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Herein, we report a Nb/ZnO nanocatalyst for the efficient conversion of levulinic acid, a platform molecule easily obtained from lignocellulosic biomass, to N-heterocycles under mild reaction conditions and the absence of solvent. Nb/ZnO nanocatalysts were synthesized by a mechanochemical-assisted and sacrificial template method, involving orange peel valorization toward nanostructured materials. Two different synthetic approaches, either one-step or two-step, as well as the amount of niobium deposited onto the ZnO support were investigated in order to obtain the nanocatalyst with the optimal catalytic properties. Results revealed the critical role of the niobium for LA conversion. The nanocatalyst containing 10 wt% of niobium and prepared following a two-step approach (10 %Nb/ZnO_2) exhibited the best catalytic performance with a 94.5% of conversion and 97.4% of selectivity towards one specific N-heterocycle compound. This work exemplifies the possibility of sustainable production of value-added compounds, in particular N-heterocycles, from biomass-derived feedstocks by playing with the design of improved catalysts. Importantly, this research area provides sustainable alternatives to the current chemical industry that is heavily dependent on fossil fuels.

The use of a biorefinery co-product, such as humins, in combination with an iron precursor in a solvent-free method yields a catalytic material with potential use in selective oxidative cleavage reactions. In particular, this catalyst was found active in the hydrogen-peroxide assisted oxidation of a naturally extracted molecule, isoeugenol, to high added-value flavouring agent, vanillin. By carrying out the reaction in continuous flow, not only a better understanding of the reaction mechanism and of the catalyst deactivation can be achieved, but also important insights for optimised conditions can be developed. The findings of this paper could pave the way to a more sustainable process for the production of a valuable food and perfume additive, vanillin.

The present work deals with the extraction of phenolic compounds from biomass through microwave-assisted processes. In this case, green walnut shell residues have being studied for the extraction o...

Environmental harmful effects of spent coffee in stream waters pushed our research group to find new applications for this waste material. A new family of magnetic nanocatalysts was synthesized bas...

The mechanochemical incorporation of catalytically active Al species in low loadings was successfully accomplished into the framework of mesoporous silica (SBA-15 and MCM-41) materials using a simple wet milling approach (with aluminum isopropoxide as source of aluminum) and a dry milling approach (using low quantities of Al-containing MOF materials). Characterization data pointed to the successful incorporation of Al species (typically with loadings of ca. 0.2–0.4 wt %) that were mostly tetrahedrically coordinated. Despite such extremely low loadings, the isolated aluminum oxide species exhibited promising activities and stability in selective mild oxidations under various conditions (microwave irradiation and mechanochemistry), including the selective oxidation of benzyl alcohol to benzaldehyde, isoeugenol to vanillin, and diphenyl sulfide to diphenyl sulfoxide, as compared to similarly synthesized impregnated catalysts.

In this work, we report the incorporation of nickel oxide nanoparticles into a metal–organic framework (MOF) structure by a solvent-free mechanochemical strategy. In particular, the zirconium-based MOF UiO-66 was modified with different Ni loadings and characterized using complementary techniques including X-ray diffraction (XRD), N2 porosimetry and X-ray photoelectron spectroscopy (XPS). The catalytic potential of the as-prepared Ni/UiO-66 materials in the hydrogenation reaction of methyl levulinate using 2-propanol as hydrogen donor solvent has been investigated under flow conditions. Under optimized conditions, the 5%Ni/UiO-66 led to the best catalytic performance (70% yield, 100% selectivity to gamma-valerolactone), which could be attributed to the higher content of the Ni species within the MOF structure. The obtained results are promising and contribute to highlighting the great potential of MOFs in biomass upgrading processes, opening the path to the sustainable development of the chemical industry.

The effective design of an active and stable catalytic system was performed by a simple modification of a commercial titania with a low platinum loading. The prepared material was fully characterized by XRD, XPS, N2 adsorption–desorption measurements, ICP-MS, TEM and SEM analyses. Such techniques corroborated the successful incorporation of Pt onto the titania surface, without affecting its original structure, morphology and chemical nature. The obtained TiO2–Pt catalyst was effectively applied in several continuous flow reactions between nitriles and carbonyl containing compounds for amine preparation. Remarkably, conversion of levulinic acid, a biomass derived molecule, was achieved with outstanding conversion (87%) and selectivity (80%) to 1-ethyl-5-methylpyrrolidin-2-one. The catalytic system demonstrated a high stability through 120 min of reaction. Moreover, the effect of the nitrile was investigated by performing the reaction with benzonitrile and ethylcyanoacetate. The TiO2–Pt catalyst was also tested in the conversion of benzaldehyde, displaying remarkable results. The influence of substitution in the aromatic ring was investigated using p-nitro-benzaldehyde and p-chloro-benzaldehyde.

