贵金属铱对氨分解用镍基催化剂的促进作用研究

用湿式浸渍法制备了不同贵金属质量分数的镍-铱双金属催化剂,以氨分解为模型反应对其催化性能进行考察.结果表明,贵金属铱的添加提高了10%Ni/γ-Al2O3的低温活性.在铱的质量分数不高于1%时,氨分解反应活性随铱质量分数的增加出现最大值(相应的Ir质量分数为0.7%),对应的10%Ni-0.7%Ir/γ-Al2O3催化剂在400 ℃时,氨分解率为43.55%,较单组分的Ni催化剂高40.0%.用H2-TPR、H2-TPD 、BET和XRD表征方法对催化剂进行了表征.结果表明,Ir与活性组分Ni之间存在协同作用.铱的添加促进了活性组分的分散、减小了镍的晶粒尺寸,且增加了催化剂活性位的数量,从而提高了催化剂的氨分解性能.     

Pyrrole synthesis using a tandem Grubbs’ carbene-RuCl3 catalytic system

A straightforward pyrrole synthesis from diallylamines is developed by using a tandem catalyst system leading to ring-closing metathesis with the second generation Grubbs’ catalyst (10%) followed by dehydrogenation in the presence of RuCl₃ × H₂O (2%).     

Synthesis of α‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh₃ catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc)₂/PPh₃, the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh₃)₄ was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.     

Selective Hydrogenation of Citral over a Carbon‐titania Composite Supported Palladium Catalyst

A novel carbon‐titania composite material, C/TiO₂, has been prepared by growing carbon nanofibers (CNFs) on TiO₂ surface via methane decomposition using Ni‐Cu as a catalyst. The C/TiO₂ was used for preparing supported palladium catalyst, Pd/C/TiO₂. The support and Pd/C/TiO₂ catalyst were characterized by BET, SEM, XRD and TG‐DTG. Its catalytic performance was evaluated in selective hydrogenation of citral to citronellal, and compared with that of activated carbon supported Pd catalyst. It was found that the Pd/C/TiO₂ catalyst contains 97% of mesopores. And it exhibited 88% of selectivity to citronellal at citral conversion of 90% in citral hydrogenation, which was much higher than that of activated carbon supported Pd catalyst. This result may be attributed to elimination of internal diffusion limitations, which were significant in activated carbon supported Pd catalyst, due to its microporous structure.     

Kinetics and mechanism of oxygen electroreduction on PtCoCr/C catalyst containing 20–40 wt % platinum

It is shown that the mechanism of oxygen electroreduction on the PtCoCr/C systems in 0.5 M H₂SO₄ is similar to that proposed for the Pt/C catalyst. The activity of ternary catalysts is by two and more times higher than that of monoplatinum catalyst. The constant k ₁ is much larger than k ₂ (k ₁ and k ₂ are the rate constants of O₂ reduction to water and H₂O₂, respectively) for all catalysts studied. This indicates that the catalytic systems are selective with respect to O₂ reduction immediately to water in the practically important potential range from 1.0 to 0.6 V. The yield of H₂O₂ increases with a shift of potential in the cathodic direction (<0.7 V) and does not exceed 1%. The sum of rate constants of further conversion of hydrogen peroxide also increases with a shift of potential in the cathodic direction. After a corrosion attack (a treatment in the acid for 24 h), a ratio between the rate constants (k ₁/k ₂) for the PtCoCr/C catalysts increases. This is caused by a considerable increase in k ₁, which is 2.84 × 10⁻² cm/s for the catalyst containing 34 wt % Pt (against 1.5 × 10⁻² cm/s for the untreated catalyst). This can be explained by the reaction proceeding on the particle surface, which was enriched in platinum in the course of corrosion treatment. The properties of platinum clusters on the alloy surface differ from those of monoplatinum as a result of the ligand effect. The amount of oxygen chemisorbed from water on this surface is lower than on Pt/C catalyst. This is the main factor determining an increase in the activity and stability of ternary catalysts.     

