Generation and characterization of supported films of transition metal and rare earth metal oxide catalysts

Summary The generation of catalytically relevant metal and/or metal oxide compounds supported on silica fibres is described. The systems investigated are Ni^o, Cu^o, Cu^o/ZnO, as well as perovskite-type La/Fe, La/Ni and La/Mn oxide phases. Ultrasound-aided generated vapours containing dissolved metal salt precursors are transferred onto preheated quartz fibres and transformed into the catalytically relevant phases by subsequent calcination. Analytical SEM and X-ray diffraction reveals the presence of differently crystalline, rough surfaces. The influence of the precursor salt and the conditions of calcination on the formation of the supported catalysts is discussed.     

Single-atom site catalysts supported on two-dimensional materials for energy applications

Single-atom site catalysts (SACs) and two-dimensional materials (2DM) have gradually become two hot topics in catalysis over the past decades. Their combination with each other can further endow the derived SACs with extraordinary properties such as high loading, identical active sites, uniform coordination environment, distinctive metal-support interaction, and enhanced catalytic activities. In this review, we highlight the recent development in this specific research topic according to the types of substrates and focus on their applications in energy conversion field. Additionally, we also make a brief introduction to the synthesis and characterization methods for SACs supported on 2DM (SACs/2DM). Finally, the challenges and perspectives are summarized based on the current development status. It is believed that this work will make contributions to the rational design and fabrication of novel SACs/2DM, promoting their practical energy applications in the future.     

Hydrodechlorination of chlorobenzene over supported metal catalysts

The use of supported Pd catalysts, with low and high metal content, for the hydrodechlorination of chlorobenzene is presented in this article. Application of microwave irradiation during preparation of catalysts resulted in the synthesis of large Pd particles at moderate temperatures. The nature of the support played a key role in the formation of cationic Pd species. The extent of interaction of the Pd species with the support, the nature of metal precursor, particularly the residual chlorine on the surface were found to significantly affect the activity of the catalysts. In the case of bimetallic catalysts also microwave heating resulted in creation of bigger particles of Pd compared to those observed in conventionally heated catalysts. Besides, it minimized alloy formation as a result of which the activity of the catalysts in hydrodechlorination was found to be higher compared to that observed on conventionally prepared catalysts. Contrary to the general observation that low dispersed Pd catalysts are preferable for high stability, by means of the deposition-precipitation method adopted for catalyst preparation it was demonstrated that even highly dispersed (low Pd containing) catalysts can exhibit comparable activity and stability. An analysis of the nature of Pd species and its role in the stability of the catalysts is presented.IICT communication No. 051224     

Di- and poly-nuclear transition metal complexes as catalysts for the metal carbonyl substitution reaction. The role of supported metals and metal oxides as catalyst promoters

Various di- and poly-nuclear transition metal complexes have been investigated as catalysts for the metal carbonyl substitution reaction. The complexes [{(η⁵-C₅H₄R)Fe(CO)₂} ₂] (R = H, Me, CO₂Me, OMe, O(CH₂)₄OH) and [{(η⁵-C₅H₅)-Ru(CO)₂} ₂] are active catalysts for a range of substitution reactions including the probe reaction [Fe(CO)₄(CNBu^t)] + Bu^tNC → [Fe(CO)₃(CNBu^t)₂] + CO. [{(η⁵-C₅Me₅)Fe(CO)₂}₂] is catalytically active only on irradiation with visible light. For [{η⁵-C₅H₅)Fe(CO)₂}₂] and a range ofisocyanides RNC ( R = Bu^t, C₆H₅CH₂, 2,6-Me₂C₆H₃), catalyst modification by substitution with isocyanide is a major factor influencing the degree of the catalytic effects observed, e.g. [{(η⁵-C₅H₅)Fe(CO)(CNBu^t)}₂] is approximately 35 times as active as [(η⁵-C₅H₅)₂FE₂(CO)₃(CNBu^t)] for the [Fe(CO)₄(CNBu^t)] → [Fe(CO)₃(CNBu^t)₂] conversion. Mechanistic studies on this system suggest that the catalytic substitution step probably involves a rapid intermolecular attack of isonitrile, possibly on a labile catalyst-substrate radical intermediate such as {[Fe(CO)₄(CNR)][(η⁵-C₅H₅)Fe(CO)₂]}; or on a reactive radical cation such as [Fe(CO)₄(CNR)]⁺ generated via electron transfer between the substrate and the catalyst. Other transition metal complexes which also catalyze the substitution of CO by isocyanide in [Fe(CO)₄(CNR)] (and [M(CO)₆] (M = Cr, Mo, W), [Mn₂(CO)₁₀], [Re₂(CO)₁₀]) include [Ru₃(CO)₁₂], [H₄Ru₄(CO)₁₂], [M₄(CO)₁₂] (M = Co, Ir) and [Co₂(CO)₈]. These reactions conform to the general mechanistic patterns established for [{(η⁵-C₅H₅)Fe(CO)₂}₂], suggesting a similar mechanism. A range of materials, notably PtO₂, PdO and Pd/C, act as promoters for the homogeneous di- and poly-nuclear transition metal catalysts, and can even be used to induce activity in normally inactive dimer and cluster complexes e.g. [Os₃(CO)₁₂]. This promotion is attributed to at least three possible effects: the removal of catalyst inhibitors, a catalyzed substitution of the homogeneous catalyst partner, and a possible homogeneous-heterogeneous interaction which promotes the formation of catalytic intermediates.     