A new eco-friendly approach for the preparation of sustainable heterogeneous palladium catalysts from rice husk-derived biogenic silica (RHP-Si and RHU-Si). The designed heterogeneously supported palladium species (RHP-Si-NH2-Pd and RHU-Si-NH2-Pd) were fully characterized and successfully employed as catalysts for various chemical transformations (C–C bond-forming reactions, aerobic oxidations and carbocyclizations). Suzuki-Miyaura transformations were highly efficient in a green solvent system (H2O:EtOH (1:1) with excellent recyclability, providing the cross-coupling products with a wide range of functionalities in high isolated yields (up to 99%). Palladium species (Pd(0)-nanoparticles or Pd(II)) were also efficient catalysts in the green aerobic oxidation of an allylic alcohol and a co-catalytic stereoselective cascade carbocyclization transformation. In the latter case, a quaternary stereocenter was formed with excellent stereoselectivity (up to 27:1 dr).

Supported Co3O4 nanoparticles on SBA-15 aluminosilicates (Al-SBA-15) with different cobalt loadings (0.5, 1, 5, 10 wt %) were synthesized by ball-milling. The synthesized materials were characterized by different techniques including, N2 adsorption measurements, XRD, TEM, EDX, ICP-MS, DRIFTs of pyridine among others. The catalysts were studied in the microwave assisted benzyl alcohol oxidation as well as in the akylation of toluene with benzyl chloride. Co3O4 catalysts exhibited moderate conversions in the selective oxidation of benzyl alcohol, with a high selectivity towards benzaldehyde. Lewis acidity increases upon the incorporation of cobalt nanoparticles onto the surface of the support which was found to significantly influence the materials in the alkylation of toluene with benzyl chloride. The high active sites accessibility of ball-milling prepared materials leads to high conversions to alkylated derivatives in short periods of time (>99 mol %, 30 min). A direct correlation acidity/activity could not be obtained in the systems, for which nanoparticle sizes and distribution could influence the observed activities.

In this work, two different strategies have been employed to explore the potential valorization of biomass waste. A TiO2-based sample was prepared by a dry-milling strategy, involving orange peel valorization toward nanostructured materials. Subsequently, ruthenium deposition was accomplished by a chemical reduction method to obtain different ruthenium loadings on the titania support. The prepared catalysts were characterized using a multitechnique approach in terms of chemical, structural, and morphological properties. Levulinic acid, a typical model molecule associated with lignocellulosic biomass, was subsequently converted into N-heterocycles in a continuous flow reactor. The prepared Ru-TiO2 systems exhibited outstanding catalytic performance in terms of conversion and selectivity in comparison with Ru/P25 and Ru/C catalytic references. Maximum activity (79% conversion, 85% selectivity to 1-ethyl-2-(ethylideneamino)-5-methylpyrrolidin-2-ol) was achieved for the sample containing 3 wt % Ru, homogeneou...

The conversion of the biomass-derived lipid, lignocellulosic and carbohydrate resources into renewable platform intermediates, chemicals and biofuels has been lately increasing in interest. The mechanistic reaction pathways, like hydro-deoxygenation, decarboxylation and hydrocracking, of the selected palmitic acid, as a model fatty acid, over Ni/ZSM-5 zeolite catalysts were studied. The ZSM-5 material with different Al/Si molar ratios was synthesized via a green template-free hydrothermal synthesis procedure, treated and subsequent functionalised with various Ni metal loadings. However, Ni/Al molar ratio was kept stoichiometric (Ni/Al = 0.5). The characteristic physicochemical properties of composite catalysts were studied by numerous characterization techniques, such as X-ray powder diffraction (XRD), scanning-, as well as high-resolution transmission electron microscopy (SEM/HRTEM), and X-ray photoelectron spectroscopy (XPS). NiO with an average particle size of 10–20 nm was found on ZSM-5 support. The relative Ni/Al atom fraction in Ni/ZSM-5 systems influenced their Lewis/Bronsted acidic sites, as well as the external exposed area of prepared heterogeneous structures. Furthermore, the mentioned morphological parameters affected predominant catalytic routes. Species’ production mechanism, as a consequence of Lewis/Bronsted centre weak/strong acidity, as well as their integral concentration, was proposed, mirroring the observed process kinetics, selectivity and turnover. It was demonstrated that the main obtained products were esters, aldehydes, alcohols, hydrocarbons and gases (CO2, CO…), produced by deoxygenation (e.g. decarbonylation), hydrogenation and cracking, less, though, through isomerisation.

A template-free, simple, effective, and reproducible integrated mechanochemical/microwave promoted methodology has been designed to derive porous silica materials from rice husk waste. Microwave-as...

The efficient electronic wiring of silica-encapsulated laccases has been applied for the first time to the bioelectrocatalytic reduction of oxygen. The synthesized silica/laccase composites were evaluated electrochemically and characterized by UV–vis, Fourier transform infrared (FT-IR), dynamic light scattering, and X-ray photoelectron spectroscopy. FT-IR measurements showed that laccase preserved its native-like structure after the biosilicification process. The one-pot biosilicification synthesis facilitated the accommodation of the enzymes in highly effective orientations for the direct electron transfer of the T1 redox centers. Consequently, the biosilicified laccase deposited on Ni electrodes exhibited an efficient bioelectrocatalytic oxygen reduction, with current densities of up to 0.94 mA/cm2.

