Supported Pd catalysts with varied Pd loadings(x=0.5 wt%, 2.0 wt%, 5.0 wt%, 7.5 wt%, 15.0 wt%) were prepared by the incipient wetness impregnation method using a ZnAl_(2)O_(4) spinel support.We found that ZnAl_(2)O_(4...Supported Pd catalysts with varied Pd loadings(x=0.5 wt%, 2.0 wt%, 5.0 wt%, 7.5 wt%, 15.0 wt%) were prepared by the incipient wetness impregnation method using a ZnAl_(2)O_(4) spinel support.We found that ZnAl_(2)O_(4) supported Pd catalysts with low Pd loadings(e.g., 0.5 wt%) are very selective in syngas conversion to methanol and dimethyl-ether(DME).XRD and TEM characterization shows that,after reduction at350℃,PdZnβ phase with Pd:Zn molar ratio of 1:1 is favored to form predominantly on the spinel support at relatively low Pd loadings,i.e.less than 5.0 wt%, while Pd-rich PdZnα alloy phase exists at Pd loadings above 5.0 wt%.A higher reduction temperature such as 500℃ can facilitate the transformation from PdZnα to PdZnβ phase in those catalysts with high Pd loading.We further found that catalysts with predominant PdZnβ phase are selective in the methanol and DME production from syngas,while the presence of PdZnα phase leads to the notable formation of alkanes byproducts,resulting in reduced methanol and DME selectivity.DME formation from dehydration of methanol depends on the acidity of catalysts,which was found to increase with Pd loading,probably due to the formation of isolated Al_(2)O_(3) as a result of Zn migrating from ZnAl_(2)O_(4) spinel phase to form the PdZn phases with Pd.展开更多
Previous results revealed that the defect and/or interface had a great impact on the electromagnetic pa-rameters of materials.In order to understand the main physical mechanisms and effectively utilize these strategie...Previous results revealed that the defect and/or interface had a great impact on the electromagnetic pa-rameters of materials.In order to understand the main physical mechanisms and effectively utilize these strategies,in this study,M Fe_(2)O_(4)and flower-like core@shell M Fe_(2)O_(4)@MoS_(2)(M=Mn,Ni,and Zn)sam-ples with different categories were elaborately designed and selectively produced in large scale through a simple two-step hydrothermal reaction.We conducted the systematical investigation on their microstruc-tures,electromagnetic parameters and microwave absorption performances(MAPs).The obtained results revealed that the large radius of M^(2+)cation could effectively boost the concentration of oxygen vacancy in the M Fe_(2)O_(4)and M Fe_(2)O_(4)@MoS_(2)samples,which resulted in the improvement of dielectric loss capabil-ities and MAPs.Furthermore,the introduction of MoS_(2)nanosheets greatly improved the interfacial effect and enhanced the polarization loss capabilities,which also boosted the MAPs.By taking full advantage of the defect and interface,the designed M Fe_(2)O_(4)@MoS_(2)samples displayed tunable and excellent com-prehensive MAPs including strong absorption capability,wide absorption bandwidth and thin matching thicknesses.Therefore,the clear understanding of defect and interface engineering made these strategies well elaborately designed and applicable to improving MAPs.展开更多
