal system of the island. Previous higher estimates of the CH 4 output at Pantelleria (Etiope et al., 2007, J. Volcanol. Geotherm. Res., 165, 76–86) were based on soil CO 2 output and CH 4/CO 2 ratios in fumarolic gases; the present work provides the first direct CH 4 flux data and it suggests that methanotrophic activity in the soil could be substantial in reducing the CH 4 emission to the atmosphere.

ChemInform Abstract: Use of NaOH as a New Activator for the Palladium‐Catalyzed Direct CH Arylation of Thiazole Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Theoretical Investigation of the Interaction between Fluorinated Dimethyl Ethers (nF= 1−5) and Water: Role of the Acidity and Basicity on the Competition between OH···O and CH···O Hydrogen Bonds

Theoretical calculations have been carried out using ab initio MP2 and B3LYP density functional methods to investigate the interaction between fluorinated dimethyl ethers (nF = 1-5) and water. Depending on the number of F atoms implanted on the dimethyl ethers, linear structures stabilized by intermolecular O(w)H(w)...O or CH...O(w) hydrogen bonds or closed structures involving both hydrogen bonds are formed. Binding energies of the hydrogen-bonded complexes range between 4 and 12 kJ mol(-1). Blue shifts of the CH stretching vibrations are predicted even in the absence of a direct CH...O interaction. The red shifts of the OH stretching vibrations of water in the open and closed structures are analyzed as well. The natural bond orbital analysis includes the sigma*(O(w)H(w)) and sigma*(CH) occupation, the hybridization of the C atom, the atomic charges, and the intra- and intermolecular hyperconjugation energies. These parameters are discussed as a function of the proton affinity (PA) of the O atom and the deprotonation enthalpy (DPE) of the CH bonds of the fluorinated ethers calculated in a previous work. (16) Our results show that the effective PA in determining the intermolecular O --> sigma*(O(w)H(w)) hyperconjugation energies decreases with increasing acidity of the CH bond. In turn, the effective acidity of the CH bond in determining the intermolecular O(w) --> sigma*(CH) hyperconjugation energies decreases with increasing basicity of the O atom.

Use of NaOH as a New Activator for the Palladium-Catalyzed Direct CH Arylation of Thiazole Derivatives

Sodium hydroxide is found to serve as a new activator for the palladium-catalyzed C-H arylation of thiazole derivatives with aryl bromides and aryl iodides. The reaction of benzothiazole proceeds smoothly with 4-bromoanisole to afford the corresponding coupling product in an excellent yield.

Oxidation of Methanol by FeO2+ in Water: DFT Calculations in the Gas Phase and Ab Initio MD Simulations in Water Solution

We investigate the mechanism of methanol oxidation to formaldehyde by ironoxido ([Fe(IV)O]2+), the alleged active intermediate in the Fenton reaction. The most likely reaction mechanisms are explored with density functional theory (DFT) calculations on microsolvated clusters in the gas phase and, for a selected set of mechanisms, with constrained Car-Parrinello molecular dynamics (CPMD) simulations in water solution. Helmholtz free energy differences are calculated using thermodynamic integration in a simulation box with 31 water molecules at 300 K. The mechanism of the reaction is investigated with an emphasis on whether FeO2+ attacks methanol at a C-H bond or at the O-H bond. We conclude that the most likely mechanism is attack by the oxido oxygen at the C-H bond ("direct CH mechanism"). We calculate an upper bound for the reaction Helmholtz free energy barrier in solution of 50 kJ/mol for the C-H hydrogen transfer, after which transfer of the O-H hydrogen proceeds spontaneously. An alternative mechanism, starting with coordination of methanol directly to Fe ("coordination OH mechanism"), cannot be ruled out, as it involves a reaction Helmholtz free energy barrier in solution of 44 +/- 10 kJ/mol. However, this coordination mechanism has the disadvantage of requiring a prior ligand substitution reaction, to replace a water ligand by methanol. Because of the strong acidity of [FeO(H2O)5]2+, we also investigate the effect of deprotonation of a first-shell water molecule. However, this is found to increase the barriers for all mechanisms.

Ab initio study of the reaction of OH radical with methyl sulfinic acid (MSIA)

The potential energy surface and various reaction channels of the MSIA + OH reaction have been investigated at the CCSD(T)/6-311 + G(2d, p)//B3LYP/6-31 + G(2d, p) level of theory. Four different hydrogen-bonded complexes were formed in the reactions. The calculations indicate that there are mainly two kinds of reaction mechanisms in the studied reactions, the direct CH 3 radical-abstraction reaction and the association–decomposition reaction. Owing to the higher barrier heights, the CH 3-abstraction pathway is not expected to be the favorable pathway. While, the association–decomposition reaction pathway, MSIA-b + OH → M2b → TS9 → H 2O + CH 3SO 2 → TS4 + H 2O → SO 2 + CH 3 + H 2O, is the most feasible reaction pathway, and SO 2 is the dominant final sulfur-containing product.

