CuWO4促进金红石TiO2光催化降解苯酚及其可能机理

已知金红石光催化降解水中有机物的活性远低于锐钛矿和板钛矿。本文报道,加入少量钨酸铜能显著加快金红石光催化降解水中苯酚。反应速率增加的幅度不仅远高于在相同煅烧温度（600 ℃）下制得的锐钛矿和板钛矿,而且随金红石煅烧温度（150-800 ℃）的增加持续增加。这些现象说明通过加入助催化剂钨酸铜,高温焙烧温度合成的金红石所具有的高的固有光催化活性可以被开发出来。此外,在过量苯酚存在下,H₂O₂的生成量随钨酸铜的加入量而先增加后减少,并且该趋势与苯酚降解速率基本一致。钨酸铜的这种正效应归结于固态的钨酸铜,而不是溶于水中的铜离子。（光）电化学测试表明,体系发生了从受光激发的金红石到钨酸铜的电子转移。这将提高光生载流子的分离效率,从而增大了O₂还原和苯酚降解的速率。     

高岭石-金系列的量子化学计算研究

在许多金矿床中 ,微金与粘土矿物密切共生与伴生。研究金在粘土矿物中的赋存形式 ,对于研究金矿床的成因及选冶工艺都具有十分重要的意义 ,也是国内外研究的重要前沿课题 [1,2 ]。不同成因类型的粘土矿物具有不同的晶体化学特征 [3] ,深入研究粘土矿物与微金矿物的晶体化学性质和表面物理化学性质 ,对于粘土矿物与微金矿物之间关系的研究 ,了解金矿床在自然界的演化过程及成因机理 ,为优化选冶工艺提供可靠的理论依据也都具有十分重要的意义。化学键对于粘土矿物与微金矿物之间关系的研究也具有重要的意义。由于高岭石结构的相对复杂性等原…     

微乳液法低温制备纳米金红石型二氧化钛的研究

以TiCl₄为原料、在十六烷基三甲基溴化铵/正己醇/水组成的微乳液体系中、在较低温度下,制备了球形、花状、捆绑丝和星形的金红石型二氧化钛纳米颗粒。研究了w值(水与CTAB物质的量之比)、反应物浓度、反应温度以及P值(正己醇与CTAB的物质的量之比)等因素对产品形貌的影响,并用TEM、XRD对产品进行了表征。     

纳米金红石型TiO2催化超声降解亚甲基蓝溶液

水溶性染料是印染工业中污染治理的主要对象,由于它们大多含有苯环,目前所使用的化学和生物等处理方法效果均不佳。而以半导体为催化剂的光催化处理方法对单一染料和实际印染废水处理效果较好。本文采用高温处理过的纳米TiO2作催化剂对亚甲基蓝溶液进行降解,大大缩短了降解时间,提高了降解率,60min降解率即可达66．8％,120min降解率则可达80％以上。而且发现利用超声波来替代紫外光对亚甲基蓝进行降解时,     

NO在MgO(001)缺陷表面吸附解离的量子化学研究

在密度泛函理论框架下,采用嵌入点电荷簇模型研究了NO在MgO(001)完整和缺陷表面上的吸附。研究结果表明:具有氧缺陷结构表面的催化活性较高,有利于NO键的削弱;当另一个NO分子进攻已吸附的NO分子时,NO键将进一步削弱,直致断裂,并伴有N2O产生,这与UPS和MIES实验观察到的现象一致。Mulliken布居分析指出,底物电子向NO转移,并填充到NO的*反键轨道上,从而导致NO键的削弱,并形成NO-。这也是可能导致形成NO-的原因。研究还表明,具有镁缺陷的MgO(001)表面对NO的解离没有催化活性。     

铜在金电极表面的选择性化学镀富集的研究

在具有催化还原活性的金电极表面,以水合肼为还原剂,在pH10.5酒石酸钾钠溶液中,通过化学镀方法,选择性地在金电极表面沉积了单层结构的铜膜。用开路电位时间谱技术(Op～t)、循环伏安法(CV)和微分脉冲伏安法(DPV)表征了该溶液还原法对铜进行选择性富集的机理和效果。证明在多种金属离子共存的复杂溶液体系中,可以避免其它离子的干扰,使铜选择性地富集到金电极表面。化学镀浴中富集到金电极表面的单层铜膜溶出电流与Cu2+的浓度在3×10-6～1×10-4mol/L范围内呈线性关系。该法已用于矿样中铜的还原富集、分离和测定,分析结果与电感耦合等离子体发射光谱法(ICP/AES)作了比较,结果满意。     