High performance Fe and N-codoped graphene quantum dot supported Pd3Co catalyst with synergistically improved oxygen reduction activity and great methanol tolerance

Designing high-performance and durable non-platinum catalysts as oxygen reduction reaction (ORR) catalysts is still a major barrier of fuel cell commercialization. In this work, simple hydrothermal and impregnation routes were applied to prepare non-platinum Pd-Co bimetallic nano-catalysts such as Fe-N doped graphene quantum dot (Fe-N-GQD) supported Pd₃Co (Pd₃Co/Fe-N-GQD 10 wt%), carbon supported Pd₃Co/C (10 wt%), graphene quantum dot supported Pd₃Co/C (10 wt%). The synthesized catalysts were physico-chemically characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electronmicroscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical investigation was carried out in three electrode half-cell system to evaluate the catalyst activity for oxygen reduction reaction (ORR), the tolerance to methanol crossover and durability. In comparison to commercial Pt/C (ETEK, 20 wt%), the Pd₃Co/Fe-N-GQD with lower weight percentage catalyst (∼10 wt%) displayed comparable electrocatalytic activity toward ORR with even higher methanol-tolerance capability and durability. The fabricated Pd₃Co/Fe-N-GQD with (10 wt %) metal loading exhibited only 20% lower activity than Pt/C (ETEK, 20 wt%) toward ORR. Nevertheless the durability study of the catalyst in acidic media showed that the Pd₃Co/Fe-N-GQD preserve 40% of its activity while Pt/C (ETEK, 20 wt%) exhibited only 20% of its initial catalytic activity for ORR. Moreover the activity loss in the presence of methanol (0.1 M) was obtained for Pt/C (ETEK, 20 wt%) and Pd₃Co/Fe-N-GQD 35% and 14%, respectively. To investigate the role of catalyst support, catalytic activities of Pd₃Co/Fe-N-GQD, Pd₃Co/C, Pd₃Co/GQD and Pd/Fe-N-GQD were compared. The results demonstrated superior catalytic activity of Pd₃Co/Fe-N-GQD which could be related to the cocatalytic role of Fe-N-GQD due to the presence numerous of active sites exposed to the reactants.     

Polymerization kinetics of octene-1 catalyzed by metallocene methylaluminoxane investigated with attenuated total reflectance fourier transform infrared (ATR-FT-IR) spectroscopy

The kinetic parameters have been measured for octene-1 solution polymerization at 120°C catalyzed by zirconocene with the cocatalyst methylaluminoxane. The polymerizations were performed in an attenuated total reflectance (ATR) reaction cell. The progress of the reactions were followed by observing the disappearance of octene-1 using the 910 cm^?1 band measured by FT-IR spectroscopy. The dependence of the reaction rate, R_p, on catalyst concentration and cocatalyst/catalyst ratio was examined. The catalyst deactivation mechanism was studied by fitting the experimental data to mathematical models involving second-order propagation and either first or second order catalyst deactivation. Second-order catalyst deactivation provided a much better fit. The calculated deactivation rate constant, k_d, is 21 (Ms)^?1. This model is used to determine the propagation rate constant for Al/Zr = 4 × 10³ as k_p = 19.9 (M s)^?1. A decrease in Al/Zr = 3 × 10² lowered the propagation rate constant, k_p, to 9.6 (M s)^?1 indicating that less than 50% of the initial Zr is active at this Al/Zr ratio.     

Palladium Encapsulated by an Oxygen-Saturated TiO2 Overlayer for Low-Temperature SO2-Tolerant Catalysis during CO Oxidation

The development of oxidation catalysts that are resistant to sulfur poisoning is crucial for extending the lifespan of catalysts in real-working conditions. Herein, we describe the design and synthesis of oxide-metal interaction (OMI) catalyst under oxidative atmospheres. By using organic coated TiO₂, an oxide/metal inverse catalyst with non-classical oxygen-saturated TiO₂ overlayers were obtained at relatively low temperature. These catalysts were found to incorporate ultra-small Pd metal and support particles with exceptional reactivity and stability for CO oxidation (under 21 vol % O₂ and 10 vol % H₂O). In particular, the core (Pd)-shell (TiO₂) structured OMI catalyst exhibited excellent resistance to SO₂ poisoning, yielding robust CO oxidation performance at 120 °C for 240 h (at 100 ppm SO₂ and 10 vol % H₂O). The stability of this new OMI catalyst was explained through density functional theory (DFT) calculations that interfacial oxygen atoms at Pd−O−Ti sites (of oxygen-saturated overlayers) serve as non-metal active sites for low-temperature CO oxidation, and change the SO₂ adsorption from metal(d)-to-SO₂(π*) back-bonding to much weaker σ(Ti−S) bonding.     

