Effects on structure by spectroscopic investigations, valence state and morphology properties of FeCo-containing SnO2 catalysts for glycerol valorization to cyclic acetals.

The effects on the structure, valence state and morphological properties of FeCo-containing SnO2 nanostructured solids were investigated. The physicochemical features were tuned by distinct synthesis routes e.g., sol-gel, coprecipitation and nanocasting, to apply them as catalysts in the glycerol valorization to cyclic acetals. Based on Mössbauer and XPS spectroscopy results, all nanosized FeCoSn solids have Fe-based phases, which contain Co and Sn included in the structure, and well-dispersed Fe3+ and Fe2+ surface active sites. Raman, FTIR and EPR spectroscopies measurements of the spent solids demonstrated structural stability for the sol-gel based solid, which is indeed responsible for the highest catalytic performance, among the nanocasted and coprecipitated counterparts. Morphological and elemental analyses illustrated distinct morphologies and composition on solid surface, depending on the synthesis route. The Fe/Co and Fe/Sn surface ratios are closely related to the catalytic performance. The improved glycerol conversion and selectivities of the solid obtained by sol-gel method was ascribed to the leaching resistance and the Sn action as a structural promoter.

Laser-power dependence effects on the structural stability of nanocomposite catalysts studied by Raman spectroscopy: On the structure-activity correlations in glycerol acetylation.

Structural properties of binary CeAl, CeMn, NiAl, CeZr, SnTi and ZrMn nanocomposite oxide catalysts were monitored towards the Laser Raman spectroscopy investigations providing new insights to control catalytic applications upon temperature ranges at which the laser power was varied. The lattice vibrational properties were investigated by varying the incident laser power during Raman measurements from 0.017 mW to 4.0 mW. Structural changes in nanocomposites were achieved upon increasing laser power, which induced local heating disorder causing the sintering of CeMn, SnTi, and ZrMn nanocomposites. The laser-power dependence effects on the structural stability of CeAl, NiAl, and CeZr were observed with high amounts of oxygen vacancy defects over CeAl upon laser power heating. Both CeMn and ZrMn exhibited phase transitions from MnO2 to α-Mn2O3 being the use of the latter nanocomposites limited to work at 1.1 mW. The structure-activity correlations for the nanocomposite oxide catalysts were evaluated through the acetylation of glycerol with acetic acid reaction to produce valuable acetins. Remarkable shifts in the Raman bands wavenumbers and other spectral changes in the lattice mode were caused by laser-induced phenomena accounting for the undesired phase formation and particle growths, as well. This resulted in a low catalytic performance of the NiAl, SnTi, CeMn and ZrMn owing to the thermal effects. Contrary, CeAl and CeZr were more active for acetins products avoiding the phase transformations due to their structural stability at high temperatures, which in turn avoided leaching of the active Ce sites during the reaction.

Correction: Carmo et al. Effects of the Incorporation of Distinct Cations in Titanate Nanotubes on the Catalytic Activity in NOx Conversion. Materials 2021, 14, 2181.

In the original publication, there was a mistake in Figure 1 as published [...].

Effects of the Incorporation of Distinct Cations in Titanate Nanotubes on the Catalytic Activity in NOx Conversion.

Effects of the incorporation of Cr, Ni, Co, Ag, Al, Ni and Pt cations in titanate nanotubes (NTs) were examined on the NOx conversion. The structural and morphological characterizations evidenced that the ion-exchange reaction of Cr, Co, Ni and Al ions with the NTs produced catalysts with metals included in the interlayer regions of the trititanate NTs whereas an assembly of Ag and Pt nanoparticles were either on the nanotubes surface or inner diameters through an impregnation process. Understanding the role of the different metal cations intercalated or supported on the nanotubes, the optimal selective catalytic reduction of NOx by CO reaction (SCR) conditions was investigated by carrying out variations in the reaction temperature, SO2 and H2O poisoning and long-term stability runs. Pt nanoparticles on the NTs exhibited superior activity compared to the Cr, Co and Al intercalated in the nanotubes and even to the Ag and Ni counterparts. Resistance against SO2 poisoning was low on NiNT due to the trititanate phase transformation into TiO2 and also to sulfur deposits on Ni sites. However, the interaction between Pt2+ from PtOx and Ti4+ in the NTs favored the adsorption of both NOx and CO enhancing the catalytic performance.

Optimizing reaction conditions and experimental studies of selective catalytic reduction of NO by CO over supported SBA-15 catalyst.