Reducing the dissolution of Mn from LiMn_(2)O_(4)(LMO)and enhancing the stability of film electrodes are critical and challenging for Li+ions selective extraction via electrochemically switched ion exchange technology...Reducing the dissolution of Mn from LiMn_(2)O_(4)(LMO)and enhancing the stability of film electrodes are critical and challenging for Li+ions selective extraction via electrochemically switched ion exchange technology.In this work,we prepared a nitrogen-doped carbon cladding LMO(C-N@LMO)by polymerization of polypyrrole and high-temperature annealing in the N2 gas to achieve the above purpose.The modified C-N@LMO film electrode exhibited lower Mn dissolution and better cyclic stability than the LMO film electrode.The dissolution ratio of Mn from the C-N@LMO film electrode decreased by 42%compared to the LMO film electrode after 10 cycles.The cladding layer not only acted as a protective layer but also functioned as a conductive shell,accelerating the migration rate of Li+ions.The intercalation equilibrium time of the C-N@LMO film electrode reached within an hour during the extraction of Li+ions,which was 33%less compared to the pure LMO film electrode.Meanwhile,the C-N@LMO film electrode retained evident selectivity toward Li+ions,and the separation factor was 118.38 for Li+toward Mg2+in simulated brine.Therefore,the C-N@LMO film electrode would be a promising candidate for the recovery of Li+ions from salt lakes.展开更多
采用低温固相燃烧法快速制备了一种具有{111}、{110}和{100}晶面的去顶角八面体LiNi_(0.08)Mn_(1.92)O_(4)(LNMO)正极材料,其高暴露{111}晶面可以减少充放电过程中Mn的溶解,面积相对较小的{110}和{100}晶面可增加Li^(+)快速扩散的通道....采用低温固相燃烧法快速制备了一种具有{111}、{110}和{100}晶面的去顶角八面体LiNi_(0.08)Mn_(1.92)O_(4)(LNMO)正极材料,其高暴露{111}晶面可以减少充放电过程中Mn的溶解,面积相对较小的{110}和{100}晶面可增加Li^(+)快速扩散的通道.测试结果表明,所合成的LNMO具有LiMn_(2)O_(4)特有的立方晶系结构,其颗粒尺寸为亚微米级.LNMO的高温电化学性能优异,在55℃,1和5 C的首次放电比容量分别为109.9和98.0 m Ah/g,分别循环300次后容量保持率为75.8%和80.5%;即使在55℃,10和15 C下分别循环1000次后仍具有48.4%和49.4%的容量保持率,而未掺杂的LiMn_(2)O_(4)于15 C循环1000次后容量损失高达98%.LNMO在55℃有较高的Li^(+)扩散系数(D=3.86×10^(-15)cm^(2)/s)和较小的电荷转移阻抗(循环前、后R_(ct)=158.0和279.8Ω)以及较低的表观活化能(E_(a)=17.63 k J/mol),说明Ni掺杂能够提高Li^(+)在尖晶石型LiMn_(2)O_(4)内的扩散速率及减小锂离子在脱嵌过程中的能垒,从而提高锂离子的扩散速率和倍率性能.对LNMO于55℃循环1000次后的极片进行X射线衍射(XRD)分析,发现LNMO电极材料的晶体结构基本保持不变,表明Ni掺杂提高了锰酸锂材料在55℃长循环过程中的晶体结构稳定性,有效抑制了Jahn-Teller效应及Mn的溶解,显著提升了其高温电化学性能.本工作为尖晶石LiMn_(2)O_(4)电极材料在高温方面的应用提供了借鉴.展开更多
基金supported by the Major Research Plan of National Natural Science Foundation of China(No.91545114 and No.91545203)the National Natural Science Foundation of China(No.21576227)。
文摘Supported Pd catalysts with varied Pd loadings(x=0.5 wt%, 2.0 wt%, 5.0 wt%, 7.5 wt%, 15.0 wt%) were prepared by the incipient wetness impregnation method using a ZnAl_(2)O_(4) spinel support.We found that ZnAl_(2)O_(4) supported Pd catalysts with low Pd loadings(e.g., 0.5 wt%) are very selective in syngas conversion to methanol and dimethyl-ether(DME).XRD and TEM characterization shows that,after reduction at350℃,PdZnβ phase with Pd:Zn molar ratio of 1:1 is favored to form predominantly on the spinel support at relatively low Pd loadings,i.e.less than 5.0 wt%, while Pd-rich PdZnα alloy phase exists at Pd loadings above 5.0 wt%.A higher reduction temperature such as 500℃ can facilitate the transformation from PdZnα to PdZnβ phase in those catalysts with high Pd loading.We further found that catalysts with predominant PdZnβ phase are selective in the methanol and DME production from syngas,while the presence of PdZnα phase leads to the notable formation of alkanes byproducts,resulting in reduced methanol and DME selectivity.DME formation from dehydration of methanol depends on the acidity of catalysts,which was found to increase with Pd loading,probably due to the formation of isolated Al_(2)O_(3) as a result of Zn migrating from ZnAl_(2)O_(4) spinel phase to form the PdZn phases with Pd.
