Green chemistry and environmental processes

Funding Information: Acknowledgments: Portuguese FCT—Fundação para a Ciência e a Tecnologia, I.P., under the Scientific Employment Stimulus—Institutional Call (CEECINST/00102/2018) and Associate Laboratory for Green Chemistry—LAQV, financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020) and the Spanish Project ref. RTI 2018-099224-B100 funded by ERDF/Ministry of Science, Innovation and Universities. S.M.-T. also acknowledges the Ramón y Cajal contract (RYC-2019-026634-I/AEI/10.13039/501100011033) from MINECO.publishersversionpublishe

Cobalt oxide-Carbon nanocatalysts with highly enhanced catalytic performance for the green synthesis of nitrogen heterocycles through Friedländer condensation.

A novel series of eco-sustainable catalysts developed by supporting CoO nanoparticles on different carbon supports, highly efficient in the synthesis of quinolines and naphthyridines, through the Friedländer condensation, are reported for the first time. Textural properties, dispersion and location of the Co-phase are influenced by the nature of the carbon support, Co-precursor salt and metal loading, having a significant impact on the catalytic performance. Thus, the presence of the mesopores and macropores in carbon aerogels together with the homogeneous distribution of the active phase favours the formation of product 3a as a function of the metal loading. However, an increase in the metal content when using CNTs indicates the formation of CoO aggregates and an optimal concentration of 3 wt% CoO was observed, providing the highest conversion values. The carbon-based catalysts herein reported can be considered to be a sustainable alternative having advantages such as easy preparation, superior stability and notably enhanced catalytic performance, operating at lower temperature and under solvent-free conditions.pre-print815 K

Heterogeneous gold nanoparticle-based catalysts for the synthesis of click-derived triazoles via the azide-alkyne cycloaddition reaction

PD/BD 135555/2018 IST-ID/263/2019A supported gold nanoparticle-catalyzed strategy has been utilized to promote a click chemistry reaction for the synthesis of 1,2,3-triazoles via the azide-alkyne cycloaddition (AAC) reaction. While the advent of effective non-copper catalysts (i.e., Ru, Ag, Ir) has demonstrated the catalysis of the AAC reaction, additional robust catalytic systems complementary to the copper catalyzed AAC remain in high demand. Herein, Au nanoparticles supported on Al2 O3, Fe2 O3, TiO2 and ZnO, along with gold reference catalysts (gold on carbon and gold on titania supplied by the World Gold Council) were used as catalysts for the AAC reaction. The supported Au nanoparticles with metal loadings of 0.7–1.6% (w/w relative to support) were able to selectively obtain 1,4-disubstituted-1,2,3-triazoles in moderate yields up to 79% after 15 min, under microwave irradiation at 150◦ C using a 0.5–1.0 mol% catalyst loading through a one-pot three-component (terminal alkyne, organohalide and sodium azide) procedure according to the “click” rules. Among the supported Au catalysts, Au/TiO2 gave the best results.publishersversionpublishe

Enhanced catalytic performance of ZnO/carbon materials in the green synthesis of poly-substituted quinolines.

A highly efficient methodology for the selective synthesis of nitrogen heterocycles via Friedländer reaction using carbon materials supported ZnO catalysts under the green chemistry domain is presented. The influence of the physicochemical properties of different carbon supports, in particular an activated carbon (AC), multi-walled carbon nanotubes (MWCNT) and a carbon aerogel (CA), on the catalytic performance is discussed. The developed catalysts are easily prepared by simple incipient wetness impregnation and a subsequent thermal treatment. These ZnO/carbon catalysts showed a great performance in the Friedländer condensation of 2-amino-5-chlorobenzaldehyde and carbonylic compounds with enolizable hydrogens, under solvent-free and mild conditions, affording in all cases selectively a total conversion to the corresponding quinoline. Both the Zn loading in combination with the developed microporosity of the selected carbon supports seem to be the key factors determining the catalytic performance. Yields obtained with ZnO/carbon composites catalysts are superior to those obtained by others widely used in fine chemistry such as, Zn-catalysts supported on mesoporous silica (SBA-15) and Zn-metal-organic-frameworks (MOF).pre-print1162 K

Fitting Biochars and Activated Carbons from Residues of the Olive Oil Industry as Supports of Fe- Catalysts for the Heterogeneous Fenton-Like Treatment of Simulated Olive Mill Wastewater