Synthesis of poly(ether ketone amide)s containing 4‐aryl‐2,6‐ diphenylpyridine moieties by a heterogeneous palladium‐catalyzed polycondensation of aromatic diiodides,aromatic diamines,and carbon monoxide

New aromatic poly(ether ketone amide)s containing 4‐aryl‐2,6‐diphenylpyridine units were prepared by the heterogeneous palladium‐catalyzed carbonylative polymerization of aromatic diiodides with ether ketone units, aromatic diamines bearing pyridine groups, and carbon monoxide. Polymerizations were performed in N,N‐dimethyl‐ acetamide (DMAc) at 120°C in the presence of a magnetic nanoparticles‐supported bidentate phosphine palladium complex [Fe₃O₄@SiO₂‐2P‐PdCl₂] as catalyst with 1,8‐diazabicycle[5,4,0]‐7‐undecene (DBU) as base and generated poly(ether ketone amide)s with inherent viscosities up to 0.79 dL/g. All the polymers were soluble in many organic solvents. These polymers showed glass transition temperatures between 219°C and 257°C and 10% weight loss temperatures ranging from 467°C to 508°C in nitrogen. These polyamides could be cast into transparent, flexible, and strong films from DMAc solution with tensile strengths of 86.4 to 113.7 MPa, tensile moduli of 2.34 to 3.19 GPa, and elongations at break of 5.2% to 6.9%. These polymers also exhibited good optical transparency with an ultraviolet‐visible absorption cut‐off wavelength in the 371 to 384‐nm range. Importantly, the new heterogeneous palladium catalyst can easily be recovered from the reaction mixture by simply applying an external magnet and recycled at least 8 times without significant loss of activity. Our catalytic system not only avoids the use of an excess of PPh₃ and prevents the formation of palladium black, but also solves the basic problems of palladium catalyst recovery and reuse.     

CoO/SiO2-Al2O3催化剂上苯胺和1,6-己二醇气相高效合成1-苯基氮杂环庚烷

研究了CoO/SiO2-Al2O3催化剂上苯胺和1,6-己二醇气相催化合成1-苯基氮杂环庚烷的反应,并采用N2吸附-脱附、X射线衍射、H2程序升温还原和NH3程序升温脱附技术对催化剂进行表征.结果表明,CoO/SiO2-Al2O3催化剂表现出较高的活性和选择性.当CoO担载量为0.3mmol/g时,催化剂前体在700℃...     

Pt 改性的高结晶度 TiO2 晶须的光催化性能

 以二钛酸钾 (K₂Ti₂O₅) 为前驱体, 通过离子交换和 800^oC 焙烧制备了 TiO₂晶须 (TiO₂(800^oC)), 并采用乙二醇胶体法, 在 TiO₂(800^oC) 样品上负载 1% Pt 纳米颗粒制成了 Pt/TiO₂(800^oC 催化剂. 采用 X 射线衍射、扫描电镜、透射电镜、X 荧光光谱和低温 N2 吸附-脱附等技术对催化剂进行了表征, 并考察了该催化剂光催化降解苯酚活性及稳定性. 结果表明, TiO₂(800^oC)样品为结晶度较高的纯锐钛矿 TiO₂, 载 Pt 后催化活性提高到原来的 2.3 倍, 具有很高的单位比表面积活性. 催化剂经 10 次重复使用后, Pt 流失量仅为 6%, 活性为新鲜催化剂的 91%. 而低结晶度的纯锐钛矿或混晶的 TiO₂ 负载 Pt 催化剂的活性和稳定性均不及 Pt/TiO₂(800^oC).     

Pd/CaCO3 in liquid poly(ethylene glycol) (PEG): an easy and efficient recycle system for partial reduction of alkynes to cis-olefins under a hydrogen atmosphere

Lindlar’s catalyst (Pd/CaCO₃) in PEG (400) has been found to be the most reusable reaction medium for selective reduction of alkynes to cis-olefins. The catalyst and PEG were recycled five times without loss of activity.     

