铜基MOF的CO氧化机理

利用第一原理密度泛函理论,研究了CO在铜基MOF(CuBTC)上氧化的反应机理.研究显示CO和O2弱吸附在轮形Cu2构筑单元铜的顶位上,并且电子从O2和CO转移到Cu,通过两个机理(Eley-Rideal机理和Langmuir-Hinshelwood机理)的研究,揭示了CO在CuBTC的氧化是准Langmuir-Hinshelwood机理,先在铜上吸附的CO和氧气先越过1.8eV的能垒形成OOCO的中间体,然后分解成CO2,同时有活性氧吸附在Cu位,活性氧与第二个CO反应生成CO2.总的来说,研究有助于理解CO在铜基MOFs的氧化.     

Au10催化CO氧化反应机理的密度泛函理论研究

采用密度泛函理论方法研究了Au10团簇催化CO氧化反应的详细机理. 对CO、O2、O、CO2四种主要吸附物及CO+O2、CO2+O、CO+O和CO+O+O四种共吸附物的吸附行为进行计算, 得到最佳活性吸附位. 模拟反应分别按照Langmuir-Hinshelwood(LH)机理和Eley-Rideal(ER)机理进行, 其中LH机理包括L1、L2两条路径, ER机理包括E1、E2两条路径. 通过对各路径活化能比较得到: 首先CO+O2→CO2+O反应按照LH机理进行的可能性较大, 并且相比较L1、L2两条路径, 由于反应按照L1路径进行时只需克服33.9和56.4 kJ•mol-1的能垒, 所以反应更易按照L1路径进行, 最佳反应路径为O2(gas)+CO(gas)→O2(ads)+CO(gas)→O2(ads)+CO(ads)→OCOO(ads)→O(ads)+ CO2(ads); 然后CO+O→CO2反应分别克服6.9和4.3 kJ•mol-1能垒, 放热352.1 kJ•mol-1, 说明低温下吸附态的O原子很容易与CO反应生成第二个CO2分子.     

铜钴团簇催化水煤气变换反应的催化活性

水煤气变换反应在质子膜燃料电池中可以除去CO,同时生成H2,因此应用于水煤气变换反应的催化剂受到了广泛的关注。为了研究团簇中掺杂单个原子对催化剂催化活性和反应机理的影响,我们采用密度泛函理论研究了Cu12Co和Cu13催化水煤气变换反应的催化活性和反应机理,其中我们考虑了三种反应机理,包括氧化还原机理、羧酸机理和甲酸基机理。通过对比研究Cu12Co和Cu13,我们发现掺杂团簇Cu12Co的催化活性比Cu13的催化活性好,而且Cu12Co和Cu13催化水煤气变换反应的最优路径都是羧基机理。在此过程中,Cu12Co和Cu13的基态结构均为Ih构型;Cu12Co和Cu13团簇上吸附H2O分子时都是在顶位上的吸附最强,而吸附CO分子最强的位点分别是顶位和洞位;对于氧化还原机理和甲酸基机理,其决速步都是OH* + * → O* + H*,而羧基机理的决速步分别是COOH* + * → CO2* + H* (Cu12Co)和2H* → H2* + * (Cu13)。本文的研究加深了我们对铜钴团簇催化水煤气变换反应的催化行为的理解。     

CO选择性氧化用Cu_1Zr_1Ce_9O_δ催化剂的红外光谱研究

采用共沉淀法制备了Cu1Zr1Ce9Oδ催化剂,用于富氢气体中CO的选择性氧化反应,利用原位漫反射红外光谱技术考察了Cu1Zr1Ce9Oδ催化剂表面上的吸附物种和反应中间产物。研究发现,H2,O2和CO物种竞争吸附于Cu1Zr1Ce9Oδ表面相同的吸附位上。氢气预处理会引起Cu1Zr1Ce9Oδ催化剂上Cu+物种的深度还原,降低了CO的吸附量。氧气预处理为催化剂提供了较多的活性氧物种,同时抑制了Cu+物种的深度还原。氦气预处理仅起到净化催化剂表面的作用。180℃时Cu1Zr1Ce9Oδ催化剂在2938.7和2843.8cm-1处出现桥式和双齿型甲酸根物种的红外吸收峰。Cu1Zr1Ce9Oδ催化剂上活性较高的氧阴离子在常温下即可将催化剂表面上吸附的CO氧化成表面碳酸根。甲酸根和碳酸根物种占据Cu1Zr1Ce9Oδ催化剂的吸附中心,导致催化剂活性降低。300℃下用氦气吹扫Cu1Zr1Ce9Oδ催化剂表面,双齿型的甲酸根物种分解生成碳酸根物种,碳酸根物种再继续分解生成CO2,释放出催化剂表面的吸附位,恢复了Cu1Zr1Ce9Oδ催化剂的活性。     

