Structure of Pd/SiO2 sol-gel and impregnated catalysts

Palladium catalysts were prepared by sol-gel and impregnation techniques both in acid and basic media. The sol-gel catalysts resulted in larger PdO crystallites than the impregnated catalysts. In both preparation methods, an acid medium promoted the formation of small metal crystallites which provided catalytic activity. A stronger metal-support interaction was found in sol-gel catalysts synthesized from a square planar palladium complex. Deactivation results in phenylacetylene hydrogenation have been attributed to palladium hydrate formation or to deposition of carbonaceous compounds. The preparation mode determined the contribution of each deactivating reaction.     

Cobalt Oxide/Silica Xerogels Powders: X-Ray Diffraction,Infrared and Visible Absorption Studies

Using x-ray diffraction, infrared and visible absorption spectroscopies we have studied: silica xerogel powders when cobalt nitrate is incorporated and mainly the evolution of the precipitated cobalt species in the SiO₂ matrix. Samples containing cobalt nitrate and prepared with a molar ratio of H₂O/TEOS of 11.67 were studied as a function of annealing temperature. It was found that the added element has a remarkable influence on the final structure of this kind of samples and at relatively high temperatures the cobalt compounds react with the silica matrix forming a cobalt silicate.     

Oxidation of Carbon Monoxide over Cu/CeO_2 Catalysts Prepared by SMAI

Introduction Carbon monoxide is ubiquitous air pollutants emitted by many sources. Total oxidation of carbon monoxide to carbon dioxide is employed to meet environmental regulations in an economic way. Precious metals (Pt, Pd) are well-known oxidation catalysts with high activity and stability, and are widely used for exhaust gas emission control. However, the high cost of precious metals and their sensitivity to sulfur poisoning have long motivated the search for substitute catalysts. …     

Preparation of Cu/SiO2 Catalyst by Solution Exchange of Wet Silica Gel

Structural formation process of Ni/SiO₂ and Cu/SiO₂ catalysts prepared by solution exchange of wet silica gel was investigated. Microstructures of Cu/SiO₂ and Ni/SiO₂ were quite different from each other. In the case of Cu/SiO₂, Cu particles with diameter of ca. 3–5 nm dispersed homogeneously at less Cu content, and the particle size of Cu as well as pore size of silica gel support increased with increasing Cu content. In the Ni/SiO₂, the Ni particles with diameter of ca. 6–10 nm gathered densely to form aggregates in silica matrix resulting in sea-island structure, whereas the size of Ni particle slightly increased with increasing Ni content. The difference in the structure of the metal-silica composites is probably caused by the difference in interaction between silica gel network and metal ions during drying and heating processes.     

CO Oxidation on Cu/MgO-SiO2 Sol-Gel Derived Catalysts

Sol-gel Cu//MgOSiO₂ catalysts were prepared gelling tetraethoxysilane (TEOS), magnesium ethoxide and copper acetylacetonate at pH 3 and pH 9. The catalysts shown specific surface areas ca. 500 m²/g and 140 m²/g for pH 9 and pH 3 preparations respectively. Si(OH) and Si(OH)₂ hydroxy groups were observed by MAS-RMN spectroscopy in both preparations. CO₂-TPD and NH₃-TPD desorption thermograms showed that acid and basic sites were formed on the catalysts surface. It has been found that the catalysts having the highest density of basic sites were the catalysts showing the highest activity for the CO oxidation. It is proposed that the catalytic activity depends of the relative Cu⁼¹/Cu⁼² stability given by the support acidity.     

新型光敏聚酰亚胺/SiO2杂化材料的制备与性能研究

通过溶胶－凝胶法制备了一种新型的光敏聚酰亚胺／二氧化硅杂化材料。研究表明当ＳｉＯ２的含量≤１０ｗｔ％时杂化材料除了保持光敏聚酰亚胺原有的感光性能外其热稳定性能、力学性能以及与基底的粘附性能均有明显地提高,同时材料的热膨胀系数也显著地降低。     

Deep Oxidation of Methane Over Cu and Ag Modified Manganese Oxide Catalysts

Cu-Mn and Ag-Mn composite oxide catalysts were prepared by the modification of high specific surface area MnO₂ precursor with Cu or Ag, and used for CH₄ deep oxidation. The results were compared with that of unmodified MnOx. It is found that both Cu and Ag additives increase the oxidation activity of manganese oxide below 420°C; however, only Ag lowers the CH₄ complete oxidation temperature (T₉₈), whereas Cu increases the T₉₈. The catalysts were characterized by means of BET, XRD and H₂-TPR. Due to the synergetic effects of Cu and Ag ions with manganese oxide, the activity of the oxygen species is improved, leading to the increase of the oxidation activities of the modified catalysts, especially below 420°C.     