The zirconium-based metal organic framework, UiO-66 (Zr), was successfully synthesized via solvothermal method, followed by various characterization including XRD, thermal analysis, N2 physisorption, and TEM. As-synthesized UiO-66 (Zr) was employed in the transformation of methyl levulinate (ML) to γ-valerolactone (GVL) via catalytic transfer hydrogenation (CTH) under continuous flow and various reaction conditions, which gave superior catalytic performance and efficiency as compared to reported catalysts. The obtained results show great potential of applying UiO-66 (Zr) in upgrading biomass derivatives to useful biofuel/chemical products, paving the way for green energy production from renewable resources.

Bioconjugates based on a redox protein and iron oxide magnetic nanoparticles were employed in the catalytic polymerization of ortho-, meta- and para-substituted phenylenediamines at room temperature for the synthesis of carbon-based fluorescent polymers. UV-Vis absorption measurements of the three obtained products showed a red shift compared to the starting materials. These results together with the FT-IR and XPS analyses confirm the successful formation of the polymers. In particular, the component quantification in the C 1s XPS spectra revealed the high proportion of C–N bonds, associated with the oxidative polymerization of the precursors. MALDI-TOF MS analysis was performed in order to determine the molecular weights of the products. The synthesized poly-oPDA, poly-mPDA and poly-pPDA resulted to have a highly green, blue and red fluorescence, respectively. The reusability of the biocatalyst and the effect of the pH were investigated in the reaction for the ortho isomer. The biocatalytic system showed optimum results when the pH was below the enzyme isoelectric point (pI).

A biocatalytic system based on laccase functionalized waste-derived iron oxide nanoparticles (LAC-DA-Fe2O3) was designed by a mechanochemical approach and employed in the electrocatalytic reduction of oxygen. Full characterization of the obtained bioconjugates revealed that the protein adopted a partially unfolded state. The mentioned configuration, together with the geometry coordination changes along the T1 center can be further related to a high bioelectrocatalytic response. A current density up to 2.9 mA cm-2 has been achieved, which is among the highest values reported in literature for laccase functionalized nanomaterials.

The present work demonstrates an efficient continuous flow methodology for the preparation of iron oxide nanoparticles supported on porous silicates. The effect of the iron precursor solution feed rate, the synthesis temperature and time and the support type on the catalyst characteristics were studied, as well on the catalytic activity in the microwave-assisted oxidation of benzyl alcohol with hydrogen peroxide and in the alkylation of toluene with benzyl chloride and with benzyl alcohol. The method appeared to deposit more α-Fe2O3 (hematite) on the support surface compared to similar catalyst materials synthesized using other methods. The catalyst deactivation observed in consecutive reaction cycles was mostly due to the blocking of active sites rather than metal leaching from the catalyst framework.

In this work, we have successfully synthesized a set of titania photocatalytic nanocomposites by the incorporation of different TiO2 content on wheat bran residues. The obtained catalysts were characterized by different techniques including UVeVis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Transmission Electron Microscopy (TEM) while their photocatalytic activity was investigated in the oxidation of benzyl alcohol under UV light irradiation. Benzaldehyde yields were ca. 20%, with conversion in the systems of ca. 33% of benzyl alcohol by using 10%Ti-Bran catalyst, as compared to 33% yield to the target product (quantitative conversion of benzyl alcohol) using commercial pure TiO2 (P-25). The photocatalytic activity results indicate that designed waste-derived nanomaterials with low TiO2 content can efficiently photocatalyze the conversion of benzyl alcohol with relative high selectivity towards benzaldehyde.

Selective and efficient production of vanillin from lignin-derived feedstocks has attracted attention to replace its current manufacturing process. Transition metal-based catalysts supported on mesoporous aluminosilicate were synthesized using a mechanochemical approach and subsequently investigated in vanillin production via the selective oxidation of isougenol. The mechanochemically synthesized catalysts exhibited a high isoeugenol conversion under mild conditions using H2O2 as oxidizing agent. Nb-based catalysts were found to provide the optimum conversion/selectivity under the investigated conditions (69% conversion, 66% vanillin selectivity, 2 h reaction). The synergistic effect between Fe/Nb and Al accounts as important key factor for optimum activity of catalytic systems.

Polysaccharides from natural sources and iron precursors were applied to develop new bio-nanocomposites by mechanochemical milling processes. The proposed methodology was demonstrated to be advantageous in comparison with other protocols for the synthesis of iron oxide based nanostructures. Additionally, mechanochemistry has enormous potential from an environmental point-of-view since it is able to reduce solvent issues in chemical syntheses. The catalytic activity of the obtained nanocatalysts was investigated in both the oxidation of benzyl alcohol to benzaldehyde and in the alkylation of toluene with benzyl chloride. The microwave-assisted oxidation of benzyl alcohol reached 45% conversion after 10 min. The conversion of the alkylation of toluene in both microwave-assisted and conventional heating methods was higher than 99% after 3 min and 30 min, respectively. The transformation of benzyl alcohol and toluene into valuable product in both the oxidation and alkylation reaction reveals a potential method for the valorization of lignocellulosic biomass.