Response of the non-premixed lifted flame to coaxial jet mixing layers

The influence of an air coflow on a non-premixed flame is studied. The purpose is to gradually disorganize the fuel (methane) jet by acting on the mixing layer while controlling the oxidizer (air) supply. For methane flow rate velocity ranging between 1 and 25 m/s, the flame adapts its behavior according to the value of the air co-flow rate velocity ranging between 0 and 1 m/s. First, two distinct processes are noticed in the flame lifting: a break point lifting process and a direct lifting process. By simultaneous measurements based on direct CH ∗-imaging and laser tomography, a criterion based on a thermal thickness, characteristic of the direct lifting process, is determined. Second, three lifted flame aspects are identifiable: a laminarized flame with a lobe-shaped base, a turbulent flame with a tubular base and a laminar flame with a totally rounded base. In particular, the two former flames are quantified by their lift-off height measured by CH ∗-imaging. To characterize the lifted flame behavior as a response to the mixing layers, the analysis introduces some global jet parameters able to take into account the local scale phenomena due to the jets’ vortices: the inner and the outer potential cores, characterizing the central and coflowing jets, respectively and the spreading of the methane jet. It is shown how much the relative organization of the mixing layers characterized by the ratio of the outer to inner potential core, is of paramount importance for the lifting process as well as for the lifted flame response (flame aspect, lift-off height, …). So, ‘macro’ parameters, introduced here, appear efficient to describe the lifted flame behavior.

Molten-salt fuel cells—Technical and economic challenges

This paper presents a personal view of the status and research needs of the MCFC and other molten-salt fuel cells. After an overview of current MCFC performance, compared with performance and cost of other fuel cells, improvements in power density and lifetime as well as cost reduction are identified as key priorities to accelerate the commercialization of the MCFC. In spite of its unfavorable public image (compared to, in particular, PEMFC and planar SOFC) MCFC technology has progressed steadily and cost reduction has been significant. Large-scale commercialization, especially in the distributed generation and cogeneration market, remains a possibility but its chances are highly dependent on a forceful and consistent energy policy, for example taking into account the externalities associated with various modes of electric power production from fossil fuels. In spite of steady improvements in performance, important defects in fundamental knowledge remain about wetting properties, oxygen reduction kinetics, corrosion paths and control mechanisms. These must be addressed to stimulate further simplification of design and find solutions to lifetime issues. Recently, alternative concepts of molten-salt fuel cells have been capturing attention. The direct carbon fuel cell (DCFC), reviving an old concept, has caught the attention of energy system analysts and some important advances have been made in this technology. Direct CO and CH 4 oxidation have also been a focus of study. Finally, the potential of nanotechnology for high-temperature fuel cells should not be a priori excluded.

Some technological aspects of methane aromatization (direct and via oxidative coupling)

The investigations on transformation of methane to benzene and naphthalene have been carried out in aim to verify and supplement earlier reported data and on this basis to estimate real industrial perspectives of the CH 4 aromatization concept, the main challenges and barriers. Methane aromatization (direct and via oxidative coupling) has been studied over Mo/HZSM-5 catalyst used both for direct methane dehydroaromatization and for aromatization of methane oxidative coupling (OCM) products. The effects of Mo content in the catalyst, temperature, space velocity, the presence of CO 2, CO, H 2O, C 2H 4, C 2H 6 and their mixtures in the feed have been studied. The effectiveness of the catalyst regeneration in the air was also examined. All results were confronted with the literature data and analyzed from technological point of view. It was confirmed that direct CH 4 aromatization process was characterized by a low CH 4 single-pass conversion, low single-pass yields of the main products (benzene, hydrogen and naphthalene) and a low catalyst stability (rapid catalyst deactivation). Various possible technological schemes were analyzed. It was concluded that real industrial chances of direct methane aromatization or aromatization via OCM would depend largely on the advancement in the cost-effective separation techniques. The methane aromatization concept was also confronted with other methane conversion processes.

