Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-ca...Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-carbonation method was developed to recover alkali and alumina from Bayer red mud under mild reaction conditions. Batch experiments were performed to evaluate the potential effects of im- portant parameters such as temperature, amount of CaO added, and CO2 partial pressure on the recovery of alkali and alumina. The results showed that 95.2% alkali and 75.0% alumina were recovered from red mud with decreases in the mass ratios of Na2O to Fe2O3 and of Al2O3 to Fe2O3 from 0.42 and 0.89 to 0.02 and 0.22, respectively. The processed red mud with less than 0.5wt% Na2O can potentially be used as a construction material.展开更多
Na2CO3, Li2CO3, and K2CO3 were used as additives to Pingshuo (PS) coal that was subsequently gasified under a CO2 stream. The catalytic gasification of coal samples by CO2 in the presence single or mixed alkali carb...Na2CO3, Li2CO3, and K2CO3 were used as additives to Pingshuo (PS) coal that was subsequently gasified under a CO2 stream. The catalytic gasification of coal samples by CO2 in the presence single or mixed alkali carbonates was investigated by thermogravimetric analysis. The experimental results indicate that the catalytic effect of Li2CO3 is significantly larger than that of Na2CO3 or K2CO3. The catalytic effect of the mixed, bi-metal carbonate containing Li2C03 and Na2C03, or Li2CO3, and K2C03, is related to the compo- sition of the catalyst and the proportion of the two components. The bi-metal carbonates having a mole ratio of 9:1 (lri:x) has the largest catalytic effect for PS coal gasification. A synergistic effect between Li and K, or Na, carbonate appears at temperatures greater than 1300 K. An un-reacted shrinking core model is suitable for kinetic analysis of catalytic gasification of coal samples in the presence of alkali carbonates. It is inappropriate, however, to evaluate the catalytic effect only by the activation energy obtained from the kinetic calculations.展开更多
The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indica...The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable.In addition,the adsorption energies increase with the introduction of the electric field.The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function.Furthermore,the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.展开更多
Metal-organic frameworks (MOFs) have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I(also named Cu-BTC or MOF-199) was...Metal-organic frameworks (MOFs) have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I(also named Cu-BTC or MOF-199) was chemically reduced by doping it with alkali metals (Li, Na and K) and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction (XRD), thermo-gravimetric analysis (TGA) and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li+, Na+ and K+, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST- 1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.展开更多
CoCu/TiO_2 catalysts promoted using alkali metals(Li, Na, K, Rb, and Cs) were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the ...CoCu/TiO_2 catalysts promoted using alkali metals(Li, Na, K, Rb, and Cs) were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO_2 catalysts and the catalytic performance for CO_2 hydrogenation to long-chain hydrocarbons(C_(5+))were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO_2 temperature-programmed desorption(TPD), and H_2-TPD, the introduction of alkali metals could increase the CO_2 adsorption and decrease the H_2 chemisorption, which could suppress the formation of CH_4, enhance the production of C_(5+), and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO_2 catalyst provided the maximum C_(5+) yield of 5.4%, with a CO_2 conversion of 18.4% and C_(5+) selectivity of42.1%, because it showed the strongest basicity and a slight decrease in the amount of H_2 desorption;it also exhibited excellent catalytic stability of more than 200 h.展开更多
The efficient citral hydrogenation was achieved in aqueous media using Pd/CMS and alkali additives like K<sub>2</sub>CO<sub>3</sub>. The alkali concentrations, reaction temperature and the Pd m...The efficient citral hydrogenation was achieved in aqueous media using Pd/CMS and alkali additives like K<sub>2</sub>CO<sub>3</sub>. The alkali concentrations, reaction temperature and the Pd metal content were optimized to enhance the citral hydrogenation under aqueous media. In the absence of alkali, citral hydrogenation was low and addition of alkali promoted to ~92% hydrogenation without reduction in the selectivity to citronellal. The alkali addition appears to be altered the palladium sites. The pore size distribution reveals that the pore size of these catalysts is in the range of 0.96 to 0.7 nm. The palladium active sites are also quite uniform based on the TPR data. The catalytic parameters are correlated well with the activity data.展开更多
