Pre-Eutectic Densification of Calcium Carbonate Doped with Lithium Carbonate

Pressureless sintering of CaCO₃ was carried out, with Li₂CO₃ (from 0.5 to 8 wt%) as an additive, under different pressures of CO₂. Densification occurs between 600 and 700°C. Sintering above the eutectic temperature (T>662°C) leads to the decomposition of calcium carbonate and the materials become expanded. At 620° under 1 kPa of CO₂, a relative density of 96% is reached. Li₂CO₃ enhances the densification process and grain growth of calcium carbonate. CO₂ pressure slows down densification and grain growth kinetics. These results are explained by the influence of carbonate and calcium ion vacancies on the sintering mechanisms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Growth of Microalgae in High CO2 Gas and Effects of SOX and NOX

Growth and lipid production of microalgae were investigated, with attention to the feasibility of making use of flue gas CO₂ as a carbon source. The effect of a high CO₂ level in artificial seawater differed from strain to strain. Three algal strains from the Solar Energy Research Institute (Golden, CO) collection were selected as good fixers of CO₂ when the level of CO₂ in the sparging gas was high. These algae also accumulated large amounts of crude lipids. SO_X and NO_X inhibited algal growth, but a green alga,Nannochloris sp. NANNO2 grew after a lag period, even when it received NO gas at the concentration of 300 ppm.     

Effects of Inoculum Physiological Stage on the Growth Characteristics of Chlorella sorokiniana Cultivated Under Different CO2 Concentrations

In order to maximize microalgae biomass production and reduce its overall costs, it is important to optimize inoculum conditions based on its physical and physiological characteristics. Chlorella sorokiniana cultures inoculated with inoculum at three different physiological stages (lag, exponential, and stationary) diluted to the same optical density were cultivated for 12?days under three different CO₂ concentrations (0.038, 5, or 10?% CO₂ v/v) and growth pattern and biomass production was observed. Samples inoculated with lag phase inoculum supplied with 5?% CO₂ achieved the maximum biomass production, whereas samples supplied with 0.038?% CO₂ never reached exponential growth. The better growth of samples inoculated with lag phase inoculum was attributed to its increased number of cells compared to the other two inocula.     

Continuous hydrogen photoproduction by Chlamydomonas reinhardtii

This study demonstrates, for the first time, that it is possible to couple sulfate-limited Chlamydomonas reinhardtii growth to continuous H₂ photoproduction for more than 4000 h. A two-stage chemostat system physically separates photosynthetic growth from H₂ production, and it incorporates two automated photobioreactors (PhBRs). In the first PhBR, the algal cultures are grown aerobically in chemostat mode under limited sulfate to obtain photosynthetically competent cells. Active cells are then continuously delivered to the second PhBR, where H₂ production occurs under anaerobic conditions. The dependence of the H₂ production rate on sulfate concentration in the medium, dilution rates in the PhBRs, and incident light intensity is reported.     

Production of optically pure d-lactic acid by Nannochlorum sp. 26A4

Microalgae were screened from seawater for greenhouse gas CO₂ fixation and d-lactic acid production by self-fermentation and tested for their growth rate, starch content, and conversion rate from starch into d-lactic acid. More than 300 strains were isolated, and some of them were found to have suitable properties for this purpose. One of the best strains, Nannochlorum, sp. 26A4, which was isolated from Sakito Island, had a starch content of 40% (dry weight), and a conversion rate from consumed starch into d-lactic acid of 70% in the dark under anaerobic conditions. The produced d-lactic acid showed a high optical purity compared with the conventional one. The proposed new d-lactic acid production system using Nannochlorum sp. 26A4 should also be an effective technology for greenhouse gas CO₂ fixation and/or conversion into industrial raw materials.     

Dry Potassium-Based Sorbents for CO<Subscript>2</Subscript> Capture

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, CaO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property of various sorbents were measured in the presence of H₂O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO₂ absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO₃)₂(OH)₂, K₂Ca(CO₃)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely convert to the original K₂CO₃ phase at temperatures below 200 °C, during the CO₂ absorption process in the presence of 9 vol.% H₂O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO₃ crystal structure was formed during CO₂ absorption. The formation of active species, K₂CO₃·1.5H₂O, by the pretreatment with water vapor and the formation of the KHCO₃ crystal structure after CO₂ absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (87 mg CO₂/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO₂ capture capacity of KMgI30 (178.6 mg CO₂/g sorbent) than that of the theoretical value (95 mg CO₂/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO₂ capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO₂ absorption, and the role of water vapor and its effects on CO₂ absorption.     

