Pd-Sn双金属催化剂催化1, 3-丁二烯加氢反应的仲氢诱导极化研究

本文首先利用等体积共浸渍法合成了一系列Pd/Sn比（原子比）不同的Pd₁-Sn_x/Al₂O₃双金属催化剂,然后通过多相催化仲氢诱导极化（PHIP）技术研究了Pd-Sn/Al₂O₃双金属催化剂上1, 3-丁二烯选择性加氢反应.结果发现催化剂的Pd/Sn比会影响1, 3-丁二烯反应活性和丁烯选择性：随着Pd/Sn比的下降,反应中1, 3-丁二烯转化率降低,丁烯选择性提高.利用PASADENA（parahydrogen and synthesis allow for dramatically enhanced nuclear alignment）技术,发现Pd/Sn比的变化影响了1-丁烯与2-丁烯之间的异构化过程：随着Pd/Sn比的下降,1-丁烯异构化率降低,这是由于Sn组分含量的提高减少了表面暴露的Pd组分,使得催化剂反应活性降低;Sn组分含量的提高同时导致了Pd电子密度的上升,使得选择性还原产物丁烯更易脱附,阻止其进一步加氢生成丁烷,并抑制了1-丁烯异构化反应过程.     

Ce、Mo助剂和分散剂对VPO催化剂物性的影响

通过在有机相制备中添加助剂和分散剂制备出一类新型的VPO催化剂。采用BET、XRD、Raman、TEM、XPS等表征手段对影响催化剂的比表面积、晶相结构以及表面V离子价态考察VPO催化剂的比表面积和晶体结构。并将催化剂应用到正丁烷选择氧化生成顺酐的反应中。实验结果表明,引入Ce、Mo助剂基本上没有明显改变催化剂的比表面积,但确实改变了催化剂的物相组成、粒子形貌及表面状态。加入Ce、Mo助剂使催化剂的选择性有了一定的提高。     

丁酮异构化的势能面分析

用密度泛函理论计算研究了丁酮异构化的势能面. 通过IRC方法确定了丁酮异构化的6个主要反应路径,相应的产物分别为1-丁烯-2-醇、2-丁烯-2-醇、丁醛或1-丁烯-1-醇、丙烯基甲醚、甲基烯丙基醚和乙烯基乙醚. 其中3个路径经过环氧丁烷,表明环氧丁烷是丁酮异构化过程中重要的中间产物. 计算得到的反应物和产物的垂直电离能与现有的实验值吻合得很好. 通过过渡态的相对能量和高能垒的数目比较,认为最可行的丁酮异构化反应路径是丁酮→1-丁烯-2-醇→2-丁烯-2-醇.     

H-SAPO-34分子筛催化醇类转化的差异性研究

本文研究了H-SAPO-34催化甲醇和丁醇转化反应及其产物分布的差异,结合气相色谱-质谱（GC-MS）联用、¹³C交叉极化魔角旋转核磁共振（¹³C CP MAS NMR）技术捕获了反应过程中生成的重要反应中间物种.甲醇转化过程以乙烯、丙烯和丁烯为主要产物;而丁醇转化过程中主要产物是丁醇脱水生成的丁烯,反应初期以丙烯和丁烯作为主要产物.两种醇类转化均以低碳烯烃作为主要产物,且存留物种和¹³C CP MAS NMR分析均观察到芳烃物种,说明H-SAPO-34催化甲醇和丁醇转化存留在催化剂上的有机物种相近.虽然起始于不同的醇类反应,但H-SAPO-34上限域空间的酸催化环境都能引导甲醇和丁醇制取低碳烯烃的反应过程.     