Neutral aqueous alkali sulfate has shown great interests for developing environmentally friendly high voltage and high energy supercapacitors. This work focuses on systematically investigating the properties of symmet...Neutral aqueous alkali sulfate has shown great interests for developing environmentally friendly high voltage and high energy supercapacitors. This work focuses on systematically investigating the properties of symmetric carbon/carbon supercapacitors in neutral aqueous alkali sulfates. At room temperature, the largest power and energy density were obtained with K2SO4 electrolyte due to the smallest cation dimensions and highest electrical conductivity. At low temperature, aqueous Li2SO4 electrolyte presents the best performance due to the largest solubility, allowing a long-term stability at temperatures ranging between 20℃ and –10℃ at a maximum voltage of 1.8 V. The excellent stability has been confirmed that capacitance retention achieves as high as 92% after 10,000 cycles. The capacitance variations with temperatures could essentially result from kinetic diffusion barrier, ion dimension changes and fewer pseudo-capacitance contributions under different temperatures. This work highlights the selected virtues of different alkali sulfate electrolytes for enhanced supercapacitors.展开更多
The surface of carbon fibre is studied which has been treated with heated sodium hydrate solution (NaOH) . It is found that the surface of carbon fibre is not corroded during the treatment. But at the same time, it is...The surface of carbon fibre is studied which has been treated with heated sodium hydrate solution (NaOH) . It is found that the surface of carbon fibre is not corroded during the treatment. But at the same time, it is also found that after this treatment, a certain number of carbonyl groups (C O) and (-COOH or ?COONa) are produced on the treated surface of carbon fibre. When carbon fiber is mixed with cement paste, the above reactive groups will link with Ca+2 in the paste, which will result in an early stage hydration of cement in inter facial areas. In addition, the experiments show that the rheological properties of cement paste reinforced with alkali-treated carbon fibre differ greatly from that of untreated carbon fibre reinforced cement paste.展开更多
粉煤灰由于含有钙镁等碱土金属氧化物导致其浆液呈碱性,直接充填井下采空区易污染地下水源。利用陕北矿区府谷电厂粉煤灰开展组分测试、浆液pH值特性测试及固碳降碱试验,基于浆液pH值与OH−浓度理论关系对粉煤灰固碳降碱反应过程进行阶...粉煤灰由于含有钙镁等碱土金属氧化物导致其浆液呈碱性,直接充填井下采空区易污染地下水源。利用陕北矿区府谷电厂粉煤灰开展组分测试、浆液pH值特性测试及固碳降碱试验,基于浆液pH值与OH−浓度理论关系对粉煤灰固碳降碱反应过程进行阶段划分并提出两级耦合的粉煤灰高效矿化方法。研究结果表明:①粉煤灰含CaO、MgO、K_(2)O等碱土金属氧化物,溶于水浆液呈高碱特性,浆液pH值随浆液浓度增大而增大,当粉煤灰浆液质量分数≥30%时,浆液pH值不受质量分数影响且粉煤灰碱土金属氧化物与水反应生成OH−速率较快,溶于水20 min,OH^(−)浓度饱和;②粉煤灰与CO_(2)发生矿化反应生成方解石型CaCO_(3),每1 kg粉煤灰可矿化封存29.57 g CO_(2);③粉煤灰与CO_(2)发生矿化粉煤灰固碳降碱过程中pH变化曲线呈“倒S”型,按降pH速率分为慢速(Ⅰ)、快速(Ⅱ)、慢速(Ⅲ)3个阶段,3个阶段的pH值分界点分别为11.39、7~8且第I阶段无法消除;④降pH与降碱不是同一概念,降碱指的是降浆液中OH−浓度,降pH第I阶段对应快速降碱阶段,降pH第Ⅱ、Ⅲ阶段对应深度降碱阶段;⑤决定粉煤灰固碳量的主要为降pH第I阶段,而非pH下降速率较大的第Ⅱ阶段,第I阶段CO_(2)利用率约为30.78%,第Ⅱ、Ⅲ阶段CO_(2)总利用率约为9.04%;⑥基于粉煤灰固碳降碱过程阶段划分及反应装置降碱速率、容积的差异性,提出两级耦合的粉煤灰高效矿化方法。研究结果对分析粉煤灰固碳降碱机理,提高粉煤灰固碳降碱效率,促进粉煤灰处置工业化应用具有重要意义。展开更多
基金financially supported by the Joint Funds of the National Natural Science Foundation of China(No.U1202274)the National Natural Science Foundation of China(No.51204040)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China(No.20120042110011)the Fundamental Research Funds for the Central Universities(No.N140204015)
文摘Red mud produced in the Bayer process is a hazardous solid waste because of its high alkalinity; however, it is rich in valuable components such as titanium, iron, and aluminum. In this study, a novel calcification-carbonation method was developed to recover alkali and alumina from Bayer red mud under mild reaction conditions. Batch experiments were performed to evaluate the potential effects of im- portant parameters such as temperature, amount of CaO added, and CO2 partial pressure on the recovery of alkali and alumina. The results showed that 95.2% alkali and 75.0% alumina were recovered from red mud with decreases in the mass ratios of Na2O to Fe2O3 and of Al2O3 to Fe2O3 from 0.42 and 0.89 to 0.02 and 0.22, respectively. The processed red mud with less than 0.5wt% Na2O can potentially be used as a construction material.
