Periodic density functional theory study of propane oxidative dehydrogenation over V2O5(001) surface

The oxidative dehydrogenation (ODH) of propane on single-crystal V(2)O(5)(001) is studied by periodic density functional theory (DFT) calculations. The energetics and pathways for the propane to propene conversion are determined. We show that (i) the C-H bond of propane can be activated by both the terminal and the bridging lattice O atoms on the surface with similar activation energies. At the terminal O site both the radical and the oxo-insertion pathways are likely for the C-H bond activation, while only the oxo-insertion mechanism is feasible at the bridging O site. (ii) Compared to that at the terminal O site, the propene production from the propoxide at the bridging O site is much easier due to the weaker binding of propoxide at the bridging O. It is concluded that single-crystal V(2)O(5)(001) is not a good catalyst due to the terminal O being too active to release propene. It is expected that an efficient catalyst for the ODH reaction has to make a compromise between the ability to activate the C-H bond and the ability to release propene.     

Li含量对Li/MgO丙烷氧化脱氢制烯烃反应催化性能的影响

采用浸渍法制备了不同Li含量的Li/MgO催化剂,并通过TG-DTA、N_2吸附及XRD等手段对其进行了表征;对丙烷在Li/MgO催化剂表面的两种吸附状态所占据的空间体积大小进行了计算,研究了Li含量对其丙烷氧化脱氢制烯烃反应催化性能的影响。结果表明,随着Li/MgO催化剂中Li含量的增加,丙烷转化率与乙烯、甲烷、乙烷和COx的选择性均先增加,在Li物质的量分数为3%时达到最高,然后随Li含量增加而降低,而丙烯选择性则出现相反的变化趋势。丙烷在Li/MgO催化剂上的吸附和反应同时受动力学和热力学两个因素的制约;Li负载量不同,反应活性位Li+O-分散状态也不同,导致产物分布发生变化。活性位分散度高时受热力学因素影响,有利于生成丙烯;活性位分散度低时受吸附动力学影响,更趋向于生成乙烯等其他产物。     

铂钌团簇及电荷对甲醇活性的理论研究

采用密度泛函理论(DFT)对钌掺杂的铂团簇阳离子([Pt_nRu_m]⁺, m + n = 3, n ≥ 1)活化甲醇C―H和O―H键反应进行了理论研究;探讨了电荷对[Pt_nRu_m]团簇反应活性的影响。电荷分析表明:(1) [Pt₃]⁺团簇中正电荷在三个Pt原子上均匀分布;掺杂Ru原子后,正电荷主要分布在Ru原子上; (2)首先活化C―H键时[Pt_nRu_m]⁺的反应活性比[Pt_nRu_m]明显提高;首先活化O―H键时只有[Pt₃]⁺比[Pt₃]团簇的反应活性有明显提高。本研究可为金属团簇调控的C―H键和O―H键的活化提供更深入的理解。     

簇合物Mo2X4(X＝S,O)电子结构和光谱性质的Ab Initio研究

在abinitio水平上对含cis/trans-MO₂S₄核和含Mo₂O₄核簇合物的电子结构进行了研究.对钼原子选取和构造了一组适合于含Mo-Mo金属键的双核钼簇合物从头算的(4s4p2d)基组,利用该基组并结合自然键轨道(NBO)方法,对含上述簇胳的3个簇合物的电子结构进行了研究,并与相应的钨簇合物进行了比较.     

丙烷脱氢负载型PtSnNa/SUZ-4催化剂中Na+助剂组分的作用

用微型催化反应装置结合X射线衍射(XRD)、H₂化学吸附、NH₃吸附-程序升温脱附(NH₃-TPD)和H₂-程序升温还原等多种物理化学手段研究了丙烷脱氢负载型PtSnNa/SUZ-4催化剂中Na⁺助剂组分的作用。结果表明,Na⁺组分可中和SUZ-4载体表面的强酸中心、提高催化剂的Pt金属分散度、抑制脱氢产物的裂解和积炭的生成,从而提高催化剂的丙烷脱氢选择性和反应稳定性。但是过量Na⁺组分的存在会削弱Sn物种与载体之间的相互作用,使其易被还原,导致催化剂丙烷脱氢活性显著下降。     

Effect of promoter Ce on silver-molybdenum-phosphate catalysts for selective oxidation of propane to acrolein

