Photodegradation Diuron herbicide with TiO2-Al2O3 catalysts supported on graphene nanoplatelets

Objective: To photodegrade Diuron with TiO2-Al2O3 nanomaterials supported on graphene nanoplatelets (GnPs) Design/methodology/approach: The synthesis of the materials was carried out by the sol-gel method under mild conditions. Subsequently, the obtained materials were subjected to thermal processing for structural stabilization and pulverized. Synthesized nanomaterials were then characterized by nitrogen adsorption/desorption, X-ray diffraction, scanning electron microscopy, and Uv-Vis spectroscopy. Results: The adsorption/desorption results indicated that the ternary TiO2-Al2O3/GnPs nanomaterials were found to have complex porosity, which suggested that TiO2-Al2O3 was formed on agglomerated GnPs. X-ray diffraction data revealed that the anatase phase of TiO2 and the g-Al2O3 phase coexist with the crystalline phase of graphene. The morphology of the materials indicates that the nanoplatelets were randomly dispersed in a continuous mixed oxide phase. About the UV analysis, the presence of GnPs at 1 wt % concentration reduces the band gap by 6%. Limitations on study/implications: The physical and chemical properties of GnPs make the material an excellent candidate for the degradation of pollutants by photocatalysis. Findings/conclusions: The addition of GnPs improved the Diuron degradation, probably by forming a nanostructured interface or heterojunction.  Objective: To photodegrade Diuron with TiO2-Al2O3 nanomaterials supported on graphene nanoplatelets (GnPs) Design/methodology/approach: The synthesis of the materials was carried out by the sol-gel method under mild conditions. Subsequently, the obtained materials were subjected to thermal processing for structural stabilization and pulverized. Synthesized nanomaterials were then characterized by nitrogen adsorption/desorption, X-ray diffraction, scanning electron microscopy, and Uv-Vis spectroscopy. Results: The adsorption/desorption results indicated that the ternary TiO2-Al2O3/GnPs nanomaterials were found to have complex porosity, which suggested that TiO2-Al2O3 was formed on agglomerated GnPs. X-ray diffraction data revealed that the anatase phase of TiO2 and the g-Al2O3 phase coexist with the crystalline phase of graphene. The morphology of the materials indicates that the nanoplatelets were randomly dispersed in a continuous mixed oxide phase. About the UV analysis, the presence of GnPs at 1 wt % concentration reduces the band gap by 6%. Limitations on study/implications: The physical and chemical properties of GnPs make the material an excellent candidate for the degradation of pollutants by photocatalysis. Findings/conclusions: The addition of GnPs improved the Diuron degradation, probably by forming a nanostructured interface or heterojunctio

Correlation of Rh Particle Size with CO Chemisorption: Effect on the Catalytic Oxidation of MTBE

This study was conducted to identify the correlation between the CO chemisorption (linear interaction and gem dicarbonyl) and the specific size of rhodium particles, and further to determine the influence of this relationship on the catalytic oxidation reaction of methyl tert-butyl ether (MTBE). During the synthesis, first, TiO2 was developed by the sol-gel method under acidic conditions. Second, Rh was deposited (1 wt %) by the incipient wetness impregnation method. Later, with the aim of controlling the particle size, the Rh/TiO2 materials were crystallized at different reduction conditions during 3 h heat treatment. The results obtained by TEM micrographs indicated that the average particle size varies between 1.0 and 8.1 nm, depending on the conditions of heat treatment. From the histogram analysis of each TEM micrograph, two correlations were made: (i) the gem-dicarbonyl interaction was typical of Rh particles ≤ 1.5 nm, and (ii) a linear interaction, bridged interaction and dentate interaction were observed in particles ≥ 1.6 nm. The gem-dicarbonyl interaction (particle size ≤ 1.5 nm) was the most active in the oxidation reaction of MTBE

Catalytic Wet Air Oxidation (CWAO) of phenol in a fixed bed reactor using supported Ru and Ru-Au catalysts: effect of gold and Ce loading