A number of synthesized supported Pd nanomaterials on aluminosilicate supports were investigated in the continuous flow hydroconversion of furfural to a range of furanic derivatives as compared to a commercial Pd/C catalyst. Excellent furfural conversions (>60%) and varying selectivities to products at mild temperatures (90 °C) could be obtained for most catalytic systems, with interesting selectivities to furfuryl alcohol (FOL), 2-methylfuran (MF) and tetrahydrofurfuryl alcohol (THFOL) depending on type of Pd catalyst. A significant deactivation with time on stream was observed for continuous flow synthesized nanomaterials with respect to commercial 5%Pd/C.

Vanillin is one of the most commonly used natural products, which can also be produced from lignin-derived feedstocks. The chemical synthesis of vanillin is well-established in large-scale production from petrochemical-based starting materials. To overcome this problem, lignin-derived monomers (such as eugenol, isoeugenol, ferulic acid etc.) have been effectively used in the past few years. However, selective and efficient production of vanillin from these feedstocks still remains an issue to replace the existing process. In this work, new transition metal-based catalysts were proposed to investigate their efficiency in vanillin production. Reduced graphene oxide supported Fe and Co catalysts showed high conversion of isoeugenol under mild reaction conditions using H2O2 as oxidizing agent. Fe catalysts were more selective as compared to Co catalysts, providing a 63% vanillin selectivity at 61% conversion in 2 h. The mechanochemical process was demonstrated as an effective approach to prepare supported metal catalysts that exhibited high activity for the production of vanillin from isoeugenol.

The acidity of Al-SBA-15 materials functionalized by ball milling with several niobium loadings (0. 25-1 wt.%) as well as with several fluorine loadings (by wet impregnation using NH4F as a precursor) was characterized and materials investigated in the esterification of valeric acid to alkyl valerates. The parent Al-SBA-15 support as well as the modified materials loaded with Nb and/or F have been catalysts synthesized characterized by X-ray diffraction (XRD), N2 physisorption measurements, and diffuse reflection infrared spectroscopy (DRIFT) among others. A special interest was paid on the acidity of the materials that was investigated by temperature-programmed desorption of pyridine. Interestingly, the characterization results for the materials containing fluorine showed up an increase in the acidity strength despite of a reduction in the number of acid sites. The catalytic performance of the as-prepared catalysts was investigated in the microwave-assisted esterification reaction of valeric acid to valerate esters. Thus, while the materials modified with niobium exhibited a lower catalytic activity as compared with the catalytic support (Al-SBA-15), the materials loaded with fluorine either onto Al-SBA-15 or on Nb1%/Al-SBA-15 materials presented enhanced conversion values of valeric acid. Therefore, it can be said that the new acid sites with enhanced strength formed by the incorporation of fluorine boost the esterification of valeric acid with alcohols to form the respective valerate ester.

The formation of furfural from xylose was investigated under heterogeneously catalyzed conditions with sulfated Starbon as a catalyst in a biphasic system. The experiments were perfomed based on the basis of a statistical experimental design. The variables considered were time, temperature and the ratio of aqueous to organic phase. The results indicate that sulfated Starbon is an effective solid acid catalyst for furfural formation. Starbon was characterised by scanning electron microscopy, N2-physisorption, thermogravimetric analysis, diffuse reflectance infrared Fourier transform, Raman spectroscopy and titration with pyridine. The maximum furfural yield and selectivity of 70 mol% were achieved with complete xylose conversion under the optimum experimental conditions. The present paper suggests that functionalized Starbon can be employed as an efficient solid acid catalyst that has significant hydrothermal stability and can be reused for several cycles to produce furfural from xylose.

Graphitic carbon nitride (g-C3N4) was successfully functionalized with a low platinum loading to give rise to an effective and stable catalytic material. The synthesized g-C3N4/Pt was fully characterized by XRD, N2 physisorption, XPS, SEM-Mapping, and TEM techniques. Remarkably, XPS analysis revealed that Pt was in a dominant metallic state. In addition, XPS together with XRD and N2 physisorption measurements indicated that the g-C3N4 preserves its native structure after the platinum deposition process. g-C3N4/Pt was applied to the catalytic conversion of levulinic acid to N-heterocycles under continuous flow conditions. Reaction parameters (temperature, pressure, and concentration of levulinic acid) were studied using 3 levels for each parameter, and the best conditions were employed for the analysis of the catalyst's stability. The catalytic system displayed high selectivity to 1-ethyl-5-methylpyrrolidin-2-one and outstanding stability after 3 h of reaction.

