In-Co二元金属氧化物上CO2催化加氢反应的选择性转变:催化反应的机理和构效关系

采用催化加氢的方式将CO₂转化为甲醇,既可以减少CO₂排放,又制备了化学品,该反应具有重要的研究意义.氧化铟(In₂O₃)作为CO2加氢制甲醇催化剂,由于其较高的CO₂活化能力和甲醇选择性,被科研工作者广泛研究.其中,将具有良好解离H2能力的过渡金属元素引入In₂O₃(M/In₂O₃)是有效提高催化剂性能的策略之一,然而,M/In₂O₃体系催化CO₂加氢反应机理及活性位点仍不清楚.本文引入Co制备了In-Co二元金属氧化物催化剂应用于CO2加氢制甲醇,结果表明,相较于In₂O₃,In-Co催化剂性能有很大提升,其中In1-Co₄催化剂上甲醇时空产率(9.7 mmol·g_cat^-1 h^-1)是In₂O₃(2.2 mmol·g_cat^-1 h^-1)的近5倍(反应条件:P=4.0 MPa,T=300℃,GHSV=24000 cm³ _STP g_cat^-1 h^-1,H2/CO₂=3).值得注意的是,尽管Co是金属元素的主体,In-Co催化剂中Co催化CO₂甲烷化的活性受到明显抑制.本文还通过多种技术系统研究了催化剂结构与反应选择性转变间的关系.采用电感耦合等离子体发射光谱、粉末X射线衍射、拉曼光谱、X射线光电子能谱和透射电子显微镜等对催化剂结构以及表面性质进行了表征.结果表明,在H₂还原气氛诱导下,In-Co催化剂表面发生重构,形成以CoO为核,以In₂O₃为壳的核壳结构,其在高压反应后仍能保持稳定;更重要的是,该核壳结构可以显著增强In-Co催化剂吸附及活化CO₂的能力.CO₂加氢反应动力学研究表明,Co催化剂上H₂分压对CO₂加氢为零级反应,而H₂分压在In-Co上的反应级数为正数;In-Co催化剂上,CO₂分压的反应级数接近于零,表明CO₂及其衍生物在In-Co的表面吸附饱和,但在纯Co上,则不会发生这种饱和吸附.通过原位DRIFTS研究了催化反应路径和关键中间物种的吸附及反应行为,发现CO₂加氢在纯Co和In-Co上的催化机理均遵循甲酸盐路径.在该催化路径中,CO₂首先加氢为甲酸盐(*HCOO)物种,随后加氢为甲氧基(*CH₃O).*CH₃O在Co催化剂上进一步加氢生成CH₄,而*CH₃O在In-Co催化剂上则会脱附生成CH₃OH.根据表征结果,本文认为,在还原性气氛下,In-Co发生了重构并生成表面富In₂O₃的核壳状结构,显著提高了催化剂对CO₂和含碳物种的吸附能力.Co和In-Co催化剂对CO₂加氢反应选择性的差异归因于催化剂对CO₂和对*HCOO等含碳中间物种的吸附稳定性不同.CO₂及其衍生的含碳中间物种在In-Co催化剂上的吸附能力比在Co催化剂上强,形成了较合适的催化剂表面C/H比,从而使*CH₃O能够脱附为CH₃OH,而不是进一步加氢为CH₄.综上,本文研究为高活性In-Co催化剂体系在CO₂加氢反应中的催化机理及行为提供了解释,为金属-氧化铟(M-In₂O₃)催化剂体系的设计提供了参考.     

CO和CH3O在Cu2O(111)表面吸附特性及共吸附的理论研究

基于密度泛函理论, 采用广义梯度近似方法结合周期平板模型, 对Cu₂O(111)非极性表面上CO和CH₃O的吸附和共吸附进行了系统的研究. 计算了CO以4种吸附模式和CH₃O以O端在Cu₂O(111)表面上的吸附, 通过对不同吸附位置的吸附能、几何构型参数和Mulliken电荷的计算和比较发现, Cu₂O(111)表面上配位未饱和铜离子(Cu_CUS)为CO的活性吸附位; 配位饱和铜离子(Cu_CSA)为CH₃O的活性吸附位. CO和CH₃O吸附于Cu₂O(111)表面后, 表面弛豫现象明显改善. CO和CH₃O与Cu₂O(111)表面能够形成共吸附体系, CO和CH₃O之间的相互作用力达到75.89 kJ/mol, 为典型的化学作用, 有助于促进CO和CH₃O反应形成表面物种CH₃OCO, 计算结果与实验事实一致.     