金属原子修饰石墨烯体系催化性能的理论研究

采用基于密度泛函理论的第一性原理方法研究了单个CO 和O2气体分子在金属原子修饰石墨烯表面的吸附和反应过程. 结果表明: 空位缺陷结构的石墨烯能够提高金属原子的稳定性, 金属原子掺杂的石墨烯体系能够调控气体分子的吸附特性. 通入混合的CO和O2作为反应气体, 石墨烯表面容易被吸附性更强的O2分子占据, 进而防止催化剂的CO 中毒. 此外, 对比分析两种催化机理(Langmuir-Hinshelwood和Eley-Rideal)对CO氧化反应的影响. 与其它金属原子相比, Al原子掺杂的石墨烯体系具有极低的反应势垒(< 0.4 eV), 更有助于CO氧化反应的迅速进行.     

金属原子修饰石墨烯体系催化性能的理论研究

采用基于密度泛函理论的第一性原理方法研究了单个CO和O2气体分子在金属原子修饰石墨烯表面的吸附和反应过程.结果表明:空位缺陷结构的石墨烯能够提高金属原子的稳定性,金属原子掺杂的石墨烯体系能够调控气体分子的吸附特性.通入混合的CO和O2作为反应气体,石墨烯表面容易被吸附性更强的O2分子占据,进而防止催化剂的CO中毒.此外,对比分析两种催化机理(Langmuir-Hinshelwood和Eley-Rideal)对CO氧化反应的影响.与其它金属原子相比,Al原子掺杂的石墨烯体系具有极低的反应势垒(0.4 e V),更有助于CO氧化反应的迅速进行.     

掺杂碱金属与碱土金属的CuO-CeO_2催化剂的漫反射红外光谱分析

CuO-CeO2系列催化剂是高效的CO选择性氧化反应的催化剂,通过原位漫反射红外光谱对掺杂碱金属和碱土金属氧化物的CuO-CeO2催化剂表面的吸附物种进行了研究。结果表明CuO-CeO2系列催化剂上,2 106 cm-1处出现CO的红外吸附峰。在反应气氛中,此峰的强度随着温度先升高后降低,说明Cu+是CO主要的活性吸附中心。低温下催化剂表面吸附的CO主要以可逆形式脱附出来,而高温下CO则以不可逆的形式脱附出来。催化剂表面在3 660 cm-1处出现尖锐的红外峰,归属于CeO2经还原产生的Ce-(OH)2偕式基团。在1 568,2 838和2 948 cm-1附近处出现甲酸根的红外谱峰,以及1 257和1 633 cm-1处出现碳酸根物种的红外峰。甲酸根物种是气相的CO与表面的羟基反应生成的产物,该物种的C—H键断裂生成碳酸根物种,这两物种均会降低催化剂的高温活性。Cu1Li1Ce9Oδ催化剂出现较强的CO2和甲酸根的红外峰,温度高于180℃时,该催化剂上还能看到微弱的CO红外峰,说明锂离子的给电子性质有利于提高Cu1Li1Ce9Oδ催化剂上CO的不可逆脱附,抑制氢的活化吸附,同时促进了甲酸根物种的生成。低温下Cu1Mg1Ce9Oδ和Cu1Ba1Ce9Oδ催化剂上CO的吸附量较多,但主要以可逆脱附形式脱附出来,对CO选择性氧化没有贡献。     

第一性原理研究CO在Cu(110)表面的吸附

本文采用基于密度泛函理论的第一性原理方法, 并同时考虑范德华力的作用, 计算并分析了CO在Cu(110)表面的吸附情况. 结果表明: 1) CO在两个表面Cu原子的短桥位位置吸附最强, 吸附能为1.28 eV. 第二稳定吸附位置为表面Cu原子的顶位, 吸附能为1.23 eV. CO在其他两个位置, 表面两个Cu的长桥位和表面四个Cu的中心位的吸附要弱一些, 约为0.86 eV 和 0.83 eV. 2) 在Cu表面吸附的CO的C-O键长有部分拉长, 这与较强的吸附能和电荷转移相应. 3) 电荷分析表明所有吸附的CO整体上从衬底上面获得部分电荷, 约为0.2 个电荷.     

