RECENT ADVANCES AND FUTURE ASPECTS IN THE LOW-TEMPERATURE CONVERSION OF SATURATED HYDROCARBONS

A brief review on the advances and future aspects in the low-temperature activation of carbon–hydrogen and carbon–carbon bonds in hydrocarbons is presented. Particular attention is given to a catalyst formulation for low-temperature conversion of hydrocarbons. An efficient catalyst design method for low-temperature activation of saturated hydrocarbons has been worked out using metal evaporation techniques. The characteristic property of such catalysts is the presence of metal particles on the surface in an atomically dispersed state. Some of the prepared catalysts cause complete hydrocracking of alkanes and cycloalkanes at 423–463K.     

负载型Pd催化剂

介绍了制备负载型钯催化剂的几种方法，以及它在反应中的应用。阐述了几种催化剂载体的优点，最后对这种催化剂的前提提出展望。     

New synthesis technique of supported ZSM-5 using organo-alumino-silicic gels

This contribution deals with the synthesis of a silicon-rich ZSM-5 obtained from an amorphous organo-alumino-silicic gel. The gel was formed by reacting a mechanical mixture of RHA (rice hull ash), silica’s source, and of natural clinoptilolite, source of alumina, with glycerol during 2 h at 200 °C. After a maturation period of one day at 60 °C, the reaction product was hydrolyzed by a tetra-propyl-ammonium (TPA) solution and then aged for two days at 135 °C in a stainless steel autoclave. After washing and drying, the X-ray pattern showed a well crystallized ZSM-5. The textural analysis of the slowly calcined solid at 500 °C for 4 h, and the SEM micrographies evidence that the zeolite was supported on mesoporous silica. The proportion of both components depends on the tunable hydrolysis conditions.     

EPOXIDATION OF FUNCTIONALIZED OLEFINS OVER SOLID CATALYSTS

Heterogeneous catalytic epoxidation of functionalized olefins in the liquid phase has been reviewed, focusing on catalyst performance and its interrelation with the crucial parameters of the catalytic systems. Efficient catalysts include supported and mixed oxides, framework-substituted (“redox”) molecular sieves, layered-type materials, heterogenized homogeneous catalysts, and some others. Among the various substrates, allylic and homoallylic alcohols, and unsaturated carbonyl compounds have received most attention so far. The great variety of available catalysts enables selective epoxidation of most substituted olefins. The mechanistic understanding of heterogeneous catalytic epoxidation is still underdeveloped, rendering catalyst design rather empirical. A considerable potential for future development lies in the area of “heterogenization” of successful homogeneous catalysts especially for asymmetric epoxidation. Crucial requirements in the development of heterogeneous catalytic epoxidation catalysts are, besides good catalytic performance and cheap oxidant, recyclability and resistance to leaching of the active component. Some of the examples shown in the literature do not fulfill the latter requirement.     

Selective transport of radio-cesium by supported liquid membranes containing calix[4]crown-6 ligands as the mobile carrier

Facilitated transport of Cs-137 across supported liquid membranes (SLM) containing a calix-crown ligand viz. caliz[4]arene-bis(crown-6) (CC), calix[4]arene-bis(o-benzocrown-6) (CBC) or calix[4]arene-bis(napthocrown-6) (CNC) was investigated. The feed consisted of dilute nitric acid solutions while the carrier solutions contained mainly CNC in several organic diluents inside the pores of polypropylene (PP) as well as PTFE flat sheet membranes. PTFE membranes containing CNC in a diluent mixture of 2-nitrophenyloctyl ether (NPOE) and n-dodecane were found to have high stability. Selectivity studies were carried out using simulated high level waste (SHLW) as well as fission products obtained from an irradiated natural uranium target.     

Transport of lithium through a supported liquid membrane of LIX54 and TOPO in kerosene

A mathematical transport model is developed for the extraction of lithium from dilute synthetic solution, simulating geothermal water, using a supported liquid membrane (SLM) of LIX54 (major component is -acetyl-m-dodecylacetophenone) and TOPO (tri-n-octylphosphine oxide) in kerosene. The model is based on fundamental mass transfer and kinetics mechanisms that account for all possible transport resistances. The model is solved numerically and is used to investigate the effect of various extraction conditions and membrane support characteristics. Reasonable agreement is found between the predicted and the experimental results reported in literature.     

Novel mesoporous aluminosilicate supported palladium-rhodium catalysts for diesel upgrading: I. Preparation and characterisation

Bimetallic PdRh (with Pd/Rh mole ratio = 2/1) catalysts supported on a mesoporous aluminosilicate have been prepared and three methods of metal incorporation in the support have been compared: direct incorporation into the synthesis gel, impregnation and ion-exchange. Physico-chemical characterisations (nitrogen adsorption–desorption, hydrogen chemisorption, transmission electron microscopy, X-ray photoelectron and extended X-ray absorption fine structure spectroscopies), as well as simulated coking and regeneration tests are described. The dispersion, metal particle size and the formation of bimetallic particles within the material depend on the method of metal incorporation. Direct incorporation and ion-exchange methods lead to co-existence of PdRh intermetallic aggregates and segregated Pd; on the other hand, the impregnation method leads to the formation of very small and well dispersed PdRh alloy particles, with Pd preferentially located on the alloy particle surface.     

Investigation of the electronic structure and spectroelectrochemical properties of conductive polymer nanotube arrays

New nanoporous polymeric templates supported on conductive substrates (gold-coated Si wafers or ITO-glass) were used to electrosynthesize polypyrrole (PPy) nanotube brushes. The influence of different synthesis conditions (template pore size, electrodeposition potential and temperature) on the resulting structure and properties of the nanotubes were investigated. X-ray photoelectron, Raman and UV-Vis-NIR spectroscopies were used to characterize the doping level, the conjugation length, and the electronic structure of PPy nanotubes. For the first time, we also report on the redox properties of PPy nanotubes using in-situ UV-Vis spectroelectrochemistry.     

The use of palladium nanoparticles supported with MCM-41 and basic (Al)MCM-41 mesoporous sieves in microwave-assisted Heck reaction

A series of supported catalysts has been obtained by grafting of chemically generated palladium nanoparticles onto basic, Cs⁺ ion-exchanged molecular sieves (Al)MCM-41 and onto the non-basic, parent material MCM-41. Catalytic activity of the catalysts has been investigated in the Heck reaction between bromobenzene and butyl acrylate under microwave irradiation. The activity of the bifunctional catalysts (Pd@Cs⁺-(Al)MCM-41) and the activity of Pd@MCM-41 combined with sodium acetate as an external base were considerably higher under microwave irradiation than activities observed for the same catalytic systems under the conventional heating. The Pd@MCM-41/NaOAc system showed higher conversions than the bifunctional catalysts presumably due to a different nature and accessible amount of the base. On the other hand, microwave irradiation seems to increase the rate of aggregation of the metallic particles and thus also catalyst deactivation as compared with the usual heating.