A series of Me_nAg_0.3Mo_0.5P_0.3O_y (Me=Cu, Zn, Mn, W, Ce, Pr, Nd) and Ag_0.3Mo_0.5P_0.3O_x catalysts were prepared. The addition of Ce to Ag_0.3Mo_0.5P_0.3O_x catalysts improved the catalytic performance in selective oxidation of propane to acrolein, and Ce_0.1Ag_0.3Mo_0.5P_0.3O_x catalysts showed the highest acrolein selectivity (28.7%) and yield (4.4%). The physicochemical properties of Ag_0.3Mo_0.5P_0.3O_x and Ce_nAg_0.3Mo_0.5P_0.3O_x (n=0.1–0.5) catalysts have been comparatively characterized by BET, XRD, H₂-TPR, XPS, EPR and C₃H₈(C₃H₆)-TPD. Significant differences in physicochemical properties between Ag_0.3Mo_0.5P_0.3O_x and Ce doped Ag_0.3Mo_0.5P_0.3O_x catalysts have been observed, which is due to the formation of the redox cycle (Ce³⁺+Mo⁶⁺Ce⁴⁺+Mo⁵⁺) in the Ce_nAg_0.3Mo_0.5P_0.3O_y catalyst. Such effect modified the reducibility, the concentration of Mo⁵⁺, the activation of propane and the transformation of possible intermediate propene to acroelin, which in return greatly influenced the catalytic performance of Ce doped Ag_0.3Mo_0.5P_0.3O_x catalysts in selective oxidation of propane to acroelin. The proper addition of Ce to Ag_0.3Mo_0.5P_0.3O_x catalyst improved the acrolein selectivity and yield.     

Tautomeric properties, conformations and structure of N-(2-hydroxyphenyl)-4-amino-3-penten-2-on

N-(2-hydroxyphenyl)-4-amino-3-penten-2-on (C₁₁H₁₃NO₂) has been studied by X-ray analysis. It crystallizes the orthorhombic space group P2₁2₁2₁ with a=8.834(1), b=10.508(2), c=11.212(2) Å, V=1040.8(3) Å³, Z=4, D_c=1.22 g cm⁻³ and μ(MoK)=0.084 mm⁻¹. The structure was solved by direct methods and refined to R=0.038 for 1373 reflections (I>2σ(I)). The title compound is photochromic and the molecule is not planar. Intramolecular hydrogen bonds occur between the pairs of atoms N(1) and O(1) [2.631(2) Å], and N(1) and O(2) [2.641(2) Å], the H atom essentially being bonded to the N atom. There is also a strong intermolecular O–HO hydrogen bonding [2.647(2) Å] between neighbouring molecules. Tautomeric properties and conformations of the title compound were investigated by semi-empirical quantum mechanical AM1 calculations and the results are compared with the X-ray results.     

单原子Co位点的CO2还原反应路径:局部配位环境的影响

在CO2还原反应(CO2RR)应中,单原子催化剂被认为是很有前途的电催化剂.Co-N4活性位点因其优异的CO选择性和活性而受到广泛关注.然而,Co位点的局部配位环境与CO2RR途径之间的相关性尚不明确.本文采用密度泛函理论(DFT)计算,研究了含1,10-菲咯啉基底的N4-大环配体(Co-N4-CPY)负载的CoN4位...     

Acyl complexes of molybdenum: structural and reactivity studies

The following structural peculiarities of the agostic acyl structure ₂R) (R = H, SiMe₃) and some characteristic chemical reactivity of the M-η²-acyl and iminoacyl linkage are described. (i) A structural comparison of the bonding parameters within three agostic acetyl Mo complexes containing the dithioacid ligand, indicates that the agostic interaction strengthens upon increasing the electron-releasing properties of the S-chelating ligand. (ii) The acyl-xanthate complex Mo(C(O)Me)(S₂COR)(CO)(PMe₃)₂ undergoes loss of a sulfur atom from the coordinated xanthate and coupling with the acyl ligand to form complexes containing coordinated alkoxythiocarbonyl and monothioacetate ligands. The latter can be metathetically replaced by KS₂COR. (iii) Upon heating at 70°C η²-acyl-dicarbonyl bispirazolilborate complexes of molybdenum of the type Mo(H₂B(pz^*)₂)(η²-C(O)Me)(CO)₂(PMe₃) (pz^* = 3,5-dimethyl-pyrazol-1-yl) yield functionalized acyl ligands derived from the stereo- and regioselective intramolecular addition of one of the B---H bonds of the H₂B(pz^*)₂ group across the C=O moiety of the η²-acyl group. (iv) The η²-acyl-isocyanide complexes {Mo}(η²-C(O)R)(CNR′) ({Mo} = Mo(H₂B(pz^*)₂)(CO)(PMe₃)) undergo irreversible thermal isomerization to the corresponding η²-iminoacyl-carbonyl derivatives {MO}(η²-C(NR′)R)(CO). This isomerization reaction follows first-order kinetics.     

