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A pressure gradient increase from normal pressure in oil zones to overpressure in dry gas zones indicates a lateral disequilibrium of pore pressure in many shale reservoirs. In this work, conditions for the preservation of the lateral pressure disequilibrium during uplift and erosion are investigated. Numerical simulations were conducted by coupling pressure–volume–temperature (PVT) and fluid dynamic calculations. Results show that temperature decrease and pore volume expansion during erosion tends to increase the pressure gradient in the gas or condensate zone and tends to decrease the pressure gradient in the black oil zone; therefore, the PVT effect tends to enhance lateral pressure disequilibrium during erosion. Low permeability is crucial for the preservation of the lateral pressure disequilibrium. The persistence of disequilibrium over geological time (tens of millions of years) requires extremely small vertical permeability (sub-picodarcy range) and horizontal permeability (10 nd or even lower). The horizontal permeability is 10–100 times smaller than laboratory measurements on shale plugs, indicating a discontinuity of laminations and fractures within a shale formation.

In this work, a simple all-nucleic acid cascade-feedback amplification strategy for homogeneous and protein enzyme-free fluorescence detection of HIV-1 related DNA (HIV-1 DNA) has been proposed by integrating catalytic hairpin assembly (CHA) circuit with double-end Mg2+-dependent DNAzyme autocatalytic feedback amplification. Here, the active double-end DNAzyme assemblies were derived from target-catalyzed CHA circuit, which further circularly cleaved the ribonucleotide-containing quenched fluorogenic hairpin substrates to generate distinctly amplified fluorescence signal. Meanwhile, the released quencher-labeled fragments as target DNA analogues were also able to autocatalyze CHA-DNAzyme reaction process, thus improving the determination sensitivity of HIV-1 DNA. The result demonstrated that the fluorescence intensity increment of double-end DNAzyme was over 3 times higher than that of single-end DNAzyme. The sensing method displayed a good linear range from 1 pM to 2 nM with a detectable minimum concentration of 1 pM and high specificity towards different mismatched target DNAs. Moreover, the practical application potential of the proposed method for target DNA detection in complex biological matrices was also assessed. Considering the appealing feature of programmable nucleic acids in CHA-DNAzyme sensing platform, the current strategy may provide a prospective design for detection of broad-spectrum nucleic acid biomarkers.

Methane, along with other short-chain alkanes from some Archean metasedimentary rocks, has unique isotopic signatures that possibly reflect the generation of atmospheric greenhouse gas on early Earth. We find that alkane gases from the Kidd Creek mines in the Canadian Shield are microbial products in a Neoarchean ecosystem. The widely varied hydrogen and relatively uniform carbon isotopic compositions in the alkanes infer that the alkanes result from the biodegradation of sediment organic matter with serpentinization-derived hydrogen gas. This proposed process is supported by published geochemical data on the Kidd Creek gas, including the distribution of alkane abundances, stable isotope variations in alkanes, and CH2D2 signatures in methane. The recognition of Archean microbial methane in this work reveals a biochemical process of greenhouse gas generation before the Great Oxidation Event and improves the understanding of the carbon and hydrogen geochemical cycles., Microbial CH4 kept the early Earth warm under the faint young sun, but clear records are lacking. Here the authors present isotopic evidence that CH4 seepage in the Canadian shield is from hydrogen biodegradation in a Neoarchean ecosystem rather than an abiotic synthesis product.

This work investigated the kinetic fractionation of clumped isotopes (13CH3D and 12CH2D2) during thethermal generation and hydrogen exchange of methane. Kinetic reaction networks involving the five most abundant isotopologues of methane are applied. Hydrogen isotope exchange is modeled with a chain reaction network constrained by thermodynamic parameters of methane isotopologues. Analytical solutions under isothermal conditions are obtained for isotope fractionations during methane generation. Both methane generation and isotope exchange are possible to result in “anticlumping” at low conversions and clumped isotope reversal at high conversions. Sensitivity of anticlumping to 13C and deuterium kinetic isotope effects (KIEs) are tested for methane generation. D-D clumping is found to be sensitive to the deuterium KIE of the capping hydrogen, especially when the quantum tunneling effect is present. Clumped isotopic compositions of methane in natural gas accumulations are affected by multiple geochemical and geological factors. Precursor methyl groups are expected to be enriched in clumped isotopes, and the enrichment results in clumped isotopic compositions more positive than the equilibrated ones at the beginning of methane generation. In the oil window to early gas window, clumped isotopes deplete with thermal maturity due to combinatorial anticlumping and gas expulsion. These two factors may bring about clumped isotopic compositions more negative than the equilibrated values. In late wet gas to dry gas window (the same range of ethane and propane decomposition), C-H bonds of methane are activated, and isotope exchange occurs through free radical reactions; as a result, clumped isotopes eventually approach equilibrium. Clumped isotopic composition of methane records the chemical, thermal and flow histories of its source rock, rather than merely the temperature state of a gas accumulation.