担载型过渡金属催化剂上甲烷同系聚合反应的研究

本文利用瞬变应答反应技术较系统地考察了担载型过渡金属催化剂上甲烷同系聚合制C2以上烃的反应, 研究发现通过采用总反应分解法操作, 可以克服甲烷同系聚合反应的热力学限制, 使该反应能在较为温和的条件下得以进行。本文还系统地探讨了影响该反应的各种因素。523K 5wt% Pt/SiO2上甲烷的最佳转化可达9,91%。Pt, Co催化剂表现出较为优越的催化性能。甲烷在催化剂表面分解产生的CHx(ad)(0<=x<=3)物种可能是该反应的活性中间体。     

Design of supported metal catalysts modified with metal oxides for hydrodeoxygenation of biomass-related molecules

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γ-Radiation produced supported metal complex catalysts : II. Cobalt carbonyl hydroformylation catalysts supported on polypropylene containing pyridine side chains

The optimum conditions necessary to prepare novel polymer supports for use in catalysis by the γ-radiation grafting of 4-vinylpyridine on to polypropylene are shown to be a total dose of 2 Mrad at a dose rate of 300 Krad h^?1 using a monomer to polymer ratio of 40 per cent mol/mol. Addition of 0.1 per cent w/v of p-tert-butylcatechol increases the grafting yield almost two fold. Comparison of the hydroformylation of 1-hexene in the presence of cobalt carbonyl supported on 4-vinylpyridine grafted on to polypropylene shows an increase in specificity, as determined by the ratio of normal/branched heptanal formed, by a factor of about 2.5 over the corresponding homogeneous catalyst. The supported system is of similar activity to the homogeneous system. The greater specificity of the supported catalyst is ascribed to the total environment surrounding the catalytically active site in which both the pyridine sidechain and the polypropylene backbone are believed to play an important role.     

FT-IR emission studies of chemisorbed species on supported metal catalysts.

Infrared emission spectra of CO adsorbed on Rh/Al₂O₃ and Pt/Al₂O₃ were studied at 420K. The bands at 2092 and 2031 cm⁻¹ were assigned to symmetric and asymmetric stretching modes of surface Rh(CO)₂ groups, respectively. The RhC stretching modes are expected just below the range of observations (420 cm⁻¹. On Pt/Al₂O₃ the bands at 2043 and 457 cm⁻¹ were assigned to CO and PtC stretching vibrations of Pt-CO surface groups, respectively. Force constant calculations give 17.3 and 16.9 Ncm⁻¹ for CO stretching and 2.55 and 3.53 Ncm⁻¹ for MC stretching on the Rh and Pt catalysts, respectively.     

Dehydrogenation of cycloalkanes over noble metal catalysts supported on active carbon

Dehydrogenation of decalin to naphthalene through tetralin and that of dicyclohexyl to biphenyl through phenylcyclohexane with Pt/C and Pd/C was investigated mainly under the liquid film state, in which the catalyst was just wet but not suspended and covered with a thin film of liquid substrate. To improve the catalytic activities, the effects of the addition of tellurium into Pd/C were investigated to reveal that the combination of tellurium, palladium and conjugated systems produced during the dehydrogenation of cycloalkames was important to the improvement of the activities.     