Selective oxidation of methane over MoO x/SiO 2: isolation of the kinetics of reactions occurring in the gas phase and on the surfaces of SiO 2 and MoO x

The selective oxidation of methane to formaldehyde over MoO x /SiO 2 was investigated to identify the contributions of methane and formaldehyde reactions occurring in the gas phase and on the surfaces of SiO 2 and dispersed MoO x to the overall observed reaction rate. Experiments were conducted with 4.5 wt% MoO 3/SiO 2 at a nominal surface concentration of 0.44 Mo nm −2. Data were acquired for CH 4/O 2 ratios from 2 to 34 and temperatures from 848 to 923 K. Homogeneous oxidation of methane was negligible, and the homogeneous oxidation of formaldehyde contributed only to a small degree. The formation of formaldehyde was found to occur largely over MoO x and only to a limited degree over SiO 2. By contrast, the rates of formaldehyde consumption over MoO x and SiO 2 were comparable. For SiO 2 the only process occurring was CH 2O decomposition, which was independent of the CH 4/O 2 ratio, whereas in the case of MoO x , CH 2O decomposition was accompanied by combustion of the H 2 formed and by direct CH 2O combustion principally to CO. A comprehensive model of the overall reaction kinetics was assembled from the kinetics determined for the reactions of methane and formaldehyde in the gas phase and on the surfaces of SiO 2 and MoO x . This model describes the observed rates of methane conversion and the formaldehyde selectivity measured experimentally as functions of temperature and CH 4/O 2 ratio. This model is then used to determine the maximum single-pass yield of CH 2O for a given temperature and CH 4/O 2 ratio. It is predicted that the maximum single-pass yield increases with reaction temperature and decreasing CH 4/O 2 ratio.

高圧下におけるメタン－酸素同軸乱流非予混合火炎の流動場計測

We carried out the flow field measurement of methane-oxygen turbulent nonpremixed flame in non-combusting and combusting situations at high pressures using LDV. The main objectives are to study the influences of combustion on the turbulence structure at high pressures and to provide detailed data on which numerical predictions on such flows can rely. Direct observation and CH* chemiluminescence detection are conducted at high pressures up to 1.0MPa. It was found that the flame length at elevated pressures became constant. From flow field measurements, the following features of flames at elevated pressure were found: (1) the existence of flame suppressed turbulence in the upstream region of the jet and enhanced it in the downstream region with increasing pressure; (2) Turbulence in the flame was more anisotropic than in the corresponding cold jet in all regions of the flow with increasing pressure; (3) Reynolds shear stresses did not change at elevated pressure; (4) Combustion processes had a marked influence on the turbulence macroscale under high pressures, however, the turbulence macroscale was not changed even with the increase in pressure.

Molecular precursor-mediated methanol dissociation on Si(1 1 1)7 × 7: ab initio study

We present an ab initio study of methanol interaction with the Si(1 1 1)7 × 7 surface using a Si(1 1 1)4 × 2 model. The study of the methanol dissociation on Si(1 1 1)4 × 2 shows that pair dissociation on adatom–restatom dangling bonds is largely favoured, in agreement with the experimental observations. The “center” type adatom is slightly more reactive than the “corner” type one, although the difference is weak. Similar behaviour is observed in both adatom types. Our results for a direct CH 3OH dissociation favouring a basic cleavage (adsorption of OH and CH 3 fragments) rather than an acidic one (adsorption of H and OCH 3 fragments), we are finally led to take a kinetic effect into consideration to reconcile theory with experiment. We show that the presence of molecular precursor states is possible. Different orientations with respect to the silicon dangling bonds of these molecular precursors are investigated. However, the corresponding energies are very close and, considering their relative energies, it is finally difficult to discriminate between acidic and basic cleavages.

Quasiclassical trajectory study of the collision-induced dissociation of CH3SH+ + Ar.

Quasiclassical trajectory calculations were carried out to study the dynamics of energy transfer and collision-induced dissociation (CID) of CH(3)SH(+) + Ar at collision energies ranging from 4.34 to 34.7 eV. The relative abundances calculated for the most relevant product ions are found to be in good agreement with experiment, except for the lowest energies investigated. In general, the dissociation to form CH(3)(+) + SH is the dominant channel, even though it is not among the energetically favored reaction pathways. The results corroborate that this selective dissociation observed upon collisional activation arises from a more efficient translational to vibrational energy transfer for the low-frequency C-S stretching mode than for the high-frequency C-H stretching modes, together with weak couplings between the low- and high-frequency modes of vibration. The calculations suggest that CID takes place preferentially by a direct CH(3)(+) + SH detachment, and more efficiently when the Ar atom collides with the methyl group-side of CH(3)SH(+).