Heat stroke (HS) models in rats are associated with severe intestinal injury, which is often considered as the key event at the onset of HS. Probiotics can regulate the gut microbiota by inhibiting the colonization of harmful bacteria and promoting the proliferation of beneficial bacteria. Here, we investigated the preventive effects of a probiotic Bacillus licheniformis strain (BL, CMCC 63516) on HS rats as well as its effects on intestinal barrier function and gut microbiota. All rats were randomly divided into four groups: control (Con) + PBS (pre-administration with 1 ml PBS twice a day for 7 days, without HS induction), Con + BL group (pre-administration with 1 ml 1 × 108 CFU/ml BL twice a day for 7 days, without HS induction), HS + PBS (PBS, with HS induction), and HS + BL (BL, with HS induction). Before the study, the BL strain was identified by genomic DNA analysis. Experimental HS was induced by placing rats in a hot and humid chamber for 60 min until meeting the diagnostic criterion of HS onset. Body weight, core body temperature, survival rate, biochemical markers, inflammatory cytokines, and histopathology were investigated to evaluate the preventive effects of BL on HS. D-Lactate, I-FABP, endotoxin, and tight-junction proteins were investigated, and the fluorescein isothiocyanate-dextran (FD-4) test administered, to assess the degree of intestinal injury and integrity. Gut microbiota of rats in each group were analyzed by 16S rRNA sequencing. The results showed that pre-administration with BL significantly attenuated hyperthermia, reduced HS-induced death, alleviated multiple-organ injury, and decreased the levels of serum inflammatory cytokines. Furthermore, BL sustained the intestinal barrier integrity of HS rats by alleviating intestinal injury and improving tight junctions. We also found that BL significantly increased the ratios of two probiotic bacteria, Lactobacillus and Lactococcus. In addition, Romboutsia, a candidate biomarker for HS diagnosis, was unexpectedly detected. In summary, BL pre-administration for 7 days has preventative effects on HS that may be mediated by sustaining intestinal barrier function and modulating gut microbiota.

The binding of ferulic acid (FA) with sodium deoxycholate (NaDC) has been investigated using fluorescence and absorption measurements. The fluorescence probe technique of pyrene reveals that the presence of FA favors the micellization of NaDC, leading to the decreased critical micelle concentrations for the formation of NaDC micelles. As NaDC molecules change gradually from monomers via primary micelles into secondary micelles, the intensities of absorption and fluorescence spectra of FA increase at low NaDC concentrations, but decrease suddenly at intermediate NaDC concentrations, and finally increase again at high NaDC concentrations. These results corroborated well with FA fluorescence lifetime data suggesting that the aryl ring of FA hydrophobically binds to the convex surface of NaDC monomers, whereas the hydrogen bonding between FA and NaDC is significantly involved in NaDC primary micelles, which is gradually overcome by the hydrophobic interaction between FA and NaDC secondary micelles. The absorption and fluorescence spectra as well as the binding constant value of FA indicate the strong binding of FA in the large hydrophobic core of NaDC secondary micelles. At low FA concentrations, the measurement of FA anisotropy suggests that FA can increase the packing order of hydrophobic surfaces in NaDC secondary micelles, whereas the high amount of FA can greatly disrupt the packing structure of NaDC secondary micelles which is ascribed to the formation of FA dimers. The spectroscopic experiments outlined here present the binding events of FA with NaDC monomers and primary and secondary micelles, which are significantly related with the hydrophobic force and hydrogen bonding as well as the unique structural characteristics of bile salt.

Explanations for the thermal decomposition of ethane and propane in sedimentary basins have long been conceptual without quantitative evidence. This work bridges the gap between 13C depletion and the conversion of ethane and propane, and confirms their thermal decomposition during the late catagenesis stage. Isotopic fractionation was rigorously investigated in a partly reversible reaction scheme for ethane and propane decompositions. Analytical solutions under isothermal conditions were derived. Non-monotonic isotopic fractionation with respect to conversion is demonstrated, which may be ignored if a steady-state approximation is applied. The results imply that depletion of 13C in ethane and propane as their molar fractions decrease (isotopic inverse with respect to thermal maturity) results from the reversible conversion from alkane to alkyl groups. Kinetic parameters were obtained for ethane and propane decomposition in sedimentary basins, and the chemical kinetic method applies to different isotopic fractionation systems. The results help to better understand the chemical form of deep carbon and the thermal conversion of gaseous hydrocarbons in the geochemical carbon cycle.

