PAM(Partitioning Around Medoids)是一种基于k-中心点的聚类算法,在处理数据集聚类时,具有较强的鲁棒性和准确性。但是,PAM算法的主要缺点是确定聚类中心点集所需的计算代价太高。对于大数据集,PAM聚类过程缓慢。提出一种利用部分距离...PAM(Partitioning Around Medoids)是一种基于k-中心点的聚类算法,在处理数据集聚类时,具有较强的鲁棒性和准确性。但是,PAM算法的主要缺点是确定聚类中心点集所需的计算代价太高。对于大数据集,PAM聚类过程缓慢。提出一种利用部分距离搜索(PDS),先前中心点标号(PMI),以及三角不等式消除(TIE)准则等搜索策略来降低中心点迭代所需计算复杂性,实现快速PAM聚类的新算法。实验结果表明,相对于基本PAM聚类算法,在保持相同聚类效果的情况下,快速PAM聚类新算法能够减少70%～90%的乘法计算量,并可节省约1/3以上的计算时间。展开更多
In this work,a novel in situ auto-reduction strategy was developed to encapsulate uniformly dispersed Pd clusters/nanoparticles in MIL-125-NH_(2).It is demonstrated that the amino groups in MIL-125-NH_(2)can react wit...In this work,a novel in situ auto-reduction strategy was developed to encapsulate uniformly dispersed Pd clusters/nanoparticles in MIL-125-NH_(2).It is demonstrated that the amino groups in MIL-125-NH_(2)can react with formaldehyde to form novel reducing groups(-NH-CH_(2)OH),which can in situ auto-reduce the encapsulated Pd^(2+)ions to metallic Pd clusters/nanoparticles.As no additional reductants are required,the strategy limits the aggregation and migration of Pd clusters and the formation of large Pd nanoparticles via controlling the amount of Pd^(2+)precursor.When applied as catalysts in the hydrogenation of phenol in the aqueous phase,the obtained Pd(1.5)/MIL-125-NH-CH_(2)OH catalyst with highly dispersed Pd clusters/nanoparticles with the size of around 2 nm exhibited 100%of phenol conversion and 100%of cyclohexanone selectivity at 70℃ after 5 h,as well as remarkable reusability for at least five cycles due to the large MOF surface area,the highly dispersed Pd clusters/nanoparticles and their excellent stability within the MIL-125-NH-CH_(2)OH framework.展开更多
An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter(NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced long...An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter(NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced longitudinal pressure gradient.But accumulation of pollutants such as N_2 and O_2 will decrease the adsorption ability of the NEG,leading to a reduction of NEG lifetime.Therefore,an NEG thin film coated with a layer of Pd,which has high diffusion rate and absorption ability for H_2,can extend the service life of NEG and improve the pumping rate of H_2 as well.In this paper,with argon as discharge gas,a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe.By SEM measurement,deposition rates of TiZrV-Pd films are analyzed under different deposition parameters,such as magnetic field strength,gas flow rate,discharge current,discharge voltage and working pressure.By comparing the experimental results with the simulation results based on Sigmund's theory,the Pd deposition rate C can be estimated by the sputtered depth.展开更多
A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. I...A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. It was found that Pd/perovskite catalysts synthesized by the spc method were more active for CO oxidation than the calcined LaCo 0 95 Pd 0 05 O 3, where Pd dispersed in the solid solution. H 2 reducing treatment in the spc method could yield not only high dispersed fine Pd particles on the perovskite surface but also oxygen deficient structure. In these perovskite supported Pd catalysts, oxygen vacancies adsorbed, activated and supplied oxygen to the active Pd sites, where the oxidation occurred with adsorbed CO. The high activities were due to the cooperative action of Pd and oxygen vacancies.展开更多
Pd/Al_(2)O_(3)was pretreated by CO,H_(2)and NaBH_(4)reduction,respectively.The reduced catalysts were tested for o-xylene oxidation and characterized by power X-ray diffraction(XRD),transmission electron microscopy (T...Pd/Al_(2)O_(3)was pretreated by CO,H_(2)and NaBH_(4)reduction,respectively.The reduced catalysts were tested for o-xylene oxidation and characterized by power X-ray diffraction(XRD),transmission electron microscopy (TEM),X-ray photoelectron spectroscopy (XPS) and temperature-programmed decomposition of palladium hydride (TPDH).The characterizations indicate the pretreatments lead to distinct Pd particle sizes and amount of surface activated oxygen species,which are responsible for the catalytic performance.Compared with H_(2)and NaBH_(4)reduction methods,CO reduction shows a strong interaction between Pd and Al_(2)O_(3)with smaller Pd particle size and more surface activated oxygen.It exhibited excellent catalytic performance,complete oxidation of 50 ppmV o-xylene at 85℃with a WHSV of 60,000 mL/(g·hr).展开更多
