Search results for "heterogeneous"
showing 10 items of 460 documents
The oxamate route, a versatile post-functionalization for metal incorporation in MIL-101(Cr): Catalytic applications of Cu, Pd, and Au
2013
Abstract A new consecutive post-functionalization method has been developed for the inclusion of additional metal functionalities in Metal Organic Frameworks (MOFs) through oxamate as chelating agent. This may result in catalytic centers of metal–organic complexes or in controlled formation of metal nanoparticles, demonstrated for Cu, Pd and Au, in the highly stable MIL-101(Cr) framework. In a first post-synthesis step, reduction of the NO 2 -MIL-101(Cr) leads to the formation of NH 2 -MIL-101(Cr). The second functionalization consists of a straightforward condensation of the amino groups of the ligand with ethyl chloro-oxoacetate resulting in the formation of free oxamates attached to the …
Reactivity of arsenic compounds on trapping masses and role of the active phase
2019
The aim of the thesis is to study the reactivity of organic arsenic compounds on various recovery masses and to identify the role of the nature of the active phase and the reaction mechanisms involved. The active phase is composed of metals (Ni, Co, Mo, Cu, Zn, Fe, etc.), pure or in a mixture, in the reduced state or in the sulphide state. The selection of the metallic phases will be carried out by molecular modeling "ab initio", and the synthesis by impregnation of metallic salts on mesoporous aluminas). The reactivity of the solids will be studied in a static reactor on simplified model loads, with kinetic monitoring. The advanced characterization of the solids after synthesis and after r…
Reconsidering TOF calculation in the transformation of epoxides and CO2 into cyclic carbonates
2020
Abstract The combination of Lewis acids and Lewis bases, currently defined as catalysts and co-catalysts (or promoter) respectively, in the reaction between epoxides and CO2 to give cyclic carbonates, is discussed, starting from examples in which the Lewis base was used in larger amount with respect to the Lewis acid. In these cases, turnover frequency (TOF) values have been usually calculated taking into account solely the amount of the Lewis acid employed. The occurrence of two distinct reaction pathways, one catalysed by the sole Lewis base and the other one catalysed by the Lewis acid/Lewis base couple, in which the Lewis acid alone does not play a catalytic role, should bring researche…
New Hybrid Organic-inorganic Multifunctional Materials Based on Polydopamine-like Chemistry
2021
Taking inspiration from the chemistry of dopamine, a simple and economic synthetic approach toward the synthesis of a series of silica-based polydopamine-like materials has been developed. Mild conditions and easy manipulation are the strongest aspects of this methodology. Such hybrid materials were successfully used as recyclable catalysts for Knoevenagel reactions.
Catechol-Functionalized Carbon Nanotubes as Support for Pd Nanoparticles
2022
Carbon nanotubes have been covalently functionalized with catechol moieties through the formation of the corresponding aryl radicals obtained by reacting 4-aminocatechol with isoamyl nitrite. The functionalized multiwalled carbon nanotubes have been in turn used to immobilize Pd(II) ions on its surface forming catechol-Pd complexes, which were reduced to Pd nanoparticles (NPs). The so-obtained hybrid material has been characterized by means of thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). This latter technique allowed to estimate the nanoparticle size (5.7 +/- 2.8 nm) wh…
Decoupled Downlink-Uplink Coverage Analysis with Interference Management for Enriched Heterogeneous Cellular Networks
2016
Heterogeneous cellular networks (HetCNets) offer a promising solution to cope with the current cellular coverage crunch. Due to the large transmit power disparity, while following maximum power received (MPR) association scheme, a larger number of users are associated with macro-cell BS (MBS) than small-cell BSs (SBSs). Therefore, an imbalance load arrangement takes place across the HetCNets. Hence, using cell range expansion-based cell association, we can balance the load across the congested MBS. However, using MPR association scheme, users’ offloading leads to two challenges: 1) macro-cell interference , in which the MBS interferes with the offloaded users, and 2) coupled downlink-uplink…
Analysis of load balancing and interference management in heterogeneous cellular networks
2017
To meet the current cellular capacity demands, proactive offloading is required in heterogeneous cellular networks (HetCNets) comprising of different tiers of base stations (BSs), e.g., small-cell BSs (sBSs) and conventional macro-cell BSs (mBSs). Each tier differs from the others in terms of BS transmit power, spatial density, and association bias. Consequently, the coverage range of each tier BSs is also different from others. Due to low transmit power, a fewer number of users are associated to an sBS as compared with mBS. Thus, inefficient utilization of small-cell resources occurs. To balance the load across the network, it is necessary to push users to the underloaded small cells from …
Enhanced Heterogeneously Catalyzed Suzuki-Miyaura Reaction over SiliaCat Pd(0)
2013
Abstract The SiliaCat Pd(0) solid catalyst can be efficiently employed in the Suzuki–Miyaura cross-coupling of an ample variety of haloarenes, including economically viable chloroarenes. The catalyst can be extensively recycled without loss of activity and with low leaching of valued palladium, opening the route to widespread utilization of the method to afford high yields of biaryls devoid of contaminating by-products.
ChemInform Abstract: Antimicrobial Activity Characterization in a Heterogeneous Group of Compounds.
2010
In this work we carry out a study of pattern recognition to detect the microbiological activity in a group of heterogeneous compounds. The structural descriptors utilized are the topological connectivity indexes. The methods followed are stepwise linear discriminant analysis (linear analysis) and artificial neural network (nonlinear analysis). Although both methods are appropriate to differentiate between active and inactive compounds, the artificial neural network is, in this case, more adequate, since it shows in a test set a prediction success of 98%, versus 92% obtained with linear discriminant analysis.
Description and evaluation of an introductory course to Matlab for a heterogeneous group of university students
2010
This paper presents the experience of the authors in teaching the Matlab™ software to students with different levels of academic training, even though all of them belong to the field of Science. Matlab™ is a worldwide standard in technical programming and computing, and its use is still growing; therefore, it is taught in many different university degree programs (Physics, Mathematics, Engineering, etc.). The course analyzed in this paper contains examples of different fields of knowledge to show the students the versatility and power of this tool. At the end of each course, which consists of 30 h, the students expressed their opinions about the content in a private opinion poll (questionna…