La_2Ce_2O_7 nanoparticles were prepared by citric acid complexation method followed by calcination at varied temperatures. Then, supported with 4 wt% Ru, they were evaluated as the catalysts for ammonia synthesis unde...La_2Ce_2O_7 nanoparticles were prepared by citric acid complexation method followed by calcination at varied temperatures. Then, supported with 4 wt% Ru, they were evaluated as the catalysts for ammonia synthesis under conditions similar with industry. With La_2Ce_2O_7 being calcinated at 700 or 800℃, the experimental results indicate that the Ru/La_2Ce_2O_7 catalyst exhibits much higher ammonia concentration or ammonia synthesis rate than that of Ru/CeO_2 and Ru/La_2O_3. In addition, Ru/La_2Ce_2O_7 possesses high stability under over-heating test. In the absence of any promotor, ammonia concentration of Ru/La_2Ce_2O_7 catalyst approaches 14% at 450℃, GHSV of 10000 h^(-1) and pressure of 10 MPa. The rate-determining step of ammonia synthesis, dissociation of N_2 is significantly facilitated by the strong metalesupport interaction(SMSI) between Ru and La_2Ce_2O_7. Due to the interaction, La_2Ce_2O_7 tends to donate electrons to Ru,resulting in the high electron density over the surface of Ru active sites which is favorable for the dissociation of N_2. Consequently, high activity is achieved.展开更多
TiNb_(2)O_(7)represents an up-and-coming anode material for fast-charging lithium-ion batteries,but its practicalities are severely impeded by slow transfer rates of ionic and electronic especially at the low-temperat...TiNb_(2)O_(7)represents an up-and-coming anode material for fast-charging lithium-ion batteries,but its practicalities are severely impeded by slow transfer rates of ionic and electronic especially at the low-temperature conditions.Herein,we introduce crystallographic engineering to enhance structure stability and promote Li+diffusion kinetics of TiNb_(2)O_(7)(TNO).The density functional theory computation reveals that Ti^(4+)is replaced by Sb^(5+)and Nb^(5+)in crystal lattices,which can reduce the Li+diffusion impediment and improve electronic conductivity.Synchrotron radiation X-ray 3D nano-computed tomography and in situ X-ray diffraction measurement confirm the introduction of Sb/Nb alleviates volume expansion during lithiation and delithiation processes,contributing to enhancing structure stability.Extended X-ray absorption fine structure spectra results verify that crystallographic engineering also increases short Nb-O bond length in TNO-Sb/Nb.Accordingly,the TNO-Sb/Nb anode delivers an outstanding capacity retention rate of 89.8%at 10 C after 700 cycles and excellent rate performance(140.4 mAh g^(−1) at 20 C).Even at−30℃,TNO-Sb/Nb anode delivers a capacity of 102.6 mAh g^(−1) with little capacity degeneration for 500 cycles.This work provides guidance for the design of fast-charging batteries at low-temperature condition.展开更多
电导率是稀土矿渣玻璃陶瓷熔融过程中最重要的物性参数之一,研究电导率对玻璃熔体熔炼工艺优化有指导作用。为了研究尾矿玻璃陶瓷生产制造的熔融过程中稀土对熔体电导率的作用,使用分析纯试剂根据玻璃陶瓷主要化学成分制备玻璃陶瓷熔体...电导率是稀土矿渣玻璃陶瓷熔融过程中最重要的物性参数之一,研究电导率对玻璃熔体熔炼工艺优化有指导作用。为了研究尾矿玻璃陶瓷生产制造的熔融过程中稀土对熔体电导率的作用,使用分析纯试剂根据玻璃陶瓷主要化学成分制备玻璃陶瓷熔体样品,采用交流四电极法研究稀土对玻璃熔体电导率的影响规律,并结合红外光谱技术分析解释熔体电导率的变化机理。研究结果表明,硅酸盐熔体中添加La_(2)O_(3)或提高CaO/SiO_(2)比值会使熔体网络结构解聚,有效提高熔体电导率,且电导率的活化能(Activation energy of electrical conductivity)与La_(2)O_(3)含量和CaO/SiO_(2)比呈负相关关系;CaO/SiO_(2)比值较低时,La_(2)O_(3)含量对活化能影响更加显著,且红外光谱曲线硅酸盐结构带高波数段变化更明显,说明熔体结构发生更强烈的解聚效应;La_(2)O_(3)在CaO/SiO_(2)比值较低时对熔体网络结构和电导率的影响更大。展开更多
