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
运用ah initio Hartree-Fock从头算,微扰MP2和密度泛函B3LYP方法在不同的基组水平上对碱金属阳离子-苯复合物体系的可能构型进行了自由优化,得到了复合物的能量最低构型为碱金属阳离子位于苯环平面的正上方,频率计算结果表明该结构为稳...运用ah initio Hartree-Fock从头算,微扰MP2和密度泛函B3LYP方法在不同的基组水平上对碱金属阳离子-苯复合物体系的可能构型进行了自由优化,得到了复合物的能量最低构型为碱金属阳离子位于苯环平面的正上方,频率计算结果表明该结构为稳定结构.复合物的键长、原子净电荷、分子轨道系数、前沿轨道能量、Mullicken键级等都表明,碱金属阳离子和苯环碳原子之间的作用包含p-π作用方式,碱金属阳离子与苯结合时电子从苯环向碱金属阳离子转移,形成电荷转移复合物.它们之间的结合方式和氢键的结合方式相似,但计算得到的热力学参数表明复合物中碱金属阳离子与苯之间的结合强度远远大于典型的氢键,尤其是锂离子-苯复合物的生成焓已和普通的化学键相当.复合物的红外特征振动频率位于200cm^(-1)附近,对应于碱金属阳离子垂直于苯环平面的来回振动,同时形成复合物后,原来位于3200cm^(-1)的苯的C—H振动红外活性消失.展开更多
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity...The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework.展开更多
基于密度泛函理论方法构建并优化了Cu MY(M为碱金属阳离子)分子筛的稳定构型,采用速控步骤CO插入CH3O形成CH3OCO反应,研究了碱金属阳离子对Cu+Y分子筛中活性中心周围电子环境及催化甲醇氧化羰基化合成碳酸二甲酯性能的影响.计算结果表明...基于密度泛函理论方法构建并优化了Cu MY(M为碱金属阳离子)分子筛的稳定构型,采用速控步骤CO插入CH3O形成CH3OCO反应,研究了碱金属阳离子对Cu+Y分子筛中活性中心周围电子环境及催化甲醇氧化羰基化合成碳酸二甲酯性能的影响.计算结果表明,Li+,Na+和K+稳定落位于Y分子筛小笼中,且随着金属离子半径的增大,CH3OH,CO,CH3O在Cu MY上的吸附能和CO/CH3O的共吸附能均逐渐增加,CO插入CH3O反应的过渡态结构稳定性逐渐降低,活化能逐渐上升,相应的反应活性逐渐下降.而落位在超笼中Ⅱ*位的Rb+与Cs+则随着离子半径的增大,反应过渡态的结构稳定性提高,克服的活化能降低,反应活性升高.不同Cu MY分子筛上催化活性顺序为Cu Li Y-Ⅰ'>Cu Cs Y-Ⅱ*>Cu Na Y-Ⅰ'>CuRb Y-Ⅱ*>Cu KY-Ⅰ'>Cu Cu Y-Ⅰ',其中Cu Li Y-Ⅰ'分子筛克服速控反应的活化能垒(52.74 k J/mol)最低.展开更多
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.
文摘运用ah initio Hartree-Fock从头算,微扰MP2和密度泛函B3LYP方法在不同的基组水平上对碱金属阳离子-苯复合物体系的可能构型进行了自由优化,得到了复合物的能量最低构型为碱金属阳离子位于苯环平面的正上方,频率计算结果表明该结构为稳定结构.复合物的键长、原子净电荷、分子轨道系数、前沿轨道能量、Mullicken键级等都表明,碱金属阳离子和苯环碳原子之间的作用包含p-π作用方式,碱金属阳离子与苯结合时电子从苯环向碱金属阳离子转移,形成电荷转移复合物.它们之间的结合方式和氢键的结合方式相似,但计算得到的热力学参数表明复合物中碱金属阳离子与苯之间的结合强度远远大于典型的氢键,尤其是锂离子-苯复合物的生成焓已和普通的化学键相当.复合物的红外特征振动频率位于200cm^(-1)附近,对应于碱金属阳离子垂直于苯环平面的来回振动,同时形成复合物后,原来位于3200cm^(-1)的苯的C—H振动红外活性消失.
基金supported by the National Natural Science Foundation of China.
文摘The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework.
文摘基于密度泛函理论方法构建并优化了Cu MY(M为碱金属阳离子)分子筛的稳定构型,采用速控步骤CO插入CH3O形成CH3OCO反应,研究了碱金属阳离子对Cu+Y分子筛中活性中心周围电子环境及催化甲醇氧化羰基化合成碳酸二甲酯性能的影响.计算结果表明,Li+,Na+和K+稳定落位于Y分子筛小笼中,且随着金属离子半径的增大,CH3OH,CO,CH3O在Cu MY上的吸附能和CO/CH3O的共吸附能均逐渐增加,CO插入CH3O反应的过渡态结构稳定性逐渐降低,活化能逐渐上升,相应的反应活性逐渐下降.而落位在超笼中Ⅱ*位的Rb+与Cs+则随着离子半径的增大,反应过渡态的结构稳定性提高,克服的活化能降低,反应活性升高.不同Cu MY分子筛上催化活性顺序为Cu Li Y-Ⅰ'>Cu Cs Y-Ⅱ*>Cu Na Y-Ⅰ'>CuRb Y-Ⅱ*>Cu KY-Ⅰ'>Cu Cu Y-Ⅰ',其中Cu Li Y-Ⅰ'分子筛克服速控反应的活化能垒(52.74 k J/mol)最低.