NO分子在金表面吸附的理论研究

气体分子在过渡族金属表面吸附是异相催化过程中的一个重要步骤.研究其在金属表面的吸附特性是了解其催化性能的基础,多年来一直是表面科学领域的研究热点.理论研究在解释吸附机理、实验现象以及证实实验结论的可靠性方面发挥着越来越重要的作用.本文使用密度泛函理论(DFT)研究了NO分子在中性及带正、负电荷的Au(111),Au(100),Au(310)和Au/Au(111)表面的吸附行为.研究结果表明,NO倾斜地吸附在金表面.在这种吸附构型中,Au原子的dz2轨道和NO分子的2π*轨道对称性匹配,并达到最大重叠.中性及带正、负电荷的Au(111),Au(100),Au(310)和Au/Au(111)表面不同吸附位对NO的反应活性不同,NO易吸附于各个金表面的顶位.计算结果显示,NO分子在Au(111)面几乎不吸附,而在Au/Au(111)的吸附能高达0.89eV.对表面金原子d态电子分波态密度分析表明,金表面对NO分子的吸附活性随着金原子配位数的减少而增强,这是由于低配位数的金原子的d态电子更靠近费米能级.当金表面增加或减少一个电子时,金表面对NO的吸附能有明显变化.正电荷的金表面对NO吸附的活性比中性的表面活性高,而带...     

室温合成金红石TiO2及其在染料敏化太阳能电池中的应用

以钛酸四丁酯为前驱体, 在室温下通过水解沉淀法合成了金红石型TiO₂纳米粒子; 用X射线衍射(XRD)研究了反应温度、酸度以及酸的种类对形成TiO₂晶型的影响. 实验结果表明, 高酸度、低温度以及Cl-有助于金红石相的生成. 在相同条件下加入一定量P105 (EO₃₇PO₅₆EO₃₇)三嵌段聚合物制备出一种金红石型粗糙聚集球. 扫描电子显微镜(SEM)结果表明这种粗糙聚集球直径大约350 nm, 比表面积测试(BET)及紫外漫反射测试发现粗糙球在保持较大比表面积的同时有散射效应. 此粗糙球与20 nm TiO₂粒子以质量比1:4混合作为工作电极的散射层并应用于染料敏化太阳能电池, 电池效率达到7.27%, 较不加粗糙球的效率提高17%; 我们认为这是因为在保持工作电极染料吸附量基本不变的条件下粗糙球提高光散射性能.     

MoO_3、NiO、ZnO在小表面金红石上的分散行为

氧化物、盐类在氧化物载体表面的自发分散是一种广泛存在的现象，文献中已报导过大量氧化物和盐类在高比表面载体上分散的研究结果［'－3］TIO。作为一种较新型的载体，与Y－AI。O。、硅胶等传统载体相比，有许多不同特性．活性组分在TIO。表面的分散状态及所得催化剂的性能已有不少报导［'－'］，但所用的TIOZ主要是较高比表面的锐钛矿型TIOZ（刘金红石型TIO。（r）和锐钛矿型TIOZ（a）的结构不同，它是高温生成相，比表面较小［'］．氧化物在金红石上的分散行为仍未见报导．我们制备了三种具有不同比表面的TIO水），系统地研…     

MoO3、NiO、ZnO在小表面金红石上的分散行为

Dispersion of MoO3, NiO, ZnO on rutile TiO2 with low specific surface area was studied with Mercury Porosimeter, SEM, XPS and Ammonia Extraction method. The dispersion thresholds of MoO3, NiO, ZnO on three rutile TiO2 carriers were obtained with XPS, and com-pared with those on anatase TiO2 with high specific surf are area. Ammonia Extraction method was used to identify the surface oxide species interarting with support surface in different strength and it was found that the proportions of oxides that can not be extracted by ammonia extraction are different for MoO3, NiO and ZnO which are supported on rutile TiO2.     

过渡金属对燃烧法制MgO负载 Cu2O催化剂的改性研究

本文以柠檬酸燃烧法制备MgO(B)载体,采用浸渍还原法以水合肼为还原剂制备Cu2O/MgO(B)催化剂,以环己醇脱氢制环己酮为探针反应,考察了过渡金属Fe、Co、Ni、Mo、Mn的添加对Cu2O/MgO(B)催化性能的影响;采用X射线衍射(XRD)、程序升温还原(TPR)、二氧化碳程序升温脱附(CO2-TPD)以及环己醇、环己酮程序升温脱附(环己醇/环己酮-TPD) 等手段对催化剂进行了表征.研究结果表明,Mn-Cu2O/MgO(B) 、 Ni-Cu2O/MgO(B)的催化性能优于Cu2O/MgO(B).其原因主要是Mn、Ni的添加使Cu2O的抗还原能力增强,Cu2O更稳定;同时,Mn和Ni的添加使Cu2O/MgO(B)催化剂对反应物和产物的吸附强度减弱;这些都有利于脱氢反应的进行.所有催化剂都呈碱性,是其具有高环己酮选择性的原因之一.     