文摘PAM(Partitioning Around Medoids)是一种基于k-中心点的聚类算法,在处理数据集聚类时,具有较强的鲁棒性和准确性。但是,PAM算法的主要缺点是确定聚类中心点集所需的计算代价太高。对于大数据集,PAM聚类过程缓慢。提出一种利用部分距离搜索(PDS),先前中心点标号(PMI),以及三角不等式消除(TIE)准则等搜索策略来降低中心点迭代所需计算复杂性,实现快速PAM聚类的新算法。实验结果表明,相对于基本PAM聚类算法,在保持相同聚类效果的情况下,快速PAM聚类新算法能够减少70%～90%的乘法计算量,并可节省约1/3以上的计算时间。
基金financial support from the National Natural Science Foundation of China(Grant No.51802015)the Research Department Closed Carbon Cycle Economy(CCCE)at the Ruhr-University Bochum,Fundamental Research Funds for the Central Universities(No.FRF-TP-20-005A3)the Fundamental Research Funds for the Central Universities and the Youth Teacher International Exchange&Growth Program(Grant No.QNXM20210016)。
文摘In this work,a novel in situ auto-reduction strategy was developed to encapsulate uniformly dispersed Pd clusters/nanoparticles in MIL-125-NH_(2).It is demonstrated that the amino groups in MIL-125-NH_(2)can react with formaldehyde to form novel reducing groups(-NH-CH_(2)OH),which can in situ auto-reduce the encapsulated Pd^(2+)ions to metallic Pd clusters/nanoparticles.As no additional reductants are required,the strategy limits the aggregation and migration of Pd clusters and the formation of large Pd nanoparticles via controlling the amount of Pd^(2+)precursor.When applied as catalysts in the hydrogenation of phenol in the aqueous phase,the obtained Pd(1.5)/MIL-125-NH-CH_(2)OH catalyst with highly dispersed Pd clusters/nanoparticles with the size of around 2 nm exhibited 100%of phenol conversion and 100%of cyclohexanone selectivity at 70℃ after 5 h,as well as remarkable reusability for at least five cycles due to the large MOF surface area,the highly dispersed Pd clusters/nanoparticles and their excellent stability within the MIL-125-NH-CH_(2)OH framework.
基金supported by the National Natural Science Funds of China(No.11205155)Fundamental Research Funds for the Central Universities(WK2310000041)
文摘An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter(NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced longitudinal pressure gradient.But accumulation of pollutants such as N_2 and O_2 will decrease the adsorption ability of the NEG,leading to a reduction of NEG lifetime.Therefore,an NEG thin film coated with a layer of Pd,which has high diffusion rate and absorption ability for H_2,can extend the service life of NEG and improve the pumping rate of H_2 as well.In this paper,with argon as discharge gas,a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe.By SEM measurement,deposition rates of TiZrV-Pd films are analyzed under different deposition parameters,such as magnetic field strength,gas flow rate,discharge current,discharge voltage and working pressure.By comparing the experimental results with the simulation results based on Sigmund's theory,the Pd deposition rate C can be estimated by the sputtered depth.
文摘A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. It was found that Pd/perovskite catalysts synthesized by the spc method were more active for CO oxidation than the calcined LaCo 0 95 Pd 0 05 O 3, where Pd dispersed in the solid solution. H 2 reducing treatment in the spc method could yield not only high dispersed fine Pd particles on the perovskite surface but also oxygen deficient structure. In these perovskite supported Pd catalysts, oxygen vacancies adsorbed, activated and supplied oxygen to the active Pd sites, where the oxidation occurred with adsorbed CO. The high activities were due to the cooperative action of Pd and oxygen vacancies.
基金supported by the National Natural Science Foundation of China (Nos. 21936005 and 21806011)。
文摘Pd/Al_(2)O_(3)was pretreated by CO,H_(2)and NaBH_(4)reduction,respectively.The reduced catalysts were tested for o-xylene oxidation and characterized by power X-ray diffraction(XRD),transmission electron microscopy (TEM),X-ray photoelectron spectroscopy (XPS) and temperature-programmed decomposition of palladium hydride (TPDH).The characterizations indicate the pretreatments lead to distinct Pd particle sizes and amount of surface activated oxygen species,which are responsible for the catalytic performance.Compared with H_(2)and NaBH_(4)reduction methods,CO reduction shows a strong interaction between Pd and Al_(2)O_(3)with smaller Pd particle size and more surface activated oxygen.It exhibited excellent catalytic performance,complete oxidation of 50 ppmV o-xylene at 85℃with a WHSV of 60,000 mL/(g·hr).
