Pt/TiO_2催化剂上的氢—氧作用 Ⅰ.氢、氧的吸咐—脱附行为以及相互促进作用

本文采用程序升温脱附(TPD)技术研究了光沉积方法制备的Pt/TiO_2催化剂经过氧化、还原后氧、氢的脱附行为.光沉积过程中,Pt/TiO_2表面上可以生成大量的吸咐氢,在TPD中脱附;同时Pt/TiO_2表面上化学吸附的水在TPD过程中也可以分解释氢.氧化处理的Pt/TiO_2在TPD过程中于550～750K温区出现氧脱附峰,随着氧化温度升高,脱附峰位向高温移动,经实验证明,这种可脱附活泼氧物种的生成是由样品前身中留存氢引起的.还原处理的Pt/TiO_2在TPD过程中分别在300～600和大于600K出现两个氢脱附峰,认为是由于表面羟基和钛—氢(Ti~(4+)—H~-)物种的分解释氢引起的Pt/TiO_2上活泼氧物种的存在,增加了样品在室温条件下的吸氢量;在中温(473～573K)这种活泼氧物种则和氢发生反应,减少了TPD过程中的脱氢量;Pt/TiO_2在大于673K温度还原,可以消除活泼氧物种的影响.     

INTRAPARTICLE DIFFUSION EFFECTS IN FISCHER-TROPSCH SYNTHESIS Ⅰ. MODELING OF DIFFUSION AND REACTION

IntroductionCatal}ticrcactionsaffcctcdb}'diffosionaIlimitationincatal}'stporcshavcbccnextensive1}dcaltx`ithinlit.rat.rcll~5I.Scvcraltcchniqucsonthcspccialcase0fFischcr-Tropschs}'nthcsis(FTS)t\crcapplicdtocxplorcthebchaviorofthiscatal}ticrcactionundercxpcrimcntalandopcrationaIconditionsI3~5l.It`"ouldbeofvaluctoindicatchcrcthatthcseinvcstigationsx"ercmainl}'bascdonthesimplcstkineticsofthcfirstordcrinH2proposedbyAndersonl6]attheearIystages.However-thesetboents,striCtlyspeaking,areinvalidfor…     

Rhodium-catalyzed addition of arylboron compounds to nitriles, ketones, and imines

The rhodium-catalyzed addition reactions of sodium tetraphenylborate and arylboronic acids to nitriles, ketones, and imines were examined. The reaction of nitriles could be carried out efficiently in the presence of a catalyst system of [RhCl(cod)]₂-dppp and H₂O to give the corresponding monoarylated products selectively. Although unactivated ketones and imines are known to be poor electrophiles for rhodium-catalyzed arylation, the phenylation of them with use of sodium tetraphenylborate proceeded smoothly in the presence of [RhCl(cod)]₂ and Rh(acac)(cod) as catalysts, respectively. The addition of NH₄Cl was found to be crucial to effectively conduct the reaction of ketones and imines.     

Metalloporphyrin Cr(TPP)Cl-catalyzed Claisen rearrangement of simple aliphatic allyl vinyl ethers and its unique stereoselectivity

The catalytic Z-selective Claisen rearrangement of simple aliphatic allyl vinyl ethers can be achieved using a chromium(III) porphyrin complex, Cr(TPP)Cl, as a catalyst: Cr(TPP)Cl significantly enhances reversal of E-Z selectivity in the thermal Claisen rearrangement of allyl vinyl ethers, especially, 4,5- and 4,6-disubstituted derivatives, at low catalyst loading.     

A useful procedure for diiodination of carbazoles and subsequent efficient transformation to novel 3,6-bis(triethoxysilyl)carbazoles giving mesoporous materials

Bis(pyridine)iodonium tetrafluoroborate (IPy₂BF₄) was successfully used as a diiodination reagent for carbazole and its derivatives to give 3,6-diiodocarbazoles in excellent yield. Subsequent rhodium-catalyzed disilylation of 3,6-diiodocarbazoles with triethoxysilane gave the corresponding 3,6-bis(triethoxysilyl)carbazoles, which are precursors for sol-gel polymerization, in good yield.     

