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1. HETEROGENEOUS CATALYSIS

Dehydration of sugars to furfurals and its valorization via different reactions:

Hydrolysis of lignocellulosic biomass can lead to the obtention of hexoses (glucose and fructose) and pentoses (xylose); then, the dehydration of these sugars to 5-hydroxymethylfurfural (HMF) and 2-furfural (FAL). Both HMF and FAL are building blocks widely applied to the next generation of biofuels, bio-based plastics, adhesive monomers, ecological adhesives, coating agents and fine chemical products. In our research group different reactions for the transformation of furfurals have been employed, some examples of these reactions are presented as follows:

a. Multicomponent reactions (MCR): We used the versatility of the furfural molecule as building block in the Biginelli and Hantzsch-type multicomponent reactions to obtain different polyfunctional nitrogenated heterocycles using green protocols, including a solvent-free reaction and a recyclable solid acid with magnetic properties (Fe3O4/SiO2-SO3H), this solid is easily separable from the reaction medium.

b. Reductive Amination: We prepare bifunctional catalysts, which can favor the reductive amination of furfural with amino or nitro compounds. This reaction should proceeds slowly without the acidic sites; however the acid sites should protonate carbonyl group making the carbonylic carbon a better electrophile and activates it more easily towards nucleophilic attacks in the first step which favors the hydrogenation of the imine and consequently the desired amine formation.

c. Selective Hydrogenation: Our researchers have studied the liquid phase furfural hydrogenation using Ir catalysts. Ir catalysts displayed a high activity and selectivity in the hydrogenation of C=O group of α, β-unsaturated aldehydes. The SMSI effect has been broadly studied for explain the catalytic behavior of this type of catalysts and the selectivity to unsaturated alcohol.

d. Oxidation of HMF: Recently, we start the study the oxidation of HMF with bimetallic catalysts (Au-Me) for obtain 2,5-furandicarboxylic acid (FDCA).

Solids developed

a. Acid solid catalysts with magnetic properties: To address the issue of reuse, sulfonated solid catalysts and heteropolyacids micellar with magnetic properties have been used. The paramagnetic properties of the solids allow easy separation of the catalyst in the reaction mixture using an external magnetic field. Aggregation of the particles can be avoided by the use of stabilizers or by the formation of a passive layer of silica or other oxide on the surfaces of nanoparticles (NPs) of iron oxide. These solids have been employed in multicomponent reactions.

b. Au-Me (Me: Ir, Pt) catalysts. Our group has studied the addition of gold over metallic catalysts (group 8-10) for increases the reduction process in distinct α, β-unsaturated carbonyl aldehydes. The possibility of that the addition of Au may modify the electronic properties of Me (group 8-10). We demonstrated that in Ir-Au/TiO2 catalysts there an electronic charge transfer from the iridium atoms to the gold.
 
2. CATALYSIS INDUCED BY METALS AND METALLIC OXIDES

 

a. Catalysis by metals

b. Acid catalysis 

c. Bifunctional catalysis 

 

3. ENANTIOSELECTIVE CATALYSIS


Metal salen complexes, such as the Jacobsen’s catalyst, have attracted much interest in the last few decades because of their unique catalytic activity, especially as non- functionalized olefin epoxidation catalysts, in the presence of terminal oxidants like iodosylbenzene (PhIO), sodium hypochlorite (NaOCl), and meta-chloroperoxybenzoic acid (m-CPBA) [1].

 
Salen ligands of Jacobsen’s catalyst bind manganese ions through four atoms, two nitrogen and two oxygen atoms. This tetradentate-binding motif is reminiscent of the porphyrin framework in the heme-based oxidative. Nonetheless, salen derivatives are more easily synthesized than porphyrins and their structures are more easily manipulated to create an asymmetric environment around the active metal site. However, this homogeneous catalyst cannot be separated from the reaction media and, subsequently, cannot be recycled.


Moreover, it suffers deactivation in homogeneous phase by either formation of dimeric μ-oxo-manganese (IV) species, which are inactive in the olefin epoxidation or oxidative degradation of the salen ligand through the imine group. The conventional ways to solve t On the other hand, the immobilized catalysts usually lead to partial loss of activity and/or enantioselectivity as compared to their analogous homogeneous catalysts hese problems are to immobilize Jacobsen-type catalysts onto solid supports. Reports on the heterogenization of Jacobsen-type catalysts have been centered on their covalent binding to organic polymers and on their encapsulation, entrapment, adsorption and covalent attachment to porous inorganic supports, such as zeolites, Si-MCM-41, Al-MCM-41 and clays, and also on activated carbon. Unfortunately, the catalytic activity of the recovered catalyst decreases during the catalytic tests of reuse.


It is found that isolating Mn(III) salen complexes onto a solid support increases the catalyst stability by suppressing the formation of inactive dimeric μ-oxo manganese(IV) species. However, the deactivation route by ligand oxidation cannot be avoided by anchoring the catalyst to a solid matrix, since it depends on the oxidation conditions. It is well known that in homogeneous phase, the catalyst acquires an appropriate geometric configuration that promotes both, the oxygen transfer from oxo-Mn(V) active species to the double bond of olefin and chiral induction [11].


In contrast, when the catalyst is not free to move due to the influence of the solid support, an inappropriate geometrical configuration can be obtained. In order to solve the previous drawbacks, in our group an alternative convenient and economical strategy is under development. It consists in adjust the solubility of homogeneous catalysts by varying the reaction conditions, resulting in the direct separation of the catalysts during the reaction. We found that using dimethyldioxirane (DMD) as oxidizing agent for the epoxidation of various olefins (cis-ethyl cinnamate, R-(+)-limonene, chromenes derivatives) with Jacobsen-type catalysts could facilitate product isolation and catalyst recovery by segregating the catalysts into a solid phase during the reaction. Now day, we are interesting to expand this approach to other olefin types (styrene derivatives), as well to increase the catalyst stability during the reuse. 




 

4.HETEROGENEOUS PHOTOCATALYSIS

In the last years, heterogeneous photocatalysis has appeared as an efficient and eco-friendly remediation technology; thus, a wide variety of VOCs in gas phase are decomposed on the UV-irradiated TiO2 surface under ambient conditions without any chemical additives.

Currently, photocatalysis based on titanium dioxide (TiO2) has also demonstrated to be a good alternative in the treatment wastewater polluted with microorganisms and organic compounds coming from different industrial and domestic activities. This less expensive technology leads to recover water sources by using artificial or direct solar light, which are available anywhere in the world.

The Grupo de Catálisis de la Universidad Pedagógica y Tecnológica de Colombia has focused its efforts on the development of new materials and alternatives for the improvement of the photocatalytic processes and reaction systems used in environmental remediation. 
 

 

 

Información actualizada: 24 de mayo de 2017

 


 
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