Papers by F. Maldonado-Hódar
Journal of Chemical Technology & Biotechnology, 2018
The aim of this study is to test different supports to deposit Au nanoparticles and determine the... more The aim of this study is to test different supports to deposit Au nanoparticles and determine the most suitable for Orange II (OII) dye degradation by a photo-assisted wet peroxidation (PWPO) process. The catalysts used (Au-Fe 2 O 3 , Au-TiO 2 , Au-ZnO and Au-Al 2 O 3) were prepared by the deposition-precipitation method; a reference catalyst from World Gold Council, hereafter denoted as Au-Fe 2 O 3 * , was also used for comparison. The catalysts were characterized in terms of surface area (S BET), gold nanoparticles size, Au loading and Au oxidation state using several techniques (namely, nitrogen adsorption at-196 ºC, X-ray photoelectron spectroscopy-XPS, and High resolution transmission electron microscopy-HR-TEM). Several runs were carried out for each material, to evaluate its efficiency in OII dye degradation by the PWPO process. All catalysts reached OII dye removals of >96% and considerable total organic carbon (TOC) degradation-between 58.4 to 80.5%. The materials had negligible Au leaching, showing large stability. For the catalyst with better performance (Au/Al 2 O 3), a parametric study was carried out to assess the effect of different variables in dye and TOC removals. Under the best conditions found an excellent efficiency of the advanced oxidation process was obtained. A simulated industrial acrylic dyeing effluent was also treated by PWPO and a very good performance was reached, with removals up to 100, 72.4 and 70.0% for color, TOC and COD, respectively, with only 2 h of reaction. Moreover, there was an improvement in the biodegradability and a non-toxic effluent was generated.
Catalysis Today, 2017
The degradation of a model dye compound (Orange II) was evaluated by wet peroxide oxidation using... more The degradation of a model dye compound (Orange II) was evaluated by wet peroxide oxidation using gold supported on alumina (Au/Al 2 O 3) as a catalyst, in a slurry batch reactor. The material was prepared by the deposition-precipitation method, which yielded nanosized gold particles well dispersed on the support, with a mean particle size of 3.6 nm. It was concluded that both adsorption and catalyzed oxidation (via hydroxyl radical formation) contribute to the dye removal. The catalyst was reused for five consecutive cycles, with no Au leaching being detected into the solution (detection limit <0.5 mg/L), showing its high stability. This was also confirmed by textural and chemical characterization of the fresh and used materials. A parametric study was carried out to assess the influence of the most important variables (hydrogen peroxide amount, catalyst concentration, reaction pH and temperature) in both dye and total organic carbon (TOC) removal. In all runs performed, gold leaching was not detected. In the best operating conditions found, high efficiencies were reached (i.e., ∼100% of dye removal, 50% of TOC reduction, 42% of chemical oxygen demand-COD-elimination). The treatment improved the biodegradability of the effluent and the obtained waste remained non-toxic (as inferred from the inhibition of Vibrio fischeri test). A simulated industrial acrylic dyeing effluent was also treated by wet peroxidation. It was found that the gold support on alumina catalyst was stable and achieved considerable removal of color (33%) and organic compounds (42% for TOC and 50% for COD) and improved the biodegradability of the wastewater.
Industrial & Engineering Chemistry Research, 2017
The degradation of Orange II was evaluated by wet peroxide oxidation using gold nanoparticles sup... more The degradation of Orange II was evaluated by wet peroxide oxidation using gold nanoparticles supported on Fe 2 O 3 , TiO 2 , ZnO and Al 2 O 3 as catalysts, in a slurry batch reactor. Materials were prepared by the same deposition-precipitation method, which yielded welldispersed nanosized gold particles (2.2 to 5.5 nm). A commercial catalyst (Au/Fe 2 O 3 supplied by the World Gold Council) was used as reference, for comparison. It was demonstrated that the efficiency of wet peroxide oxidation for the Orange II removal and organics mineralization depends on the type of oxide used and the loading and diameter of gold. The Au/Al 2 O 3 material, with the highest BET surface area, showed the highest turnover frequency (TOF) value, and also higher total organic carbon (TOC) and Orange II removals. The catalysts were reused for consecutive cycles, with no Au leaching being detected into the solution, showing their high stability. This stability was confirmed by textural and chemical characterization of the fresh and used materials.