A bio-modified nanomaterial based on horse hemoglobin (Hb) and cobalt oxide magnetic nanoparticles (Co3O4 MNPs) was synthesized using a simple solventless mechanochemical dry milling step. Dopamine (DA) was employed as a robust scaffold to design the stable nanostructures. The nitrogen band (400 eV) in the XPS spectrum, together with zeta potential measurements, supports the presence of Hb in the obtained nanostructure. Additionally, the amide I and amide II bands at 1654 cm−1 and 1545 cm−1 in the FT-IR spectrum suggest that Hb does not undergo changes in its secondary structure. This assumption was also confirmed by Resonance Raman spectroscopy. TEM images reveal a homogeneous distribution of the Hb–DA–Co3O4, with a particle diameter of 10.1 ± 0.2 nm. The functionalised materials exhibited a relevant magnetism, preserved upon functionalisation. The functionalised Hb–DA–Co3O4 nanocomposite was successfully employed in the design of a supercapacitor (specific capacitance average: 115 F g−1) with excellent cycling durability, with over 94% specific capacitance retained after 1000 cycles.

Hydrogenation of levulinic acid (LA) towards γ-valerolactone (GVL) is one of the most promising reactions in the field of biomass valorization to fine chemicals and liquid transportation fuels. Bimetallic Ni-Pt and Ni-Ru supported on ZrO 2 and γ-Al 2 O 3 were successfully utilized in this work as highly active and GVL-selective catalysts for the solvent-free hydrogenation of levulinic acid (LA) using formic acid (FA) as a hydrogen source in a microwave reactor, with results further translated into a continues flow system to prove the reaction mechanism. The supported bimetallic catalysts and their corresponding monometallic counterparts were characterized using N 2 -sorption, elemental analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Under microwave irradiation, 100% selectivity to GVL was achieved using both mono- and bimetallic catalysts. Bimetallic Ni-Ru supported on γ-Al 2 O 3 shows the highest LA conversion (71%) among the studied catalysts. This high activity is attributed to a larger Ru° concentration on the surface of γ-Al 2 O 3 in comparison to ZrO 2 as well as to the textural properties of γ-Al 2 O 3 (i.e., surface acidity, specific surface area). In contrast, ZrO 2 ‐based catalysts exhibited a higher stability with respect to γ-Al 2 O 3 -based after four consecutive runs of reaction.

A simple and effective ultrasound-assisted wet impregnation method was developed for the preparation of magnetically separable TiO2/maghemite-silica photo-active nanocomposites. The resulting nanomaterials were characterized by several techniques and subsequently tested for their photocatalytic activities in the liquid phase selective oxidation of benzyl alcohol. An unprecedented selectivity in organic media (90% in acetonitrile) towards benzaldehyde was achieved at a benzyl alcohol conversion of ca. 50%, being remarkably superior in terms of activity to any other supported transition metal catalysts reported to date as well as commercial titania Evonik P-25 photocatalyst.

Niobium loaded SBA-15 aluminosilicates with different metal loadings (0.5 and 1 wt. %), were mechanochemically synthesized as catalysts for Friedel-Crafts alkylation reactions. The physicochemical properties of these materials were investigated by means of N2 adsorption/desorption measurements, ICP-MS, DRIFT of Py-adsorption among other characterisation techniques. Niobium-loaded materials as well as their respective support displayed a mesoporous nature and the typical structure of SBA-15 materials. The impact of the incorporation of niobium on the aluminosilicate support on the acidic properties was investigated in the alkylation of toluene using benzyl alcohol and benzyl chloride as alkylating agents. The modification of SBA-15 aluminosilicates with Nb particles incorporated a low number of active sites shown to be highly active in alkylation reactions, reaching quantitative conversion in short reaction times (> 10 min), especially for the alkylation of toluene with benzyl chloride, catalysed by Lewis acid sites. The small increase in Lewis acid sites is going to lead to enhanced catalytic activities.

Humins, a by-product of biomass chemical conversion technologies, still present controversies in their structural and mechanistic identification. Traditional studies of the structure and mechanism have focused so far on their syntheses from key molecules (sugars, HMF) and spectroscopic analyses of the as-synthesized oligomers/macromolecules. Herein, we propose structural and mechanism insights based on a novel down-up approach involving the decomposition of humins viacatalytic reactions in continuous flow and interpretation of product molecules. The apparent co-existence of different mechanisms proposed in literature is observed upon product distribution analysis, and the key molecules taking part into humins formation are identified, including furanics, levulinates, sugar-derived molecules, and others. This work shows the complexity of humins formation, and their need of valorization.

Catalyst design and surface modifications of magnetic nanoparticles have become attractive strategies in order to optimize catalyzed organic reactions for industrial applications. In this work, silica-coated magnetic nanoparticles with a core-shell type structure were prepared. The obtained material was successfully functionalized with sulfathiazole groups, which can enhance its catalytic features. The material was fully characterized, using a multi-technique approach. The catalytic performance of the as-synthesized material was evaluated in 1) the oxidation of benzyl alcohol to benzaldehyde and 2) the microwave-assisted alkylation of toluene with benzyl chloride. Remarkable conversion and selectivity were obtained for both reactions and a clear improvement of the catalytic properties was observed in comparison with unmodified &gamma, Fe2O3/SiO2 and &gamma, Fe2O3. Noticeably, the catalyst displayed outstanding magnetic characteristics which facilitated its recovery and reusability.