基金supports of the National Natural Science Foundation of China (No.20776092)the Natural Science Foundation of Shanxi Province(No. 2008011019)+1 种基金the Shanxi Research Foundation to Returned Scholars (No. 2007-30)the Shanxi Province Basic Conditions Plat form for Science and Technology Project (No. 2010091015)
文摘Na2CO3, Li2CO3, and K2CO3 were used as additives to Pingshuo (PS) coal that was subsequently gasified under a CO2 stream. The catalytic gasification of coal samples by CO2 in the presence single or mixed alkali carbonates was investigated by thermogravimetric analysis. The experimental results indicate that the catalytic effect of Li2CO3 is significantly larger than that of Na2CO3 or K2CO3. The catalytic effect of the mixed, bi-metal carbonate containing Li2C03 and Na2C03, or Li2CO3, and K2C03, is related to the compo- sition of the catalyst and the proportion of the two components. The bi-metal carbonates having a mole ratio of 9:1 (lri:x) has the largest catalytic effect for PS coal gasification. A synergistic effect between Li and K, or Na, carbonate appears at temperatures greater than 1300 K. An un-reacted shrinking core model is suitable for kinetic analysis of catalytic gasification of coal samples in the presence of alkali carbonates. It is inappropriate, however, to evaluate the catalytic effect only by the activation energy obtained from the kinetic calculations.
基金Project supported by the Key Program of the National Natural Science Foundation of China(Grant Nos.21031001 and U1034003)the National Natural Science Foundation of China(Grant Nos.20971040 and 21173072)the Cultivation Fund of the Key Scientific and Technical Innovation Project,Ministry of Education of China(Grant No.708029)
文摘The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation.The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable.In addition,the adsorption energies increase with the introduction of the electric field.The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function.Furthermore,the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.
文摘Metal-organic frameworks (MOFs) have attracted much attention as adsorbents for the separation of CO2 from flue gas or natural gas. Here, a typical metal-organic framework HKUST-I(also named Cu-BTC or MOF-199) was chemically reduced by doping it with alkali metals (Li, Na and K) and they were further used to investigate their CO2 adsorption capacities. The structural information, surface chemistry and thermal behavior of the prepared adsorbent samples were characterized by X-ray powder diffraction (XRD), thermo-gravimetric analysis (TGA) and nitrogen adsorption-desorption isotherm analysis. The results showed that the CO2 storage capacity of HKUST-1 doped with moderate quantities of Li+, Na+ and K+, individually, was greater than that of unmodified HKUST-1. The highest CO2 adsorption uptake of 8.64 mmol/g was obtained with 1K-HKUST-1, and it was ca. 11% increase in adsorption capacity at 298 K and 18 bar as compared with HKUST- 1. Moreover, adsorption tests showed that HKUST-1 and 1K-HKUST-1 displayed much higher adsorption capacities of CO2 than those of N2. Finally, the adsorption/desorption cycle experiment revealed that the adsorption performance of 1K-HKUST-1 was fairly stable, without obvious deterioration in the adsorption capacity of CO2 after 10 cycles.
文摘CoCu/TiO_2 catalysts promoted using alkali metals(Li, Na, K, Rb, and Cs) were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO_2 catalysts and the catalytic performance for CO_2 hydrogenation to long-chain hydrocarbons(C_(5+))were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO_2 temperature-programmed desorption(TPD), and H_2-TPD, the introduction of alkali metals could increase the CO_2 adsorption and decrease the H_2 chemisorption, which could suppress the formation of CH_4, enhance the production of C_(5+), and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO_2 catalyst provided the maximum C_(5+) yield of 5.4%, with a CO_2 conversion of 18.4% and C_(5+) selectivity of42.1%, because it showed the strongest basicity and a slight decrease in the amount of H_2 desorption;it also exhibited excellent catalytic stability of more than 200 h.
