Ni-B非晶态合金中电子转移问题的DFT研究

根据Ni-B非晶态结构的短程有序、Ni和B之间是较强的化学作用和结构中存在B-B直接相连的实验事实,选择了Ni~mB~2^(^1^)(m=1-4)原子簇模型,用DFT方法对其进行高水平的量子化学计算,结果表明,模型体系中,B原子供给Ni原子电子,这与非晶态合金的实验结果一致,为了此较,同时选择了NiB^(^2^)(m=1-4)模型,计算结果与实验不符,这说明NiB~2^(^1^)(m=1-4)原子簇模型更能反映非晶态的结构特点。     

Ni-P非晶态合金中电子转移问题的DFT研究

根据Ni-P非晶态合金结构的短程有序、Ni和P之间具较强化学作用和结构中不存在P-P直接相连的实验事实,选择了Ni~nP(n=1-6)原子簇模型,用密度泛函理论方法对其进行计算。结果表明,在模型体系中,随着P含量的减少,电子转移方向发生变化,P原子由得电子变为失电子。这与Ni-P非晶态合金的实验结果一致,说明Ni~nP(n=1-6)原子簇模型能反映Ni-P非晶态合金的结构特点。     

非晶态合金Fe80P20局域结构和性质的量子化学研究

According to the structure features of Fe80P20, A series of clusters Fe4P were designed and focused on studying the stability of local structure, charge distribution and chemical bond. Using the DFT method,energy and structure of Fe4P clusters were optimized and analyzed. The computational results showed that the energy of cluster 1(2) has the lowest energy, and the possibility of its existence in the Fe8oP20 is high. Analyzing the transition states among the clusters, it was found that the clusters in the doublet state are more stable than those in the quartet state. The numbers of the Fe-P bond in the clusters play important roles in the cluster stability and electrons transfer properties. The more numbers of Fe-P bonds in the clusters, the higher the cluster stability, and the weaker the ability of P atom to get electron. The number of Fe atoms, which has bonding interactions with the P atom, is direct proportional to the average 3d orbit population of Fe atom. Basing on the orbital population, average magnetic moments of each Fe atom in the Fe4P clusters were calculated, and they are all smaller than that of single metal Fe atom. This suggests that all Fe4P clusters have soft magnetic property and they are expected to be perfect material for preparing soft magnetic apparatus.     

Ni-Co-B非晶态合金的结构和催化活性的理论研究

利用一系列原子簇模型Ni~xCo~3~-~xB~2(x=1～3)对Ni-Co-B非晶态合金的电子结构进行了SCC-DV-Xα计算。结果表明,Ni-B非晶态合金的催化加氢活性可通过Co的引入而得到改进。结合EXAFS和活性试验的结果,得出Ni和Co对非晶态Ni-Co-B合金的结构的稳定性有一种协同作用的结论。     

超细Ni-B非晶态合金催化糠醛液相加氢制备糠醇

报道了超细Ni－B非晶态合金应用于糠醛液相选择加氢制备糠醇，研究发现，Ni－B非晶态合金催化剂对糠醇的选择性接近100％，而且其催化活性显著高于RaneyNi和超细Ni催化剂，进一步的研究表明，对于Ni-B非晶态合金，其在423K以下进行热处理时，未出现明显的晶化；但在高温下，逐渐发生晶化，并导致催化活性和选择性显著下降，在XRD、SEM、XPS和氢吸附等一系列表征的基础上，初步探讨了催化活性与催化剂结构的关系，并考察了高温晶化对催化性能的影响。     

EXAFS研究Ni-B和Ni-Ce-B超细非晶态合金的退火晶化

采用同步辐射EXAFS技术定量地研究化学还原法制备的Ni-B和Ni-Ce-B超细非晶态合金中Ni原子的局域环境结构随退火温度升高而产生的变化,结果表明,对于Ni-B和Ni-Ce-B超细非晶态合金初始样品：Ni-Ni最邻近配位壳层的平均键长RNi-Ni、配位数N、热无序σT、结构无序σs分别为0．275nm,11.9.0.0069nm,0.034nm;0.276nm,12.4,0.0067nm,0.035nm,Ni-B最邻近配位壳层的RNi-B,N, σT,σs分别为0．215nm,2.7,0.0055nm,0.0048nm;0.214nm,2.0,0.0058nm,0.0042nm,Ni-Ni配位的σs很大,是其σT的4－5倍,比Ni－B配位的σs大近一个数量级,在300℃退火后,Ni－B样品开始发生晶化生成晶态Ni3B,其RNi-Ni和σs分别为0．254nm和0．011nm,σs降低近2倍;而．3％原子比的Ce掺入后使Ni-Ce-B超细非晶态合金的晶化温度升高100℃左右。在500℃退火后,Ni－B样品的结构参数与Ni箔的相近,但Ni-Ce-B样品中的Ni-Ni配位的σs仍为0．0073nm,Ni-B配位的N为1．2,表明稀土元素Ce（以CeO2)显著增强了Ni与B的相互作用,且同时使退火晶化成的Ni晶结构产生畸变。     