基金This work was supported by the Fund of Fok Ying Tung Edu-cation Foundation,the Major Research Project of Innovative Group of Guizhou province(No.2018-013)Open Fund from Henan Uni-versity of Science and Technology,the National Science Foundation of China(Nos.11964006 and 11774156)the Foundation of the National Key Project for Basic Research(No.2012CB932304)for fi-nancial support。
文摘Previous results revealed that the defect and/or interface had a great impact on the electromagnetic pa-rameters of materials.In order to understand the main physical mechanisms and effectively utilize these strategies,in this study,M Fe_(2)O_(4)and flower-like core@shell M Fe_(2)O_(4)@MoS_(2)(M=Mn,Ni,and Zn)sam-ples with different categories were elaborately designed and selectively produced in large scale through a simple two-step hydrothermal reaction.We conducted the systematical investigation on their microstruc-tures,electromagnetic parameters and microwave absorption performances(MAPs).The obtained results revealed that the large radius of M^(2+)cation could effectively boost the concentration of oxygen vacancy in the M Fe_(2)O_(4)and M Fe_(2)O_(4)@MoS_(2)samples,which resulted in the improvement of dielectric loss capabil-ities and MAPs.Furthermore,the introduction of MoS_(2)nanosheets greatly improved the interfacial effect and enhanced the polarization loss capabilities,which also boosted the MAPs.By taking full advantage of the defect and interface,the designed M Fe_(2)O_(4)@MoS_(2)samples displayed tunable and excellent com-prehensive MAPs including strong absorption capability,wide absorption bandwidth and thin matching thicknesses.Therefore,the clear understanding of defect and interface engineering made these strategies well elaborately designed and applicable to improving MAPs.
基金supported by the National Natural Science Foundation of China(Grant Nos.U21A20303,22078217 and U20A20141).
文摘Reducing the dissolution of Mn from LiMn_(2)O_(4)(LMO)and enhancing the stability of film electrodes are critical and challenging for Li+ions selective extraction via electrochemically switched ion exchange technology.In this work,we prepared a nitrogen-doped carbon cladding LMO(C-N@LMO)by polymerization of polypyrrole and high-temperature annealing in the N2 gas to achieve the above purpose.The modified C-N@LMO film electrode exhibited lower Mn dissolution and better cyclic stability than the LMO film electrode.The dissolution ratio of Mn from the C-N@LMO film electrode decreased by 42%compared to the LMO film electrode after 10 cycles.The cladding layer not only acted as a protective layer but also functioned as a conductive shell,accelerating the migration rate of Li+ions.The intercalation equilibrium time of the C-N@LMO film electrode reached within an hour during the extraction of Li+ions,which was 33%less compared to the pure LMO film electrode.Meanwhile,the C-N@LMO film electrode retained evident selectivity toward Li+ions,and the separation factor was 118.38 for Li+toward Mg2+in simulated brine.Therefore,the C-N@LMO film electrode would be a promising candidate for the recovery of Li+ions from salt lakes.
文摘采用低温固相燃烧法快速制备了一种具有{111}、{110}和{100}晶面的去顶角八面体LiNi_(0.08)Mn_(1.92)O_(4)(LNMO)正极材料,其高暴露{111}晶面可以减少充放电过程中Mn的溶解,面积相对较小的{110}和{100}晶面可增加Li^(+)快速扩散的通道.测试结果表明,所合成的LNMO具有LiMn_(2)O_(4)特有的立方晶系结构,其颗粒尺寸为亚微米级.LNMO的高温电化学性能优异,在55℃,1和5 C的首次放电比容量分别为109.9和98.0 m Ah/g,分别循环300次后容量保持率为75.8%和80.5%;即使在55℃,10和15 C下分别循环1000次后仍具有48.4%和49.4%的容量保持率,而未掺杂的LiMn_(2)O_(4)于15 C循环1000次后容量损失高达98%.LNMO在55℃有较高的Li^(+)扩散系数(D=3.86×10^(-15)cm^(2)/s)和较小的电荷转移阻抗(循环前、后R_(ct)=158.0和279.8Ω)以及较低的表观活化能(E_(a)=17.63 k J/mol),说明Ni掺杂能够提高Li^(+)在尖晶石型LiMn_(2)O_(4)内的扩散速率及减小锂离子在脱嵌过程中的能垒,从而提高锂离子的扩散速率和倍率性能.对LNMO于55℃循环1000次后的极片进行X射线衍射(XRD)分析,发现LNMO电极材料的晶体结构基本保持不变,表明Ni掺杂提高了锰酸锂材料在55℃长循环过程中的晶体结构稳定性,有效抑制了Jahn-Teller效应及Mn的溶解,显著提升了其高温电化学性能.本工作为尖晶石LiMn_(2)O_(4)电极材料在高温方面的应用提供了借鉴.