Linear covariations between stable isotopic compositions of methane, ethane and propane have long been observed in natural gas accumulations; e.g., a plot of δ13Cpropane versus δ13Cethane of natural gas fall along a straight line. This work investigates physicochemical mechanisms behind the correlations and derives the theoretical slope value for each correlation line. Most slopes are close to the values of statistical distribution, which are 2/3 (0.67) for δ13Cpropane vs. δ13Cethane, 2 for δ13Cmethane vs. δ13Cethane, and 3/4 (0.75) for δ2Hpropane vs. δ2Hethane. When detailed kinetic isotopic effects are considered, the theoretical slope values of δ13Cpropane vs. δ13Cethane and δ2Hpropane vs. δ2Hethane change slightly to 0.68 and 0.73, respectively; the slope of δ13Cmethane vs. δ13Cethane is about 2.4. These slopes are consistent to field data of natural gas generated from kerogen before dry gas window. An exception is the slope of the δ2Hmethane vs. δ2Hethane correlation line; the deviation of field data from theoretical slope suggests that the reaction path of methane generation differs from that of ethane and propane generation; proton shift is probably involved in methane generation. The physical meanings of intra-molecular isotopic fractionation in propane and clumped isotopic fractionation in methane are discussed based on statistical and kinetic analysis.

The levels of K-ras gene mutation was thought to be closely related to the early diagnosis of colorectal cancer and the evaluation of the efficacy of targeted drugs. Here, a high-efficiency, enzyme- and label-free electrochemical sensor for K-ras G12D point mutation (K-ras G12DM) determination was developed by concatenation of split Mg2+-dependent DNAzyme and hybridization chain reaction (HCR). The presence of target induced split DNAzyme to assemble into an intact and activated conformation, catalyzing the cyclic cleavage of substrates to produce a mass of intermediates. Subsequently, the intermediate products triggered downstream HCR events to form long notched dsDNA, which would couple a large amount of methylene blue (MB) through π − π stacking interactions to generate a significant electrochemical signal. Under optimal conditions, this sensor platform achieved a highly sensitive detection of the target, with the lowest detection limit of 0.5 f. and a good linear relationship in the range of 0.5 f. to 50 nM. Furthermore, the biosensor not only easily distinguished target from high concentrations of mismatched target analogs, but also detected rare mutations with mutation frequencies as low as 0.001%. Due to its low cost, high sensitivity and high specificity, this strategy has broad prospects for other low-abundance targets and point mutations.

A kinetic compositional model covering the generation of methane through pentanes is calibrated with both experimental and field data. A continuous distribution of activation energy ( E = E 0 + yE s ) is applied to describe the heterogeneity of hydrocarbon generation kinetics, with E 0 (activation energy E at conversion y = 0) as the location parameter and E s as the scale parameter. The best fit gives E 0 = 53.0 kcal/mol and E s = 4.0 kcal/mol for methane generation with frequency factor A = 3 × 10 11 s −1 . The values of E 0 and E s for the generation of ethane, propane, n -butane and n -pentane decrease with carbon chain length, with a constant A value. The generation of branched alkanes (isobutane and isopentane) has higher E 0 and narrower E s values compared with the generation of their n -alkane isomers. The model adequately describes natural gas compositional properties with thermal maturation, including: (1) decreased wetness, (2) a log-log relation between the C 2 H 6 through C 5 H 12 concentration, and (3) increased i -C 4 H 10 / n -C 4 H 10 and i -C 5 H 12 / n -C 5 H 12 with thermal maturity. The contribution of secondary-cracking gas at higher maturity, which may change the above trends, was also quantified.

