The fascinating effect of niobium as catalytic promoting agent.

Niobium is a very important element in catalysis, active component of many catalytic systems. But it is not only a major component in many catalytic systems; in addition, it is usually used as a key promoter, because it has a rich complex chemistry and is able to react with many elements forming a wide range of compounds and oxide phases with complex structures. Thus, present contribution makes a brief review on the main industrial catalytic processes in with niobioum have been used as a promoting agent during the last decade. The uses of niobium as main component in the catalytic formulations have not been considered

Groups IV, V and VI metal oxide-containing hydrotalcite catalysts: state of the art on their catalytic applications

The present contribution is a review paper that summarizes the structure, properties and catalytic applications of hydrotalcite based materials when they are modified by the incorporation of oxide metals from groups 4, 5 and 6. The unique properties of hydrotalcites, with a double layer structure able to host ions in the interlayer space and its basicity, together with the properties of transitions metal oxides from groups 4, 5 and 6, leads to materials highly promising as catalysts. The incorporation can form dispersed species of those oxides on the hydrotalcite-like structure, which acts as support, or by the incorporation of those elements into the hydrotalcite structure. The structure and properties of these materials have been reviewed and analyzed, in order to give a detailed description of the main factors that affect the catalytic properties of these interesting materials.Funding for open access charge: Universidad de Málaga/CBU

Carbon materials as template for the preparation of mixed oxides with controlled morphology

Resumen del libro de actas del Congreso: 5th Czech-Italian-Spanish Conference on Molecular Sieves and Catalysis, celebrado en Segovia del 16 al 19 de junio de 2013Bulk mixed oxide catalysts are widely used for many applications, such as catalysts for selective oxidation processes, electrocatalysts for fuel cells, gas sensors, and solid oxide electrolysers for the production of hydrogen. VPO (vanadium and phosphorous oxides) are one of the bulk mixed oxide materials which are of interest nowadays since they are active catalysts for saturated hydrocarbon activation. With the conventional synthesis procedures for preparing bulk mixed oxides is really difficult to control the morphology and the porous structure of these materials. In practice, there are just a few works about the synthesis of mixed oxide materials with controlled morphology. The aim of this work was to describe new approaches for the preparation of VPO mixed oxides materials with spherical morphology. A carbon material was prepared using cellulose as starting material by hydrothermal treatment with phosphoric acid at 200ºC and carbonized at 500ºC. SEM analysis showed that carbon spheres with diameter up to 0.5 m were prepared by this procedure. These phosphorous containing carbon material was impregnated with the appropriate amount of vanadium oxide species in order to obtain a monolayer of VOx species on the surface of the carbon materials following a procedure described previously (1). By this manner, a carbon supported VOx material with spherical morphology was obtained (VPO/Csph). The calcination of this material was optimized in order to obtain VPO spheres with diameter up to 1-2 m and with BET area values close to 100 m2/g. Figure 1 shows a SEM image of this sample (VPOsph). The presence of vanadium pyrophosphate phase, which has been described as the active phase of this catalytic system, was identified by XRD and Raman spectroscopy. Thus, the chemical composition as well as the morphology and porous structure of these new spherical materials makes them quite promising as catalysts

Dissolvable Topical Formulations for Burst and Constant Delivery of Vitamin C

Healthy skin has a high vitamin C concentration that protects against ultraviolet (UV)-induced damage, promotes wound healing, and lowers cancer risk. The present contribution describes two drug delivery systems for topical administration of vitamin C. The electrospun poly(vinyl alcohol) (PVA) nanofiber carrier of vitamin C exhibits a burst release profile (66 mg/g/h followed by 6.3 mg/g/h). In comparison, a new composite PVA nanofiber–molecular capsule delivers vitamin C at a constant rate (8.2 mg/g/h) with a zeroth-order release profile for better therapeutic management. Both delivery systems protect vitamin C and afford increased heat stability. The molecular capsules of β-cyclodextrin with the vitamin C inclusion complex are immobilized on cellulose acetate and electrosprayed onto an electrospun PVA nanofiber mat

A new versatile x–y–z electrospinning equipment for nanofiber synthesis in both far and near field.

This work describes a versatile electrospinning equipment with rapid, independent, and precise x–y–z movements for large-area depositions of electrospun fibers, direct writing or assembly of fibers into sub-millimeter and micron-sized patterns, and printing of 3D micro- and nanostructures. Its versatility is demonstrated thought the preparation of multilayered functional nanofibers for wound healing, nanofiber mesh for particle filtration, high-aspect ratio printed lines, and freestanding aligned nanofibers

Activated carbons as catalytic support for Cu nanoparticles

There are a wide range of catalytic applications for Cu-based nanoparticles materials, since Cu is an abundant and inexpensive metal and Cu nanoparticles possess unusual electrical, thermal and optical properties. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. A previous work have explored the possibilities of SBA-15 (1,2) as support for Cu nanoparticles. In the present contribution, those results will be compared with the use of a carbon material as support, since activated carbon present many advantages with respect SBA, as the high surface area.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Morphological changes of vanadyl pyrophosphate due to thermal excursions