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。     

In situ DRIFTS研究NO在Cu-ZSM-5上的表面吸附及选择性催化还原

Cu-ZSM-5分子筛催化剂选择性催化还原NO具有较好的低温活性,在613 K时NO还原成N2的转化率达70.6%。原位漫反射红外光谱(In situ DRIFTS)是研究催化剂表面吸附物种及催化机理的重要方法,应用该方法在298～773 K范围原位考察了以C₃H₆为还原剂及富O₂ 条件下,NO在Cu-ZSM-5催化剂上的表面吸附及选择性催化还原。认为NO在Cu-ZSM-5催化剂上还原为N₂的过程中,NO以一系列NO_x吸附态形式与丙稀的活化物种(C_xH_y或C_xH_iyO_z)反应,生成有机中间体,再进一步反应,最终生成N₂。有机中间体存在一个明显的从有机胺物种到腈(或—CN)再到有机氮氧物种(R—NO₂或R—ONO)的过程,催化剂表面形成有机中间物种是关键步骤,Cu的作用是促进NO_x形成,O₂ 的作用是促进C₃H₆活化,并且是有效产生有机-氮氧化物不可缺少的条件。     

钒钨铈催化剂的低温SCR反应机理研究

本文使用等体积浸渍法制备了钒钨铈(V2O5-WO3/CeO2)选择性催化还原(SCR)脱硝催化剂,并使用一系列的原位傅里叶变换红外(In-situ FTIR)光谱详细研究了该催化剂的低温SCR反应过程(本文选用200℃)。通过将原位红外光谱与化学诱捕法耦合使用,成功捕捉并识别了低温SCR的不稳定反应中间产物亚硝酸盐(nitrites),并以该亚硝酸盐物种为主要的反应活化产物,建立了基于NO氧化活化的低温SCR还原半圈反应动力学模型.该动力学模型可准确描述V2O5-WO3/CeO2催化剂低温SCR中NO与表面吸附NH3的瞬态反应过程。     

环戊二烯与二氢呋喃类化合物Diels-Alder反应的理论研究

采用量子化学密度泛函理论(DFT)在B3LYP/6-311++G **水平上对环戊二烯与2(5H)-呋喃酮、丁烯二酸酐和2,5-二氢呋喃的Diels-Alder反应机理进行了理论研究,并且考虑了溶剂化效应和取代基效应对反应机理及能垒的影响。结果表明,本文所涉及的环戊二烯与二氢呋喃类化合物的Diels-Alder加成反应是以协同方式进行的;羰基取代基的吸电子作用是造成产物中C(1)-C(2)、C(3)-C(4)键键长增加的主要原因;反应所涉及到的FMO相互作用主要是环戊二烯的HOMO与二氢呋喃类化合物的LUMO之间的相互作用,羰基对反应活化能的影响主要是通过降低呋喃类化合物的LUMO能级,减小与环戊二烯的HOMO的能级差异,从而有利于反应进行的;反应2的活化能垒最低,从动力学的角度考虑在室温下可以进行。     

Zn-Y/BEA上乙醇一步法制1，}3-丁二烯的反应机理及优异催化剂筛选

随着beta分子筛负载双金属催化剂的开发,乙醇一步法制1,3-丁二烯}取得了突破性进展. 然而,从乙醇到丁二烯的反应机理复杂,尚未完全阐明,也缺乏基于中心金属原子的催化剂筛选. 本文采用密度泛函理论计算方法,系统地研究了乙醇在Zn-Y/BEA催化剂上一步法制丁二烯的机理. 结果表明,乙醇脱氢更倾向于在Zn位点进行,决速步骤的反应热仅为0.77 eV;羟醇缩合生成丁二烯更倾向于在Y位点进行,决速步骤的反应热仅为0.69 eV. 基于所揭示的反应机理,选择了六种元素代替Y来筛选用于该反应的Zn-M/BEA(M=Sn、Nb、Ta、Hf、Zr、Ti)的优良组合. 结果表明,与其他六种催化剂相比,Zn-Y/BEA仍是最优选的催化剂,Zn-Zr/BEA、Zn-Ti/BEA和 Zn-Sn/BEA也是乙醇转化为丁二烯的可行催化剂. 本工作不仅揭示了Zn-Y/BEA催化乙醇一步法制丁二烯的反应机理,而且为该反应提供了其他可能的催化剂选择.     

FTIR研究半预聚物法聚氨酯脲密封材料固化过程的表观动力学及氢键化作用

采用原位FTIR技术跟踪了半预聚物法聚醚型聚氯酯脲的固化过程,研究了其固化过程的宏观动力学.原位FTIR的光谱数据表明,随着反应时间的增加.脲键羰基的吸收逐渐增强,脲羰基的波数位置呈阶跃式向低波数方向移动.脲键羰基的氢键化作用逐渐增强.不含催化剂时,硬段优先形成,不利于NCO与OH的反应.氨酯羰基的峰高增加缓慢.脲键的生成对NCO/OH反应生成氨酯键无催化作用.     

