CO2 Consumption Rate Research Articles

Chemical balance of the Yellow River source region, the northeastern Qinghai-Tibetan Plateau: Insights about critical zone reactivity

Rivers play a vital role in geochemical processes of the critical zone. As the Third Pole, the geochemical processes of the Qinghai-Tibetan Plateau are vital to global element cycles. The Yellow River source region is located in the northeastern Qinghai-Tibetan Plateau, yet there has been little research concerning water chemistry in this region. In this study, river water and rain samples were collected to analyze the stable isotopes and major ion chemistry in the Yellow River source region. The δ18O and δD values ranged from −12.9‰ to −4.5‰ and from −95.7‰ to −36.7‰, respectively. The stable isotopic values of tributaries were lower than those in the main stream, and the construction of the dam could result in the enrichment of δ18O and δD. The stable isotopic values showed that precipitation was the main source of river water. The total dissolved solids (TDS) in river water ranged from 214.9 to 563.2 mg/L, and calcium and bicarbonate were the dominant ions. The average contributions of atmospheric input, evaporites, silicates, and carbonates to the dissolved load of river water were 1.8%–12.5%, 12.4%–15.9%, 18.1%–18.4%, and 56.7%–64.3%. The silicate and carbonate weathering rates were 2.3–2.5 t/km2/yr and 17.4–19.6 t/km2/yr, respectively. The chemical denudation rate in the study area was about 23.0–26.8 t/km2/yr, comparable to the world average value. The CO2 consumption rates by silicate and carbonate weathering were 91–94 × 103 moL/km2/yr and 185–208 × 103 moL/km2/yr, respectively. The TDS flux in the study area was 6.1 × 109 kg/yr, which accounted for 38–47% of that of the Yellow River into the sea. This study showed that although as an alpine arid area, the Yellow River source region had a comparable chemical denudation rate to the world average value, and even higher CO2 consumption rates by silicate and carbonate weathering than some of the large rivers in the world.

Mechanism of Carbon Monoxide Dissociation on a Cobalt Fischer-Tropsch Catalyst.

The way in which the triple bond in CO dissociates, a key reaction step in the Fischer–Tropsch (FT) reaction, is a subject of intense debate. Direct CO dissociation on a Co catalyst was probed by 12C16O/13C18O scrambling in the absence and presence of H2. The initial scrambling rate without H2 was significantly higher than the rate of CO consumption under CO hydrogenation conditions, which indicated that the surface contained sites sufficiently reactive to dissociate CO without the assistance of H atoms. Only a small fraction of the surface was involved in CO scrambling. The minor influence of CO scrambling and CO residence time on the partial pressure of H2 showed that CO dissociation was not affected by the presence of H2. The positive H2 reaction order was correlated to the fact that the hydrogenation of adsorbed C and O atoms was slower than CO dissociation. Temperature‐programmed in situ IR spectroscopy underpinned the conclusion that CO dissociation does not require H atoms.

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 2. Fischer-Tropsch Synthesis.

Fischer–Tropsch (FT) synthesis is one of the most complex catalyzed chemical reactions in which the chain-growth mechanism that leads to formation of long-chain hydrocarbons is not well understood yet. The present work provides deeper insight into the relation between the kinetics of the FT reaction on a silica-supported cobalt catalyst and the composition of the surface adsorbed layer. Cofeeding experiments of 12C3H6 with 13CO/H2 evidence that CHx surface intermediates are involved in chain growth and that chain growth is highly reversible. We present a model-based approach of steady-state isotopic transient kinetic analysis measurements at FT conditions involving hydrocarbon products containing up to five carbon atoms. Our data show that the rates of chain growth and chain decoupling are much higher than the rates of monomer formation and chain termination. An important corollary of the microkinetic model is that the fraction of free sites, which is mainly determined by CO pressure, has opposing effects on CO consumption rate and chain-growth probability. Lower CO pressure and more free sites leads to increased CO consumption rate but decreased chain-growth probability because of an increasing ratio of chain decoupling over chain growth. The preferred FT condition involves high CO pressure in which chain-growth probability is increased at the expense of the CO consumption rate.