Catalysts of Ru and Ru−Au prepared by the wet impregnation and Deposition-Precipitation methods supported on ZrO modified by CeO(10 and 20 wt%) synthetized by sol-gel method, in order to study Au and CeO addition effect in the catalytic wet air oxidation of phenol, carried out in an automatized continuous fixed-bed reactor using oxygen as an oxidizing source. Characterizations of the catalysts were made by X-ray Diffraction (XRD), Specific Surface Area (BET), X-ray Photoelectron Spectroscopy\ua0(XPS), Transmission Electronic Microscopy\ua0(TEM), Scanning Electronic Microscopy (SEM), Ultraviolet–visible Spectroscopy (UV-vis) and Temperature Programmed Desorption of Ammonia (NH-TPD). The effect of Au is reflected in the selectivity to CO of the catalysts Ru-ZrO and Ru−Au-ZrO with the increase in selectivity from 89 to 95% related to the increase in acidity which increases from 70 to 102 (μmol of NH/ gCat). Ce loading effect in this case was important to the enhance the CO selectivity explained by the formation of Ce-O-M that could favor the oxygen transfer between the catalyst surface and the adsorbed species by a redox mechanism

Effect of gold addition by the recharge method on silver supported catalysts in the catalytic wet air oxidation (CWAO) of phenol

Catalysts Ag/ZrO -CeO and Au/ZrO -CeO were synthesized by a deposition-precipitation method and Ag-Au/ZrO -CeO was prepared using a recharge method for the second metal (Au). The materials were characterized by physisorption of N , XRD, ICP, UV-vis RDS, H2-TPR, XPS and TEM. The results obtained show that the specific areas for monometallic materials were 29-37 m g and 27-74 m g for bimetallics. The tetragonal crystal phase of ZrO stabilizes when CeO quantity increases. Using XPS an increment in Ce species abundance was determined for bimetallic catalysts in contrast to the monometallic ones; according to the Ag 3d region, this metal oxidation was observed when augmenting the content of CeO in the materials, and with Au the opposite effect was produced. It was determined by TEM, that the average size of the metallic particles was smaller at bimetallic catalysts due the preparation method. Catalytic activity was evaluated by CWAO of phenol, the Ag-Au/ZrO -CeO catalyst with 20% wt of cerium reached a degradation of 100% within an hour, being the most active catalyst. Maleic, formic and oxalic acid were identified as reaction intermediates; and at the end of the reaction acetic acid was identified as the main by-product, because it is the most refractory and the conditions for oxidation must be more severe

Doping of TiO2 Using Metal Waste (Door Key) to Improve Its Photocatalytic Efficiency in the Mineralization of an Emerging Contaminant in an Aqueous Environment

Photocatalysis is an effective advanced oxidation process to mineralize recalcitrant contaminants in aqueous media. TiO2 is the most used photocatalyst in this type of process. To improve the deficiencies of this material, one of the most used strategies has been to dope TiO2 with metallic ions. Chemical reagents are often used as dopant precursors. However, due to the depletion of natural resources, in this work it was proposed to substitute chemical reagents and instead use a metallic residue (door key) as a doping precursor. The materials were synthesized using the sol–gel method and calcined at 400 °C to obtain the crystal structure of anatase. The characterization of the materials was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy–energy-dispersive X-ray analysis (SEM-EDX) methods X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). The results obtained indicate that Cu+/Cu2+ and Zn2+ ions coexist in the support, which modifies the physicochemical properties of TiO2 and improves its photocatalytic efficiency. The synergistic effect of the dopants in TiO2 allowed the mineralization of diclofenac in an aqueous medium when T-DK (1.0) was used as photocatalyst and simulated solar radiation as an activation source

Facile Synthesis of ZnO-CeO2 Heterojunction by Mixture Design and Its Application in Triclosan Degradation: Effect of Urea

In this study, simplex centroid mixture design was employed to determine the effect of urea on ZnO-CeO. The heterojunction materials were synthesized using a solid-state combustion method, and the physicochemical properties were evaluated using X-ray diffraction, nitrogen adsorption/desorption, and UV–Vis spectroscopy. Photocatalytic activity was determined by a triclosan degradation reaction under UV irradiation. According to the results, the crystal size of zinc oxide decreases in the presence of urea, whereas a reverse effect was observed for cerium oxide. A similar trend was observed for ternary samples, i.e., the higher the proportion of urea, the larger the crystallite cerium size. In brief, urea facilitated the co-existence of crystallites of CeO and ZnO. On the other hand, UV spectra indicate that urea shifts the absorption edge to a longer wavelength. Studies of the photocatalytic activity of TCS degradation show that the increase in the proportion of urea favorably influenced the percentage of mineralization

Synthesis of Supported Metal Nanoparticles (Au/TiO2) by the Suspension Impregnation Method