The possibility of autocatalysis during thermochemical sulfate reduction (TSR) by gaseous hydrocarbons was investigated by examination of previously reported laboratory and field data. This reaction was found to be a kinetically controlled non-autocatalytic process, and the apparent lack of autocatalysis is thought to be due to the absence of the required intermediate species. Kinetic parameters for chemical and carbon isotopic fractionations of gaseous hydrocarbons affected by TSR were calculated and found to be consistent with experimentally derived values for TSR involving long-chain hydrocarbons. Model predictions based on these kinetic values indicate that TSR by gaseous hydrocarbon requires high-temperature conditions. The oxidation of C 2–5 hydrocarbons by sulfate reduction is accompanied by carbon isotopic fractionation with the residual C 2–5 hydrocarbons becoming more enriched in 13 C. Kinetic parameters were calculated for the stable carbon isotopic fractionation of gaseous hydrocarbons that have experienced TSR. Model predictions based on these kinetics indicate that it may be difficult to distinguish the effects of TSR from those of thermal maturation at lower levels of hydrocarbon oxidation; however, unusually heavy δ 13 C 2+ values (>−10‰) can be diagnostic of high levels of conversion (>50%). Stoichiometric and stable carbon isotopic data show that methane is stable under the investigated reaction conditions and is likely a product of TSR by other gaseous hydrocarbons rather than a significant reactant. These results indicate that the overall TSR reaction mechanism for oxidation of organic substrates containing long-chain hydrocarbons involves three distinct phases as follows: (1) an initial slow and non-autocatalytic stage characterized by the reduction of reactive sulfate by long-chain saturated hydrocarbons; (2) a second autocatalytic reaction phase dominated by reactions involving reduced sulfur species and partially oxidized hydrocarbons; (3) and a final, or late-stage, TSR reaction in which hydrocarbon oxidation continues at a slower rate via the non-autocatalytic reduction of sulfate by gaseous hydrocarbons.

Functional star-shaped 4-arm poly(ethylene glycol)-b-poly[(e-caprolactone-co-γ-amino-e-caprolactone)] (4-arm PEG-b-P(CL-co-ACL) was synthesized through ring-opening polymerization. The structure of the copolymer was confirmed by 1H NMR, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). To further understand the copolymers, the difference of the conversion rate between e-caprolactone (CL) and γ-(carbamic acid benzyl ester)-e-caprolactone (CABCL) and the detailed deprotection condition were studied. The thermal property of the copolymer was analyzed by WAXR and differential scanning calorimetry (DSC), which demonstrated that the thermal property could be well adjusted. The pH-responsive behavior of the copolymers was studied in detail by dynamic light scattering (DLS), pH titration, and pyrene fluorescence methods, which indicated that it could form micelles and exhibit pH responsibility. Moreover, the copolymer was nontoxic and had good biocompatibility according to the results by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay.

Carbon isotopic composition (δ 13 C) reversals with respect to maturity trends have been reported for ethane and propane in Barnett Shale gas in the Fort Worth Basin, U.S.A. This trend also exists in some conventional gas reservoirs, such as in the Ordos Basin, China and Appalachian Basin, U.S.A. Fractionation during mass transport is unlikely to be a significant mechanism, because its effect is minor under geological conditions, it would have caused more obvious reversal for methane than for ethane and propane, and mass transport can not account for the occurrence of the trend both inside and outside source rocks. This paper demonstrates that the reversal may result from mixing of indigenous primary gas (generated directly from kerogen) and secondary gas (generated from oil and condensate) within source rocks, and presents deconvolution results using end-members derived from a kinetic isotope fractionation model. The results, including the wetness and mixing ratio of primary and secondary gases, are consistent with geological conditions. Condensates may be the major precursor of the secondary gas in shale when the reversal occurs. A complete trend of δ 13 C variations in methane and ethane with maturity is proposed that is based on the indigenous mixing mechanism.