Mechanism of Cobalt-Catalyzed CO Hydrogenation: 1. Methanation.

The mechanism of CO hydrogenation to CH4 at 260 °C on a cobalt catalyst is investigated using steady-state isotopic transient kinetic analysis (SSITKA) and backward and forward chemical transient kinetic analysis (CTKA). The dependence of CHx residence time is determined by 12CO/H2 → 13CO/H2 SSITKA as a function of the CO and H2 partial pressure and shows that the CH4 formation rate is mainly controlled by CHx hydrogenation rather than CO dissociation. Backward CO/H2 → H2 CTKA emphasizes the importance of H coverage on the slow CHx hydrogenation step. The H coverage strongly depends on the CO coverage, which is directly related to CO partial pressure. Combining SSITKA and backward CTKA allows determining that the amount of additional CH4 obtained during CTKA is nearly equal to the amount of CO adsorbed to the cobalt surface. Thus, under the given conditions overall barrier for CO hydrogenation to CH4 under methanation condition is lower than the CO adsorption energy. Forward CTKA measurements reveal that O hydrogenation to H2O is also a relatively slow step compared to CO dissociation. The combined transient kinetic data are used to fit an explicit microkinetic model for the methanation reaction. The mechanism involving direct CO dissociation represents the data better than a mechanism in which H-assisted CO dissociation is assumed. Microkinetics simulations based on the fitted parameters confirms that under methanation conditions the overall CO consumption rate is mainly controlled by C hydrogenation and to a smaller degree by O hydrogenation and CO dissociation. These simulations are also used to explore the influence of CO and H2 partial pressure on possible rate-controlling steps.

Kinetics and mechanistic studies of CO-rich hydrogen production by CH4/CO2 reforming over Praseodymia supported cobalt catalysts

The production of hydrogen and syngas by catalytic methane dry reforming is often accompanied by carbon deposition. In order to mitigate the effect of carbon deposition, it is important to have a full understanding of the elementary steps involve in the methane dry reforming over a given catalyst. This will enable the proper design and optimization of such catalyst to minimize catalyst deactivation by carbon deposition. In this study, the kinetic and mechanistic features of 20 wt%Co/Pr2O3 catalyst in the methane dry reforming reaction has been investigated as a function of CH4 and CO2 partial pressures and reaction temperature. The 20 wt%Co/Pr2O3 catalyst was synthesized by wet impregnation method and characterized for its physicochemical properties by TGA, XRD, N2-physisorption analysis, TEM, FESEM, EDX, H2-TPR, NH3 and CO2. The excellent physicochemical properties of the 20 wt%Co/Pr2O3 catalysts resulted in a high rate of CH4(rCH4) and CO2(rCO2)consumption. The highest values of 3.6 mmol gcat−1 min−1 and 3.2 mmol gcat−1 min−1 were obtained for rCH4 and rCO2, respectively at 50 kPa and 1023 K. The kinetic behavior of the as-synthesized 20 wt%Co/Pr2O3 catalyst in the methane dry reforming reaction was measured in a fixed bed stainless steel reactor at CH4/CO2 partial pressure range of 5–50 kPa and temperature range of 923–1023 K. The data obtained from the kinetic measurement were fitted into seven Langmuir-Hinshelwood (LH) Models. The Model were statistically discriminated using root mean square deviation (rmsd) and coefficient of determination (R2). The statistical analysis revealed that LH kinetic Model 7 (2-step dual site rate determining steps (RDS) involving CH4 activation by metal Co and C gasification by adsorbed CO2 on support site) fits very well the experimental data. The R2 values of 0.962, 0.982, and 0.989 as well as, rmsd values of 0.095 0.038, and 0.035 were obtained at 923, 973, and 1023 K respectively. Activation energies of 61.67 and 32.52 kJ/mol were obtained for the rate of consumptions of CH4 and CO2, an indication that lower energy barrier is required for the activation of CO2 compared to CH4. Based on Model 7, the mechanism of the methane dry reforming reaction over the 20 wt%Co/Pr2O3 catalyst can best be described by 2-step dual site rate determining steps whereby the activation of CH4 by the metal Co resulted in hydrogen and carbon formation. The carbon formed was subsequently gasified by the lattice oxygen released from the activation of the CO2 by the support site.