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。     

A DFT periodic study of the vanadyl pyrophosphate (1 0 0) surface

The unique ability of the vanadyl pyrophosphate (1 0 0) surface to activate n-butane and then selectively oxidise the hydrocarbon to maleic anhydride was investigated using modern quantum chemical methods. Bulk (VO)₂P₂O₇, together with stoichiometric and phosphorus-enriched (1 0 0) surfaces, were analysed using periodic density functional theory calculations. Also simulated was surface ionic relaxation from bulk geometry, and surface hydration. Density of states (DOS) plots show that, whether stoichiometric or phosphorus-enriched, bulk terminated or relaxed, bare or hydrated, local covalent reactivity at the (1 0 0) surface is controlled by vanadium species. Terminal P-O oxygen species are the most nucleophilic surface oxygens, as indicated by their predominance of sub-vanadium high-lying valence band levels. A periodic treatment of (VO)₂P₂O₇(1 0 0) hence gives results qualitatively identical to those obtained from earlier cluster calculations. Simulation of surface ionic relaxation shows that in-plane P-O-V oxygens may also be involved in rupture of substrate C-H bonds for mild oxidation, while surface hydration calculations indicate that dissociative chemisorption of water may play a key role in perpetuation of the selective oxidation cycle.     

The partial catalytic oxidation of toluene on vanadium and molybdenum oxides

The partial catalytic oxidation of toluene on pure and mixed vanadium and molybdenum oxides was studied over the temperature range 300–500°C. The main reaction products were maleic anhydride (MA), benzaldehyde (BA), and carbon oxides (CO _x ) depending on the catalyst composition and reactor temperature. The samples containing more than 50% vanadium were characterized by conversion and selectivity close to those of pure vanadium oxide V₂O₅. Reaction temperature was found to influence the amount of products formed, primarily the amounts of MA and BA. The role played by the generation of the singlet molecular oxygen form in the samples and its influence on the selectivity of the reaction is considered.     

Immobilization of metalloporphyrins on P(4VP-co-St)/SiO2 by the quaternarization reaction

Poly(4vinylpyridine-co-styrene) (P(4VP-co-St)) was grafted on silica gel particles in the manner of “grafting from”, and the grafting particle P(4VP-co-St)/SiO₂ was gained. The chloromethylation reaction for the tetraphenylporphyrin (TPP) was performed using a chloromethylation reagent, 1,4-bis(chloromethyoxy)butane which was uncarcinogenic, and the tetra-chloromethylphenyl-porphyrin (TMCPP) was prepared. Then, the quaternization reaction between the benzyl chloride groups on TMCPP and pyridine groups of the grafted P(4VP-co-St) macromolecules occurred and the bonding of TMCPP on the particles P(4VP-co-St)/SiO₂ was realized, resulting in the functional composite-type particles TMCPP-P(4VP-co-St)/SiO₂. Subsequently, the metallation of the bonded particles TMCPP-P(4VP-co-St)/SiO₂ was carried out via the coordination reaction between TMCPP-P(4VP-co-St)/SiO₂ and metal salt, resulting in the supported metalloporphyrin (MP) catalysts MP-P(4VP-co-St)/SiO₂. The supported catalysts were characterized by UV-Vis spectra. The effects of various factors on the bonding process of TMCPP on P(4VP-co-St)/SiO₂ were studied in detail. In addition, the catalytic activity of the supported catalysts MP-P(4VP-co-St)/SiO₂ have been studied in oxidation process of ethyl benzene with molecular oxygen to acetophenone without the use of sacrificial co-reductant. The experimental results showed that the tetra-chloromethylphenyl-porphyrin (TMCPP) could be successfully bonded onto the P(4VP-co-St)/SiO₂ surfaces by means of the quaternization reaction between TMCPP and the pyridine groups on grafted P(4VP-co-St) macromolecules. The supported catalysts MP-P(4VP-co-St)/SiO₂ exhibited the fine catalytic activity. Moreover, the supported cobalt porphyrin was more active than the supported iron and manganese porphyrins.     