文摘The efficient citral hydrogenation was achieved in aqueous media using Pd/CMS and alkali additives like K<sub>2</sub>CO<sub>3</sub>. The alkali concentrations, reaction temperature and the Pd metal content were optimized to enhance the citral hydrogenation under aqueous media. In the absence of alkali, citral hydrogenation was low and addition of alkali promoted to ~92% hydrogenation without reduction in the selectivity to citronellal. The alkali addition appears to be altered the palladium sites. The pore size distribution reveals that the pore size of these catalysts is in the range of 0.96 to 0.7 nm. The palladium active sites are also quite uniform based on the TPR data. The catalytic parameters are correlated well with the activity data.
基金supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy,Office of Science,Office of Basic Energy Sciences
文摘Neutral aqueous alkali sulfate has shown great interests for developing environmentally friendly high voltage and high energy supercapacitors. This work focuses on systematically investigating the properties of symmetric carbon/carbon supercapacitors in neutral aqueous alkali sulfates. At room temperature, the largest power and energy density were obtained with K2SO4 electrolyte due to the smallest cation dimensions and highest electrical conductivity. At low temperature, aqueous Li2SO4 electrolyte presents the best performance due to the largest solubility, allowing a long-term stability at temperatures ranging between 20℃ and –10℃ at a maximum voltage of 1.8 V. The excellent stability has been confirmed that capacitance retention achieves as high as 92% after 10,000 cycles. The capacitance variations with temperatures could essentially result from kinetic diffusion barrier, ion dimension changes and fewer pseudo-capacitance contributions under different temperatures. This work highlights the selected virtues of different alkali sulfate electrolytes for enhanced supercapacitors.
文摘The surface of carbon fibre is studied which has been treated with heated sodium hydrate solution (NaOH) . It is found that the surface of carbon fibre is not corroded during the treatment. But at the same time, it is also found that after this treatment, a certain number of carbonyl groups (C O) and (-COOH or ?COONa) are produced on the treated surface of carbon fibre. When carbon fiber is mixed with cement paste, the above reactive groups will link with Ca+2 in the paste, which will result in an early stage hydration of cement in inter facial areas. In addition, the experiments show that the rheological properties of cement paste reinforced with alkali-treated carbon fibre differ greatly from that of untreated carbon fibre reinforced cement paste.
文摘粉煤灰由于含有钙镁等碱土金属氧化物导致其浆液呈碱性,直接充填井下采空区易污染地下水源。利用陕北矿区府谷电厂粉煤灰开展组分测试、浆液pH值特性测试及固碳降碱试验,基于浆液pH值与OH−浓度理论关系对粉煤灰固碳降碱反应过程进行阶段划分并提出两级耦合的粉煤灰高效矿化方法。研究结果表明:①粉煤灰含CaO、MgO、K_(2)O等碱土金属氧化物,溶于水浆液呈高碱特性,浆液pH值随浆液浓度增大而增大,当粉煤灰浆液质量分数≥30%时,浆液pH值不受质量分数影响且粉煤灰碱土金属氧化物与水反应生成OH−速率较快,溶于水20 min,OH^(−)浓度饱和;②粉煤灰与CO_(2)发生矿化反应生成方解石型CaCO_(3),每1 kg粉煤灰可矿化封存29.57 g CO_(2);③粉煤灰与CO_(2)发生矿化粉煤灰固碳降碱过程中pH变化曲线呈“倒S”型,按降pH速率分为慢速(Ⅰ)、快速(Ⅱ)、慢速(Ⅲ)3个阶段,3个阶段的pH值分界点分别为11.39、7~8且第I阶段无法消除;④降pH与降碱不是同一概念,降碱指的是降浆液中OH−浓度,降pH第I阶段对应快速降碱阶段,降pH第Ⅱ、Ⅲ阶段对应深度降碱阶段;⑤决定粉煤灰固碳量的主要为降pH第I阶段,而非pH下降速率较大的第Ⅱ阶段,第I阶段CO_(2)利用率约为30.78%,第Ⅱ、Ⅲ阶段CO_(2)总利用率约为9.04%;⑥基于粉煤灰固碳降碱过程阶段划分及反应装置降碱速率、容积的差异性,提出两级耦合的粉煤灰高效矿化方法。研究结果对分析粉煤灰固碳降碱机理,提高粉煤灰固碳降碱效率,促进粉煤灰处置工业化应用具有重要意义。