Catalysis Communications, 2017
Au nanoparticles (2.2 nm) deposited on TiO 2 by the deposition-precipitation method were found to... more Au nanoparticles (2.2 nm) deposited on TiO 2 by the deposition-precipitation method were found to be extremely active and stable for CO 2 hydrogenation to CO. A CO 2 to CO yield up to 50% was achieved at temperatures as low as 400 ºC for at least 60 h. Under identical reaction conditions, both bare TiO 2 and Au/Al 2 O 3 were practically inactive for CO 2 reduction. The unique combination of the Au nanoparticles and TiO 2 supportlinked to a peculiar synergistic effectis essential to the enhanced CO 2 reduction activity.
Molecular Catalysis, 2017
The aim of this work is to explore the influence of the support (M x O y : Al 2 O 3 , CeO 2 , Fe ... more The aim of this work is to explore the influence of the support (M x O y : Al 2 O 3 , CeO 2 , Fe 2 O 3 , TiO 2 and ZnO) on the physicochemical characteristics and the N 2 O decomposition (deN 2 O) performance of supported gold nanoparticles (Au/M x O y). Both the bare oxides and the Au/oxide catalysts were characterized by several methods (BET, XRD, SEM, HR-TEM, XPS and H 2-TPR) and comparatively evaluated in order to gain insight into the structure-property relationships. A close correlation between the catalytic performance and the redox properties (reducibility and oxygen mobility) of oxide carriers was revealed on the basis of a redox type mechanism, resulting in the following deN 2 O activity order: Fe 2 O 3 » CeO 2 > ZnO > TiO 2 > Al 2 O 3. In contrast, no significant effect of textural/structural characteristics on the deN 2 O performance was found. Addition of gold to the oxides facilitates the surface oxygen reduction and, consequently, the deN 2 O performance, without, however, affecting the activity order. When oxygen is in excess in the feed stream (N 2 O + O 2) a slight inhibition was observed for all samples, due to the competitive adsorption of both reactants on the catalyst surface. On the basis of a kinetic analysis the superior performance of Fe 2 O 3based samples can be attributed to the optimum compromise between the activation energy and the pre-exponential factor under the present conditions.
International Journal of Hydrogen Energy, 2016
Au/TiO 2 catalysts were synthesized by three different methods, with different gold loadings, and... more Au/TiO 2 catalysts were synthesized by three different methods, with different gold loadings, and tested for the low temperature wateregas shift (WGS) reaction. Gold was loaded by a Double Impregnation Method (DIM), DepositionePrecipitation (DP) and Liquid Phase Reductive Deposition (LPRD). For each procedure, catalysts were synthesized with three different loadings of gold, up to ca. 2.5 wt.%, identified as 1, 2 or 3 for low, intermediate or high amounts of nanosized gold, respectively. The prepared materials were characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Temperature Programmed Reduction (TPR) and Absorption Atomic Spectroscopy (AAS). The performance of the catalysts was compared based on the CO conversions (X CO) and turnover frequencies (TOFs) obtained in the WGS reaction. The two best catalysts obtained were Au/TiO 2-DP-3 and Au/TiO 2-LPRD-3. Both showed X CO and TOF values higher than that of the commercial Au/TiO 2-WGC (supplied by the World Gold Council). Although TOF was higher for Au/TiO 2-LPRD-3 (at 250e300 C), this sample suffers deactivation. The Au/TiO 2 DP-3 material was thus selected as the best synthesized catalyst, with a X CO z 85% at 300 C (X CO of the WGC sample was z52% at 300 C). The Au/TiO 2 DP-3 material has small gold nanoparticles before and after use, which can account for the improved catalytic activity, well known to be related with gold nanoparticle size. However, stability was found to be better for the WGC sample.