非晶态Ni-B合金对苯加氢催化行为的研究

非晶态合金材料由于其结构的特殊性,如无向性、密集性、长程无序的极端缺陷和短程有序的规管性等,在机械功能和能动功能方面都具有特殊性质.从80年代开始,它作为催化新材料,不断显示出许多特殊催化性能.因此开展非晶态合金材料催化剂的研究将可能开发出新型多功能的高效催化剂.然而用一般淬冷法制备的非晶态合金     

稀土对非晶态NiB合金催化剂性能的影响

研究了Ｅｕ,Ｇｄ,Ｔｂ对化学还原法制备非晶态ＮｉＢ合金催化剂的加氢及抗硫性能的影响。Ｅｕ,Ｇｄ,Ｔｂ的加入可提高ＮｉＢ合金的催化活性和抗硫性。其原因是稀土元素与ＮｉＢ合金间存在的相互作用。ＮｉＢ合金催化剂的活性中心与还原态的镍及镍＝硼－氧物种有关。     

Ni-B非晶态合金超细微粒的表面性质

非晶态合金具有短程有序和长程无序的结构特点,其优良的催化性能引人注目.但通常熔体急冷法制备的非晶样品表面积甚小.近年来采用化学还原方法制备使非晶态合金兼具超细微粒的性质,从而为非晶态合金在多相催化过程中的应用展示了诱人的前景.因此,研究非晶态合金超细微粒的表面性质就具有重要意义.Okamoto 等发现在用NaBH_4还原水溶液中Ni~(2+)离子制得的Ni-B 超细微粒表面除存在以合金方式结合的Ni、B 物类外还存在由B 水解产生的硼氧化物类,但未能将微粒表面性质与合金结构进行关联.本文报导不同结构状态下Ni-B 超细微粒表面性质的研究结果.     

Ni-B非晶态合金催化苯丙酮酸加氢合成苯丙氨酸

通过化学还原法制备了纳米非晶态Ni-B合金催化剂,考察了其对苯丙酮酸胺化加氢合成苯丙氨酸的催化性能.结果表明,相对于传统雷尼镍和漆原镍催化剂,非晶态合金催化剂表现出更为优异的活性和选择性,并且当非晶态Ni-B合金负载在SiO2载体上时,其活性和选择性均得到较大提高(高达97.67%).非晶态合金催化剂对苯丙氨酸合成反应表现出较好活性和选择性的原因主要是硼提供部分电子给镍的效应以及非晶态合金颗粒的纳米尺寸效应.     

取代基对醌的结构及电子转移能力的影响

用半经验的AM1,abinitio(HF/3-21G,HF/6-31G^*),及密度泛函[B3LYP/6-31G^*,B3LYP/6-311G(d,p)]方法对1,4-苯酯及其阴离子的结构与性质进行了研究。在此基础上用AM1及BLYP/6-31G(d,p)方法对泛醌Q~0,用AM1方法对泛醌Q~1,泛醌Q~2及其阴离子的结构与性质进行了研究。研究结果表明,由于取代基的影响,泛醌的环平面发生了扭曲,环上原子不再位于同一平面上。结构的变化导致了电子分布发生了变化,并由此导致了偶极矩随6位上取代基的增大而增大。随着6位支链的增长,泛醌的电离势逐渐减小而电子亲和势逐渐增大,泛醌传递电子的能力增强。在上述研究的基础上,对1,4-苯醌及泛醌的自交换电子转移反应过程进行了过程,计算了反应的内重组能,溶剂重组能及电子转移速率常数。结果表明内重组能的大小与取代基的长短无直接关系,而与得电子前后醌的结构变化程度密切相关。除高频振动的变化外,低频振动的变化对内重组能也有显著的贡献。计算所得1,4-苯醌自交换电子转移反应速率常数与实验值相符得很好。     

First principle MD study on the structural and electronic properties of liquid and amorphous NI81B19 and NI80P20 alloy

Atomic and electronic structures of liquid and amorphous Ni₈₁B₁₉ and Ni₈₀P₂₀ alloys were simulated by ab initio molecular dynamics. Pair correlation function, bond pair analysis, electronic population analysis, and density of states were calculated. It was found that amorphous Ni₈₁B₁₉ and Ni₈₀P₂₀ alloys can be prepared by rapid quenching, and their structures are similar to those of liquid alloys. Bond pair analysis indicated that the environment of each atom in Ni₈₁B₁₉ system is dominated by icosahedral and distorted icosahedral inherent structures; however, in Ni₈₀P₂₀ system, the tetrahedral order is preponderant. Strong interactions occur between the d‐electrons of Ni and the p‐electrons of B (or P), which leads to the covalent interactions between Ni and B (or P) atoms. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