Unconventional rock or sediment units require stimulation to produce retained petroleum due to the combined effects of petroleum viscosity and matrix permeability. Despite intense study, current methods to identify unconventional sweet spots remain largely empirical, i.e., most rely on a cookbook of independent organic and inorganic geochemical measurements that are compared with those of productive rock units. A sweet spot is a volume of rock having favorable porosity, permeability, fluid properties, water saturation, and/or rock stress that is likely to produce more petroleum than surrounding rock. Many methods to identify sweet spots are time-consuming, require discrete samples (i.e., cannot be completed while drilling), and are not at the proper sampling scale to most effectively identify target intervals. Improved work flows are needed that incorporate rapid, properly scaled geochemical and geomechanical measurements that can be completed while drilling, coupled with fully integrated three-dimensional (3D) basin and petroleum system modeling (BPSM) that reduces the risk associated with predicting sweet spots. For example, the development of saturate-aromatic-resin-asphaltene (SARA) modeling can be used to predict the composition of petroleum that remains in unconventional rock units. As another example, calibrated 3D BPSM that includes Langmuir sorption parameters can be used to predict sorption capacity and sorbed gas content throughout targeted subsurface formations. Organic and inorganic geochemical logs offer independent means to identify sweet spots. Organic geochemical logs are commonly based on direct measurements of carbonate content and pyrolysis response, but they require discrete samples at predetermined depth intervals, which are typically analyzed in the laboratory rather than at the well site. Inorganic geochemical logs are based on indirect calculation of mineral content and total organic carbon (TOC) content without the need to collect samples. Although inorganic geochemical logs do not determine the quality or thermal maturity of the kerogen, they provide continuous data with depth and can be quantified in real time during drilling. Current tools to map shale gas or shale oil sweet spots include nominal measures of richness (e.g., total organic carbon or TOC, hydrogen index, thickness), thermal maturity (e.g., maximum burial depth, vitrinite reflectance, Rock-Eval Tmax), trapping mechanism (e.g., tight shale or juxtaposed organic-rich and lean units within the target interval), porosity and permeability, and stress or the tendency to fracture (e.g., brittleness index). Wireline measurements of TOC offer continuous data with depth, but many need to be calibrated against discrete organic geochemical measurements. Additional parameters to identify sweet spots in vertical sections include the oil saturation index, continuum flow isotopic fractionation during gas release from crushed samples, and the stable carbon isotopic rollover of ethane, propane, and other gases. Isotopic rollover has been observed in shale gas plays and some conventional reservoirs and it appears to result from mixing of primary and secondary gas cracked from kerogen and retained liquid, respectively. Most unconventional rock units that display rollover are overpressured and productive, although some rollovers occur in areas having both good and poor production.

Compound-specific carbon and hydrogen isotopic compositions of three natural gas round robins were calibrated by ten laboratories carrying out more than 800 measurements including both on-line and off-line methods. Two-point calibrations were performed with international measurement standards for hydrogen isotope ratios (VSMOW and SLAP) and carbon isotope ratios (NBS 19 and L-SVEC CO 2 ). The consensus δ 13 C values and uncertainties were derived from the Maximum Likelihood Estimation (MLE) based on off-line measurements; the consensus δ 2 H values and uncertainties were derived from MLE of both off-line and on-line measurements, taking the bias of on-line measurements into account. The calibrated consensus values in ‰ relative to VSMOW and VPDB are: NG1 (coal-related gas): Methane: δ 2 H VSMOW = − 185.1‰ ± 1.2‰, δ 13 C VPDB = − 34.18‰ ± 0.10‰ Ethane: δ 2 H VSMOW = − 156.3‰ ± 1.8‰, δ 13 C VPDB = − 24.66‰ ± 0.11‰ Propane: δ 2 H VSMOW = − 143.6‰ ± 3.3‰, δ 13 C VPDB = − 22.21‰ ± 0.11‰ i -Butane: δ 13 C VPDB = − 21.62‰ ± 0.12‰ n -Butane: δ 13 C VPDB = − 21.74‰ ± 0.13‰ CO 2 : δ 13 C VPDB = − 5.00‰ ± 0.12‰ NG2 (biogas): Methane: δ 2 H VSMOW = − 237.0‰ ± 1.2‰, δ 13 C VPDB = − 68.89‰ ± 0.12‰ NG3 (oil-related gas): Methane: δ 2 H VSMOW = − 167.6‰ ± 1.0‰, δ 13 C VPDB = − 43.61‰ ± 0.09‰ Ethane: δ 2 H VSMOW = − 164.1‰ ± 2.4‰, δ 13 C VPDB = − 40.24‰ ± 0.10‰ Propane: δ 2 H VSMOW = − 138.4‰ ± 3.0‰, δ 13 C VPDB = − 33.79‰ ± 0.09‰ All of the assigned values are traceable to the international carbon isotope standard of VPDB and hydrogen isotope standard of VSMOW.

Fractionation of carbon isotopes of methane in natural gas due to mass transport is evaluated based on statistical thermodynamics, microkinetics and fluid dynamics analysis. A continuum flow model with coupled adsorption/desorption and diffusion is defined and calibrated to describe isotope fractionation of natural gas due to flux in low permeability rocks. Isotopic fractionations due to post-generation mass transport are evaluated with analytical and numerical solutions under different conditions. Calculations strongly suggest that isotopic fractionation in adsorption/desorption systems are mostly dominated by mass transport, rather than the fractionation between adsorbate phase and gas phase. At steady state, the fractionation is determined by the drop of partial pressure and the diffusivity difference of the isotopologues. At non-steady state, the coupling of adsorption/desorption may bring about non-linear deviation of isotope fractionation. Stronger adsorption affinity and larger adsorption capacity result in a remarkably negative isotopic composition of early gas, but this is not the case of the weak adsorption of methane on organic matter. Large isotopic fractionation due to gas transport may happen under laboratory conditions with sufficient degassing, but the fractionation is limited under geological conditions.