Vanadyl pyrophosphate (VPP) is the active catalytic phase that converts n-butane to maleic anhydride in fixed beds, fluidized beds, and DuPont’s circulating fluidized bed (CFB). The original CFB concept was based on the Mars van-Krevelen reaction mechanism in which the solid lattice contributes all of the oxygen to partially oxidize the n-butane. However, to maintain high activity and selectivity requires that the surface lattice is oxidized; thus, DuPont co-fed pure oxygen through 926 nozzles at three levels in the CFB. Since pure oxygen was fed independently of the butane stream, the gas composition at the nozzle crosses the explosion envelope and the local temperature could rise several 100 ∘C. Furthermore, the gas composition in the exhaust pipe downstream of the cyclone was within the explosion envelope. The temperature in these two regions periodically exceeded 700∘C, which was sufficiently high to deactivate the catalyst and turn it black. Here, we reproduced the high temperature conditions to examine the changes in catalyst morphology. A TA-Q500 heated the fresh catalyst to 800 ∘C under nitrogen and air flow. The VPP catalyst turned black above 700 ∘C in air but not in nitrogen. The catalytic surface area and pore volume of the fresh calcined catalyst decreased from 23 m2g−1 and 0.14 cm3g−1 to 12 m2g−1, and 0.09 cm3g−1 in the equilibrated catalyst. New bonds form and the active VPP reacts with silica to form VO(P2SiO8)

Kinetic study of propane ODH on electrospun vanadium oxide-based submicron diameter fiber catalyst

A rigorous kinetic study of the oxidative dehydrogenation (ODH) reaction of propane on a vanadium oxide-based submicron diameter fiber catalyst has been developed. The proposed kinetic model simulates the conversion- selectivity profiles, the surface coverage of the different adsorbed species and the oxidation state of the cata- lyst for the studied operating conditions of temperature, space–time and inlet partial pressures of propane and oxygen. The activation energy of the rate determining step (RDS), the first hydrogen abstraction from propane, is 104 kJ⋅mol 1. The model predicts that although the reaction seems to be pseudo-zero order with respect to oxygen in a broad range of conditions, the catalyst may not be fully oxidized during reaction. The accuracy of the model when predicting the oxidation state of the catalyst has been experimentally confirmed by analyzing the catalytic fixed bed after reaction. The reduction degree of the catalyst will depend on its intrinsic chemical nature and reaction conditions, increasing with the space–time and in detriment of the overall reaction rate. Conse- quently, the propane turnover frequency (TOF) will also depend on the reaction conditions and space–time, even changing along the fixed-bed reactor.Funding for open access charge: Universidad de Málaga / CBU

VPO catalysts using activate carbons as template. ODH of propane

Resumen comunicación a congreso internacionalVanadium phosphates is one of the most studied heterogeneous catalytic systems due to its properties to activate alkanes. In fact, they are used commercially for the oxidation of n-butane to maleic anhydride and experimental studies have shown that vanadium phosphates are also effective catalysts for propane and pentane partial oxidation. The most active phase of VPO catalysts is made up of a well-crystallized (VO)2P2O7, which is considered to possess unique structural and surface features to allow the activation of alkanes. This phase is generally generated by calcination of the precursor VOHPO4·0.5H2O. A new strategy to obtain this precursor has been analyzed in this study. The proposed methodology is simple and low cost and implies the use of a carbon material as a template to obtain the mixed oxide with a developed porous structure. Several VPO catalysts were prepared by using different activated carbons, which were obtained from lignocellulosic waste, as template. The carbonaceous materials were obtained by chemical activation with phosphoric acid of olive stones and by liquid phase impregnation of zeolite templates with lignin solution. Both porous carbons were impregnated with a solution containing the dissolved vanadium phosphate precursor. This solution was prepared by mixing water with ammonium metavanadate, phosphoric acid and oxalic acid in the precise amounts to obtain a V/P atomic ratio of 1. Finally, in order to remove the carbonaceous matrix and to obtain the active phase (VO)2P2O7, the impregnated samples were calcined in air at 500 ºC for 6 h. The presence of the desired active phase (VO)2P2O7 was confirmed by using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and X-ray diffraction (XRD). The porous structure was characterized by N2 adsorption-desorption at -196 ºC. Catalytic tests were performed in a fixed bed microreactor under a gas flow mixture (W/F = 0,075 g·s·mL-1) containing propane, oxygen and helium (45.7/11.4/42.9 vol. %). The reaction was studied at different temperatures from 500 to 575 ºC. The use of a carbon as a template results in VPO catalysts with relatively high development of the porous structure (apparent surface area of 40 m2/g), compared to those reported in the literature. These catalysts present propane conversions up to 22 % with selectivities to propylene as high as 60 %. It is noteworthy that selectivities to ethylene about 25% were also observed, which is a highly valued product in the chemical industry. These results are comparable to those reported in the literature for supported vanadium oxides at higher space times.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Advances in electrospun composite polymer/zeolite and geopolymer nanofibers: A comprehensive review.

Política de acceso abierto: https://v2.sherpa.ac.uk/id/publication/16964Electrospinning is widely recognized as an efficient, simple, and cost-effective technique for producing nanofibers. It has successfully led to the fabrication of various ultrafine polymer composites. This method has spurred extensive research in fields such as medicine, electronics, chemistry, and physics, where producing materials via electrospinning is very promising for revolutionizing many fields. This paper presents a comprehensive review of the latest research and developments on electrospun composite polymer/zeolite nanofibers and geopolymers. The study examines processing, structure, characterization, and potential applications. Detailed information on these composites, including their specific electrospinning conditions, has been thoughtfully summarized in this work. Furthermore, we address important concerns related to the technology’s limitations and existing research challenges. In the studies analyzed, a diverse range of polymers was employed, the most frequent were polyvinyl alcohol, polycaprolactone, and polylactic acid. The applications of zeolite/polymer composites were equally varied, encompassing fields such as catalysis, filtration, adsorption, and pesticide residue analysis in food samples. Moreover, these composites were found to be useful in the medical sector, including applications in dental tissue engineering and for treating bacterial infections.Part of this study was funded by project TED2021-130756B-C31 MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” by the European Union Next GenerationEU/PRTR). Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES) Project Number 88881.142487/2017-01; CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico (Grant 401697/2022-3