This work reports a new technique called “Suspension Impregnation Method” (SiM) as an alternative to the “Incipient Impregnation Method” (IiM) for the synthesis of noble metal (Au) nanoparticles. The SiM was used to synthesize gold nanoparticles supported by titanium oxide and compared with those of IiM. The reactor for the SiM technique was based on the principles of mixing, heat, and mass transfer of the suspension reactors and the metal particle synthesis was processed in situ under the oxidation reduction potentials. Three different conditions were established to observe the effect of pH on the size of the metal particles: acid (HCl), neutral (water) and alkaline (urea). The samples were characterized by nitrogen adsorption, X-Ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA), Transmission Electron Microscopy (TEM) and CO2 adsorption. The surface area was slightly modified, and the average pore diameter was reduced in all materials. The structure of the titanium oxide was not altered. A deposit of organic material was detected in samples synthesized in alkaline medium for both methods. The pH influenced the formation of conglomerates in IiM and resulted in large particle sizes (3–9 nm). In contrast, an in situ reduction in the species in SiM resulted in smaller particle sizes than IiM (2–3 nm)

γ-Valerolactone Production from Levulinic Acid Hydrogenation Using Ni Supported Nanoparticles: Influence of Tungsten Loading and pH of Synthesis

γ-Valerolactone (GVL) has been considered an alternative as biofuel in the production of carbon-based chemicals; however, the use of noble metals and corrosive solvents has been a problem. In this work, Ni supported nanocatalysts were prepared to produce γ-Valerolactone from levulinic acid using methanol as solvent at a temperature of 170 °C utilizing 4 MPa of H2. Supports were modified at pH 3 using acetic acid (CH3COOH) and pH 9 using ammonium hydroxide (NH4OH) with different tungsten (W) loadings (1%, 3%, and 5%) by the Sol-gel method. Ni was deposited by the suspension impregnation method. The catalysts were characterized by various techniques including XRD, N2 physisorption, UV-Vis, SEM, TEM, XPS, H2-TPR, and Pyridine FTIR. Based on the study of acidity and activity relation, Ni dispersion due to the Lewis acid sites contributed by W at pH 9, producing nanoparticles smaller than 10 nm of Ni, and could be responsible for the high esterification activity of levulinic acid (LA) to Methyl levulinate being more selective to catalytic hydrogenation. Products and by-products were analyzed by 1H NMR. Optimum catalytic activity was obtained with 5% W at pH 9, with 80% yield after 24 h of reaction. The higher catalytic activity was attributed to the particle size and the amount of Lewis acid sites generated by modifying the pH of synthesis and the amount of W in the support due to the spillover effect

2,5-Dimethylfuran Production by Catalytic Hydrogenation of 5-Hydroxymethylfurfural Using Ni Supported on Al₂O₃-TiO₂-ZrO₂ Prepared by Sol-Gel Method: The Effect of Hydrogen Donors

5-Hydroxymethylfurfural (5-HMF) has been described as one of the 12 key platform molecules derived from biomass by the US Department of Energy, and its hydrogenation reaction produces versatile liquid biofuels such as 2,5-dimethylfuran (2,5-DMF). Catalytic hydrogenation from 5-HMF to 2,5-DMF was thoroughly studied on the metal nickel catalysts supported on Al2O3-TiO2-ZrO2 (Ni/ATZ) mixed oxides using isopropanol and formic acid (FA) as hydrogen donors to find the best conditions of the reaction and hydrogen donor. The influence of metal content (wt%), Ni particle size (nm), Nickel Ni0, Ni0/NiO and NiO species, metal active sites and acid-based sites on the catalyst surface, and the effect of the hydrogen donor (isopropanol and formic acid) were systematically studied. The structural characteristics of the materials were studied using different physicochemical methods, including N2 physisorption, XRD, Raman, DRS UV-Vis, FT-IR, SEM, FT-IR Pyad, H2-TPD, CO2-TPD, H2-TPR, TEM and XPS. Second-generation 2,5-DMF biofuel and 5-HMF conversion by-products were analyzed and elucidated using 1H NMR. It was found that the Ni0NiO/ATZ3WI catalyst synthesized by the impregnation method (WI) generated a good synergistic effect between the species, showing the best catalytic hydrogenation of 5-HMF to 2,5-DMF using formic acid as a hydrogen donor for 24 h of reaction and temperature of 210 °C with 20 bar pressure of Argon (Ar)