两个含N-皮考林酰肼铁配合物的合成和结构表征

合成了含N-乙酰皮考林酰肼(简写为Haphz)的铁配合物[Fe₂(aphz)₂(μ-CH₃O)₂Cl₂]·CH₃OH(1,C₁₉H₂₆Cl₂Fe₂N₆O₇,Mr=633.06)和含N-苯甲酰皮考林酰肼(简写为Hphphz)的铁配合物Fe(phphz)Cl₂(2,C₁₃H₁₀Cl₂FeN₃O₂,Mr=366.99).2个配合物均属三斜晶系,空间群为P     

Oxidative Dehydrogenation of Propane over a VO2‐Exchanged MCM‐22 Zeolite: A DFT Study

The adsorption and the mechanism of the oxidative dehydrogenation (ODH) of propane over VO₂‐exchanged MCM‐22 are investigated by DFT calculations using the M06‐L functional, which takes into account dispersion contributions to the energy. The adsorption energies of propane are in good agreement with those from computationally much more demanding MP2 calculations and with experimental results. In contrast, B3LYP binding energies are too small. The reaction begins with the movement of a methylene hydrogen atom to the oxygen atom of the VO₂ group, which leads to an isopropyl radical bound to a HO? V? O intermediate. This step is rate determining with the apparent activation energy of 30.9 kcal mol^?1, a value within the range of experimental results for ODH over other silica supports. In the propene formation step, the hydroxyl group is the more reactive group requiring an apparent activation energy of 27.7 kcal mol^?1 compared to that of the oxy group of 40.8 kcal mol^?1. To take the effect of the extended framework into account, single‐point calculations on 120T structures at the same level of theory are performed. The apparent activation energy is reduced to 28.5 kcal mol^?1 by a stabilizing effect caused by the framework. Reoxidation of the catalyst is found to be important for the product release at the end of the reaction.     

In situ UV-vis-NIR diffuse reflectance and Raman spectroscopy and catalytic activity studies of propane oxidative dehydrogenation over supported CrO3/ZrO2 catalysts

The molecular structures, oxidation states, and reactivity of 3 and 6% CrO3/ZrO2 catalysts prepared by incipient wetness impregnation were examined under different conditions. The in situ Raman spectroscopic studies under dehydrated conditions reveal that the 3 and 6% CrO3/ZrO2 catalysts possess equal amounts of monochromate and polychromate species. Consequently, monolayer coverage on this ZrO2 support is about 3% CrO3. The 6% CrO3/ZrO2 possesses an additional Raman band due to Cr2O3 crystals corresponding to the remaining 3% CrO3. Furthermore, during reaction conditions the polychromate species is preferentially reduced, the monochromate species are slightly affected, and the Cr2O3 crystals are not affected. The in situ UV-vis-NIR diffuse reflectance spectroscopy results reveal that under steady-state reaction conditions the extent of reduction and edge energy position of surface Cr6+ cations increase with an increase in reduction environment for the 3 and 6% CrO3/ZrO2 samples. Propane oxidative dehydrogenation (ODH) studies reveal that the catalytic activity expressed in moles of propane converted per gram catalyst per second is similar for the two catalysts, which is consistent with equal amounts of molecularly dispersed chromia present. The turnover frequency for the 6% CrO3/ZrO2 catalyst is, however, smaller than that for the 3% CrO3/ZrO2 sample due to the presence of Cr2O3 crystals, which are relatively inactive for propane ODH. For this catalytic system and for the experimental conditions used, propene, CO, and CO2 are primary products. Furthermore, the 33-39% propene selectivity is not affected by the C3H8/O2 ratio for both catalysts. Structure-reactivity studies suggest that the molecularly dispersed species are present in equal amounts in the 3 and 6% CrO3/ZrO2 samples as Cr6+ monochromate and polychromate species are the most effective catalytic active sites taking part in the propane ODH reaction.     