H2 Production via the Steam Reforming of Methanol Over NiAl-layered Double Hydroxide Derived Catalysts

This article reviews our recent results on the steam reforming of methanol over a series of NiAl-layered double hydroxide catalysts prepared by the co-precipitation method. The influence of calcination temperature, reaction temperature, pretreatment temperature and atmospheres, inorganic salt ions and steam to methanol ratio on the catalytic performance was studied. The major products for many of the catalysts were H₂, CO, CO₂ and CH₄. However, the product composition varies significantly with the experimental parameters and high selectivity for CO₂ and H₂ was observed under various conditions, showing the potential of Ni based catalysts for the production of highly pure hydrogen.     

Preparation of hollow nanospheres g-C3N4 loaded by Keggin type Cu mono-substituted heteropoly acid with enhanced visible-light harvesting and electron transfer properties for high-efficiency photocatalysis

Abstract

A series of heterojunction catalysts (CuCN-X) were successfully fabricated by loading the different amounts of Keggin type Cu mono-substituted heteropoly acid (HPW₁₁Cu) on the surface of hollow nanospheres g-C₃N₄ (HSCN). The HSCNs were prepared by using SiO₂ as a hard template. The chemical structure, porosity, morphology and electronic property of the prepared catalysts were investigated using XRD, SEM, N₂-absorption isotherm and XPS. The results indicated that the modified HSCN show prominent absorption in the visible light range and decrease the band gap. The greatly enhanced photocatalytic activity of obtained CuCN-X have been shown by the degradation of Rhodamine B (RhB), reduction of CO₂ and production of photocatalytic hydrogen under visible light irradiation. More significantly, CuCN-15 has shown significantly improved photocatalytic performance at 4.5, 3.5 and 3.3 times higher that of than HSCN for the degradation of RhB, reduction of CO₂ and production of photocatalytic hydrogen, respectively. Furthermore, the mechanism for the enhanced photocatalytic activity of CuCN-X is proposed to be due to the formation of heterojunction. The electrons can be rapidly transferred from HSCN to HPW₁₁Cu, in which facilitate charge separation and charge transfer.     

Stimulatory effect of red light on starch accumulation in a marine green alga,chlamydomonas sp. strain MGA161

A marine green alga,Chlamydomonas sp. strain MGA161 was cultivated under illumination of red and white lights. The growth rate under red light illumination was almost the same as that in the basic conditions under white light illumination, but red light-grown cells accumulated almost twice as much starch as white light-grown cells. Although there was a slight decrease in carbonic anhydrase activity, red light-illuminated cells had almost 2.3 times the fructose-l,6-diphos-phatase activity of white light-illuminated cells. Red light might stimulate starch accumulation by increasing the amounts of enzymes related to carbon fixation through the phytochrome system. Cells grown under red light degraded 1.6 times as much starch and produced 1.7 times as much hydrogen and 1.6 times as much ethanol compared with cells grown under white light during 12 h of dark anaerobic fermentation.     

A New Type of Photocatalysis Initiated by Photoexcitation of Adsorbed Carbon Dioxide on ZrO2

ZrO₂ has been found to be an effective photocatalyst for reduction of CO₂ by hydrogen or methane at room temperature. The effective photon energy is less than the band gap energy of ZrO₂ (5.0 eV), indicating that photoexcitation of bulk ZrO₂ is not involved. The reaction is initiated by photoexcitation of surface carbonates derived from adsorption of CO₂ to convert it to a CO₂ ^– radical, which in turn reacts with hydrogen or methane to form surface formate. The formate is stable at temperatures below 573 K, but works as a reductant of CO₂ under photoirradiation. A new type of reaction mechanism is proposed.     

Aldol Condensations Catalyzed by PEG400 and Anhydrous K2CO3 Without Solvent

Abstract

Aldol condensations of aromatic aldehydes with ketones under solvent‐free conditions to synthesize α,β‐unsaturated ketones in good to excellent yields using PEG400 and powdered anhydrous K₂CO₃ as catalysts at 90 °C and 120 °C are described.     

Synthesis, characterization and hydrogen storage capacity of MS2 (M = Mo, Ti) nanotubes

The structure, morphology and hydrogen-storage capacity of MS₂ (M = Mo, Ti) nanotubes prepared by different experimental methods were studied. It was found that the MoS₂ nanotubes treated by KOH displayed the gaseous storage capacity of 1.2 wt% hydrogen (under the hydrogen pressure of 3 MPa and 25°C) and the electrochemical discharge capacity of 262 mAh/g (at the discharge current density of 50 mA/g and 25°C) that corresponds to about 1.0 wt % hydrogen. In comparison, TiS₂ nanotubes can store 2.5 wt% hydrogen under the hydrogen pressure of 4 MPa and 25°C. The results show that MS₂ compound nanotubes are promising materials for hydrogen storage. __________ Translated from Acta Scientiarum Naturalium Universitatis Nankaiensis, 2005, 38(4) (in Chinese)     

