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This study explores the effects of liquid-phase and gas-phase oxidation treatments on a low-ash activated carbon (RGC30) and its subsequent use as a metal-free catalyst for the hydrogenation of 1-chloro-4-nitrobenzene. Characterisation of the catalysts was accomplished through N2 and CO2 adsorption at −196 °C and 0 °C, respectively, together with techniques like X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, thermogravimetric analysis (TGA) and temperature-programmed desorption (TPD). In particular, it is observed that the catalytic activity depends on the specific oxidation treatment applied, which leads to the generation of different oxygenated groups on the carbon surface. Consequently, through precise control of oxygen groups via thermal treatment under inert conditions, it is found that the most influential groups for the hydrogenation of 1-chloro-4-nitrobenzene are basic groups incorporating Cdouble bondO bonds, such as quinones and carbonyls. Furthermore, certain groups, like phenols, exhibit a detrimental impact on the catalytic activity.

Carbon materials have emerged as a new generation of catalysts for the crucial industrial hydrogenation of nitroarenes. Activated carbon, known for its cost-effectiveness and facile modifiability, stands out among various carbon materials. This study focuses on the preparation of N and P co-doped carbons for catalysing the hydrogenation of 1-chloro-4-nitrobenzene. Comprehensive characterisation using thermal analysis (TGA-MS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, N2 adsorption at -196 ºC, and ICP-MS was performed. The synergistic effect of N and P was evident, with co-doped carbons outperforming their mono-doped counterparts, underscoring the significance of nitrogen. N,P-codoped activated carbon emerges as a promising, active, stable, and selective metal-free catalyst for the hydrogenation of 1-chloro-4-nitrobenzene, leading to 4-chloroaniline.

Capítulo I. Introducción. El uso creciente de fertilizantes nitrogenados es responsable de la permeación de especies de nitrógeno a través de las capas del suelo y de la contaminación de las aguas subterráneas. El consumo humano de agua con altos niveles de nitratos (el nivel máximo permitido es de 50 mg·L-1) puede producir metahemoglobinemia y hasta cáncer. Los nitratos pueden reducirse a nitritos en el cuerpo humano. El nitrito se combina con la hemoglobina, que contiene el ion ferroso (Fe2+), para formar la metahemoglobina, que contiene la forma férrica (Fe3+) del hierro. La mayor afinidad de la metahemoglobina por el oxígeno conduce a una reducción general de la capacidad de los glóbulos rojos para liberar oxígeno a los tejidos. Cuando la concentración de metahemoglobina es demasiado alta en los glóbulos rojos, se puede producir hipoxia tisular. Esta enfermedad, conocida como el síndrome del bebé azul, es fatal para el recién nacido. Se dispone de procesos fisicoquímicos, biológicos y catalíticos para eliminar los nitratos del agua. Los métodos fisicoquímicos, como el intercambio iónico, la ósmosis inversa y la electrodiálisis, eliminan los nitratos del agua potable, pero los concentran en otros lugares, con el consiguiente problema de eliminación de la salmuera generada de los residuos de nitratos. La desnitrificación biológica transforma los nitratos en nitrógeno molecular, pero es difícil de realizar y puede convertirse en otra fuente de contaminación del agua con bacterias. La reducción catalítica de las especies de nitrato para formar nitrógeno se ha considerado como una tecnología alternativa para la reducción de nitratos. La reducción de nitratos se realiza generalmente con hidrógeno (H2) en presencia de catalizadores metálicos. Se pueden utilizar sistemas monometálicos como Pt o Pd, y también sistemas bimetálicos que combinan un metal hidrogenante (Pd, Pt) y un metal promotor (Cu, In, Sn), dispersados en diferentes soportes con una superficie específica

Nitrogen-doped carbons were obtained by the pyrolysis of polyaniline (PANI), which had been previously synthesized by chemical oxidative polymerization of aniline at two different temperatures (0 and 25 °C). A series of activation treatments with steam under different experimental conditions were carried out in order to develop carbon porosity. It has been shown that the experimental polymerization conditions greatly affect the properties of the N-doped carbons and their reactivity to the steam activation treatment. Carbons were characterized by N2 adsorption at −196 °C, CHNS Elemental Analysis and XPS and their hydrophilicity/hydrophobicity were assessed by water adsorption measurements. The carbons prepared from PANI synthesized at 0 °C showed a more developed porosity and specific surface area than those obtained from PANI synthesized at 25 °C. The increase in the activation temperature produces the loss of the nitrogen heteroatom. Adsorption of water and toluene depends on the amount of surface nitrogen atoms as well as on the pore structure developed in the carbon.

