Enhancement of Brønsted acidity in zeolitic catalysts due to an intermolecular solvent effect in confined micropores

Solid-state NMR and DFT calculation studies certified the presence of an intermolecular solvent effect for molecules confined in microporous zeolite, leading to a notable increase in Br?nsted acidity of the solid acid catalyst.     

用升降算符法计算多原子分子振动-转动能级

自70年代起,Handy^[1]等,用变分法计算了H₂、SO₂等分子的振动-转动光谱,所得结果与实验吻合。但因在于计算久期行列式元素的积分,其计算方法不易推广。     

Influence of temperature on the structure of liquid water

Molecular dynamics simulations have been carried out for liquid water at 7 different temperatures to understand the nature of hydrogen bonding at molecular level through the investigation of the effects of temperature on the geometry of water molecules. The changes in bond length and bond angle of water molecules from gaseous state to liquid state have been observed, and the change in the bond angle of water molecules in liquid against temperature has been revealed, which has not been seen in literature so far. The analysis of the radial distribution functions and the coordinate numbers shows that, on an average, each water molecule in liquid acts as both receptor and donor, and forms at least two hydrogen bonds with its neigbors. The analysis of the results also indicates that the water molecules form clusters in liquid.     

还原温度对Ni／Al2O3催化剂上H2,CO吸附的影响

采用程序升温还原与程序升温逐步活化、Ｈ２、ＣＯ室温吸附、Ｈ２程序升温脱附相结合的方法，研究了Ｎｉ／Ａｌ２Ｏ３催化剂上还原活化温度对其吸脱附性能的影响．实验发现，Ｎｉ／Ａｌ２Ｏ３催化剂上，在不同温度还原的不同Ｎｉ氧化物物种，经相应温度活化后可形成不同性质的Ｈ２、ＣＯ吸附中心．催化剂经５２３Ｋ及５７３Ｋ活化后可形成极细的与Ａｌ２Ｏ３有一定相互作用的吸附中心，在这类中心上，Ｈ２的室温吸附量极小，但有一定的高温Ｈ２吸附量，且高温吸附的Ｈ２要在较高温度下才能脱附，ＣＯ在其上则可能是按单金属中心多ＣＯ方式吸附的．催化剂经６７３Ｋ和７２３Ｋ活化后均形成较强的Ｈ２、ＣＯ吸附中心，ＣＯ在这些中心上可能是按线式和桥式两种方式吸附的．催化剂经６７３Ｋ活化后，形成的中心上吸附的Ｈ２可在相对较低的温度下脱附．Ｎｉ／Ａｌ２Ｏ３经７７３Ｋ处理会发生烧结，因而丧失室温Ｈ２、ＣＯ吸附能力．     

猝发强流多脉冲电子束源物理设计

给出一台脉冲间隔100～1 000 ns、脉冲数2~5个、二极管电压3 MV、引出束流强度2.5 kA的猝发多脉冲电子束源的物理设计及初步调试结果。在设计中,采用感应叠加和阻抗匹配方案获得二极管高电压脉冲;试验中分别采用天鹅绒和大发射面储备式热阴极获得猝发多脉冲电子束。调试结果表明:采用大发射面热阴极可避免阴极等离子体产生,确保二极管在猝发多脉冲状态下稳定运行。初步调试获得大于2.7 MV猝发三脉冲二极管高压,并获得1.6 kA的三脉冲电子束流。     

非线性特征值问题的正解

本文着重考察非线性特征值问题u"+λg(t)f(u)=0, 0相似文献   

几种金属材料宏观断裂形式的试验研究

总结了几种金属材料在常规破坏试验过程中的断裂现象，分析了不同材料不同应力三维度下的几种宏观断裂形式，结果表明，金属材料在不同受力形式下，随应力状态参数Rσ从大向小变化，断裂机理从穿晶脆断，向以孔洞扩张聚合、局部剪切带的扩展转化，材料可能依次发生解理脆断、孔洞正断、有孔洞影响的剪断、无孔洞影响的剪断等四种断裂形式，材料断裂危险点与断裂条件也随着发生变化。     

脆性材料破坏与莫尔理论存在的问题

材料受力时应力状态不同，则断裂过程物理机理会发生改变，脆性材料受拉时发生的拉断与受压时发生的剪断，是两种不同物理机理的断裂形式，而莫尔强度理论用一个断裂条件解决这两种断裂形式的强度问题，是否合理需要讨论，结合灰铸铁HT200材料在不同受力条件下的断裂破坏试验，对此问题进行了研究，结果表明，莫尔理论对复杂应力状态下材料断裂不能合理、准确地进行强度计算。     

Quantum chemical study on asymmetric catalysis reduction of imine

The asymmetric catalysis reaction is considered to be an important way by which chiral compounds are generated. Chiral 1,3,2-oxazaborolidine, as an effective asymmetric catalyst, is used widely in the enantioselective reduction of prochiral ketones, imines, and carbon-carbon double bonds[1—3]. Up to now, a number of quantum chemical modeling investigations of the en-antioselective reduction of prochiral ketones with borane catalyzed by chiral oxazaborolidines have been carried out[4—7]. Howe…     

E-R分子轨道定域化方法与分子结合能

自编了E-R^[1]定域化计算程序,对HF、LiH、BH、Li₂、Be₂、CO和CH₄等分子作了计算。确定的酉变换算出的定域分子轨道正确。计算了各分子的定域分子轨道能量ε、加和能E′和结合能E″^[2],得到三点结论。