CO2 Capture from High-Humidity Flue Gas Using a Stable Metal–Organic Framework

The flue gas from fossil fuel power plants is a long-term stable and concentrated emission source of CO₂, and it is imperative to reduce its emission. Adsorbents have played a pivotal role in reducing CO₂ emissions in recent years, but the presence of water vapor in flue gas poses a challenge to the stability of adsorbents. In this study, ZIF-94, one of the ZIF adsorbents, showed good CO₂ uptake (53.30 cm³/g), and the calculated CO₂/N₂ (15:85, v/v) selectivity was 54.12 at 298 K. Because of its excellent structural and performance stability under humid conditions, the CO₂/N₂ mixture was still well-separated on ZIF-94 with a separation time of 30.4 min when the relative humidity was as high as 99.2%, which was similar to the separation time of the dry gas experiments (33.2 min). These results pointed to the enormous potential applications of ZIF-94 for CO₂/N₂ separation under high humidity conditions in industrial settings.     

Customizing Pore System in a Microporous Metal–Organic Framework for Efficient C2H2 Separation from CO2 and C2H4

Selective-adsorption separation is an energy-efficient technology for the capture of acetylene (C₂H₂) from carbon dioxide (CO₂) and ethylene (C₂H₄). However, it remains a critical challenge to effectively recognize C₂H₂ among CO₂ and C₂H₄, owing to their analogous molecule sizes and physical properties. Herein, we report a new microporous metal–organic framework (NUM-14) possessing a carefully tailored pore system containing moderate pore size and nitro-functionalized channel surface for efficient separation of C₂H₂ from CO₂ and C₂H₄. The activated NUM-14 (namely NUM-14a) exhibits sufficient pore space to acquire excellent C₂H₂ loading capacity (4.44 mmol g⁻¹) under ambient conditions. In addition, it possesses dense nitro groups, acting as hydrogen bond acceptors, to selectively identify C₂H₂ molecules rather than CO₂ and C₂H₄. The breakthrough experiments demonstrate the good actual separation ability of NUM-14a for C₂H₂/CO₂ and C₂H₂/C₂H₄ mixtures. Furthermore, Grand Canonical Monte Carlo simulations indicate that the pore surface of the NUM-14a has a stronger affinity to preferentially bind C₂H₂ over CO₂ and C₂H₄ via stronger C-H···O hydrogen bond interactions. This article provides some insights into customizing pore systems with desirable pore sizes and modifying groups in terms of MOF materials toward the capture of C₂H₂ from CO₂ and C₂H₄ to promote the development of more MOF materials with excellent properties for gas adsorption and separation.     

Gram-Scale Synthesis of an Ultrastable Microporous Metal-Organic Framework for Efficient Adsorptive Separation of C2H2/CO2 and C2H2/CH4

A highly water and thermally stable metal-organic framework (MOF) Zn₂(Pydc)(Ata)₂ (1, H₂Pydc = 3,5-pyridinedicarboxylic acid; HAta = 3-amino-1,2,4-triazole) was synthesized on a large scale using inexpensive commercially available ligands for efficient separation of C₂H₂ from CH₄ and CO₂. Compound 1 could take up 47.2 mL/g of C₂H₂ under ambient conditions but only 33.0 mL/g of CO₂ and 19.1 mL/g of CH₄. The calculated ideal absorbed solution theory (IAST) selectivities for equimolar C₂H₂/CO₂ and C₂H₂/CH₄ were 5.1 and 21.5, respectively, comparable to those many popular MOFs. The Q_st values for C₂H₂, CO₂, and CH₄ at a near-zero loading in 1 were 43.1, 32.1, and 22.5 kJ mol⁻¹, respectively. The practical separation performance for C₂H₂/CO₂ mixtures was further confirmed by column breakthrough experiments.     

基于密度泛函理论对等离子体中H/CO2相互作用的第一性原理研究

深入理解辐照条件下氢同位素与CO₂反应的微观机制,可为聚变堆氘氚燃料循环工艺的优化设计提供数据支撑。基于此,采用第一性原理计算研究了等离子体放电条件下H₂和CO₂的微观反应机制,研究了不同温度和氢同位素效应对反应过程的影响。通过内禀反应坐标（IRC）算法结合反应过渡态获得4条初始反应路径,并对比研究了生成产物CH₄及CH₃OH的2条路径在热力学上的容易程度,以及不同氢同位素对各个反应的影响。研究发现,氚的自发衰变或等离子体中的高能电子都会诱导氢同位素与CO₂发生反应,形成CO、H₂O、CH₄及CH₃OH等产物;在高能电子诱导CO₂的离解后,由4条初始反应路径组成的复杂反应可以自持发生,且该复杂反应中存在2种倾向;升高反应温度对CO₂转化为有机物（CH₄和CH₃OH）具有一定的促进作用。     