Activated carbon (AC) is a common material of choice in catalysis, as it is a suitable support material for many catalytic reactions. In this work, the effect of cobalt nanoparticles on activated carbon derived from a biomass waste, peach stone, is reported. The presence of cobalt during heat treatments at 900 °C under reductive (H2) and inert (He) atmospheres resulted in the appearance of an intense 2D band in the Raman spectra, indicating a high degree of graphitization. Temperature-programmed reduction and desorption experiments were conducted to evaluate the activation reactions. Quenched solid density functional theory (QSDFT) analysis using N2 adsorption data revealed that cobalt increased pore development in the samples, regardless of the atmosphere (reductive or inert) used.

A series of TiO2 – based photocatalysts have been prepared by the incorporation of 10 wt% of various carbon-based nanomaterials as modifying agents to titania. More specifically, commercial TiO2 P25 was modified through a wet impregnation approach with methanol with four different carbon nanostructures: single-walled carbon nanotubes (SWCNTs), partially reduced graphene oxide (prGO), graphite (GI), and graphitic carbon nitride (gCN). Characterization results (XPS and Raman) anticipate the occurrence of important interfacial phenomena, preferentially for samples TiO2/SWCNT and TiO2/prGO, with a binding energy displacement of 1.35 eV and 1.54 eV, respectively, in the Ti2p contribution. These findings could be associated with an improved electron-hole mobility at the carbon/oxide interface. Importantly, these two samples constitute the most promising photocatalysts for Rhodamine B (RhB) photodegradation, with nearly 100% conversion in less than 2 h. These promising results must be associated with intrinsic physicochemical changes at the formed heterojunction structure, and the potential dual-role of the composites able to adsorb and degrade RhB simultaneously. Cyclability tests confirm the improved performance of the composites (e.g., TiO2/SWCNT, 100% degradation in 1 h) due to the combined adsorption/degradation ability, although the regeneration after several cycles is not complete due to partial blocking of the inner cavities in the carbon nanotubes by non-reacted RhB. Under these reaction conditions, Rhodamine-B xanthene dye degrades via the de-ethylation route.

This study presents an integrated approach combining aqueous phase reforming (APR) and hydrodeoxygenation (HDO) for the hydrotreatment of guaiacol, a model compound representing lignin-derived phenols in pyrolysis bio-oils. The APR process enables in-situ H2 generation, eliminating the need for an external hydrogen source. We examine the interplay between metal species, the Pt-promoting effect on Ni–Pt catalyst supported on activated carbon (AC), and the choice of hydrogen source (methanol or glycerol). Amongst the monometallic catalysts, a 1% Pt/AC catalyst notably achieved over 96% guaiacol conversion at 300 °C with either hydrogen source. Interestingly, when 0.5–1% of the Ni loading is replaced with Pt, the resulting bimetallic Ni–Pt/AC catalysts demonstrate a significant improvement in guaiacol conversion, reaching 70% when methanol is employed as the hydrogen source. Surprisingly, no comparable enhancement in guaiacol conversion is observed when employing glycerol as the hydrogen source. This observation underlines one of the pivotal effects of the hydrogen source on catalyst performance. X-ray photoemission spectroscopy (XPS) pinpointed strong Ni–Pt interactions in the catalyst. It also revealed distinctive electronic features of Ni–Pt/AC, which are favourable for steering selectivity towards cyclohexanol rather than phenol when Pt loading is increased from 0.5 to 1%. Moreover, Pt enhanced catalyst stability by inhibiting the oxidation of Ni sites and mitigating Ni–Pt phase sintering. Overall, our findings offer important insights into integrating APR and HDO processes, the promotion effect of Pt, and the importance of hydrogen source selection in terms of guaiacol conversion and catalyst stability.