基金Project supported by National Natural Science Foundation of China(21776257)
文摘La_2Ce_2O_7 nanoparticles were prepared by citric acid complexation method followed by calcination at varied temperatures. Then, supported with 4 wt% Ru, they were evaluated as the catalysts for ammonia synthesis under conditions similar with industry. With La_2Ce_2O_7 being calcinated at 700 or 800℃, the experimental results indicate that the Ru/La_2Ce_2O_7 catalyst exhibits much higher ammonia concentration or ammonia synthesis rate than that of Ru/CeO_2 and Ru/La_2O_3. In addition, Ru/La_2Ce_2O_7 possesses high stability under over-heating test. In the absence of any promotor, ammonia concentration of Ru/La_2Ce_2O_7 catalyst approaches 14% at 450℃, GHSV of 10000 h^(-1) and pressure of 10 MPa. The rate-determining step of ammonia synthesis, dissociation of N_2 is significantly facilitated by the strong metalesupport interaction(SMSI) between Ru and La_2Ce_2O_7. Due to the interaction, La_2Ce_2O_7 tends to donate electrons to Ru,resulting in the high electron density over the surface of Ru active sites which is favorable for the dissociation of N_2. Consequently, high activity is achieved.
基金supported by the National Natural Science Foundation of China(22279026,2247090373)the Natural Science Foundation of Chongqing(CSTB2022NSCQ-MSX1401)+2 种基金the China Postdoctoral Science Foundation(2024M764198)the National Natural Science Foundation of China(22509044)the Fundamental Research Funds for the Central Universities(grant no.HIT.OCEF.2022017).
文摘TiNb_(2)O_(7)represents an up-and-coming anode material for fast-charging lithium-ion batteries,but its practicalities are severely impeded by slow transfer rates of ionic and electronic especially at the low-temperature conditions.Herein,we introduce crystallographic engineering to enhance structure stability and promote Li+diffusion kinetics of TiNb_(2)O_(7)(TNO).The density functional theory computation reveals that Ti^(4+)is replaced by Sb^(5+)and Nb^(5+)in crystal lattices,which can reduce the Li+diffusion impediment and improve electronic conductivity.Synchrotron radiation X-ray 3D nano-computed tomography and in situ X-ray diffraction measurement confirm the introduction of Sb/Nb alleviates volume expansion during lithiation and delithiation processes,contributing to enhancing structure stability.Extended X-ray absorption fine structure spectra results verify that crystallographic engineering also increases short Nb-O bond length in TNO-Sb/Nb.Accordingly,the TNO-Sb/Nb anode delivers an outstanding capacity retention rate of 89.8%at 10 C after 700 cycles and excellent rate performance(140.4 mAh g^(−1) at 20 C).Even at−30℃,TNO-Sb/Nb anode delivers a capacity of 102.6 mAh g^(−1) with little capacity degeneration for 500 cycles.This work provides guidance for the design of fast-charging batteries at low-temperature condition.
文摘电导率是稀土矿渣玻璃陶瓷熔融过程中最重要的物性参数之一,研究电导率对玻璃熔体熔炼工艺优化有指导作用。为了研究尾矿玻璃陶瓷生产制造的熔融过程中稀土对熔体电导率的作用,使用分析纯试剂根据玻璃陶瓷主要化学成分制备玻璃陶瓷熔体样品,采用交流四电极法研究稀土对玻璃熔体电导率的影响规律,并结合红外光谱技术分析解释熔体电导率的变化机理。研究结果表明,硅酸盐熔体中添加La_(2)O_(3)或提高CaO/SiO_(2)比值会使熔体网络结构解聚,有效提高熔体电导率,且电导率的活化能(Activation energy of electrical conductivity)与La_(2)O_(3)含量和CaO/SiO_(2)比呈负相关关系;CaO/SiO_(2)比值较低时,La_(2)O_(3)含量对活化能影响更加显著,且红外光谱曲线硅酸盐结构带高波数段变化更明显,说明熔体结构发生更强烈的解聚效应;La_(2)O_(3)在CaO/SiO_(2)比值较低时对熔体网络结构和电导率的影响更大。