Journal of environmental management, Jan 23, 2015
This work deals with the treatment of a recalcitrant effluent, from the dyeing stage of acrylic f... more This work deals with the treatment of a recalcitrant effluent, from the dyeing stage of acrylic fibres, by combination of the heterogeneous Fenton's process in a continuous stirred tank reactor (CSTR) with biological degradation in a sequential batch reactor (SBR). Three different catalysts (a commercial Fe/ZSM-5 zeolite and two distinct Fe-containing activated carbons - ACs - prepared by wet impregnation of iron acetate and iron nitrate) were employed on the Fenton's process, and afterwards a parametric study was carried out to determine the effect of the main operating conditions, namely the hydrogen peroxide feed concentration, temperature and contact time. Under the best operating conditions found, using the activated carbon impregnated with iron nitrate, 62.7% of discolouration and 39.9% of total organic carbon (TOC) reduction were achieved, at steady-state. Furthermore, a considerable increase in the effluent's biodegradability was attained (BOD5:COD ratio increase...
Applied Catalysis A: General, 2014
The low temperature water-gas-shift reaction has been studied over a series of nanosized Au/Fe2O3... more The low temperature water-gas-shift reaction has been studied over a series of nanosized Au/Fe2O3 catalysts. The effect of the synthesis method on the catalytic activity has been analysed. A series of catalysts with different Au loadings has been prepared by different methods: Deposition-Precipitation (DP), Liquid Phase Reductive Deposition (LPRD) and Double Impregnation Method (DIM). The Au/Fe2O3 catalysts prepared by DP showed the highest CO conversion. The catalysts were characterised by hydrogen temperature programmed reduction (TPR-H2), high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction and X-ray photoelectron spectroscopy. TPR-H2 analysis revealed that gold promotes the reducibility of the Fe2O3 support, which is crucial in this redox reaction. HRTEM evidences a very good dispersion of gold over the iron support, with nanoparticles in the range 2.2-3.1 nm for the DP and LPRD series, and a negligible increase in the average particle size of the used samples. For the DIM series, much larger Au particles (~6.6 nm) were obtained.
ChemCatChem, 2017
Carbon aerogels doped with transition metals are found to be efficient and reusable catalysts inv... more Carbon aerogels doped with transition metals are found to be efficient and reusable catalysts involved in the selective synthesis of quinolines. Interestingly, we report herein the first aldol‐based reactions, particularly the Friedländer reaction, catalyzed by zero‐valent metal nanoparticles, the activity of which is mainly related with the nature of the metal. Co0‐ and Cu0‐doped aerogels resulted in the most active catalysts. Resorcinol–formaldehyde Cu‐doped and steam‐activated (RFCuS) aerogel represents an alternative nanocatalyst to the metal–organic framework CuBTC showing similar reactivity but superior thermal and chemical stability. The unusual reactivity observed could be explained by the in situ generation of the Co0–CoII catalytic system formed in the activation of ethyl acetoacetate.
Journal of Molecular Catalysis A: Chemical, 1996
The effect of doping NiMoO4 with increasing Cs concentrations (1, 3 and 6%), on the crystalline s... more The effect of doping NiMoO4 with increasing Cs concentrations (1, 3 and 6%), on the crystalline structure, chemical nature and catalytic behaviour for the oxidative dehydrogenation of butane, was studied. The atomic ratio Mo/Ni = 1 and the cesium concentration were checked by several techniques (X-ray photoelectron spectroscopy, atomic absorption, inductively coupled plasma spectroscopy). The structural study of the α-
The degradation of Orange II dye (OII) by a heterogeneous Fenton-like process was studied using a... more The degradation of Orange II dye (OII) by a heterogeneous Fenton-like process was studied using a catalyst with 5 wt.% of iron after ion-exchange in a Na-Y zeolite support. The catalyst was characterized by X-ray diffraction (XRD), N2 adsorption, atomic absorption spectroscopy and X-ray fluorescence (XRF). The effect of the initial concentrations of H2O2 and OII, pH and temperature on the degradation rate of OII was investigated by carrying out experiments in a batch reactor. The OII concentration histories (i.e., concentration evolution along reaction time) were described by a simple semi-empirical kinetic model, based on the Fermi's equation, which captures simultaneously the influence of all the reaction conditions with a few adjustable parameters. The adherence of the model to the data was remarkable, and the effect of the operating conditions on the obtained fitting parameters-apparent rate constant and transition timewas analyzed.