Contribution of forests to the carbon sink via biologically-mediated silicate weathering: A case study of China

During silicate weathering, atmospheric carbon dioxide (CO2) is consumed and base cations are released from silicate minerals to form carbonate and bicarbonate ions, which are finally deposited as carbonate complexes. Continental silicate weathering constitutes a stable carbon sink that is an important influence on long-term climate change, as it sequesters atmospheric carbon dioxide at a million-year time scale. Traditionally, CO2 sequestered through silicate weathering is estimated by measuring the flux of the base cations to watersheds. However, plants also absorb considerable amounts of base cations. Plant biomass is often removed from ecosystems during harvesting. The base cations are subsequently released after decomposition of the harvested plant materials, and thereby enhance CO2 consumption related to weathering. Here, we analyze plant biomass storage-harvest fluxes (production and removal of biomass from forests) of base cations in forests across China to quantify the relative contribution of forest trees to the terrestrial weathering-related carbon sink. Our data suggest that the potential CO2 consumption rate for biomass-related silicate weathering (from the combined action of with afforestation/reforestation, controlled harvesting and rock powder amendment) in Chinese forests is 7.9±4.1Tg CO2yr−1. This represents ~34% of the chemical weathering rate in China. Globally, forests may increase CO2 sequestration through biologically-mediated silicate weathering by ~32%.

The effects of CO2 and H2 on CO metabolism by pure and mixed microbial cultures

BackgroundSyngas fermentation, the bioconversion of CO, CO2, and H2 to biofuels and chemicals, has undergone considerable optimization for industrial applications. Even more, full-scale plants for ethanol production from syngas fermentation by pure cultures are being built worldwide. The composition of syngas depends on the feedstock gasified and the gasification conditions. However, it remains unclear how different syngas mixtures affect the metabolism of carboxidotrophs, including the ethanol/acetate ratios. In addition, the potential application of mixed cultures in syngas fermentation and their advantages over pure cultures have not been deeply explored. In this work, the effects of CO2 and H2 on the CO metabolism by pure and mixed cultures were studied and compared. For this, a CO-enriched mixed culture and two isolated carboxidotrophs were grown with different combinations of syngas components (CO, CO:H2, CO:CO2, or CO:CO2:H2).ResultsThe CO metabolism of the mixed culture was somehow affected by the addition of CO2 and/or H2, but the pure cultures were more sensitive to changes in gas composition than the mixed culture. CO2 inhibited CO oxidation by the Pleomorphomonas-like isolate and decreased the ethanol/acetate ratio by the Acetobacterium-like isolate. H2 did not inhibit ethanol or H2 production by the Acetobacterium and Pleomorphomonas isolates, respectively, but decreased their CO consumption rates. As part of the mixed culture, these isolates, together with other microorganisms, consumed H2 and CO2 (along with CO) for all conditions tested and at similar CO consumption rates (2.6 ± 0.6 mmol CO L−1 day−1), while maintaining overall function (acetate production). Providing a continuous supply of CO by membrane diffusion caused the mixed culture to switch from acetate to ethanol production, presumably due to the increased supply of electron donor. In parallel with this change in metabolic function, the structure of the microbial community became dominated by Geosporobacter phylotypes, instead of Acetobacterium and Pleomorphomonas phylotypes.ConclusionsThese results provide evidence for the potential of mixed-culture syngas fermentation, since the CO-enriched mixed culture showed high functional redundancy, was resilient to changes in syngas composition, and was capable of producing acetate or ethanol as main products of CO metabolism.