Zinc oxide has a variety of applications in catalysis both as support and as active phase for hydrogenation or dehydrogenation reactions. This review provides an overview of the surface chemistry of ZnO nanoparticles concerning the interaction with small molecules such as CO, CO 2 , H 2 , H 2 O, and CH 3 OH, which are relevant for the catalytic synthesis of methanol and the water gas shift reaction. These interactions were studied by combining surface-sensitive methods such as infrared spectroscopy, temperature-programmed desorption, and adsorption calorimetry. A thorough understanding of the processes occurring on the different exposed facets of the ZnO particles in an atmosphere of reactive gases was achieved based on the comparison with results obtained in ultra-high vacuum with single-crystalline surfaces, i.e. under well-defined conditions, and by using first-principles calculations.

The interaction of carbon monoxide and oxygen with gold particles supported on zinc oxide, alumina, and titania was investigated by microcalorimetry. Multiple processes were detected during CO adsorption, including adsorption of CO on the gold particles and support, oxidation of CO, and formation of carbonates. The rate of O2 adsorption was much slower than that of CO adsorption. The heats and entropies of CO adsorption on the Au sites indicated that the interaction between CO and Au supported on TiO2 is much stronger than that between CO and Au supported on ZnO. The Au/ZnO sample had the largest amount of lattice oxygen (7.6 μmol/g), which reacted with CO to give CO2.

The adsorption of carbon dioxide on differently pretreated polycrystalline ZnO was studied by thermodynamic and kinetic methods. The uptake of CO2 observed in a static Tian−Calvet microcalorimeter ...

The adsorption of CO on polycrystalline ZnO powder samples was investigated as a function of the pretreatment by applying static adsorption microcalorimetry and temperature-programmed desorption (TPD). Mainly weak adsorption sites were found to be present on the exposed ZnO surfaces but also a minor amount of highly active sites (>0.1 μmol/m2). On the majority sites, the adsorption of CO is weak, as reflected by the isotherms and the TPD profiles, with a maximum heat of adsorption of about 40 kJ/mol, which decreases with increasing coverage and also with an increasing amount of surface hydroxyl groups. The standard adsorption entropy is derived to amount to −102 J mol−1 K−1. These weak adsorption sites are hardly influenced by the pretreatment in flowing oxygen, hydrogen, or helium. On the highly active sites, as probed by small doses of CO in the calorimetric experiments, different exothermic (>100 kJ/mol) and endothermic surface reactions occur in addition to CO adsorption, depending on the gas atmosphe...

The back-titration of atomic oxygen chemisorbed on metallic copper using carbon monoxide is investigated by microcalorimetry. Results from simulations based on a microkinetic model of the back-titration are used for processing of microcalorimetric data. In addition, surface oxidation of copper by nitrous oxide is investigated by microcalorimetry. The results are compared with results obtained by nitrous oxide reactive frontal chromatography and by static oxygen adsorption studied by microcalorimetry. The heat of adsorption of nitrous oxide on copper amounts to 304 kJ mol−1, and the heat of adsorption of carbon monoxide on surfaceoxidized copper is in the range from 120 to 70 kJ mol−1.

Standard entropies of adsorption (Δs0) of CO on different materials (Cu catalysts, Au catalysts, ZnO and to TiO2) are obtained from static adsorption microcalorimetry, adsorption isobars and temperature-programmed desorption, based on the thermodynamics of adsorption on energetically heterogeneous surfaces. Vibrational entropies of the surfaces svibα are normally between the rotational and the standard translational entropy of CO in gas phase, and decrease with increasing adsorption energy, which agrees with the explanation of statistical thermodynamics. Δs0 reflects both the mobility of adsorbates and the specific adsorbate-adsorbent interaction. Limits for reasonable values of the entropy of adsorption are proposed.

A profound microkinetic analysis of the influence of re-adsorption and of surface energetic heterogeneity on temperature-programmed desorption (TPD) experiments is performed on the basis of the Wigner-Polanyi equation. Exact solutions for TPD experiments under both re-adsorption-free and re-adsorption-dominated conditions from energetically homogeneous surfaces are presented. TPD experiments from energetically heterogeneous surfaces with uniform energy distribution are analyzed considering the surface diffusion of adsorbates. Convenient mathematical approaches are derived to evaluate the TPD profiles for first-order and second-order desorption. It is shown that, when the heterogeneity is strong and the coverage is not close to 0 or 1, the slope in the plot of ln(T p /β) versus 1/(RT p ) yields the differential heat of adsorption for freely occurring re-adsorption at Θ = Θ p . In the absence of re-adsorption, the differential desorption energy at Θ = Θ p can be derived from the slope. Two case studies show that the thermodynamic parameters, especially the surface energy distribution, can be obtained successfully from TPD experiments based on the derived methods.