Fabrication and characterizations of a polymer hybrid OA/MA/St-TiO2

A nano-hybrid composite of octadecyl acrylate/maleic anhydride/styrene (OA/MA/St) encapsulating nano-TiO₂ with an average particle size of 30-60 nm was fabricated based on chemical modification of nanotitania. The polymer hybrid OA/MA/St-TiO₂ and nano-TiO₂ were characterized by infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), static contact angle (CA) as well as transmission electron microscopy (TEM). FT-IR spectra and TGA results suggest that the copolymer OA/MA/St adheres on the surface of nano-TiO₂ through physical adsorption and chemical bonding. The calculated reacted OH surface density is about 0.6 OH/nm², and the modification efficiency is approximately 27.28%. In addition, when the molar ratio of OA/MA/St is 7:2:1, the hybrid shows the strongest hydrophobicity, and its static contact angle reaches as high as 146°. TEM image of the hybrid OA/MA/St-TiO₂ reveals that the modified particles have good dispersibility and compatibility with n-hexane.     

Mössbauer spectroscopy and nuclear inelastic scattering studies on polynuclear oxo-bridged iron catalyst—first results

Polynuclear iron catalysts are interesting materials because of their novel properties. In the future they may help to replace high cost and hazardous heavy metal catalysts by efficient, non toxic and economic iron compounds. In this work, we present some preliminary results on a novel polynuclear oxo-bridged iron catalyst. The chemical environment of the metal species (Fe) was studied under Gif-type conditions (Fe catalyst/Zn/O₂ in pyridine/acetic acid) with cyclohexene as substrate. Such Gif-type catalysts are able to catalyse the selective oxidation of alkanes and alkenes. The characterization was done by Mössbauer spectroscopy and nuclear inelastic scattering. In order to identify the intermediate species during the reaction (selective oxidation using molecular O₂), a freeze-quench technique was used. This also helps to understand the kinetics of the chemical reaction.     

制备条件及添加稀土对SO_4~(2-)/ZrO_2-Al_2O_3固体超强酸酸性影响的研究

用共沉淀法制备了SO4 2 -/ZrO2 -Al2 O3 固体超强酸 ,并采用低温陈化和添加稀土La对其制备方法进行改进 .通过样品催化正丁烷异构化反应考察了该固体超强酸中nZr和nAl的最佳配比为 1∶2 .该法制备的样品的IR显示 ,在 1393cm-1处的吸收峰强度较常温陈化样品大大增加 .XRD分析表明 ,低温陈化和加入稀土添加剂的样品在6 5 0℃焙烧温度下 ,出现了亚稳态的ZrO2 四方晶相的晶体是表面酸性和催化活性增加的微观原因 .样品催化合成八乙酸蔗糖酯反应结果同样证明 ,在相同的时间内 ,低温陈化和添加稀土添加剂的样品具有较好的催化活性     

Vanadium phosphates on mesoporous supports: model catalysts for solid-state NMR studies of the selective oxidation of n-butane

SBA-15 was utilized as mesoporous support for the dispersion of vanadium phosphate (VPO) compounds. Loading of SBA-15 with VPO compounds was found to be accompanied by decreasing ²⁹Si MAS NMR signals of Q² (Si(2Si,2OH)) and Q³ (Si(3Si,1OH)) silicon species, which indicates coverage of the mesoporous support by the guest compounds. The ⁵¹V MAS NNR spectra of the activated VPO/SBA-15 catalysts consist of patterns typical for the α_II- and β-phases of vanadyl orthophosphate. In the ³¹P MAS NMR spectra of the activated VPO/SBA-15 catalysts, signals of β-, δ-, and α_II-VOPO₄ phases could be identified. Upon conversion of n-butane-¹³C₄, a strong decrease of the ³¹P MAS NMR signals characteristic for the δ-VOPO₄ phase occurred, while by ¹³C MAS NMR spectroscopy the formation of maleic anhydride, carbon monoxide, and carbon dioxide was observed. This finding supports the active role of the δ-VOPO₄ phase in the selective oxidation of n-butane on VPO/SBA-15 catalysts.     

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.