Magnetically separable nanocatalysts were synthesized by incorporating ironnanoparticles on a mesoporous aluminosilicate (Al-SBA-15) through a mechanochemical grindingpathway in a single step. Noticeably, magnetic features were achieved by employing biomass wasteas a carbon source, which additionally may confer high oxygen functionalities to the resultingmaterial. The resulting catalysts were characterized using X-ray diffraction, X-ray photoelectronspectroscopy, transmission electron microscopy, scanning electron microscopy, porosimetry, andmagnetic susceptibility. The magnetic nanocatalysts were tested in the selective oxidative cleavagereaction of isoeugenol and vanillyl alcohol to vanillin. As a result, the magnetic nanocatalystsdemonstrated high catalytic activity, chemical stability, and enormous separation/reusabilityqualities. The origin of catalytic properties and its relationship with the iron oxide precursor wereanalyzed in terms of the chemical, morphological, and structural properties of the samples. Suchanalysis allows, thus, to highlight the superficial concentration of the iron entities and the interactionwith Al as key factors to obtain a good catalytic response.

Polysaccharides extracted from natural sources can be used as starting material for the preparation of nanoparticle supported composites. A novel family of bio-nanocomposites was mechanochemically synthesized by using niobium oxide and enzymatically produced polysaccharides. The structural, textural and surface properties of nanomaterials, were determined by X-Ray diffraction (XRD), nitrogen adsorption-desorption (N₂ porosimetry), pulse chromatography, infrared spectroscopy (ATR-IR) and dynamic light scattering (DLS). Selective oxidation of isoeugenol to vanillin was carried out to demonstrate the catalytic activity of the Nb-polysaccharides nanocomposites. Interestingly, most of our material showed high conversion of isoeugenol (60&ndash, 70%) with selectivity to vanillin over 40%. The optimum conversion and selectivity were achieved with a reaction time between 8 and 24 h.

Alkyl esters are high added value products useful in a wide range of industrial sectors. A methodology based on a simple sol-gel approach (biosilicification) is herein proposed to encapsulate enzymes in order to design highly active and stable biocatalysts. Their performance was assessed through the optimization of valeric acid esterification evaluating the effect of different parameters (biocatalyst load, presence of water, reaction temperature and stirring rate) in different alcoholic media, and comparing two different methodologies: conventional heating and microwave irradiation. Ethyl valerate yields were in the 80&ndash, 85% range under optimum conditions (15 min, 12% m/v biocatalyst, molar ratio 1:2 of valeric acid to alcohol). Comparatively, the biocatalysts were slightly deactivated under microwave irradiation due to enzyme denaturalisation. Biocatalyst reuse was attempted to prove that good reusability of these sol-gel immobilised enzymes could be achieved under conventional heating.

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) in vapor-phase is economically more viable route if compared to reaction in liquid-phase. To improve the GVL yield in the vapor-phase reaction, the optimization of nickel modified zeolite as bi-functional catalyst (Ni/HZSM-5) was studied. Ni/HZSM-5 materials with fixed Al/Si molar ratio of 0.04 and different nominal Ni/Si molar ratios (from 0.01 to 0.05) were synthesized without the use of organic template and with the most affordable sources of silica and alumina. Materials were characterized by X-ray powder diffraction, SEM-EDX, TEM-EDX, pyridine TPD and DRIFTS, H2-TPR, N2 physisorption and isoelectric point. In the synthesized materials, 61-83 % of nickel is present as bulk NiO and increases with nickel content. Additionally, in all catalysts, a small fraction of Ni2+ which strongly interacts with the zeolite support was detected (10-18 %), as well as Ni2+ acting as charge compensating cations for Bronsted acid sites (7-21 %). Increasing the nickel content in the catalysts leads to a progressive decrease of Bronsted acid sites (BAS) and concomitant increase of Lewis acid sites (LAS). When BAS/LAS is approaching to 1 and at the same time the amount of NiO reducible active sites is around 80%, the bi-functional Ni/HZSM-5-3 catalyst (Ni/Al = 0.59) leads to 99 % conversion of LA and 100 % selectivity to GVL at 320 oC. This catalyst also shows stable levulinic acid hydrogenation to GVL in 3 reaction cycles conducted at 320 oC. The concerted action of the following active sites in the catalyst is a key element for its optimized performance: 1) Ni metallic active sites with hydrogenation effect, 2) Lewis acid sites with dehydration effect and 3) nickel aluminate sites with synergetic and stabilising effects of all active sites in the catalyst.

The continuous flow hydroconversion of furfural to a range of furanic derivatives was carried out using a range of metal-containing heterogeneous catalysts in order to provide insights into the reaction pathways for the hydrogenation of furfural. Most of the catalysts used provided excellent furfural conversion (>60%) and varying selectivities to products at mild temperatures (90 °C), including furfuryl alcohol (FA), 2-methylfuran (2-MF), 2-methyltetrahydrofuran (2-MTHF) and furanic intermediates, depending on the flow conditions and the investigated catalyst.