The radiogenic and stable Sr isotope geochemistry of basalt weathering in Iceland: Role of hydrothermal calcite and implications for long-term climate regulation

Several studies have examined the geochemistry of Icelandic rivers to quantify the relationship between basalt weathering and long-term climate regulation. Recent research has suggested that the chemical weathering of hydrothermal and metamorphic calcite contributes significant quantities of HCO3− to the Icelandic riverine flux (Jacobson et al., 2015). Because the HCO3− derives from volcanic CO2 that was sequestered in mineral form prior to atmospheric injection, the strength of the basalt weathering feedback occurring in Iceland may be lower than previously realized. To test these hypotheses, we analyzed the radiogenic and stable Sr isotope composition (87Sr/86Sr and δ88/86Sr) of the same suite of water, rock, and mineral samples as examined in Jacobson et al. (2015), and we developed a simple model of the long-term Ccycle that considers the transformation of volcanic CO2 to HCO3− during subsurface silicate weathering, which is a precursor to hydrothermal calcite formation.Interpretations based on 87Sr/86Sr and Ca/Sr ratios suggest that conservative, three-component mixing between basalt, calcite, and atmospheric deposition adequately explains river geochemistry. On average, the δ88/86Sr values of glacial and non-glacial rivers (0.414‰ and 0.388‰, respectively) are generally higher than those for basalt (0.276‰); however, calcite δ88/86Sr values (0.347‰) are also higher than those for basalt and span the range of riverine values. Thus, riverine δ88/86Sr values are also consistent three-component mixing between basalt, calcite, and atmospheric deposition. Isotopic fractionation is not required to explain riverine trends. Finally, model equations for the long-term Ccycle demonstrate that subsurface silicate weathering reduces the magnitude of the volcanic CO2 degassing flux, which in turn causes the atmosphere to stabilize at lower pCO2 values compared to the case where no subsurface silicate weathering occurs. However, the proportion of the net volcanic C flux introduced to the atmosphere-ocean system as HCO3− after subsurface silicate weathering does not regulate long-term climate. Because hydrothermal calcite simply sequesters some of this HCO3− and delays its transmission to the atmosphere-ocean system until it dissolves at the surface later in time, it can be concluded the weathering of hydrothermal calcite bearing non-atmospheric C also has no effect on long-term climate regulation. Icelandic riverine HCO3− fluxes should be corrected for the hydrothermal calcite weathering contribution prior to quantifying atmospheric CO2 consumption rates by basalt weathering at the Earth’s surface.

Carbon-dioxide biofixation and phycoremediation of municipal wastewater using Chlorella vulgaris and Scenedesmus obliquus.

The pure cultures of microalgae Chlorella vulgaris ATCC 13482 and Scenedesmus obliquus FACHB 417 were grown in municipal wastewater in 7-L airlift bubble column photobioreactor supplied with 5% CO2/air (v/v). Batch experiments were conducted at 25°C with 14-h light/10-h dark cycle for a period of 10days. The CO2 capture efficiencies for both the microalgae were monitored in terms of their respective biomass productivities, carbon contents, and CO2 consumption rates. In the present study, the initial concentration of ammonia (43.7mgL-1) was decreased to 2.9 and 3.7mg L-1 by C. vulgaris and S. obliquus, respectively. And, the initial concentration of phosphate (18.5mgL-1) was decreased to 1.1 and 1.6mgL-1 by C. vulgaris and S. obliquus, respectively. CO2 biofixation rates by C. vulgaris and S. obliquus, cultivated in municipal wastewater, were calculated to be 140.91 and 129.82mgL-1day-1, respectively. The findings from the present study highlight the use of microalgae for wastewater treatment along with CO2 uptake and biomass utilization for pilot scale production of biodiesel, biogas, feed supplements for animals, etc., thus minimizing the production costs.

Temporal and spatial variations of rock weathering and CO2 consumption in the Baltic Sea catchment