生物体系中电子转移机理的研究Ⅱ: 分子间电子转移及 电子供、受体间不同基 团的影响

利用自编程序MOPAC-ET中AM1方法,及KT(Koopman'sTheorem)法,研究了二苯负离子体系的分子间电子转移现象,计算了其电子供、受体在不同距离下的V~A~B及它们之间的相关性,另外,还对两苯环间不同介入基团对电子转移的影响做了初步研究,发现不同的介入基团存在着较大的差异。     

乙腈液相选择性加氢中Ni-B非晶态合金和Raney Ni催化性能的比较

以乙腈液相选择性加氢为目标反应，分别考察了超细Ni-B非晶态合金和Rancy Ni的催化性能，发现两者的质量比活性相似，但单位活性比表面积上前者的活性及对乙胺的选择性显著高于后者，乙胺的最高得率前者为67．6％后者为40％。通过催化剂的系统表征，结合考察乙腈加氢反应的动力学，从几何效应和电子效应两方面阐述了Ni-B非晶态合金催化性能与催化剂结构和表面电子态的关系。     

Effects of lanthanum addition on Ni-B amorphous alloy catalysts used in anthraquinone hydrogenation

Amorphous Ni-B alloys with or without lanthanum were prepared by KBH₄ reduction, characterized by ICP, BET surface area measurement, XRD, TPD, H₂ chemisorption, etc., and studied in the hydrogenation of anthraquinone. The addition of lanthanum chloride in the preparation procedure leads to the incorporation of lanthanum oxide and the decrease of Ni:B ratio in the Ni-B amorphous alloy. In comparison with Ni-B, the presence of lanthanum oxide in the amorphous alloy lead to higher BET area, higher extents of H₂ chemisorption and desorption, the shift of H₂ desorption peaks to lower temperatures, and higher TOF and reaction rate in the hydrogenation of anthraquinone. The effects of lanthanum were attributed to its dispersion of Ni, leading to much more active centers and the donation of electrons to Ni and therefore activating the adsorbed hydrogen and weakening the binding energy between nickel and hydrogen. As a result, both TOF and the reaction rate in the hydrogenation of anthraquinone were increased with the addition of lanthanum. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ab initio description of photoabsorption and electron transfer in a doubly-linked porphyrin-fullerene dyad

Structure, photoabsorption and excited states of two representative conformations obtained from molecular dynamics (MD) simulations of a doubly-linked porphyrin-fullerene dyad DHD6ee are studied by using both DFT and wavefunction based methods. Charge transfer from the donor (porphyrin) to the acceptor (fullerene) and the relaxation of the excited state are of special interest. The results obtained with LDA, GGA, and hybrid functionals (SVWN, PBE, and B3LYP, respectively) are analyzed with emphasis on the performance of used functionals as well as from the point of view of their comparison with wavefunction based methods (CCS, CIS(D), and CC2). Characteristics of the MD structures are retained in DFT optimization. The relative orientation of porphyrin and fullerene is significantly influencing the MO energies, the charge transfer (CT) in the ground state of the dyad and the excitation of ground state CT complex (g-CTC). At the same time, the excitation to the locally excited state of porphyrin is only little influenced by the orientation or cc distance. TD-DFT underestimates the excitation energy of the CT state, however for some cases (with relatively short donor-acceptor separations), the use of a hybrid functional like B3LYP alleviates the problem. Wavefunction based methods and CC2 in particular appear to overestimate the CT excitation energies but the inclusion of proper solvation models can significantly improve the results.     

Theoretical study on electron transfer in biological systems (III)

Iritramolwular electron transfer of nlctal-containing spiro π-electron system was studied by AM1 method in the MOPAC-ET program developed by the present group. The results indicated that with the increasing of the outer electric field F, the activation energy of the reaction decreased. When F reaches a certain threshold value, the activation energy barrirr becomcs zero and the rate of reaction achieves the largest value. The results also indicated that electron transfer matrix elements V_AB and reorganization energy λ were not obviously affected by outer electric field while the exothermicity ΔE was directly proportional to it.     

尿嘧啶水助质子转移反应机理的研究

用密度泛函理论,在B3LYP/6-311++G**计算水平下分别对尿嘧啶所有的气相、液相、过渡态和质子转移异构体的结构进行全优化,获得它们在气相和水相中的几何结构和电子结构,PGM反应场溶剂模型用于水相计算.结果显示:在气相和水相中,水参与反应降低了互变异构质子迁移的反应活化能,对互变异构质子迁移的反应起到催化作用,但...