Role of electrokinetic phenomena in the preparation of supported metal catalysts

A model accounting for the effect of electrokinetic phenomena on the prepartion of supported metal catalysts by wet impregnation is presented. The model is able to explain the dependence of catalyst distribution profile and loading on the concentration of the impregnant, on the pH and ionic strength of the impregnating solution, as well as on the presence of a co-impregnating species.     

Synthesis and characterization of nickel catalysts supported on different carbon materials

Nickel catalysts supported on various carbon materials such as multiwall carbon nanotubes, shortened length carbon nanotubes, graphite and amorphous carbon were synthesized, characterized and tested in cyclohexene hydrogenation reaction. We have found that carbon nanotube supports are superior to graphite and amorphous carbon both in terms of catalytic activity and stability.     

不可还原材料负载的纳米金催化剂:理性设计与优化

近年来,负载型金催化剂被视为多相催化工业化进程中的机遇和挑战,因而广受研究.载体的选取可以有效调控纳米金催化剂的化学结构及催化活性.针对载体本身对反应是否具有活性,可将其分为活性载体与惰性载体.活性载体主要为具有还原性的金属氧化物;而惰性载体,诸如碳基材料、氧化硅、氧化铝等,多为反应条件下不具备还原性或不可进行还原处理...     

Catalytic decomposition of methylene chloride on oxidative carbon supported metal oxide catalysts

Several carbon supported chromium oxide catalysts were prepared by varying textural and surface properties of support and tested for methylene chloride oxidation. They were investigated by TGA and XPS. The difference in acidity and high valence of chromium led to difference in activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetics of lactose and rhamnose oxidation over supported metal catalysts

Several mono- and bimetallic Pd, Pt, Rh and Ru supported on alumina and active carbon catalysts were characterized by CO chemisorption, nitrogen adsorption, XPS and XRD and acidity titrations were performed for active carbon supported catalysts. These catalysts were tested in oxidation of two sugars, namely lactose and rhamnose, at 60 °C and at 70 °C under slightly alkaline conditions (pH 8) with molecular oxygen. The results revealed that there is an optimum metal particle size in a range of 3-10 nm giving the highest initial TOFs for both oxidations. Furthermore, the catalytic activities and conversions were related to other catalyst properties, such as the type and amount of promoters and the presence of different phases. In situ catalyst potential measurements revealed that there is an inverse correlation between the increase of catalyst potential as a function of sugar conversion and the catalyst activity after prolonged reaction times. This method is a valuable tool for in situ characterization of catalysts correlating well with their activities.     

Advanced chemical design with supported metal complexes for selective catalysis

This review covers several recent topics of novel catalyst design with supported metal complexes on oxide surfaces for selective catalysis such as chiral self-dimerization to create asymmetric oxidative coupling catalysis, surface functionalization with achiral reagents to promote asymmetric catalysis, and molecular imprinting to design shape-selective catalysis. The new concepts and designs find wide applications to a variety of selective catalysts.     

Kinetics of hydrogenation of cyclododeca-3,7-diene-1-one on supported metal catalysts

The kinetics of hydrogenation of cyclododeca-3,7-diene-1-one on commercially available supported metal catalysts has been studied in ethyl alcohol solutions at 323–363 K and 0.1–2.5 MP a pressure of hydrogen. The experimental data have been related to kinetic equations of the Langmuir-Hinshelwood type. The reaction schemes which best fit the experimental data are shown.     

Physics of ultra-thin phthalocyanine films on semiconductors

This paper focuses on the structural arrangements, as seen in scanning tunneling microscopy, chemical and electric properties, as studied especially by high resolution synchrotron radiation photoelectron spectroscopy and energy loss spectroscopy of sub-monolayer up to few monolayer thin films of phthalocyanines adsorbed on narrow band gap III–V semiconductors where they form ordered superstructures, as well as on silicon surfaces. Special emphasis will be put on non-planar metal phthalocyanines where the central atom is either lead or tin. These molecules have been studied in detail from the experimental point of view as well as theoretically by ab initio quantum calculations. Comparison with metal free and metal substituted planar phthalocyanines (H₂Pc, CuPc, CoPc, …) adsorbed on semiconductors or noble metal surfaces is included. Perspectives and novel potential applications are finally outlined.