This study provides the first estimate of silicate and carbonate weathering rates and derived CO2 consumption rates for the Baltic Sea catchment using river chemistry data of 78 rivers draining into the Baltic Sea. The silicate weathering rates (denoted as total dissolved solids) of individual river basin range from 0.014Tg/year to 4.55Tg/year and the carbonate weathering rates range from 0.079Tg/year to 6.49Tg/year. The total CO2 consumption across the Baltic catchment is approximately 3.9TgC/year and is almost equally shared by silicates and carbonates. Uncertainty associated with the weathering estimate is around 32%, which is mainly caused by incomplete pollution correction for a few major rivers in the south. The calculations for the boreal river basins have higher certainties because of less human impacts. The CO2 consumption rate of individual river basin vary between 0.53 and 5.66gC/m2/year with an average of 2.97gC/m2/year, in which carbonates consume CO2, 1.4gC/m2/year and silicates take 1.5gC/m2/year. This is in the same range as has been reported for the Mackenzie River and Siberian river basins, but at the lower range of tropical rivers, suggesting the Baltic Sea catchment holds solid weathering signals for high-latitude systems, especially in the pristine boreal silicate-dominated areas. The amount of CO2 consumed by weathering in the Baltic Sea catchment accounts for approximately 3–30% of the net ecosystem carbon exchange (10–100gC/m2/year), implying that weathering contributes as a significant sink of atmospheric CO2. Although many studies have shown the positive relation between temperature and weathering rates in various river catchments, multiple regression analysis using the 40-year continuous records of river chemistry in the boreal area of the Baltic Sea catchment reveals a strong correlation between weathering flux and precipitation, but no statistically significant correlation between weathering and temperature. This suggests not only that temperature is not necessarily to be primary controlling factor for weathering rates, but also besides precipitation, other factors, like increased soil organic matter contents and water path changes may have high impact on weathering rates. The 40-year data analysis also shows generally increasing weathering fluxes by 10–20% in the pristine boreal area over the past decades. This indicates that increased CO2 consumption by weathering and the resulting elevated dissolved inorganic carbon delivery to the ocean act as a negative feedback for ocean acidification, such as the Arctic Ocean that has become more acidic due to high terrestrial organic carbon delivery together with increased river water input.

Synergistic Effect of Fe–Co Bimetallic Catalyst on FTS and WGS Activity in the Fischer–Tropsch Process: A Kinetic Study

The kinetics of Fischer–Tropsch (FT) and water–gas shift (WGS) reactions were investigated through detailed experimentation over a laboratory prepared 10Fe/20Co/SiO2 catalyst. An investigation was undertaken to understand the prevailing mechanism of CO activation over a Fe–Co bimetallic catalyst. The mechanisms of CO adsorption and intermediate formation are different over an iron and cobalt catalyst, which finally affect the rate of CO consumption. The mechanism of CO consumption in the FT and WGS reactions over this catalyst has been studied in the light of the synergistic effect due to the presence of both Fe and Co phases. These different phase formations (active sites) were investigated using characterization techniques, namely, XRD, TEM, and SAED. The reaction kinetic study was performed at industrial relevant reaction conditions (T = 473–553 K, P = 1–3 MPa, GHSV = 1800–6600 mL/gcat-h, H2/CO molar ratio = 0.5–2.5) in a continuous fixed bed reactor. The models based on rate of CO consumption were der...

Modeling and optimization of Fischer-Tropsch synthesis over Co-Mn-Ce/SiO2 catalyst using hybrid RSM/LHHW approaches

Operating conditions considerably affect the energy required for Fischer-Tropsch synthesis, depending on the catalyst composition and reactor type (catalyst system). This paper reports the use of cobalt-manganese-cerium supported on silica as a novel CO hydrogenation catalyst, to produce hydrocarbons in a fixed bed micro-reactor. Response surface methodology (RSM) was applied to study the effects of temperature, pressure, feed ratio and their interactions on CO consumption rate, and the selectivity of light olefins (light olefinity), methane and C5+ hydrocarbons. Quadratic mathematical models adequately described the responses in this catalyst system. According to Langmuir Hinshelwood Hougen Watson (LHHW) approach, kinetic mechanism of the reaction was found to be an associative adsorption of H2 and CO. Statistical analysis demonstrated that pressure and feed ratio were the most important factors for the production of C5+ and light alkenes, respectively. Model graphs indicated that minimum methane selectivity was achieved at 523.15 k and 2 bar. The maximum amounts of light olefins and heavier hydrocarbons were obtained at H2/CO = 1 and H2/CO = 2, respectively. Characterization of precursor and calcined catalyst (before and after the reaction) was carried out using SEM and BET techniques.

Is basalt weathering a major mechanism for atmospheric CO<sub>2</sub> consumption?