CO在尖晶石结构CuCr2O4(111)表面上的吸附理论研究

采用密度泛函理论，研究了CO在具有尖晶石结构的过渡金属氧化物CuCr2O4(100)表面上的吸附. 几何构型优化结果表明，CO倾向于以碳端吸附在Cu原子上，吸附能达到133.2 kJ/mol. 吸附在五配位的Cr原子上也比较稳定，吸附能为57.5 kJ/mol. 吸附后，C-O键伸长，振动频率出现红移，表明分子被活化. 同时分析了吸附前后态密度的变化，探讨了CO与底物的成键机理.     

第一性原理研究CO在Cu(110)表面的吸附

本文采用基于密度泛函理论的第一性原理方法,并同时考虑范德华力的作用,计算并分析了CO在Cu(110)表面的吸附情况.结果表明:1)CO在两个表面Cu原子的短桥位位置吸附最强,吸附能为1.28 e V.第二稳定吸附位置为表面Cu原子的顶位,吸附能为1.23 e V.CO在其他两个位置,表面两个Cu的长桥位和表面四个Cu的中心位的吸附要弱一些,约为0.86 e V和0.83 e V.2)在Cu表面吸附的CO的C-O键长有部分拉长,这与较强的吸附能和电荷转移相应.3)电荷分析表明所有吸附的CO整体上从衬底上面获得部分电荷,约为0.2个电荷.     

General insight into CO oxidation: a density functional theory study of the reaction mechanism on platinum oxides

CO oxidation on PtO2(110) has been studied using density functional theory calculations. Four possible reaction mechanisms were investigated and the most feasible one is the following: (i) the O at the bridge site of PtO2(110) reacts with CO on the coordinatively unsaturated site (CUS) with a negligible barrier; (ii) O2 adsorbs on the bridge site and then interacts with CO on the CUS to form an OO-CO complex; (iii) the bond of O-OCO breaks to produce CO2 with a small barrier (0.01 eV). The CO oxidation mechanisms on metals and metal oxides are rationalized by a simple model: The O-surface bonding determines the reactivity on surfaces; it also determines whether the atomic or molecular mechanism is preferred. The reactivity on metal oxides is further found to be related to the 3rd ionization energy of the metal atom.     

Mechanistic study of the CO oxidation reaction on the CuO (111) surface during chemical looping combustion

Cu-based oxides oxygen carriers and catalysts are found to exhibit attractive activity for CO oxidation, but the dispute with respect to the reaction mechanism of CO and O₂ on the CuO surface still remains. This work reports the kinetic study of CO oxidation on the CuO (111) surface by considering the adsorption, reaction and desorption processes based on density functional theory calculations with dispersion correction (DFT-D). The Eley–Rideal (ER) CO oxidation mechanism was found to be more feasible than the Mars-van-Krevelen (MvK) and Langmuir–Hinshelwood (LH) mechanisms, which is quite different from previous knowledge. The energy barrier of ER, LH, and MvK mechanisms are 0.557, 0.965, and 0.999 eV respectively at 0 K. The energy barrier of CO reaction with the adsorbed O species on the surface is as low as 0.106 eV, which is much more active in reacting with CO molecules than the lattice O of CuO (111) surface (0.999 eV). A comparison with the catalytic activity of the perfect Cu₂O (111) surface shows that the ER mechanism dictates both the perfect Cu₂O (111) and the CuO (111) surface activity for CO oxidation. The activity of the perfect Cu₂O (111) surface is higher than that of the perfect CuO (111) surface at elevated temperatures. A micro-kinetic model of CO oxidation on the perfect CuO (111) surface is established by providing the rate constants of elementary reaction steps in the Arrhenius form, which could be helpful for the modeling work of CO catalytic oxidation.     