Vibrational frequencies of CO adsorbed on silica supported Mo atoms from density functional calculations

The interaction of CO with silica supported molybdenum atoms has been studied by means of density functional calculations and cluster models. Experimentally two bands in the IR spectra of adsorbed CO have been observed at 2170 and 1990 cm⁻¹ with vibrational shifts of +27 and −153 cm⁻¹, respectively, with respect to the gas-phase molecule, the peak at +27 cm⁻¹ has been related to the presence of neutral Mo atoms anchored to two oxygen atoms of the SiO₂ substrate. Possible reactive sites at the Mo/SiO₂ interface have been explored as candidates for CO adsorption. Mo atoms in various formal oxidation states, from +II to +VI, have been considered. Both molecular and cluster models of the Mo/SiO₂ interface have been employed. The analysis shows that a neutral Mo(II) atom, proposed to be responsible for the blue-shift of ν(CO), is not likely to be the origin of the IR band at 2170 cm⁻¹. Only Mo atoms in high oxidation states or Mo cations carrying a real positive charge can account for the positive shifts in the CO frequency.     

Electron counting and bonding analysis in triruthenium clusters containing sulfoximido ligands: true or false electron-deficient systems?

Triruthenium clusters containing a methylphenylsulfoximido cap or bridge, Ru₃(CO)₉(μ₂-H)[μ₃-NS(O)MePh] (1), Ru₃(CO)₁₀(μ₂-H)[μ₃-NS(O)MePh] (2), Ru₃(CO)₈(μ₃-η²-CPhCHBu)[μ₃-NS(O)MePh] (3), Ru₃(CO)₉(μ₃-η²-PhCCCCHPh)[μ₂-NS(O)MePh] (4), and Ru₃(CO)₇(μ₂-CO)(μ₃-η²-PhCCCCHPh)[μ₃-NS(O)MePh] (5) have been examined by EHT and DFT calculations in order to analyze the bonding present in the clusters and to establish the electron counting. They clearly show that a μ₃-sulfoximido group is not a 3e⁻ ligand as one may be led to think at first sight, but rather acts as a three-orbital/5e⁻ system, i.e. should be considered as isolobal to an N---R⁻ ligand. Because of some delocalization of its π-type orbitals on the sulfur and oxygen atoms, it is expected to bind slightly less strongly to metal atoms than classical imido ligands. Once in a μ₂ coordination mode, the sulfoximido ligand retains a lone pair on its pyramidalized N atom and becomes a two-orbital/3e⁻ ligand. It follows that clusters 1, 2, 4 and 5 are electron-precise, whereas cluster 3 is electron deficient with respect to the 18e⁻ rule but obeys the polyhedral skeletal electron pair electron-counting rules. Consistently, all the calculated clusters exhibit large HOMO–LUMO gaps and no trace of electron deficiency can be found in their electronic structures.     

一个二维钴配位聚合物的合成、结构及光催化性质

以N,N'-二(3-吡啶基)-吡啶-3,5-二甲酰胺(bppdca)和2-巯乙酸基烟酸(L)为混合配体,利用水热合成方法获得了一个二维的Co(Ⅱ)配位聚合物:{[Co(bppdca)(L)]·3H₂O}_n,并通过元素分析、IR和单晶X射线衍射等技术手段确定了其结构。该配合物分子式为C₂₅H₂₄N₆O₉SCo,单斜晶系,P2₁/c空间群,a=1.07419(9) nm,b=0.86166(6) nm,c=2.9853(2) nm,β=96.772(1)°,Z=4,V=2.743 9(4) nm³,M_r=643.49,D_c=1.558 g/cm³,F(000)=1324,μ=0.766 mm^-1,S=1.051,R=0.0406,wR=0.1160。 晶体结构分析表明,配合物中的CoⅡ与来自2个bppdca配体的2个N原子、1个L阴离子的单齿羧基O原子和S原子以及来自另一个L阴离子的一个羧基中的2个O原子配位形成八面体配位构型。 相邻的Co^Ⅱ通过L阴离子连接成一维螺旋链[Co(L)]_n,相邻的左、右螺旋链通过成对的bppdca配体拓展成二维配位网络。 最终,相互平行的二维网络通过氢键作用拓展成三维超分子框架。 另外,还研究了该化合物的热稳定性、电化学性质、荧光性质以及选择性光催化性质。CCDC: 1010786     

Investigation of Propene Oligomerization Catalyst Series Derived from Complex of Ferric Sulfate and Nickel Sulfate

Some paper have reported that catalyt of NiSO₄/γAlO₃ has a very high oligomerization activity for propene, but the over tri oligomerization selectivity is very low^[1].The catalyt of Fe₂(SO₄)₃/γ-Al₂O₃ has a very high over trioligomerization selectivity, but oligomerization activity was lower then catalysis of NiSO₄/γ-Al₂O₃ for propene and stability of catalysis was not as good as catalysis of NiSO₄/γ-Al₂O₃^[2].In this paper the catalysis of Fe_(2/3)xNi_1-xSO₄-P₂O₅/γ-Al₂O₃ for propene oligomerization has been systematically studied, the effect of the activation method, the stability and reaction conditions on activity and selectivity were investigated. Fe_(2/3)xNi_1-xSO₄-P₂O₅/γ-Al₂O₃ catalysis was preparared by impregnation.The factors affecting catalyst performance for propene oligomerization are as follows.     