In the science of global change, a main focus of researchers who investigate the global carbon cycle is determining the fate of missing carbon sinks. Because atmospheric CO2 that is consumed by carbonate chemical weathering is thought to return to the atmosphere through the precipitation of carbonate, it is widely accepted that it is silicate weathering, rather than carbonate weathering, that constitutes the major mechanism of atmospheric CO2 consumption. In particular, the chemical weathering of basalt, which is a type of silicate rock, is considered to be an important “carbon sink” due to the CO2 drawdown that occurs during the basalt-carbonic acid reaction. However, the high CO2 consumption rates of basalt chemical weathering may also derive from the following four aspects, as identified in the extant literature. First, study areas with high carbon fluxes (CF) are usually ocean islands, volcanic arcs or situated in tropical regions, where precipitation is high, which results in large runoff depth. This may be one of the primary reasons for the high CF, since CF is equal to the product of the runoff depth and the concentration of bicarbonate. In addition, because of the presence of chemostatic behaviors of the concentration of bicarbonate, CF is mainly determined by runoff depth. In other words, high runoff depth will directly result in high CF. Furthermore, the interface between water and minerals will be enlarged, while the saturation state of water will be decreased, by the increase of runoff depth. Therefore, more minerals will take part in the dissolution, and the dissolving capacity of water will be increased. However, this kind of high CF results from high runoff depth, rather than basaltic properties. Second, the high concentration of dissolved inorganic carbon (DIC) may result from the chemical weathering of trace amounts of carbonate dispersed in silicate rock, rather than silicate minerals. This should be regarded as the contribution of carbonate chemical weathering, rather than silicate chemical weathering. Third, the reactions between exogenous acid and trace amounts of carbonate will contribute to DIC fluxes, during which no atmospheric CO2 is consumed. Fourth, the CO2 that participates in the rock chemical weathering in basalt watersheds may be from a deep-source, rather than the atmosphere or soil. If this is the case, the deep-source CO2 consumed by rock chemical weathering will be released into the atmosphere with the precipitation of carbonate in the oceans. In other words, the riverine DIC may become a carbon source instead of a carbon sink. Therefore, further research is needed to conclusively determine whether basalt chemical weathering constitutes a major consumption mechanism for atmospheric CO2.

Effects of Catalyst Activity, Particle Size and Shape, and Process Conditions on Catalyst Effectiveness and Methane Selectivity for Fischer–Tropsch Reaction: A Modeling Study

We investigate effects of catalyst activity, catalyst particle shape (sphere, slab, and hollow cylinder), size (i.e., diffusion length), catalyst distribution (uniform vs eggshell type distribution for a spherical particle), and process conditions (temperature, pressure, syngas composition, and conversion level) on catalyst effectiveness factor and methane selectivity inside the catalyst pellet. In numerical simulations we utilize kinetic parameters for CO consumption rate and CH4 formation rate determined from experiments with a highly active Co/Re/γ-Al2O3 catalyst. It is found that the use of small spherical particles (0.2–0.5 mm) or eggshell distribution for larger spherical particles with catalyst layer thickness less than approximately 0.13 mm is needed to avoid negative impact of diffusional limitations on CH4 selectivity under typical Fischer–Tropsch synthesis operating conditions. For monolith reactors with wash-coated catalyst, diffusional limitations can be avoided by using a catalyst layer thic...

Carbon dioxide consumption of the microalga Scenedesmus obtusiusculus under transient inlet CO2 concentration variations.