Reaction mechanism for CO oxidation on Cu(3 1 1): A density functional theory study

The microscopic reaction mechanism for CO oxidation on Cu(3 1 1) surface has been investigated by means of comprehensive density functional theory (DFT) calculations. The elementary steps studied include O₂ adsorption and dissociation, dissociated O atom adsorption and diffusion, as well as CO adsorption and oxidation on the metal. Our results reveal that O₂ is considerably reactive on the Cu(3 1 1) surface and will spontaneously dissociate at several adsorption states, which process are highly dependent on the orientation and site of the adsorbed oxygen molecule. The dissociated O atom may likely diffuse via inner terrace sites or from a terrace site to a step site due to the low barriers. Furthermore, we find that the energetically most favorable site for CO molecule on Cu(3 1 1) is the step edge site. According to our calculations, the reaction barrier of CO + O → CO₂ is about 0.3 eV lower in energy than that of CO + O₂ → CO₂ + O, suggesting the former mechanism play a main role in CO oxidation on the Cu(3 1 1) surface.     

Dense coating of surface mounted CuBTC Metal-Organic Framework nanostructures on silk fibers, prepared by layer-by-layer method under ultrasound irradiation with antibacterial activity

The growth of Cu₃(BTC)₂ (BTC = 1,3,5-benzenetricarboxylate), also known as CuBTC and HKUST-1, Metal-Organic Framework (MOF) nanostructures on silk fibers were achieved by layer-by-layer technique in alternating bath of Cu(OAc)₂·2H₂O and H₃BTC solutions under ultrasound irradiation. The effect of pH, reaction time, ultrasound irradiation and sequential dipping steps in growth of the CuBTC Metal-Organic Framework nanostructures has been studied. These systems depicted a decrease in the size accompanying a decrease in the sequential dipping steps. In addition, dense coating of silk fibers with CuBTC MOF results in decrease the emission intensity of silk fibers. The silk fibers containing CuBTC Metal-Organic Framework exhibited high antibacterial activity against Escherichia coli and Staphylococcus aureus. The samples were characterized with powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) spectra and scanning electron microscopy (SEM). XRD analyses indicated that the prepared CuBTC MOF nanostructures on silk fibers were crystalline.     

CuO/Al2O3、CuO/CeO2-Al2O3和CuO/La2O3-Al2O3催化剂中CuO物种被CO氧化的比较

用浸渍法制备了CuO/Al2O3 (Cu/Al)、CuO/CeO2- Al2O3 (Cu/CeAl)和CuO/La2O3-Al2O3(Cu/LaAl)催化剂. 通过原位XRD、Raman和H2-TPR方法， 对催化剂中的CuO物种以及CuO-Al2O3的固-固相反应进行了表征. 结果表明，对于Cu/Al催化剂，CuAl2O4存在于CuO与Al2O3层之间，CuO以高分散和晶相两种相态存在于催化剂的表层；对于Cu/CeAl催化剂，除了少量高分散和晶相的CuO存在于表层外，大部分CuO迁移到了CeO2的内层，     

单晶硅上化学气相沉积铜薄膜的机理研究

在自行设计、建立的MOCVD系统上,以Cu(hfac)2为反应前驱物在单晶硅上进行铜薄膜的化学气相沉积,并用AFM、SEM对铜核的成长机理进行了研究．结果表明,反应初期,单晶硅上铜核的成长为岛状,反应后期为先层状后岛状．利用XPS对铜薄膜成长的反应机理进行了探讨,由薄膜的Cu2p、Ols、Fls、Si2p谱可推论出,XPS谱中所出现的C=O、OH及CF3／CF2可能为Cu(hfac),当Cu(hfac)2在高温下分解成Cu(hfac)及hfac后,H2还原表面的hfac生成OH基,反应进行一段时间,OH基浓度大到一定的程度后,与Cu(hfac)2热裂解产生的hfac作用生成HO-hfac并脱附,使表面的铜的氧化物被还原以及发生Cu(hfac)2与H2的氧化还原反应．     

Cu纳米粒催化CO2还原反应机理的理论研究

此文采用密度泛函理论,研究了Cu₃₈纳米粒催化剂模型,分别研究了CO₂和H₂O分子在催化剂上不同吸附位,确了稳定的吸附构型,并进一步研究了CO₂催化还原反应机理,确定催化剂的活性.本文主要研究催化CO₂还原生成CO过程,研究了两条可行的反应路径,路径I为水分子的H原子直接转移到CO₂上,路径II为H原子先迁移到Cu₃₈纳米粒上再转移到CO₂上,研究结果发现此步反应机理路径I优先.从微观角度解释了实验研究结果.     