Adsorption kinetics on energetically heterogeneous surfaces under isothermal conditions is analyzed using the uniform energy distribution model. Considering the quasi-equilibrium of surface diffusion between the adsorption sites with different energy, the kinetic equations d Θ / d t = ( k a p − A d K diff ) ( 1 − Θ ) for first-order adsorption and d Θ / d t = k a p ( 1 − Θ ) 2 − A d K diff Θ ( 1 − Θ ) for dissociative adsorption are obtained, where K diff is a coefficient describing the surface diffusion equilibrium, which depends on the coverage and the energy distribution. Under isochoric conditions with p decreasing due to adsorption, surface diffusion accelerates the rate towards equilibrium significantly, as observed in static calorimetric adsorption experiments. An approximate solution in Lagergren form is derived for this condition.

Base catalysis is of importance for organic synthesis in general and fine chemicals manufacture in particular. Activated hydrotalcites have recently received a great deal of attention as solid base catalysts; however, no systematic work on the nature of their active sites has been published up till now. In this work two different methods have been applied to activate Mg-Al hydrotalcites to obtain Brønsted-base catalysts for liquid-phase condensation reactions. Activation via thermal treatment followed by rehydration (HT-reh) resulted in irregularly stacked platelets ( approximately 60 nm), whereas the sample activated via aqueous ion-exchange (HT-exc) preserved its original hexagonal hydrotalcite platelets ( approximately 100 nm). The specific activity for the self-condensation of acetone of HT-reh was over 10 times that of HT-exc. The enthalpy of CO2 adsorption on the activated hydrotalcites determined with calorimetry to gain insight into the strength of the basic sites showed very similar values. IR spectra of adsorbed CDCl3 as probe molecule on the differently activated samples revealed large differences in adsorbed amounts, but again the strength of the basic sites appeared to be the same. These results point to steric hindrance for the substrate molecules as the main factor determining differences in catalytic activity. The high accessibility of Brønsted-base sites in HT-reh is proposed to involve a distorted edge structure of the platelets. The edge structure of exchanged samples could be distorted too, either by exchange under reflux conditions or under ultrasonic treatment. In line with the proposed model, the distorted exchanged samples displayed a much higher catalytic activity than HT-exc.

The so-called “large-medium gas field” means a gas field with proven reserves equal to or larger than 100 × 108 m3. Up to 1997, 23 coal-formed great-medium fields are discovered in China, excluding two in Taiwan Province. Their proven reserves take 50.9% in total natural gas reserves. Therefore, the coal-formed great-medium gas field plays a decisive role in natural gas reserves and the study of their controlling factors is very important both in theory and in practice. There are six major controlling factors on the formation of coal-formed large-medium gas fields: (i) The generating center of coal-formed gas and its surrounding area; (ii) low potential area; (iii) late pool-forming period; (iv) traps related to the paleo-uplifits in coal-formed gas area; (v) above or between abnormally pressured compartments; (vi) faulted traps related to coal-bed.

Summary Fluid pressure is a key factor in determining hydrocarbon productivity of unconventional plays. Most unconventional plays have experienced uplift accompanied by erosion after the maximum burial depth, which has altered the fluid pressure in both fluid dynamics and thermodynamics. In this study, we calculate the fluid pressure variation of unconventional plays during uplift, taking into account the factors of hydrocarbon compositions, thermal history, initial pressure, and sealing conditions . The calculation considers both fluid dynamics (Darcy flow and diffusion) and thermodynamics (pressure-volume-temperature relations hips). The results show that uplift with an ideal sealing condition may enhance the overpressure of gas reser voirs and that of most volatile oil reservoirs with gas to oil ratio (GOR) > 1000 scf/bbl, and decrease the overpr essure (or form underpressure) in black oil reservoirs with GOR < 500 scf/bbl. Good sealing layers with low permeabilit y, high capillary pressure and low diffusivity are required to keep the abnormal pressure in unconventional reservoirs.