The extensive microalgae diversity offers considerable versatility for a wide range of biotechnological applications in environmental and production processes. Microalgal cultivation is based on CO2 fixation via photosynthesis and, consequently, it is necessary to evaluate, in a short time and reliable way, the effect of the CO2 gas concentration on the consumption rate and establish the tolerance range of different strains and the amount of inorganic carbon that can be incorporated into biomass in order to establish the potential for industrial scale application. Dynamic experiments allow calculating the short-term microalgal photosynthetic activity of strains in photobioreactors. In this paper, the effect of step-changes in CO2 concentration fed to a 20L bubble column photobioreactor on the CO2 consumption rate of Scenedesmus obtusiusculus was evaluated at different operation times. The highest apparent CO2 consumption rate (336μmolm-2s-1 and 5.6% of CO2) was 6530mgCO2gb-1d-1 and it decreased to 222mgCO2gb-1d-1 when biomass concentration increased of 0.5 to 3.1gbL-1 and 5.6% of CO2 was fed. For low CO2 concentrations (<3.8%) the pH remained close to the optimal value (7.5 and 8). The CO2 consumption rates show that S. obtusiusculus was not limited by CO2 availability for concentrations above of 3.8%. The CO2 mass balance showed that 90% of the C-CO2 transferred was used for S. obtusiusculus growth.

Development of kinetic model for CO hydrogenation reaction over supported Fe–Co–Mn catalyst

After determining CO consumption rate, the production rate of methane, paraffin, olefin and chain growth probability factor (α) was derived and described.

The effect of the nanofibrous Al2O3 aspect ratio on Fischer-Tropsch synthesis over cobalt catalysts.

A series of nanofibrous alumina materials with diameters of 4-6 nm and with different aspect ratios ranging from 3 to 16 were prepared. Cobalt impregnated catalysts were prepared by means of incipient wetness impregnation on alumina nanofibers while the 'rearranged' catalysts were prepared by using ultrasonication assistance to mix the fibers with the Co3O4 nanoparticles. The effects of the alumina nanofiber aspect ratios on the Co catalyst structure and performance for Fischer-Tropsch synthesis were studied. The pore size of the two series of catalysts increased as the aspect ratio of the alumina nanofiber increased. For impregnated catalysts, large Co3O4 particles were formed on the external surface of the alumina support when the aspect ratio was 3 and 5, while the crystallite sizes of Co3O4 increased from 13.3 nm to 15.6 nm with the increase of the aspect ratio from 7 to 16. The four 'rearranged' catalysts possessed similar and homogeneously dispersed Co3O4 crystallites of 9.5 nm. As expected the reduction behavior of the two series of catalysts was primarily influenced by the Co3O4 crystallite size and structure. The FT data of the two series of catalysts indicate that dispersed Co catalysts on alumina nanofibers with large aspect ratios having large inter-crystallite pores significantly improve the catalyst activity and C5+ selectivity. The FT data of the 'rearranged' catalysts strongly demonstrated that the internal mass transfer of reactants and products increased with a decrease in inter-crystallite pore size, resulting in a decrease of C5+ selectivity and C3 olefin/paraffin ratio, and an increase of CH4 selectively, while the CO consumption rate was little altered. Furthermore, catalytic stability tests showed that the alumina nanofibers with larger aspect ratios inhibited Co migration and coalescence in the matrices of the nanofibrous alumina, and this significantly enhanced the stability of the catalyst. The Cop/Al2O3-16 catalyst possessing uniformly distributed cobalt, improved reducibility and large pores is the preferred choice to generate high catalytic activity, stability and C5+ selectivity.

Rock Weathering Characteristics and the Atmospheric Carbon Sink in the Chemical Weathering Processes of Qingshuijiang River Basin

Carbon sink produced during rock weathering is critical to global carbon cycles. In this work, the major ion chemistry and ion sources of Qingshuijiang River Basin were investigated. The principal component analysis, mass balance approach and deduction method were applied for estimating the weathering rate and atmospheric CO2 consumption via the chemical weathering of rocks. The results demonstrated that the chemical weathering of carbonate and silicate rocks within the drainage basin was the main source of the dissolved chemical substances in the Qingshuijiang River Basin, prior to carbonate rock weathering. Some 58.28% of the total dissolved chemical substances were derived from the chemical weathering of carbonate rock, 17.38% from the dissolution of silicate rock, and 17.74% from atmospheric CO2 contribution rates. The chemical weathering rate of this catchment was estimated to be 109.97t·(km2·a)-1, which was comparable to Wujiang River Basin, but higher than the average of global rivers. Furthermore, the atmospheric CO2 consumption rate was estimated to be 7.25×105 mol·(km2·a)-1. The CO2 flux consumed by the rock chemical processes within this catchment was 12.45×109 mol·a-1, of which about 63.13%(7.86×109 mol·a-1) was resulted from carbonate weathering and 36.87%(4.59×109 mol·a-1) from silicate weathering. The CO2 consumed by rock chemical weathering in the Qingshuijiang River reduced the atmospheric CO2 level and constituted a significant part of the global carbon budget. Correlation and spatial distribution analysis of SO42-, F-, NO3- showed that anthropogenic activities contributed remarkably to dissolved solutes and associated CO2 consumption worldwide, and anthropogenic inputs probably contributed some 4.87% to the dissolved solutes in the Qingshuijiang River.