Novel solvent-free reaction of C60 with active methylene compounds in the presence of Na2CO3 under high-speed vibration milling

Inorganic base, Na₂CO₃, was utilized to replace organic base, DBU, in the Bingel reaction employing diethyl bromomalonate under the mechanochemical ‘high-speed vibration milling’ conditions to give the cyclopropanated C₆₀1 in high yield. In contrast, reactions of C₆₀ with diethyl malonate and ethyl acetoacetate in the presence of Na₂CO₃ under HSVM conditions afforded 1,4-bisadduct 2 and dihydrofuran-fused C₆₀ derivative 3, respectively.     

Formation of different products during photo-catalytic reaction on TiO<Subscript>2</Subscript> suspension in water with and without 2-propanol under diverse ambient conditions

Studies on photo-catalytic reduction of CO₂ using TiO₂ photo-catalyst (0.1%, w/v) as a suspension in water was carried out at 350 nm light. CO₂ from both commercially available source, as well as generated in situ through 2-propanol oxidation, was used for this study. The photolytic products such as hydrogen (H₂), carbon monoxide (CO) andmethane (CH₄) generated were monitored in TiO₂ suspended aqueous solution with and without a hole scavenger, viz., 2-propanol. Similar photolytic experiments were also carried out with varying ambient such as air, O₂, N₂ and N₂O. The yields of CO and CH₄ in all these systems under the present experimental conditions were found to be increasing with light exposure time. H₂ yield in N₂-purged systems containing 2-propanol was found to be more as compared to the without 2-propanol system. The rate of H₂ production in N₂-purged aqueous solutions containing 0.1% TiO₂ suspension were evaluated to be 0.226 and 5.8 μl/h, without and with 0.5 M 2-propanol, respectively. This confirmed that 2-propanol was an efficient hole scavenger and it scavenged photo-generated holes (h⁺), allowing its counter ion, viz., e⁻, to react with water molecule/H⁺ to yield more H₂. The formation of both CO and CH₄ in the photolysis of CO₂-purged aqueous solutions containing suspended TiO₂ in absence of 2-propanol reveal that the generation of CH₄ is taking place mainly through CO intermediate. In presence of air/O₂, the yield of H₂ in the system without 2-propanol was observed to be negligible as compared to the system containing 2-propanol in which low yield of H₂ was obtained with a formation rate of approx. 0.5 μl/h.     

CdS插层的K4Nb6-xCuxO17复合物的制备及其光催化制氢活性

以Nb2O5,K2CO3和CuO为原料经高温固相反应合成K4Nb6-xCuxO17催化剂,并通过层间离子交换反应,胺插入反应以及硫化反应制备CdS插层K4Nb6-xCuxO17复合催化剂(K4Nb6-xCuxO17/CdS)。利用X射线衍射(XRD),X射线光电子能谱(XPS),场发射扫描电镜(SEM),X射线能谱仪(EDX),紫外-可见漫反射(UV-Vis),分子荧光光谱(PL)等技术对催化剂进行表征。考察了催化剂的可见光催化制氢活性。结果表明,Cu离子掺杂进入K4Nb6O17晶格中,CdS位于K4Nb6O17层间。CdS插层K4Nb6-xCuxO17催化剂的最大吸收光波长约为550 nm。催化剂制氢活性有明显提高,紫外光和可见光下3 h产氢量分别达到279.83 mmol.gcat-1和7.11 mmol.gcat-1。最后讨论了复合催化剂光生电荷转移机理。     

Bioelectrosynthesis as an alternative to photosynthesis

The CO₂ reduction processes have been discussed as a way of designing an ecologically totally closed technology. An electric current and molecular hydrogen are the two related available agents that can be discussed as ecologically pure reductants. The most important products are liquid and gaseous fuels, the products of large-scale organic synthesis, monomers, and amino acids. For CO₂ reduction, the necessary energy consumption and H₂ costs were calculated. For complex organic molecules, amino acids for instance, the energy consumption does not make up the main portion of the costs. The biocatalytic systems of CO₂ reduction based on cryoimmobilized cells are described. Conversion of CO₂ into L-lysine with electrochemical decomposition of water was effected on the laboratory scale. A general unit for diverse technological processes can be a bioelectrosynthetic Index Entries: Bioelectrosynthesis; CO₂ reduction; liquid fuels; amino acids; immobilized cells; economic estimates. modulus, an electrochemical hydrogen generator coupled with a biocatalytic converter of hydrogen and oxygen. The systems for bioelectrosynthesis of motor fuels and essential amino acids have been economically estimated and characterized. The possibilities of combining the solar energy transformation and H₂–CO₂ conversion have been discussed.