Copper oxide on Cu/Al2O3-TiO2 catalystsTG,FTIR-CO absorption and catalytic activity in the NO reduction by CO

TG, FTIR-(CO absorption), and catalytic activity in the NO reduction by CO were used to characterize Cu/Al₂O₃-TiO₂ catalysts prepared by co-gelling aluminum tri-sec-butoxide and titanium iso-propoxide at pH 9 and at pH 3 gelling conditions. Under nitrogen flow, copper oxide decomposition, oxygen storage capacity (OSC) and sample dehydroxylation (total mass loss) was followed by TG. The CuO decomposition forming Cu⁰, Cu⁺¹ was observed by means of FTIR (CO absorption) spectra. In pH 9 sample the large amount of Cu⁰ was observed. At low total mass loss and high Cu⁰/Cu⁺¹+Cu⁺² ratio (pH 9 sample) a lowest light-off in the NO reduction by CO was observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Quantum Chemical Studies on the Mechanism of Producing Oxygenates in Fischer-Tropsch Synthesis on M/SiO2(M = Ni,Ru,Rh,Pd)

EHMO calculations and orbital analyses of fragment;;have been performed for the formation of oxygenates in Fischer-Tropsch synthesis on the butterfly model for four different metal (Ni,Ru,Rh,Pd) catalysts supported on SiO2.Calculations were made for the four processes,i.e.,CO-dissociation;Coupling of CO and H to produce CHO;Insertion of CO to M-CH3;insertion of CH2 to M-CH3 On the basis of comparing the degree of CO bonds activation and the energy barriers of the foregoing processes for these four catalysts,it is concluded that Ni/SiO2 can be used as the methanation catalyst.On Ru/SiO2 and Rh/SiO2 C2-oxygenated compound can be produced (acetaldehyde),especially Rh/SiO2 is the even better catalyst,and Pd/SiO2 is a methanol synthesis catalyst.     

SiO2负载型铁系催化剂催化乙烯齐聚的研究

制备了硅胶负载型2,6-二亚胺基吡啶铁系齐聚催化剂。考察了不同负载温度,聚合中乙烯加压方式,催化剂的加入量以及丙烯对乙烯齐聚活性和α-烯烃分布的影响。结果表明,低温负载有利于催化剂活性提高,分段加压可以使催化剂的活性周期增加,聚合温度平稳,单位助催化剂MAO转化的乙烯量增加,而α-烯烃的选择性基本不变。Fe催化剂负载后,以单位助催化剂MAO计算的乙烯转化率提高。增加催化剂的量后,单位助催化剂MAO转化的乙烯量增加。在乙烯齐聚中加入少量丙烯催化剂的活性降低,α-烯烃分布向低碳方向移动。     

CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究

采用ＸＲＤ、ＵＶ－ｖｉｓ　 ＤＲＳ、ＥＳＲ和微分吸附量热等技术,考察了铬担载量分别为２．５、５和 １０ｗｔ％的 ＣｒＯｘ／ＳｉＯ２催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Ｃｒ的氧化态和聚集形式。随着Ｃｒ担载量从２．５ｗｔ％到１０ｗｔ％的逐渐增大,催化剂表面占主导地位的Ｃｒ物种由ＣｒＯ３单体转为多聚ＣｒＯ３和Ｃｒ２Ｏ３晶相。在 ＣＯ２气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为 ２． ５ｗｔ％ ＣｒＯｘ／ＳｉＯ２ ＞５ｗｔ％ ＣｒＯｘ／ＳｉＯ２＞１０ｗｔ％ ＣｒＯｘ／ＳｉＯ２,反应过程中的原位 ＥＳＲ和 ＵＶ－ｖｉｓＤＲＳ测定结果表明,催化剂表面的反应活性中心为Ｃｒ５＋, Ｃｒ５＋可由催化剂预处理过程中 Ｃｒ３＋的氧化及丙烷反应过程中 ＣｒＯ３单体的还原产生,在反应中 ＣＯ２可使Ｃｒ３＋重新氧化为Ｃｒ５＋。     