Electronic processes in NO dimerization on Ag and Cu clusters: DFT and MRMP2 studies

Experimentally observed NO dimerization on Cu and Ag surfaces is surprising because binding energy of NO dimer is very small in gas phase. MRMP2, MP2 to MP4, CCSD(T), and DFT studies of NO dimerization on Ag₂ and Cu₂ clusters disclosed that the CCSD(T) method could be applied to this reaction on Ag₂ and Cu₂ unlike NO dimerization in gas phase which exhibits significantly large nondynamical electron correlation effect. Charge-transfer (CT) from Ag₂ and Cu₂ to NO moieties plays important role in N N bond formation between two NO molecules. This CT considerably decreases nondynamical correlation effect. Also, the DFT method could be applied to this NO dimerization, if appropriate DFT functional is used; all pure functionals examined here and most of the hybrid functionals underestimated the activation barrier (E_a), while only ωB97X provided E_a similar to CCSD(T)-calculated value. NO dimerization on similar Cu₂ and Cu₅ needs moderately larger E_a than those on Ag₂ and Ag₅, because frontier orbital participating in the CT exists at lower energy in Cu₂ and Cu₅ than in Ag₂ and Ag₅. The E_a decreases in the order Ag₂ >> Ag₃₈ > Ag₇ ∼ Ag₅ and the reaction energy (ΔE) is positive (endothermic) in Ag₂ but significantly negative in Ag₃₈, Ag₇, and Ag₅, indicating that various Ag clusters could be effective for NO dimerization except for Ag₂. The decreasing order of E_a and increasing order of exothermicity are attributed to increasing order of the frontier orbital energy of Ag₂ < Ag₃₈ < Ag₇ ∼ Ag₅. © 2018 Wiley Periodicals, Inc.     

不同晶相TiO2负载Cu2O催化甲醛乙炔化反应

分别以金红石相和锐钛矿相TiO₂为载体, 采用液相还原-沉积法制备了Cu₂O/TiO₂催化剂. 采用氮气物理吸附-脱附(N₂-physisorption)实验、 氢气程序升温还原(H₂-TPR)、 X射线衍射(XRD)、 X射线光电子能谱(XPS)、 CO红外光谱(CO-IR)及高分辨透射电子显微镜(HRTEM)等技术, 研究了不同晶相TiO₂载体对Cu₂O/TiO₂结构及其催化甲醛乙炔化反应性能的影响. 结果表明, 以金红石相TiO₂为载体的催化剂炔化活性明显高于以锐钛矿相TiO₂为载体的催化剂, 原因在于金红石相TiO₂主要暴露(110)晶面, 其与铜物种的配位环境及较高的空位密度形成了更多的Cu—O—Ti结构物种, 表现为Cu₂O与TiO₂之间强的相互作用. 这导致Cu₂O高效转变为乙炔亚铜活性物种, 并保持了较高的分散度与稳定性, 抑制了过度还原物种金属Cu的生成, 进而使催化剂表现出较高的催化性能.     

Pd(Cu)在MgO(100)表面吸附CO和O2的理论研究

采用固体镶嵌势能模型和DFT/B3LYP方法研究了在Pd/MgO和Cu/MgO表面吸附CO和O₂分子的电子性质. 计算结果表明, 在完美MgO(100)表面Pd原子对CO和O₂的吸附能分别为206.5和84.8 kJ/mol, 因此可知Pd原子更容易吸附CO分子; 而当Pd原子附着于有氧缺陷的MgO表面时, 它对两种分子的吸附都非常弱. 相反, 附着于MgO表面的Cu原子对O₂分子的吸附更为有利, 其吸附能在140～155 kJ/mol之间. 研究结果还表明, 对于双分子吸附体系, 即CO＋CO, CO＋O₂, O₂＋O₂体系, 双分子之间的结合力可减小完美MgO表面上Pd原子与被吸附分子的相互作用, 使吸附能减少了46～96 kJ/mol. 而对于在MgO表面上的Cu原子, 只有O₂＋O₂ 体系使吸附能减少了大约50～71 kJ/mol.     