Biomass derived Fe-N/C catalyst for efficiently catalyzing oxygen reduction reaction in both alkaline and neutral pH conditions

Fe-N/C is a promising oxygen reduction reaction (ORR) catalyst to substitute the current widely used precious metal platinum. Cost-effectively fabricating the Fe-N/C material with high catalytic activity and getting in-depth insight into the responsible catalytic site are of great significance. In this work, we proposed to use biomass, tea leaves waste, as the precursor to prepare ORR catalyst. By adding 5% FeCl₃ (wt%) into tea precursor, the pyrolysis product (i.e., 5%Fe-N/C) exhibited an excellent four-electron ORR activity, whose onset potential was only 10 mV lower than that of commercial Pt/C. The limiting current density of 5%Fe-N/C (5.75 mA/cm²) was even higher than Pt/C (5.44 mA/cm²). Compared with other biomass or metal organic frameworks derived catalysts, 5%Fe-N/C showed similar ORR activity. Also, both the methanol tolerance and material stability performances of as-prepared 5%Fe-N/C catalyst were superior to that of Pt/C. X-ray adsorption fine structure characterization revealed that the FeN₄O₂ might be the possible catalytic site. An appropriate amount of iron chloride addition not only facilitated catalytic site formation, but also enhanced material conductivity and reaction kinetics. The results of this work may be useful for the Fe based transition metal ORR catalyst design and application.     

Optimization study by Box-Behnken design (BBD) and mechanistic insight of CO2 methanation over Ru-Fe-Ce/γ-Al2O3 catalyst by in-situ FTIR technique

The utilization of carbon dioxide for methanization reactions in the production of synthetic natural gas (SNG) is of increasing interest in energy-related issues. The use of CO₂ as a raw material in methanization reactions in the formation of SNG is of increasing concern associated with energy problems. The effect of three independent process parameters (calcination temperature, ceria loading and catalyst dosage) and their interactions in terms of conversion of CO₂ was considered by response surface methodology (RSM). Box-Behnken design (BBD) revealed that the optimized parameters were 1000 °C calcination temperature, 85%wt ceria loading and 10 g catalyst dosage, which resulted in 100% conversion of CO₂ and 93.5% of CH₄ formation. Reaction intermediate study by in situ FTIR showed that carboxylate species was the most active species on the catalyst surface. In-situ FTIR experiments revealed a weak CO₂ adsorption, that exist namely as carboxylate species over the trimetallic catalyst. As a result, dissociated hydrogen over ruthenium reacts with surface carbon, leading to *CH, which subsequently hydrogenated to produce *CH₂, *CH₃ and finally to the desired product methane. The use of in situ-FTIR study indicated that the CO₂ methanation mechanism does not involve CO as a reaction intermediate. The more detailed mechanism of CO₂ methanation pathways involved over Ru-Fe-Ce/γ-Al₂O₃ catalyst is discussed in accordance with IR-spectroscopic data. The better catalytic activity and stability over Ru-Fe-Ce (5:10:85)/γ-Al₂O₃ catalyst calcined at 1000 °C showed the presence of moderate basic sites for CO₂ adsorption.     

Polymerization of MMA catalyzed by different novel mixed ligand lanthanocene{(Cp)(Cl) LnSchiff-base (THF)},(COT) -Ln(methoxyethylindenyl)(THF) /Al (i -Bu)_3 systems

This article deals that the rare earth metal complexes along with Al(i'-Bu),can catalyze the polymerization of methyl-methacrylate (MMA) into high molecular weight poly(MMA) along with narrow molecular weight distributions (MWD).A typical example was mentioned in the case of {Cp(Cl) Sm-Schiff-base(THF)} which expresses maximum (conv.% = 55.46 and Mn=354×103) efficiency along with narrow MWD (Mw/Mn<2) at 60℃.The resulting polymer was partially syndiotactic (>60%).The effect of the catalyst,temperature,catalyst/MMA molar ratio,catalyst/Al( i-Bu)3 molar ratio on the polymerization of MMA at 60℃ were also investigated.     