This study presents an integrated approach combining aqueous phase reforming (APR) and hydrodeoxygenation (HDO) for the hydrotreatment of guaiacol, a model compound representing lignin-derived phenols in pyrolysis bio-oils. The APR process enables in-situ H2 generation, eliminating the need for an external hydrogen source. We examine the interplay between metal species, the Pt-promoting effect on Ni–Pt catalyst supported on activated carbon (AC), and the choice of hydrogen source (methanol or glycerol). Amongst the monometallic catalysts, a 1% Pt/AC catalyst notably achieved over 96% guaiacol conversion at 300 °C with either hydrogen source. Interestingly, when 0.5–1% of the Ni loading is replaced with Pt, the resulting bimetallic Ni–Pt/AC catalysts demonstrate a significant improvement in guaiacol conversion, reaching 70% when methanol is employed as the hydrogen source. Surprisingly, no comparable enhancement in guaiacol conversion is observed when employing glycerol as the hydrogen source. This observation underlines one of the pivotal effects of the hydrogen source on catalyst performance. X-ray photoemission spectroscopy (XPS) pinpointed strong Ni–Pt interactions in the catalyst. It also revealed distinctive electronic features of Ni–Pt/AC, which are favourable for steering selectivity towards cyclohexanol rather than phenol when Pt loading is increased from 0.5 to 1%. Moreover, Pt enhanced catalyst stability by inhibiting the oxidation of Ni sites and mitigating Ni–Pt phase sintering. Overall, our findings offer important insights into integrating APR and HDO processes, the promotion effect of Pt, and the importance of hydrogen source selection in terms of guaiacol conversion and catalyst stability.

Activated carbons doped with nitrogen and/or sulfur have been obtained by pyrolysis followed of steam activation of a sulfur containing polymer (polythiophene) and two nitrogen-containing polymers (polyaniline and polypyrrole). These polymers were synthesized by oxidative chemical polymerization in aqueous media of their corresponding monomers. The influence of the steam activation on the textural properties and surface chemistry of the carbons has been evaluated and their catalytic activity has been determined in the hydrogenation reaction of 1-chloro-4-nitrobenzene. The degree of conversion in the reaction depends on the development of adequate porosity in the activated carbon (which is determined by the activation conditions) together with the presence of heteroatoms that act as active catalytic sites, with S showing considerably greater effectiveness than N. A compromise between an acceptable level of doping with sulfur and an adequate porosity is necessary, which has been achieved in a carbon obtained from polythiophene pyrolyzed at 900 °C and steam activated at 800 °C for 4 h, with a specific surface area of 742 m2/g and S content of 1.71 at%.

Transition metal phosphides (TMP) have gained great interest as catalysts for hydrogenation reactions due to their physical and chemical properties. Among these reactions, the hydrogenation of nitroarenes to the corresponding anilines is of great industrial importance, as these compounds are precursors of high value-added chemicals. In this work, we present the microwave-assisted synthesis of cobalt phosphide nanoparticles supported on carbon, and its application in the hydrogenation of 1-chloro-4-nitrobenzene. The catalysts were characterised by transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and N2 adsorption at −196 °C. It could be observed that the catalytic activity depends on the reduction temperature, since it determines the crystalline phase of the phosphide. Thus, we found that the most active phase for the hydrogenation of 1-chloro-4-nitrobenzene corresponds to a phosphorus-rich cobalt phosphide obtained at low reduction temperatures.

This study presents an integrated approach combining aqueous phase reforming (APR) and hydrodeoxygenation (HDO) for the hydrotreatment of guaiacol, a model compound representing lignin-derived phenols in pyrolysis bio-oils. The APR process enables in-situ H2 generation, eliminating the need for an external hydrogen source. We examine the interplay between metal species, the Pt-promoting effect on Ni–Pt catalyst supported on activated carbon (AC), and the choice of hydrogen source (methanol or glycerol). Amongst the monometallic catalysts, a 1% Pt/AC catalyst notably achieved over 96% guaiacol conversion at 300 °C with either hydrogen source. Interestingly, when 0.5–1% of the Ni loading is replaced with Pt, the resulting bimetallic Ni–Pt/AC catalysts demonstrate a significant improvement in guaiacol conversion, reaching 70% when methanol is employed as the hydrogen source. Surprisingly, no comparable enhancement in guaiacol conversion is observed when employing glycerol as the hydrogen source. This observation underlines one of the pivotal effects of the hydrogen source on catalyst performance. X-ray photoemission spectroscopy (XPS) pinpointed strong Ni–Pt interactions in the catalyst. It also revealed distinctive electronic features of Ni–Pt/AC, which are favourable for steering selectivity towards cyclohexanol rather than phenol when Pt loading is increased from 0.5 to 1%. Moreover, Pt enhanced catalyst stability by inhibiting the oxidation of Ni sites and mitigating Ni–Pt phase sintering. Overall, our findings offer important insights into integrating APR and HDO processes, the promotion effect of Pt, and the importance of hydrogen source selection in terms of guaiacol conversion and catalyst stability.