Facially Dispersed Polyhydride Cu9 and Cu16 Clusters Comprising Apex‐Truncated Supertetrahedral and Square‐Face‐Capped Cuboctahedral Copper Frameworks

By using a linear tetraphosphine, meso‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm), nona‐ and hexadecanuclear copper hydride clusters, [Cu₉H₇(μ‐dpmppm)₃]X₂ (X=Cl ( 1 a ), Br ( 1 b ), I ( 1 c ), PF₆ ( 1 d )) and [Cu₁₆H₁₄(μ‐dpmppm)₄]X₂ (X₂=I₂ ( 2 c ), (4/3) PF₆?(2/3) OH ( 2 d )) were synthesized and characterized. They form copper‐hydride cages of apex‐truncated supertetrahedral {Cu₉H₇}²⁺ and square‐face‐capped cuboctahedral {Cu₁₆H₁₄}²⁺ structures. The hydride positions were estimated by DFT calculations to be facially dispersed around the copper frameworks. A kinetically controlled synthesis gave an unsymmetrical Cu₈H₆ cluster, [Cu₈H₆(μ‐dpmppm)₃]²⁺ ( 3 ), which readily reacted with CO₂ to afford linear Cu₄ complexes with formate bridges, leading to an unprecedented hydrogenation of CO₂ into formate catalyzed by {Cu₄(μ‐dpmppm)₂} platform. The results demonstrate that new motifs of copper hydride clusters could be established by the tetraphosphine ligands, and the structures influence their reactivity.     

A DFT Study on the Structure and Properties of Cu/Cr2O3 Catalyst

Using DFT method, the stable adsorption configurations of Cu₄ cluster on Cr₂O₃ (0001) surface were investigated. The regular tetrahedron structure and the planar structures were considered as the initial adsorption configuration of Cu₄ cluster, respectively. The adsorption energies of the two structures were also calculated. The simulation result indicated that the adsorption energy of the regular tetrahedron structure was higher than that of the planar structure, and thus the regular tetrahedron structure was confirmed to be the stable adsorption configuration for Cu₄ cluster on Cr₂O₃ (0001) surface. Moreover, it was observed that the Cu₄ cluster showed the definite stable adsorption sites on Cr₂O₃ (0001) surface, namely 3‐fold O sites. During the adsorption process of Cu₄ cluster onto Cr₂O₃ (0001) surface, the Cu₄ cluster could bond with more Cr or O atoms on the surface, and the apparent charge transfer also occurred correspondingly. Meanwhile, the Cu₄ cluster and Cr₂O₃ (0001) surface would bond in the form of local polarization to enhance the stability of adsorption configuration.     

Study of nano‐Cu/SiO2 catalysts for highly selective hydrogenation of acetophenone

Hydrogenation of acetophenone over nano‐Cu/SiO₂ catalysts was investigated. The catalysts, prepared by a liquid precipitation method using various precipitating agents, were characterized using low‐temperature nitrogen adsorption, X‐ray diffraction, temperature‐programmed desorption of ammonia, hydrogen temperature‐programmed reduction, transmission electron microscopy and X‐ray photoelectron spectroscopy. It was found that the catalysts prepared by a homogeneous precipitation method had better activity and stability than those prepared by a co‐precipitation method. The catalyst prepared using urea as precipitating agent had well‐dispersed copper species, high surface area and abundant pore structure. The catalytic performance and mechanism of the Cu/SiO₂ catalysts were further studied. It was found that the activity and stability of the catalysts could be improved by adjusting the proportion of Cu⁺/(Cu⁺ + Cu⁰). The sample prepared using urea as precipitating agent presented higher activity and selectivity. Also, the catalyst prepared using urea maintained a high catalytic performance while being continuously used for 150 h under the optimal reaction conditions.     

CO2 Reduction Mechanism on the Cu2O(110) Surface: A First-Principles Study

Cu₂O is an attractive catalyst for the selective reduction of CO₂ to methanol. However, the mechanism of the reaction and the role of the Cu species in different oxidation states are not well understood yet. In this work, by first-principles calculations, we investigate the mechanism of the reaction on the Cu₂O(110) surface, which is the most selective for methanol, in different degrees of reduction: ideal surface, slightly reduced surface (SRS), and partially reduced surface (PRS). The most favorable reaction pathways on the three surfaces were identified. We found that Cu(I) on the ideal surface is not capable of chemisorbing CO₂, but surface oxygen serves as the active site which selectively converts CO₂ to CH₃OH with a limiting potential of −0.77 V. The Cu(0) on the SRS and PRS promotes the adsorption and reduction of CO₂, while the removal of the residue O* becomes potential/rate limiting with a more negative limiting potential than the ideal surface. The SRS is selective to methanol while the PRS becomes selective to methane. The result suggests that the key to high methanol selectivity is to avoid the reduction of Cu(I), which provides a new strategy for the design of more efficient catalysts for selective CO₂ reduction to methanol.