Studies on TiO2/SiO2 and Pd/TiO2/SiO2 Catalysts in Photoreduction of CO2 with H2O to Methanol

The development of industry induced a massive increase in the emission of carbon dioxide into the atmosphere. A large amount of CO₂ and its general availability causes that it could be a cheap reactant in a reaction that runs in a way similar to photosynthesis in plants. Pure TiO₂ and metal doped TiO₂ are the most studied semiconductor catalysts for photoreduction of CO₂. The TiO₂/SiO₂ and Pd/TiO₂/SiO₂ catalysts were prepared and studied by temperature-programmed desorption, X-ray diffraction analysis, SEM-EDS, temperature-programmed reduction and then used for the methanol synthesis. The photoactivity of Pd/TiO₂/SiO₂ catalysts in the reduction of CO₂ with H₂O was tested at room temperature using photoreactor equipped with 16 lamps. The wavelength was characteristic of near ultraviolet. Post-reaction products were identified with gas chromatograph equipped with the flame ionization detector. Pd doping made the catalysts photoactive and the photoactivity of catalysts was changing as follows: 1%Pd/5%TiO₂/SiO₂ > 1% Pd/10% TiO₂/SiO₂ > 1% Pd/15% TiO₂/SiO₂. Optimum ultraviolet radiation time in the photoreduction of CO₂ to methanol was 7 h. An addition of Pd does not change the surface of the carrier.     

Preparation of monometallic (Pd,Ag) and bimetallic (Pd/Ag,Pd/Ni,Pd/Cu) nanoparticles via reversed micelles and their use in the Heck reaction

The metal nanoparticles (NPs) have been prepared using a water-in-oil microemulsion system of water/dioctyl sulfosuccinate sodium salt (aerosol-OT, AOT)/isooctane at 25 °C. Since the NPs produced in this system can endure forcing conditions (100 °C), this system has been used for the synthesis of nano-catalysts in the Heck reactions. FE-SEM, DLS, and UV/vis analyses have been used to characterize the surface morphology, size, and proof of the formation of all the prepared metal NPs, respectively. In addition, the effects of some reaction parameters (here, bases and solvents) were optimized. Differences in the catalytic properties of the synthesized NPs have also been investigated. Consequently, the Pd/Cu (4:1) bimetallic NP showed the highest activity in the C–C coupling reaction of the iodobenzene with the styrene, thus it is employed as the superior catalyst in this study. Therefore, the Pd/Cu (4:1) bimetallic NPs were further investigated using TEM and XRD analyses. This catalyst system is also reusable for six runs with very negligible reduction in the efficiency.     

V2O5/TiO2 Catalytic Xerogels Raman and EPR Studies

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V₂O₅/TiO₂ catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm^–1 and polymeric vanadates by two broad bands in the region from 900 to 960 cm^–1 and 770 to 850 cm^–1. The Raman spectra do not exhibit characteristic peaks of crystalline V₂O₅. These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V⁴⁺ ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V⁴⁺ ions are located in sites with octahedral symmetry substituting for Ti⁴⁺ ions in the rutile structure. Magnetically interacting V⁴⁺ ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V₂O₅, a partial oxidation of V⁴⁺ to V⁵⁺ is apparent from the EPR results.     

Ni,Pd／Al2O3对丙酮加氢一步合成甲基异丁基酮性能比较

研究了Ａｌ２Ｏ３负载Ｎｉ、Ｐｄ催化剂上丙酮加氢一步合成甲基异丁基酮的反应活性。考察了不同Ｎｉ含量和不同Ｐｄ含量对活性的影响。结果表明，在载体Ａｌ２Ｏ３中加入不同含量的ＳｉＯ２后，会改善载体的性能，Ｎｉ／Ａｌ２Ｏ３催化剂中添加稀土元素Ｌａ或Ｃｅ后可改善催化剂的稳定性。     