新型含硅表面活性剂的合成及性能研究

含有双胺基的三硅氧烷中的伯胺基与D-葡萄糖酸-δ-内酯进行酰胺化,仲胺基与低聚乙二醇甲醚缩水甘油醚、二缩水甘油醚进行烷基化,制备了新型含硅表面活性剂Me₃SiOSiMeR¹OSiMe₃ [R¹=(CH₂)₃NR²(CH₂)₂NHCO(CHOH)₄CH₂OH; R²=H, CH₂CH(OH)CH₂O(CH₂CH₂O)_xCH₃, x=1, 2, 3] (1a, 2a～2c)和(CH₂OCH₂)_y(Me₃SiOSiMeR³OSiMe₃)₂ [R³=(CH₂)₃NR⁴～(CH₂)₂NHCO(CHOH)₄CH₂OH; R⁴=CH₂CH(OH)CH₂OCH₂, y=0, 1, 2] (3a～3c).这些化合物的结构用¹H, ¹³C核磁共振仪和元素分析仪进行鉴定.研究了这些新型含硅表面活性剂的界面性能,在浓度分别为10^-4和10^-5 mol·L^-1时可以将水的表面张力降低至约21 mN·m^-1.     

In-Co二元金属氧化物上CO2催化加氢反应的选择性转变:催化反应的机理和构效关系

采用催化加氢的方式将CO₂转化为甲醇,既可以减少CO₂排放,又制备了化学品,该反应具有重要的研究意义.氧化铟(In₂O₃)作为CO2加氢制甲醇催化剂,由于其较高的CO₂活化能力和甲醇选择性,被科研工作者广泛研究.其中,将具有良好解离H2能力的过渡金属元素引入In₂O₃(M/In₂O₃)是有效提高催化剂性能的策略之一,然而,M/In₂O₃体系催化CO₂加氢反应机理及活性位点仍不清楚.本文引入Co制备了In-Co二元金属氧化物催化剂应用于CO2加氢制甲醇,结果表明,相较于In₂O₃,In-Co催化剂性能有很大提升,其中In1-Co₄催化剂上甲醇时空产率(9.7 mmol·g_cat^-1 h^-1)是In₂O₃(2.2 mmol·g_cat^-1 h^-1)的近5倍(反应条件:P=4.0 MPa,T=300℃,GHSV=24000 cm³ _STP g_cat^-1 h^-1,H2/CO₂=3).值得注意的是,尽管Co是金属元素的主体,In-Co催化剂中Co催化CO₂甲烷化的活性受到明显抑制.本文还通过多种技术系统研究了催化剂结构与反应选择性转变间的关系.采用电感耦合等离子体发射光谱、粉末X射线衍射、拉曼光谱、X射线光电子能谱和透射电子显微镜等对催化剂结构以及表面性质进行了表征.结果表明,在H₂还原气氛诱导下,In-Co催化剂表面发生重构,形成以CoO为核,以In₂O₃为壳的核壳结构,其在高压反应后仍能保持稳定;更重要的是,该核壳结构可以显著增强In-Co催化剂吸附及活化CO₂的能力.CO₂加氢反应动力学研究表明,Co催化剂上H₂分压对CO₂加氢为零级反应,而H₂分压在In-Co上的反应级数为正数;In-Co催化剂上,CO₂分压的反应级数接近于零,表明CO₂及其衍生物在In-Co的表面吸附饱和,但在纯Co上,则不会发生这种饱和吸附.通过原位DRIFTS研究了催化反应路径和关键中间物种的吸附及反应行为,发现CO₂加氢在纯Co和In-Co上的催化机理均遵循甲酸盐路径.在该催化路径中,CO₂首先加氢为甲酸盐(*HCOO)物种,随后加氢为甲氧基(*CH₃O).*CH₃O在Co催化剂上进一步加氢生成CH₄,而*CH₃O在In-Co催化剂上则会脱附生成CH₃OH.根据表征结果,本文认为,在还原性气氛下,In-Co发生了重构并生成表面富In₂O₃的核壳状结构,显著提高了催化剂对CO₂和含碳物种的吸附能力.Co和In-Co催化剂对CO₂加氢反应选择性的差异归因于催化剂对CO₂和对*HCOO等含碳中间物种的吸附稳定性不同.CO₂及其衍生的含碳中间物种在In-Co催化剂上的吸附能力比在Co催化剂上强,形成了较合适的催化剂表面C/H比,从而使*CH₃O能够脱附为CH₃OH,而不是进一步加氢为CH₄.综上,本文研究为高活性In-Co催化剂体系在CO₂加氢反应中的催化机理及行为提供了解释,为金属-氧化铟(M-In₂O₃)催化剂体系的设计提供了参考.     

醇-二苯甲酮光化夺氢反应活泼自由基的ESR研究

本文用自由基捕捉剂2,3,4,6-四甲基亚硝基苯(ND)及苯亚甲基叔丁基氮氧化合物(PBN)与ESR相结合的方法研究了CnH_2n+1OH(n=1,2,…8)、(CH₃)₂CH(CH₂)_nOH(n=0,1,2)、CH₂=CHCH₂OH及C₆H₅CH₂OH等十三种醇与二苯甲酮的光化夺氢反应中的活泼自由基,结果表明: 1.用ND时,二苯酮分别夺取CnH_2n+1OH、(CH₃)₂CH(CH₂)_nOH及RCH₂OH(R=CH₂=CH、C₆H₅)中α-C、叔-C及α-C上的氢,而捕捉到C_n-1H_2n-1CHOH、(CH₃)₂CH(CH₂)_nOH及RCHOH自由基。 2.用PBN时,捕捉的自由基与ND捕获的相同。     