蜂窝状Ho改性Fe-Mn/TiO2催化剂的制备及其低温选择催化还原(SCR)脱硝性能

采用模压法制备了蜂窝状Ho改性的Fe-Mn/TiO₂催化剂,研究了结构助剂、黏合剂和造孔剂等对成型催化剂低温选择催化还原（SCR）脱硝性能的影响。优选出一套理想的成型参数：水粉质量比为40%且逐次分批加入;结构助剂玻璃纤维的用量为10%（质量分数）;黏合剂羧甲基纤维素的用量为5%（质量分数）;助挤剂甘油的添加量为10%（质量分数）且分批加入;造孔剂活性炭粉的用量为2%（质量分数）。该蜂窝状催化剂在120 ℃下脱硝率维持在90%以上,并且在SO₂体积分数低于0.02%时具有一定的抗硫抗水性。表征结果表明,成型后蜂窝状催化剂比表面积降低,颗粒分散程度明显减弱,并且表面酸量和表面Mn⁴⁺含量下降,对催化活性有一定的影响。     

Decomposition of nitrous oxide on AlFe-PILC catalyst

Summary Two AlFe-PILC catalysts were prepared with different OH/metal ratio and applied in nitrous oxide (N₂O) decomposition reactions. The 100% conversion of N₂O with NH₃into N₂and H₂O was achieved below 500^oC with both applied catalysts. However, the activity of catalysts in direct conversion of N₂O into N₂and O₂did not exceed 40 % below 500^oC. In this reaction the activity of AlFe-PILC catalyst synthesized at higher OH/metal ratio (4) is higher compared to the activity of AlFe-PILC catalyst with OH/metal ratio (2). Free FeO·Fe₂O₃particles were registered in the AlFe-PILC catalyst with higher OH/metal ratio (4).     

Effect of Calcined Temperature on Coke Deposition for Autothermal Reforming of Methane with Ni-Cu Catalyst

Ni/CuO-ZrO₂-CeO₂-Al₂O₃ catalysts were prepared by co-precipitation method at pH=9 and using Na₂CO₃ as the precipitant. The Ni loading (mass fraction) of the catalysts was 10%. The catalysts were characterized by X-ray diffraction, temperature-programmed oxidation (TPO), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The effects of calcined temperature of support on coke deposition were studied. TPO, SEM and XPS results indicated there was no peak of higher temperature oxygen consumption on Ni/CuO-ZrO₂-CeO₂-Al₂O₃catalyst (support was calcined at 800 ^oC), which could lead to the deactivation of the catalyst. The carbon species were carbonate and inactive carbon (filamentous carbon species) on the surface of catalyst reacting for 40 h which perhaps led to the deactivation of the catalyst.     

Synthesis of ϵ‐Caprolactam from Cyclohexanone Oxime Using Zeolites Hβ, HZSM‐5, and Alumina Pillared Montmorillonite

The Beckmann rearrangement of cyclohexanone oxime (CHO) to ?‐caprolactam (?‐C) was studied in a plug flow reactor at 300–400°C under atmospheric pressure by using Hβ, ZSM‐5, and alumina pillared montmorillonite. With Hβ(X) Y zeolites, raising the SiO₂/Al₂O₃ molar ratio (X) results in the enhancement of catalyst acid strength with concomitant decrease of the total acid amount. In creasing the calcination temperature (Y) causes remarkable diminution of catalyst surface area, acid strength, and acid amount. A similar trend was found for AlPMY catalysts. In there action of CHO, the initial catalytic activity correlates well with the total acid amount of various catalysts except for Hβ(10) Y (Y > 600°C). The reaction proceeds on both Brönsted and Lewis acid sites and the catalyst deactivation most likely occurs at the strong Brönsted acid sites. The effect of solvents in the feed on the catalytic results was also investigated; it was found that polar solvents such as ethanol or n‐butanol give high ?‐C yield and longer catalyst life time. In the reaction of CHO/C₂H₅OH over Hβ(10)800 at 400°C and W/F 74.6 gh/mol, the CHO conversion and ?‐C yield remain 100% and 92%, respectively, for at least 20 h time‐on‐stream. The reaction paths and the mechanism for ?‐C formation are proposed.