V2O5/TiO2 Catalyst Xerogels: Method of Preparation and Characterization

This work describes a modified sol-gel method for the preparation of V₂O₅/TiO₂ catalysts. The samples have been characterized by N₂ adsorption at 77 K, X-ray Diffractometry (XRD), Scanning Electronic Microscopy (SEM/EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). The surface area increases with the vanadia loading from 24 m² g^–1 for pure TiO₂ to 87 m² g^–1 for 9 wt% of V₂O₅. The rutile form is predominant for pure TiO₂ but becomes enriched with anatase phase when vanadia loading is increased. No crystalline V₂O₅ phase was observed in the diffractograms of the catalysts. Analysis by SEM showed heterogeneous granulation of particles with high vanadium dispersion. Two species of surface vanadium were observed by FT-IR spectroscopy: a monomeric vanadyl and polymeric vanadates. The vanadyl/vanadate ratio remains practically constant. Ethanol oxidation was used as a catalytic test in a temperature range from 350 to 560 K. The catalytic activity starts around 380 K. For the sample with 9 wt% of vanadia, the conversion of ethanol into acetaldehyde as the main product was approximately 90% at 473 K.     

Action of a Fluorescent Chemosensor for Cu2+ Encapsulated in Silica Xerogel

The fluorescent chemosensor of the type Ant-NH-O-O-NH-Ant for Cu²⁺ ions has been designed by means of a supramolecular approach, as follows: two anthracene (Ant) fragments as fluorophore subunits have been linked by a noncyclic NH-O-O-NH quadridentate ligand as a receptor. The interaction of Cu²⁺ - receptor is signalled through the enhancement of the anthracene fluorescence when the receptor, i.e., the dioxodiamine chain subunit of the sensor is able to stop a photoinduced electron-transfer mechanism. The experiments with the chemosensor encapsulated in silica xerogel by the sol-gel processing are described.     

Synthesis of Pt, Pd, Pt/Ag and Pd/Ag nanoparticles by microwave-polyol method

Pt, Pd, Pt-Ag and Pd-Ag bimetallic nanoparticles were synthesized in ethylene glycol and glycerol using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It has been observed that PVP is capable of complexing and stabilizing nanoparticles. Mixed clusters were formed by simultaneous reduction of the metal ions. The clusters were characterized using UV-Vis spectra, XRD and dynamic light scattering. To understand the mechanism of formation of mixed nanoparticles, several experimental parameters such asin situ irradiation of mixed metal salts and mixing of individual sols were attempted.     

单层分散型Pd/Ni双金属催化剂的制备及其催化加氢性能

通过置换反应制备了Pd/Ni双金属催化剂,利用X射线衍射、CO化学吸附和吸附H2的程序升温脱附对其进行了表征,并测定了该催化剂对环己烯、苯乙烯和丙酮气相加氢反应的催化性能.结果发现,在这种催化剂中Pd原子单层分散在金属Ni的表面,因而该催化剂表现出比浸渍法制备的相同Pd含量的Pd/Ni-im和Pd/-γAl2O3催化剂更高的催化加氢活性.     

硼离子对铕掺杂SiO2干凝胶发光性能的影响

采用溶胶-凝胶法制备了Al单掺和B，Al共掺的Eu掺杂SiO2干凝胶。利用荧光光谱、IR，XRD，DSC，TG／DTG等技术研究了硼离子、退火温度对样品发光性质的影响。经500℃以上退火处理用248nm激发的样品，产生Eu^3＋离子^5D0→^7FJ的特征发射，^5D0→^7F1的跃迁分裂为两个峰。比较615nm处的发光强度，掺硼酸样品的发光强度是不加硼酸发光强度的3．3倍。这是因为B离子的加入，在材料中形成了Si—O—B键，破坏了网络的对称性，加强了Eu^3＋的红光发射。当退火温度上升到850℃用350nm激发时，样品有很强的Eu^2＋蓝光发射。Al单掺的发射中心在437nm处，发射半峰宽约为70nm，而B，Al共掺样品的发光中心蓝移到425nm处，单掺样品的蓝光强度几乎是共掺样品强度的2倍。这是由于硼酸的加入改变了基质的网络结构，从而导致单掺和共掺样品发射峰位和强度的改变。