Selective catalytic reduction of NO with CO (CO-SCR) was investigated based on optimizing the operating conditions by response surface methodology (RSM) and by appropriately choosing the supported SBA-15 catalysts. The effects of the CO-SCR reaction parameters such as NO:CO molar ratios and oxygen concentrations on the catalytic performance were determined by RSM to evaluate the NO conversion using a first-order polynomial model. The CuO/SBA-15 and Fe2O3/SBA-15 catalysts were synthesized by a hydrothermal method and characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), N2 adsorption-desorption (BET), scanning electron microscopy coupled to energy dispersive X-Ray spectroscopy (SEM-EDS), and Fourier transform infrared spectroscopy (FTIR) to investigate the physicochemical properties of the solids. The RSM showed a very good agreement between predicted values and experimental results with the Pareto analysis confirming the accuracy and reliability of the model. The optimized results indicated the maximum NO conversion at 500 °C with using the NO to CO molar ratio of 1:2 (500:1000 ppm) in the absence of oxygen. Under these conditions, CuO/SBA-15 catalyst achieved 99.7% of NO conversion, whereas Fe2O3/SBA-15 had 98.1% of the catalytic parameter. Catalytic tests in CO-SCR reaction were performed on both catalysts at optimum operating conditions with CuO/SBA-15 exhibiting better performance compared to that of Fe2O3/SBA-15. The results revealed that CuO/SBA-15 was a promising catalyst for CO-SCR of NO due to the well-dispersed CuO phase on SBA-15 surface that allows the solid being more tolerant to the presence of oxygen.

Acid Red 66 Dye Removal from Aqueous Solution by Fe/C-based Composites: Adsorption, Kinetics and Thermodynamic Studies.

The presence of synthetic dyes in water causes serious environmental issues owing to the low water quality, toxicity to environment and human carcinogenic effects. Adsorption has emerged as simple and environmental benign processes for wastewater treatment. This work reports the use of porous Fe-based composites as adsorbents for Acid Red 66 dye removal in an aqueous solution. The porous FeC and Fe/FeC solids were prepared by hydrothermal methods using iron sulfates and sucrose as precursors. The physicochemical properties of the solids were evaluated through X-ray diffraction (XRD), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared s (FTIR), Raman and Mössbauer spectroscopies, nitrogen adsorption-desorption isotherms, Electron Paramagnetic Resonance (EPR) and magnetic saturation techniques. Results indicated that the Fe species holds magnetic properties and formed well dispersed Fe3O4 nanoparticles on a carbon layer in FeC nanocomposite. Adding iron to the previous solid resulted in the formation of γ-Fe2O3 coating on the FeC type structure as in Fe/FeC composite. The highest dye adsorption capacity was 15.5 mg·g-1 for FeC nanocomposite at 25 °C with the isotherms fitting well with the Langmuir model. The removal efficiency of 98.4% was obtained with a pristine Fe sample under similar experimental conditions.

Raman studies of nanocomposites catalysts: temperature and pressure effects of CeAl, CeMn and NiAl oxides.

High temperature and pressure effects on the physicochemical properties of binary oxides catalysts were investigated. The nanocomposites catalysts comprising of CeAl, CeMn and NiAl were characterized through various physicochemical techniques. A study of the temperature and pressure induced phenomena monitored by Raman spectroscopy was proposed and discussed. Spectral modifications of the Raman modes belonging to the CeMn suggest structural changes in the solid due to the MnO2 phase oxidation with increasing temperature. The thermal expansion and lattice anharmonicity effects were observed on CeMn due to lack of stability of the lattice vacancies. The CeAl and NiAl composites presented crystallographic stability at low temperatures however, undertake a phase transformation of NiO/Al2O3 into NiAl2O4, mostly without any deformation in its structure with increasing the temperature. It was also inferred that the binary oxides are more stables in comparison with monoxides. Detailed pressure-dependent Raman measurements of the T2g phonon mode of CeMn and NiAl revealed that the pressure contributes to modify bonds length and reduces the particles sizes of the solids. On the contrary, high pressure on CeAl sample improved the stability with addition of Al2O3 in the CeO2 lattice. The results then suggest a good stability of CeAl and NiAl composite catalysts at high pressure and low temperature and show how to prospect of tuning the catalysis for surface reactions entirely through in situ spectroscopic investigations means.

Temperature and high pressure effects on the structural features of catalytic nanocomposites oxides by Raman spectroscopy.

Structural characterizations of nanostructured oxides were studied by X-ray diffraction (XRD), Raman and infrared spectroscopy. The oxides catalysts namely, SnO2, ZrO2, CeO2, MnOx, Al2O3 and TiO2 were prepared by a nanocasting route and the effect of the temperature and pressure on the stability of the solids was evaluated. Raman spectra showed that ZrO2 and TiO2 exhibited phase transitions at moderate temperatures whereas CeO2, SnO2 and MnOx had an effective creation of defects in their structures upon annealing at elevated temperatures. The results suggested also that the effect of the temperature on the particles growth is related to the type of oxide. In this regard, phase transition by up to 600°C accelerated the sintering of ZrO2 and CeO2 grains compared to TiO2, SnO2 and MnOx counterparts. Under hydrostatic pressures lower than 10GPa, rutile TiO2 and tetragonal ZrO2 exhibited pressure induced phase transition whereas CeO2 and SnO2 were stable at pressures close to 15GPa. The experiments revealed that the nanostructured SnO2 oxide exhibited stable performance at relatively high temperatures without phase transition or sintering, being suitable to be used as catalysts in the range of temperature and pressure studied.