A series of biochars and activated carbons (ACs) was prepared combining carbonization and physical or chemical activation of cheap and abundant residues of the olive oil industry. These materials were used as Fe-support to develop low-cost catalysts for the heterogeneous Fenton-like oxidation of simulated olive mill wastewater (OMW), the highly pollutant effluent generated by this agroindustry. Commercial ACs were also used as reference. All catalysts prepared were extensively characterized and results related with their performances in the catalytic wet peroxide oxidation (CWPO). Results showed a linear relationship of the textural properties of the catalysts with the adsorptive and catalytic performance, as well as the preferential adsorption and degradation of some phenolic compounds (caffeic and gallic acids) by specific interactions with the catalysts’ surface. Despite the best performance of catalysts developed using commercial supports, those prepared from agro-industrial residues present some advantages, including a smaller catalyst deactivation by iron leaching. CWPO results show that catalysts from physically activated olive stones are the most promising materials, reaching total organic carbon and toxicity reductions of 35% and 60%, respectively, as well an efficient use of H2O2, comparable with those obtained using commercial supports. This approach showed that the optimized treatment of this type of residues will allow their integration in the circular economic process of the olive oil production

Treatment of high-strength olive mill wastewater by combined Fenton-like oxidation and coagulation/flocculation

The efficiency of Fenton/Fenton-like processes on the oxidation of organic matter from real olive mill wastewater (OMW) is described. Tests were performed in lab-scale batch reactors and the influence of different operational parameters was evaluated, namely: type of iron salt, effect of pH readjustments during the reaction, reactants addition method and Fe3+/H2O2 mass ratio. For the Fenton-like system (Fe3+/H2O2) it was found that H2O2 consumption and consequently total organic carbon (TOC) degradation rate are significantly affected by the reagents addition method, especially in earlier stages of the reaction, although the overall extent of TOC removal is not. Results showed that the gradual addition of H2O2 along with pH readjustments during the process led to better chemical oxygen demand (COD) and total phenolic content (TPh) reduction. Operating at pH(0) = 3.0, T-0 = 25 degrees C, [Fe3+]= 1.0 g.L-1 and Fe/H2O2 = 0.04, 34.9% of TOC, 55.7% of COD and 81.4% of TPh were removed after 180 min. The same conditions were applied with the assistance of artificial radiation (photoFenton-like process) with slight organic matter degradation improvement (41.8% of TOC, 63.2% of COD and 83.8% of TPh removals). The catalyst's (ferric chloride salt) ability to act as a coagulant/flocculant after the oxidative process was also checked, being reached a global reduction of 76.7% for COD and 96.4% for TPh after 1 h of sedimentation and no further pH adjustments. Moreover, the effluent's biodegradability (BOD5:COD ratio) after the combined process improved from the initial value of 0.11 to 0.33, and toxicity against the bioluminescent Vibrio fischeri bacteria decreased from 53% to 4%, putting into evidence the possibility of coupling downstream a biological unit so that the final effluent meets legal discharge limits

Heterogeneous Fenton's oxidation using Fe/ZSM-5 as catalyst in a continuous stirred tank reactor

This work is the first known report dealing with the heterogeneous Fenton-like process in a continuousstirred tank reactor. A Fe/ZSM-5 zeolite was used as catalyst for degradation of an azo dye (Orange II, OII)-containing solution.A parametric study was carried out to evaluate the effect of the main operating conditions in the basketreactor performance, namely temperature (in the range 10-70 C), pH (1.5-4.0), feed hydrogen peroxideconcentration - [H2O2]feed (1.75-20.0 mM), contact time - W/Q (10-200 mg min/mL), residence time -tresid (30-180 min) and the size of the catalyst particles (0.25 5 mm), for a OII feed concentration of 0.1 mM. Under the best operating conditions found(pH = 3.0, T = 70 C, [H2O2]feed = 6 mM, W/Q = 200 mg min/mL, dp2 and tresid = 90 min), it was achieved91% of discoloration and 36% of mineralization, at steady-state. Moreover, it was found a removal of29% in terms of the chemical oxygen demand (COD), being worth noting the improvement in the effluentbiodegradability (k0 - oxygen uptake rate - increased from 9.3 to 23.2 mgO2/(gVSS h)) and the fact that thefinal effluent is non-toxic (0.0% of Vibrio fischeri inhibition).The stability of the catalyst performance was checked during five consecutive runs. The crucial factorfor the catalyst long-term use is the leaching of iron, which in all runs reached very low levels (e.g. only0.173 mg/L of iron for the run in the optimized conditions, corresponding to only 0.13% of leaching). Thecatalyst was characterized by different techniques before and after the reactions (namely SEM/EDS andN2 adsorption); textural and chemical transformations during its use can be considered negligible (exceptfor very acidic conditions of pH = 1.5) favoring the catalytic stability of the Fe-zeolite