低温加氢催化剂的设计: 理论与实践

简要总结了我们在C=C及C=O双键低温加氢双金属催化剂方面的最新研究成果. 首先, 我们以环己烯加氢为探针反应, 证明了平行使用多种研究手段的重要性, 包括单晶表面的基础研究与DFT计算, 多晶表面的合成与表征, 负载型催化剂的制备与性能测试等. 其次, 总结了双金属催化剂在其他加氢反应, 如丙烯醛C=O双键的选择性加氢, 苯的低温加氢, 以及乙炔的选择性加氢等反应中的应用. 最后, 讨论了利用金属碳化物代替贵金属Pt以减少双金属催化剂中Pt用量的可能性.     

Physicochemical properties of Ti-grafted SBA-15

Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al₂O₃ catalyst exhibited much better catalytic activity than the Rh-Ni/-Al₂O₃ catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe₃O₄—Cr₂O₃) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date.     

Cu-Ce/γ-Al2O3对硬脂酸催化水热脱氧产生烷烃的效果

利用等体积浸渍法制备Cu-Ce/γ-Al₂O₃催化剂，并在无H₂存在的条件下对硬脂酸进行催化水热液化。对催化剂进行BET比表面积分析和X射线衍射（XRD）分析可知，Cu-Ce/γ-Al₂O₃催化剂中存在CuO和CeO₂两种晶型，在300℃条件下水热反应12 h后具有更好的热稳定性。通过对硬脂酸进行水热液化实验和对生物油进行气相色谱-质谱（GC-MS）分析发现，加入Cu-Ce/γ-Al₂O₃催化剂能够获得最高的硬脂酸转化率（94.71%）和总烃产率（81.41%），水热液化脱氧效果最好。分析正烷烃的产率，结果发现硬脂酸在高温水热条件下主要发生脱羧反应。Cu-Ce/γ-Al₂O₃催化剂的加入能够同时促进反应过程中脱羧反应、加氢脱氧反应和裂化反应。此外，Cu-Ce/γ-Al₂O₃还能够促进羰基基团的脱除，有效减少产物中的醛和酮类物质。     

SYNTHESIS OF DBN AND ITS CATALYTIC PERFORMANCE FOR METHANOL CARBONYLATION TO METHYL FORMATE

1 , 5-diazabicyclo['1, 3, 0]non-5-ene(DBN) has been synthesized in our laboratory, and its catalytic activity and selectivity for methanol carbonylation to methyl formate (MF) have been studied. The experimental results have demonstrated that the synthetic processes of DBN used for the present work are reasonable and feasible. The total yield of three steps of DBN synthsis is approximate to 80%. The activity evaluation has shown that DBN can effectively catalyze the carbonylation reaction of methanol in the presence of propylene oxide (PO) promoter. PO-promoted DBN is a novel catalytic system superior to sodium methoxide.     

Preparation and Properties of Composite Polypyrrole/Pt Catalyst Systems

Three different methods for the preparation and modification of conducting polymer/noble metal catalyst systems consisting of polypyrrole (PPy) and platinum (Pt) are described for the anodic oxidation of methanol. The first method consists of the electrochemical deposition of a thin PPy film on glassy carbon substrate, which is modified with Pt either by electroreduction of hexachloroplatinate, codeposition from a nanodispersed Pt solution, or incorporation of tetrachloroplatinate as counterion followed by cathodic reduction. A second method is based on the preparation of nanoscale PPy(PSS) particles by chemical polymerization with polystyrenesulfonate PSS^– as the counterion. This material is a favorable catalyst support for nanodispersed Pt due to its mixed electronic and cationic conductivity. To study the electrochemical properties, the particulate system PPy(PSS)/Pt is fixed in a carbon fiber electrode. A third method was developed which brings the polypyrrole in close contact to a proton exchanger membrane (Nafion) using a special chemical deposition procedure. This method is useful for preparing a membrane electrode assembly (MEA) consisting of Nafion/PPy/Pt. The structural, morphological, and electrocatalytic properties for methanol oxidation were studied depending on the preparation method applied using surface analytical techniques (TEM, SEM, and EDX) and electrochemical measurements (cyclic voltammetry and transient techniques).