Industrial & Engineering Chemistry Research
Journal of Materials Chemistry A
A series of carbon xerogels doped with different percentages of TiO2 has been studied as a tentat... more A series of carbon xerogels doped with different percentages of TiO2 has been studied as a tentative means of preparing electrodes for supercapacitors.
Journal of environmental management, Jan 25, 2015
The denitrification of polluted water was studied by using supported E-coli bacteria. The physico... more The denitrification of polluted water was studied by using supported E-coli bacteria. The physicochemical characteristics of supports and the influence of these properties on the bacteria performance were analyzed. Inorganic supports oxides and zeolites were selected in order to cover a wide range of porosity and surface chemical properties and the denitrification process systematically studied. Consecutive denitrification cycles in batch experiments and the toxicity of supports were also analyzed. The acidity of supports provokes a slower reduction processes, favoring also a high concentration of intermediate nitrites in solution for longer periods. The [Formula: see text] reduction is faster than the [Formula: see text] one, being also less influenced by the support characteristics. Anyway, the total denitrification is reached in all cases. The best performance was obtained with bacteria supported on mesoporous and non-acid silica support.
Separation and Purification Technology, 2015
This work is the first known report dealing with the heterogeneous Fenton-like process in a conti... more This work is the first known report dealing with the heterogeneous Fenton-like process in a continuous stirred 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 basket reactor performance, namely temperature (in the range 10-70 o C), pH (1.5-4.0), feed hydrogen peroxide concentration-[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< dp1 < 0.60, 0.60 < dp2 < 0.80 mm and as pellets, dp3 > 5 mm), for a OII feed concentration of 0.1 mM. Under the best operating conditions found (pH = 3.0, T = 70 o C, [H2O2]feed = 6 mM, W/Q = 200 mg.min/mL, dp2 and tresid = 90 min), it was achieved 91% of discoloration and 36% of mineralization, at steady-state. Moreover, it was found a removal of 29% in terms of the chemical oxygen demand (COD), being worth noting the improvement in the effluent biodegradability (k'-oxygen uptake rate-increased from 9.3 to 23.2 mgO2/(gVSS.h)) and the fact that the final effluent is non-toxic (0.0% of Vibrio fischeri inhibition). The stability of the catalyst performance was checked during five consecutive runs. The crucial factor for the catalyst long-term use is the leaching of iron, which in all runs reached very low levels (e.g. only 0.173 mg/L of iron for the run in the optimized conditions, corresponding to only 0.13% of leaching). The catalyst was characterized by different techniques before and after the reactions (namely SEM/EDS and N2 adsorption); textural and chemical transformations during its use can be considered negligible (except for very acidic conditions of pH = 1.5) favoring the catalytic stability of the Fe-zeolite.
... good metal dispersion, with the metal being intimately linked or trapped inside the organic m... more ... good metal dispersion, with the metal being intimately linked or trapped inside the organic matrix and ... was also observed in glassy carbons from polyfurfuryl alcohol 39 and in carbon aerogels, 34 in ... in the R values can be due to the shrinkage of the carbon aerogel particles with ...
Tungsten catalysts supported on activated carbon were prepared using tungsten hexacarbonyl, ammon... more Tungsten catalysts supported on activated carbon were prepared using tungsten hexacarbonyl, ammonium tungstate, and tungsten pentaethoxide. The catalysts were pretreated in He, dry air, or wet air at 623 K for 6 h before being characterized by N 2 adsorption at 77 K, temperature-programmed desorption, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, and by testing their behavior in the decomposition reaction of isopropanol. The dispersion of the supported tungsten oxide phase and their surface acidity depended on the metal precursor and atmosphere of pretreatments. Thus, the highest dispersion and surface acidity were found for the catalyst prepared from W(CO) 6 and the lowest dispersion for that prepared from (NH 4) 2 WO 4. Dry air gave the highest dispersion, whereas wet air yielded the highest surface acidity. Air pretreatments of the catalyst prepared from W(CO) 6 seem to create metal oxide-support interactions, because of the very low particle size of the supported tungsten oxide phase and its homogeneous distribution.
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Papers by F. Maldonado-Hódar