CH3CH2O+HCHO反应机理及主通道速率常数

采用CCSD(T)/cc-pVDZ//B3LYP/6-311++G(d,p)双水平计算方法研究了CH₃CH₂O+HCHO反应的微观反应机理. 结果表明, 标题反应主要存在5个抽氢和3个氢迁移异构化反应通道, 其中抽氢通道R→ IMa(CH₃CH₂O…CH₂O)→TS1→ IM1b→P1(CH₃CH₂OH+CHO)为优势通道, 其表观活化能为14.65 kJ/mol. 利用变分过渡态理论(CVT)并结合小曲率隧道效应模型计算了主通道R1在275~1000 K温度范围内的速率常数k^TST, k^CVT和k^CVT/SCT, 在此温度区间内表观反应速率常数三参数表达式为k^CVT/SCT=2.26×10^-17 T^0.57 exp(-1004/T), 显示具有正温度系数效应.     

碳氟醇对阳离子表面活性剂表面活性及胶团反离子结合度的影响

用表面张力及电动势法研究了C₁₀H₂₁N(CH₃)3Br、C₁₂H₂₅N(CH₃)3Br与C₃F₇CH₂OH混合水溶液的表面与胶团性质。结果表明,对于阳离子表面活性剂,C₃F₇CH₂OH的加入一方面增加表面活性,另一方面降低胶团反离子结合度。后者不同于阴离子表面活性剂/C₃F₇CH₂OH混合体系,可归因于C₃F₇CH₂OH略有酸性,因而具备一些类似阴离子表面活性剂的性质。     

理论空燃比天然气汽车尾气中H2O和O2对CH4与NO反应的影响

共沉淀法制备CeZrYLa+LaAl 复合氧化物载体, 等体积浸渍法制备了Pt 催化剂, 用于研究理论空燃比天然气汽车(NGVs)尾气净化反应中CH₄与NO的反应规律. 并考察了10% (体积分数, φ)H₂O和计量比O₂对CO₂存在时的CH₄+NO反应的影响. 结果表明: 对于不同条件下的NO+CH₄反应, 主要生成N₂和CO₂, 高温区有CO生成. 低温区无O₂时可以生成N₂O, 有O₂时可以生成NO₂; 添加10% (φ)的H₂O后, CH₄ 转化活性降低, NO转化活性基本不变, 这是由于H₂O减弱了CH₄与CO₂的重整反应, 但是对CH₄与NO的反应基本没有影响; 添加计量比的O₂后, CH₄转化活性提高, 而NO转化活性降低, 这是由于O₂和NO之间存在竞争吸附, CH₄被O₂氧化为主要反应, 从而减弱了NO的转化; 同时添加计量比的O₂和10% (φ) H₂O, CH₄与CO₂的重整反应受到抑制,CH₄与NO的反应、甲烷蒸汽重整反应和甲烷被O₂氧化反应同时发生, CH₄和NO的转化活性均提高.     

高温沉淀铁基催化剂上费托合成含氧化合物生成机理的研究

采用漫反射原位红外光谱法及化学捕获方法,考察了费托合成过程中高温沉淀铁基催化剂表面吸附物种的变化,并探讨了含氧化合物的生成机理。结果表明,CO在高温沉淀铁基催化剂上有线式和桥式两种吸附态存在,同时,CO的吸附在催化剂表面生成大量含氧化合物前驱体。费托原位实验捕获到了一些较关键的中间产物:表面乙酸盐、表面酰基、甲氧基等。同时发现高温沉淀铁基催化剂表面具有以下反应共性:醇类可与表面羟基结合生成烷氧基团;催化剂表面的吸附分子具有氧化性;一些基础化学物质如OH^-、晶格氧等可以与甲醇或乙醛分子发生反应。对CH₃OH + CO及CH₃I + CO + H₂两个反应的化学捕获实验表明,酰基是C₂⁺含氧化合物的重要中间产物,酰基加氢是形成C₂⁺含氧化合物的关键步骤。根据表面中间产物及反应特性,得到了高温沉淀铁基催化剂上费托合成含氧化合物的生成机理。     

低能氮离子注入乙醇重水溶液的GC-MS分析

将氮气常压弧光放电产生的N⁺在放电间隙电场的加速下“注入”到乙醇的重水溶液中,利用气相色谱-质谱(GC-MS)分析样品,证实有氘代产物(DCH₂CH₂OH)和羟基取代产物(DOCH₂CH₂OH)生成,这表明低能N⁺诱发水溶液中的反应与水分子分解产生的自由基有关.同时,产物中还检测到乙酸(CH₃COOD )和氨基乙醇(HOCH₂CH₂ND₂),说明反应是在氧化性氛围中进行的,而这种氧化作用可能亦与水分子分解产生的氢氧根自由基有关.氨基乙醇则可能是氮离子俘获重水中的氘形成氨基继而与乙醇反应生成的,这也是氮“沉积”在溶液中的重要形式.这些结果对初步揭示低能离子与水溶液体系反应的机理具有一定的意义.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.