A solventless mechanochemical approach was employed to obtain a bioconjugate (BSA–DA–Fe2O3) based on bovine serum albumin (BSA) and dopamine (DA) coated iron oxide magnetic nanoparticles. UV-vis measurements of the obtained material showed a distinctive peak at 280 nm which, together with the presence of N on the surface of the nanomaterial (a band at 400 eV in the XPS spectrum) and zeta potential measurements, confirmed the successful immobilization of the protein. Additionally, the presence of two bands at 1652 and 1545 cm−1 in the FT-IR spectra of both BSA and BSA–DA–Fe2O3 and steady-state fluorescence analysis validated that the protein preserved its native-like structure after the mechanochemical milling process. Also the functionalized MNPs preserved their magnetic properties as have been demonstrated by their magnetic susceptibility value.

Biomass conversion into chemicals, materials and fuels emerged in the past decade as the most promising alternative to the current petroleum-based industry. However, the chemocatalytic conversion of biomass and bio-derived sugars often leads to numerous side-products, such as humins. The limited characterization of humin materials restricts their study for possible future applications. Thus, herein photophysical studies on humins and separated humin fractions were carried out using steady-state and time-resolved fluorescence techniques. This paper aims to add to the literature important information for scientists involved in the photophysical studies.

Several catalysts with a 10 wt% loading of zirconium supported on BEA-75 (Si/Al = 37.5) and ZSM-5 (with two different Si/Al = ratio of 15 and 25, respectively) zeolites have been synthesized via ball-milling (mechanochemistry). Samples were characterized by N2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The incorporation of ZrO2 nanoparticles on the zeolitic material lead to the formation of catalysts with the ability of transform methyl levulinate into γ-valerolactone (GVL). However, the selectivity towards GVL was negatively affected due to side reactions caused by both Lewis and Bronsted acid sites on the zeolites employed as support. The role of each acid site in the selected reaction could be addressed by selective poisoning with different bases (pyridine and 2.6-dimethylpiridine). In general, the deactivation of the active sites by the different bases significantly increased the selectivity towards GVL, completely quenching competitive side reactions, pointing out GVL formation can be promoted by Zr(IV) species according to the Meerwein-Ponndorf-Verley (MPV) mechanism.

The current acid-catalyzed conversion of biomass feedstocks yields substantial quantities of undesired by-products called humins, for which applications are yet to be found. This work aims to provide a starting point for valorisation of humins via preparation of humin-based iron oxide catalytic nanocomposites from humins and thermally treated humins (foams) via solvent-free methodologies including ball milling and thermal degradation. The prepared materials were found to be active in the microwave-assisted selective oxidation of isoeugenol (conversions >87%) to vanillin, proving the feasibility to use humin by-products as template/composite materials.

Mechanochemically synthesized Ag-based nanohybrids with unprecedented low toxicity in biomedical applications DOI: 10.1016/j.envres.2017.01.010 URL: http://www.sciencedirect.com/science/article/pii/S0013935116312269 Filiació URV: SI Inclòs a la memòria: SI A simple and innovative mechanochemical approach was employed to synthesize Ag-polysaccharide nanohybrid materials that were proved to exhibit remarkable surface properties and structures for biomedical applications. The synthesized Ag nanomaterials possessed an unprecedented low cytotoxicity against human cell lines A549 and SH-SY5Y as compared to similarly reported Ag nanomaterials due to the stability and low release of Ag+ and high biocompatibility of the nanohybrids.

Pure magnetic metallic nickel was synthesized by a simple and fast microwave-assisted method using a monomode microwave reactor. Nickel chloride was employed as metal precursor, while an environmental-friendly mixture of ethylene glycol and ethanol was simultaneously used as solvent and reducing agent. The parameters combination, for the occurrence of the reaction, of the mixture molar fraction, and the metal precursor concentration was developed. The influence of the temperature and the time of the irradiation was investigated. The best performance (71% yield) was achieved at 250 °C in 5 min of microwave irradiation. The phase and the morphology of the metal were analyzed by X-ray diffraction, scanning emission microscopy, and transmission electron microscopy, while the surface area was determined by nitrogen physisorption. The material exhibited a strong magnetic behavior. The metallic nickel showed high catalytic activity for the hydrogenolysis of benzyl phenyl ether, a lignin model compound, in a microwave-assisted environmental-friendly reaction.

A convenient and environmentally friendly protocol for the preparation of biaryls at room temperature under continuous flow conditions is reported. A simple reductive homo-coupling Ullmann-type reaction was performed in an H-Cube mini using commercially available supported Pd catalysts under mild reaction conditions, with quantitative conversion to target products. Commercial Pd catalysts were found to be highly stable under the investigated reaction conditions, with a minimum Pd leaching into solution after several reaction runs (ca. 20 h on stream).