Physiological and biochemical responses of the green alga Pachycladella chodatii (SAG 2087) to sodicity stress

The effects of various concentrations of different carbon sources (Na2CO3 and NaHCO3) as sodicity stress on growth parameters, CO2 consumption rate, enzyme activity, intracellular lipid content, and fatty acid profiles of Pachycladella chodatii were studied. Generally, the total chlorophyll was increased by increasing the concentrations of Na2CO3 and NaHCO3. The biomass productivity as well consumption rate of carbon dioxide of P. chodatii reached the highest values with increasing concentrations of Na2CO3 and NaHCO3. The soluble protein content of P. chodatii was highest at the lowest Na2CO3 and NaHCO3 concentrations. The addition of different concentrations of Na2CO3 and NaHCO3 in the growth media induces lipoxygenase and superoxide dismutase specific activity. Catalase and total antioxidant enzymes were increased by supplementing the growth media with 60 and 45mgl−1 of Na2CO3 and NaHCO3, respectively. Hydrogenase uptake activity in P. chodatii increased gradually in all treated cultures with the time elapsed recording the maximum activity after 11days of growth especially at 60, 45mgl−1 of Na2CO3 and NaHCO3 respectively. Lipids content was increased at low concentration of Na2CO3 (40 and 15mgl−1) and NaHCO3 (60, 45mgl−1) respectively. Subsequent to algal cultivation in different concentrations of Na2CO3, the cultures were filtered and biodiesel was prepared by direct esterification of dry algal biomass. Methyl esters of palmitic, elaidic and stearic acids represented the major components while myristic, pentadecanoic and 9,12-octadecenoic acids represented a minor component of biodiesel produced from P. chodatii treated with different concentrations of Na2CO3 and NaHCO3.

Geochemistry of the dissolved loads of the Liao River basin in northeast China under anthropogenic pressure: Chemical weathering and controlling factors

This study focuses on the chemical and Sr isotopic compositions of the dissolved load of the rivers in the Liao River basin, which is one of the principal river systems in northeast China. Water samples were collected from both the tributaries and the main channel of the Liao River, Daling River and Hun-Tai River. Chemical and isotopic analyses indicated that four major reservoirs (carbonates (+gypsum), silicates, evaporites and anthropogenic inputs) contribute to the total dissolved solutes. Other than carbonate (+gypsum) weathering, anthropogenic inputs provide the majority of the solutes in the river water. The estimated chemical weathering rates (as TDS) of silicate, carbonate (+gypsum) and evaporites are 0.28, 3.12 and 0.75t/km2/yr for the main stream of the Liao River and 7.01, 25.0 and 2.80t/km2/yr for the Daliao River, respectively. The associated CO2 consumption rates by silicate weathering and carbonate (+gypsum) weathering are 10.1 and 9.94×103mol/km2/yr in the main stream of the Liao River and 69.0 and 80.4×103mol/km2/yr in the Hun-Tai River, respectively. The Daling River basin has the highest silicate weathering rate (TDSsil, 3.84t/km2/yr), and the Hun-Tai River has the highest carbonate weathering rate (TDScarb, 25.0t/km2/yr). The Raoyang River, with an anthropogenic cation input fraction of up to 49%, has the lowest chemical weathering rates, which indicates that human impact is not a negligible parameter when studying the chemical weathering of these rivers. Both short-term and long-term study of riverine dissolved loads are needed to a better understanding of the chemical weathering and controlling factors.