Theoretical study of some 1,3-substituted (1,3-diketonato)borondifluorides. Potential energy curve relevant to the barrier crossing reaction

Ab initio Hartree-Fock calculations utilising STO-3G, 3-21G^* and 6-31G^* basis sets have been performed on three neutral and highly polar molecules, (diformylmethine)borondifluoride, (acetylacetonato)borondifluoride and (dibenzylmethine) borondifluoride. The calculated and experimental structures are well correlated when using the HF/3-21G^* basis set, except for the structure parameters involving the boron atom. The HF/6-31G^* basis set does not improve the accuracy in structure calculations. The conformational analysis is in agreement with the experimentally observed C_2v symmetrical structures, where the boron atom is tetrahedrally coordinated. The calculations support a one-dimensional ground state barrier crossing reaction for (dibenzylmethine)borondifluoride, where the phenyl torsion is the most likely reaction coordinate. Both HF/6-31G^* calculations and the second-order Møller-Plesset correction with the 3-21G^* basis set suggest an activation energy of the ground state reaction of about 30 kJ mol⁻¹. The ground state barrier crossing reaction kinetics is evaluated by the Kramers theory. The calculated ground state parameters relevant to the barrier crossing reaction are compared with the experimentally observed excited state values.     

新型二维网状双席夫碱银配合物的合成与结构

席夫碱配体由于在合成上具有极大的灵活性和良好的配位能力 ,因而席夫碱 -金属配合物的研究一直受到广泛重视 .多年来 ,席夫碱配体由简单的单齿发展到多齿和大环配体 .此外 ,过渡金属的席夫碱配合物具有独特的结构、性能和广泛的应用 ,如氧化还原 [1] 、催化 [2 ] 以及生物体系的化学模拟 [3 ] ;另一方面 ,由于银原子配位方式的多样性 (二、三、四和五配位 ) ,便于人们对超分子化合物的组装规律进行系统研究 ,因而银配合物的研究正日益引起人们极大的兴趣 [4～ 7] .鉴于此 ,我们设计合成了一个新的四齿席夫碱配体 L ,研究了其与 CF3 SO3 …     

4-硝基咪唑A-带激发态结构动力学

通过共振拉曼光谱实验和量子化学计算的方法研究了4-硝基咪唑(4NI)A-带激发态衰变动力学.对4NI的振动光谱、紫外电子吸收光谱、荧光光谱和共振拉曼光谱进行了指认.在全活化空间自洽场法(CASSCF)/6-31G(d)计算水平下获得了单重激发态S1(nOπ*)和S2(ππ*)和势能面交叉点S1(nOπ*)/S2(ππ*)的优化几何结构和能量,分析了A-带共振拉曼光谱的强度模式特征,获得了短时结构动力学,并结合全活化空间自洽场法(CASSCF)理论计算结果确定了4NI在S2(ππ*)态衰变通道主要是S2,FC→S2,min(ππ*)→S0辐射弛豫.     

Non-empirical molecular orbital studies of the possibility of ferromagnetic ordering in isoelectron-substituted ferrocarbon modifications

The vertical singlet-triplet (ST) splitting in the C₃H₆ molecule and C₂BH⁻₆ and C₂NH⁺₆ ions has been investigated by means of ab initio calculations. The molecular geometry was either taken as that corresponding to the UHF/6-31G^* or UHF/6-31+G^* energy minimum of the triplet configuration (for C₃H₆, C₂BH⁻₆, C₂NH⁺₆), or was extracted from the ferrocarbon crystal (for C₃H₆). Polarized split-valence basis sets (6-31G^*, 6-31+G^* and 6-311G^**) and fourth-order Møller-Plesset perturbation theory at the MP4SDTQ level of approximation provides more reliable ST splitting values, than the MP4SDQ level, the latter being the most accurate method used in our previous work. These calculations prove the presence of ferromagnetic ordering within the same quasi-graphite plane of ferrocarbon crystal. The presence of such ordering has been shown within the same quasi-graphite plane upon substitution of sp³ carbon atoms by ions B⁻, N⁺ and so on.