The adsorption of CO on polycrystalline TiO2 was investigated by static adsorption microcalorimetry. The initial differential heat of adsorption (qdiff,0) of CO on polycrystalline titania is 40 kJ/mol, and the standard adsorption entropy (Deltas0) is -104 J mol(-1) K(-1). These results are consistent with those derived from temperature-programmed desorption and FTIR results in the literature. The good reproducibility of the isotherms and the stable qdiff indicate that the lattice oxygen and hydroxyl groups on titania surface are basically not reactive to adsorbed CO.

Adsorption on heterogeneous surfaces with three basic energy distribution models (uniform model, exponential model, and normal-like model) is studied. Exact analytical solutions of the adsorption isotherms and the heats of adsorption are derived for the uniform and exponential models, and, with these solutions including a numerical solution for the normal-like model, the behavior of the differential heat of adsorption and the "apparent" standard adsorption entropy concerning the overall surface is described as a function of coverage and temperature. The approximations underlying the isotherms and heats of adsorption in the Temkin, Freundlich, and Langmuir-Freundlich types of adsorption are rationalized. By comparing these empirical formulas to the exact solutions, the level of these approximations is found to be identical, which is similar to the "condensation approximation". Their preconditions are that either the temperature is low enough, or the surface is strongly heterogeneous. Generally, they are suitable for the middle coverage range. The exact solutions provide a method to obtain more information on the heats, entropy, and heterogeneity of the catalyst surface from the calorimetric measurement of the heat of adsorption.

A reliable method for adsorption systems in equilibrium is established to derive coverage-dependent kinetics and thermodynamics from the volumetric data obtained during the static microcalorimetric measurement of heats of adsorption. The Wigner-Polanyi equation is applied to analyze the pressure change as a function of time during stepwise dosing of the adsorptive until thermodynamic adsorption-desorption equilibrium is established. For carbon monoxide adsorption on a hydrogen-reduced Cu/ZnO/Al2O3 catalyst, the adsorption rate constant (ka) is found to be in the range from 10(-6) to 10(-4) Pa(-1) s(-1), and the desorption rate constant (kd) from 10(-4) to 10(-2) s(-1), both increasing with fractional coverage theta. The kinetically derived equilibrium constant Ktheta is in good agreement with Ktheta obtained from the adsorption isotherm. RT ln(Kp0) and the differential heat of adsorption (qdiff) were found to decrease in parallel, reflecting a normal Temkin-type heterogeneity.

CO adsorption on the ternary methanol synthesis Cu/ZnO/Al2O3 catalyst was studied in detail by means of adsorption microcalorimetry and flow temperature-programmed desorption (TPD). Based on these experimental data, we established a microkinetic analysis method, which provides information about the adsorption kinetics of CO on the catalyst surface. Experimentally derived microcalorimetric heats of adsorption were applied in a microkinetic model to simulate TPD curves with varying initial coverage. Two approaches were used: an integral approach based on evaluation of the integral heats of adsorption which predicts the experimental TPD curves roughly and provides first approximations for the preexponential factors. The second, more detailed approach was based on the simulation of the adsorption isotherm taking the experimentally determined coverage-dependence of the heat of adsorption into account. This approach led to a significantly improved agreement between experimental and simulated TPD curves. Moreover, it was possible to derive the standard entropy of adsorption. The general applicability of our approaches is demonstrated by analyzing the CO TPD and microcalorimetry data obtained with a binary ZnO-free Cu/Al2O3 catalyst.

A systematic series of binary and ternary copper catalysts was investigated using the methanol synthesis reaction at atmospheric pressure. Strong metal-support interactions between copper and zinc oxide induced by strongly reducing conditions were probed by the adsorption of carbon monoxide, which was monitored qualitatively and quantitatively by a combination of microcalorimetry, temperature-programmed desorption experiments and Fourier transform infrared spectroscopy. For the zinc oxide-containing catalysts, the pretreatment in flowing carbon monoxide at 493 K resulted in a severe decoration of the copper metal particles with ZnOx adspecies, whereas after methanol synthesis at 493 K the state of the copper was essentially identical to that seen after hydrogen reduction. Copper was always found to be present in its zero-valent state.

Carbon isotopic composition of methane in Ordovician gas reservoir in the Changqing Gasfield can reflect the dominance of Upper Paleozoic coaltype gas despite its high mature degree. The12C-rich ethane in the Ordovician reservoir (δ13C2 < −29%), known as a marker as oiltype gas, does not indicate the Ordovician marine carbonate as main source rock, it is because of the relative less ethane content in coaltype gas than in oiltyped gas due to generation and migration. The way of Upper Paleozoic coaltype gas migrating into the Ordovician reservoir is widely through the unconformlty instead of only through the erosion groove in the weathering crust.