Reaction mechanism of spinel CuFe2O4 with CO during chemical-looping combustion: An experimental and theoretical study

Spinel CuFe₂O₄ is a promising oxygen carrier due to its synergistic enhanced performance. A fundamental understanding of the reaction mechanism between oxygen carrier and fuels is important for a rational design of highly efficient oxygen carrier. The reaction mechanism of spinel CuFe₂O₄ with CO during chemical-looping combustion (CLC) was studied based on thermogravimetric analyses (TGA) and density functional theory (DFT) calculations. Two distinct reaction stages were clearly observed. CuFe₂O₄ was mainly transformed into Cu and Fe₃O₄ with a rapid reaction rate in the initial stage, and then product Fe₃O₄ was slowly reduced to FeO or even to Fe. The reactivity of CuFe₂O₄ is much higher than that of Fe₂O₃, which is ascribed to the existence of Cu. The enhanced oxygen evolution activity of CuFe₂O₄ at low temperature is validated by both the experimental and theoretical methods. Three types of surface oxygen coordinated with different metal atoms show different reactivity. Two kinds of reaction pathways are involved in CO oxidation over CuFe₂O₄. In the one-step reaction pathway, CO directly reacts with the oxygen bonding to two octahedral Cu and one octahedral Fe atoms to form a CO₂ molecule without an energy barrier, which corresponds to the surface oxygen consumption observed in TGA experiments. In the possible two-step reaction pathway, CO first adsorbs on the surface, and then reacts with the oxygen bound to one octahedral Cu and two octahedral Fe atoms to generate CO₂ by surmounting an energy barrier of 10.84 kJ/mol, which is the most kinetically and thermodynamically favorable pathway.     

原位DRIFTS研究CH4部分氧化和CO2重整的耦合

8%Ru-5?/γ-Al2O3催化剂对于甲烷的低温活化具有较好的催化活性,在500℃下甲烷、二氧化碳和氧气的耦合反应中,吸热反应二氧化碳重整和放热反应甲烷部分氧化进行耦合强化,使得耦合反应中的甲烷转化率为38.8%。用原位漫反射傅里叶红外光谱法对钌系催化剂耦合甲烷部分氧化和二氧化碳重整反应体系机理进行研究。CO在8%Ru-5?/γ-Al2O3上吸附,表明CO在催化剂表面上波数为2 167 cm-1(2 118 cm-1)和2031 cm-1(2 034 cm-1)处形成孪生态Ru(CO)2和Ce(CO)2吸附物种,而且高温下CO吸附物种很容易从催化剂表面脱附出来。原位漫反射红外实验结果表明甲烷部分氧化反应时催化剂表面上有吸附物种碳酸根、甲酰基(甲酸盐)和一氧化碳的形成,其中表面的甲酰基和甲酸盐物种是甲烷部分氧化反应的主要活性中间物,这些中间活性中间体由甲烷吸附态CHx和催化剂表面的氧吸附态结合而形成的,随后这种中间物种再分解为CO产物;甲烷和二氧化碳重整反应时没有新的吸附物种产生,由此提出重整反应的机理是吸附态的甲烷和二氧化碳在催化剂活性中心上进行活化解离而生成合成气;甲烷、二氧化碳和氧气耦合反应过程中出现新的羟基物种(桥式羟基Ru-(OH)2),耦合反应机理复杂可能是由部分氧化和重整两类反应机理的复合,其中桥式羟基Ru-(OH)2参与了反应的进行。     

Monitoring surface reactions with scanning tunneling microscopy: CO oxidation on p(2 × 1)-O pre-covered Cu(110) at 400 K

Scanning tunneling microscopy (STM) is used to study the oxidation of CO on O pre-covered Cu(110) in the steady state at 400 K at the atomic level. There is a strong preference for CO to react with oxygen along the p(2 × 1) oxygen rows. The reaction appears to occur initially at the outer edge of an oxygen island, creating defects in the overlayer structure. Once created, oxygen overlayer defects are more reactive than non-defect sites and play a dominant role in sustaining the reaction. Copper atoms that make-up the p(2 × 1) oxygen overlayer structure add to terrace edges after oxygen supply is exhausted and do not form small Cu islands that could eventually lead to surface roughening.