Petroleum, natural gas and coal supply most of the energy consumed worldwide and their massive utilization has allowed our society to reach high levels of development in the past century. The shift towards a bio-based economy has been recently promoted with ambitious targets to replace an important fraction of fossil fuels by renewable sources within 20 years. Biomass emerged as a highly suitable alternative for this bio-based revolution as an ideal substitute for petroleum in the production of fuels, chemicals and carbon-based materials. Consequently, a number of ongoing efforts have been devoted to biomass conversion/valorization towards valuable products using a number of (bio)catalytic strategies. Based on these premises, the present Special Issue of Catalysts was aimed to provide a number of broad and multifaceted contributions in the field of catalytic biomass conversion towards the production of high added value products from sugars (hemicellulose and cellulose fraction) and lignin as well as related biomass conversion strategies. In this regard, Song et al. contributed to develop an efficient dehydration of fructose to HMF using heteropolyacid salts [1]. Along similar lines, two additional contributions for the Special Issue from Li et al. [2] and Fachri et al. [3] disclosed the catalytic aqueous conversion of glucose and inulin into HMF using Lewis acid and metal salts catalysts, respectively, providing also interesting modelling insights into the proposed chemistries. The produced furanic derivatives in these contributions as well as related compounds (e.g., sorbitol) have also promising prospects to be further upgraded to fuel components for blends. Pizzi et al. provided a nice approach towards high throughput screening of a range of heterogeneous catalysts for the conversion of furfural to bio-based fuel components [4] in a similar way to the approach proposed by Iglesias et al. for the conversion of furfural to furfuryl alcohol via Meerwein-Ponndorf-Verley reduction using Zr-SBA-15 [5], while valuable jet-fuel range hydrocarbons could also be produced from biomass-derived sorbitol using Ni-HZSM-5/SBA-15 catalysts [6]. Such biomass-engineered products have a significant potential to replace current petroleum-derived analogues with improved biocompatibility and a reduced environmental footprint. Levulinic acid and levulinates are related interesting platform molecules that can be derived from biomass and subsequently upgraded towards chemicals and biofuel precursors. Along these lines, Wang et al. proposed the utilization of cheap and environmentally friendly Nb/Al oxide catalysts for the conversion of kiwifruit waste to levulinic acid [7]. Additionally, the direct conversion of carbohydrates into ethyl levulinate using potassium phosphotungstate as efficient catalyst was reported by Zhao et al. [8]. Further conversion of levulinic acid to gamma-valerolactone (GVL) could also take place efficiently on nickel/alumina catalysts [9]. Hydrogenation and hydrodeoxygenation of lignin and lignocellulosic pyrolysis has also been another hot topic in recent times due to the possibility to produce aromatics and cyclic derivatives from biomass. Yi et al. proposed a highly efficient hydrogenation of lignin derived monophenols towards cyclohexanols using Pd/alumina catalysts [10]. Co-pyrolysis behavior of cotton straw mixtures and their catalytic hydrodeoxygenation were also investigated by Hua et al. [11] using Ni-Mo/alumina catalysts. Additional contributions to the Special Issue included the selective production of aromatics from 2-octanol on Zn-exchanged MFI zeolites [12], the electrocatalytic oxidation of cellulose to gluconate on carbon aerogel supported gold nanoparticles anodes [13] and the steam reforming of bioethanol to hydrogen catalyzed by Co/ceria catalysts [14]. The Guest Editors sincerely hope that the results presented as part of this Special Issue of most varied topics can serve as a starting point for further innovations in the catalytic conversion of biomass and look forward to enjoying further improvements in the aforementioned topics and fields in the future.

A proof of concept of laser-assisted heterogeneously catalysed processes at room temperature using silica supported gold nanoparticles is reported. Au/SiO2 nanoparticles were laser-irradiated at 532 nm (SPR maximum absorbance) to catalyse the selected reaction, namely the production of 4-benzoylmorpholine from benzaldehyde and morpholine via amide formation, for which quantitative yields to the target amide were obtained after 3–5 h of reaction. The protocol could also be extended to a tandem oxidation/amidation process which shows the potential of the proposed approach for the promotion of liquid-phase organic reactions at room temperature.

International audience; Carbon-supported Pd nanoparticles have been proved to be efficient dual hydrogenation–oxidation nanocatalysts in both the selective aqueous oxidation of benzyl alcohol and the hydrogenation of furfural in water under microwave irradiation. Nanocatalysts based on trioctylphosphine and triphenylphosphine-stabilized-Pd NPs on oxidized carbon support were found to be the most active. The presence of oxygen groups on the surface of the carbon support, particularly those of acidic character, improve the Pd NPs immobilization as well as the water affinity, and consequently the catalytic performances of the system.

Biomass conversion into useful chemicals, materials and fuels emerged as a promising alternative toward replacing the current production of most of these commodities and specialty products from petroleum feedstocks. Interestingly, not only end products but also side-products from biomass valorization have a significant potential for future research and further conversion into novel families of useful derivatives. Based on such potential, the proposed contribution has been aimed to focus on catalytic insights into the production of three particular biomass-derived side products from the hemicellulosic fraction, namely methyl levulinate (MeL), Furfural and Humins using both homogeneous and heterogeneously catalyzed processes.