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

Silva, Antonio N. da; Neto, Antônio Chaves Assis; Manoel, C.; A.L., Jose; Freire, Paulo; Filho, J. Mendes; Oliveira, Alcinéia C.; Lang, Rossano

doi:10.1016/j.saa.2018.02.064

Cited by 6 publications

(10 citation statements)

References 42 publications

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“…As presented in Figure a, within applied voltages ranging from 0.726 to 1.226 V (vs RHE), NiO/CeO 2 NW@CC exhibited two distinguishable Raman peaks at 455 and 624 cm −1 , which could be referred to as the presence of NiOCe. [ 59,60 ] Remarkably, when the voltage was increased to 1.326 V, two new peaks at 487 and 565 cm −1 belonging to NiOOH species dominated in the Raman spectra, [ 61 ] which was in accordance with the aforementioned results. As the applied voltage was further increased, the peaks related to NiOOH became stronger.…”

Section: Resultssupporting

confidence: 77%

Pseudo‐Periodically Coupling NiO Lattice with CeO Lattice in Ultrathin Heteronanowire Arrays for Efficient Water Oxidation

Yang

Dai

Chen

et al. 2021

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Transition metal oxides (TMOs) have been under the spotlight as promising precatalysts for electrochemical oxygen evolution reaction (OER) in alkaline media. However, the slow and incomplete self‐reconstruction from TMOs to (oxy)hydroxides as well as the formed (oxy)hydroxides with unmodified electronic structure gives rise to the inferior OER performance to the noble metal oxide ones. Herein, a unique dual metal oxides lattice coupling strategy is proposed to fabricate carbon cloth‐supported ultrathin nanowires arrays, which are composed of pseudo‐periodically welded NiO with CeO2 nanocrystals (NiO/CeO2 NW@CC). When served as an OER precatalyst in 1.0 m KOH, the NiO/CeO2 NW@CC shows an ultralow overpotential of 330 mV at 50 mA cm−2, along with an impressive cycle durability of more than 3 days even at 50 mA cm−2, surpassing CC‐supported NiO and commercial IrO2 catalysts. The combined experimental and theoretical investigations unveil that the atomic coupling of CeO2 can not only appreciably trigger the generation of oxygen vacancies and expedite phase transformation of NiO into active NiOOH, but also in situ create a chemical bond with the formed NiOOH and enable the electron injection, thus effectively inhibiting the aggregation of the accessible NiOOH nanodomains and optimizing their reaction free energy towards oxygen‐containing intermediates.

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Section: Resultssupporting

confidence: 77%

Pseudo‐Periodically Coupling NiO Lattice with CeO Lattice in Ultrathin Heteronanowire Arrays for Efficient Water Oxidation

Yang

Dai

Chen

et al. 2021

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“…Three characteristics Raman bands are present for NiAl 2 O 4 , as expected from the group theory for an inverse spinel structure with Ni in octahedral (NiO) and tetrahedral sites (NiAl). [ 38 ] For NiO, two bands are present with Ni in octahedral sites, in very good agreement with the literature. Identification of these bands is given in Table 3 .…”

Section: Resultssupporting

confidence: 89%

Lignin Depolymerization by Catalytic Hydrodeoxygenation Performed with Smectitic Clay‐Based Materials

et al. 2020

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The present investigation aims at exploring the application of low‐cost catalysts based on smectitic clays to the hydrodeoxygenation (HDO) of Cynara cardunculus derived lignin. Two types of clay minerals, montmorillonite and saponite, are pillared and decorated with suitable metals by means of an optimized process and characterized by X‐ray powder diffraction (XRPD), porosity, scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), Fourier‐transform infrared spectroscopy (FTIR), UV–vis–NIR, Raman, and thermogravimetric analysis (TGA). Alkaline lignin is obtained from steam‐treated cardoon. Lignin depolymerization is conducted in a bench‐scale apparatus under subcritical conditions, at relatively low temperature (320 °C), for 3 h, under 5‐6 MPa of total pressure. Four catalysts are tested, namely, Fe/Al‐pillared montmorillonite (FAMO) and saponite (FASA), and Ni‐exchanged Ni/Al‐pillared montmorillonite (Ni–Ni/AMO) and saponite (Ni–Ni/ASA). Results indicate that mineral clay–based catalysts result effectively in the hydrogenolysis of lignin, producing several low molecular weight aromatics and other species, with overall conversions in the range 60–70%. Montmorillonite‐based catalysts yield the highest substrate conversion, with a prevalence of phenols and substituted phenols, whereas only Ni–Ni/ASA generates a higher abundance of aliphatic hydrocarbons. Overall, data indicate that smectitic clays are promising catalyst supports for products‐oriented HDO of lignin.

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“…A broad absorption band centered at 3460 cm −1 is visible with low intensity for all samples, which corresponds to the hydrogen-bonded O-H stretching ν(O-H) of physisorbed water. Another possible assignment of this band could be the structural hydroxyl groups present in the oxides, which is consistent with previous reports [13,30]. Moreover, weak absorption bands emerged at approximately 1644 cm −1 are assigned to the bending vibration δ(O-H) of hydroxyl groups (Figure 2b).…”

Section: Structural Characterizationssupporting

confidence: 91%

“…Raman spectra of the unsupported solids are characterized by the presence of four weak bands located in the low-frequency region at approximately 260, 320, 482 and 672 cm −1 (Figure 2c). According to the findings, the corundum-type structure, e.g., γ-Al2O3 phase has a D 6 3d symmetry with seven Raman active phonon modes and the signals assigned as those of 2A1g+5Eg modes are observed at 378, 418, 432, 451, 578, 645 and 751 cm −1 [30,31]. This is in agreement with the bands found in the FTIR spectra.…”

Section: Structural Characterizationssupporting

confidence: 86%

“…Interestingly, long exposure times, such as 50 scans applied to the samples under study allow the observed weak Raman bands for the unsupported samples. This clearly suggests that the aforesaid signals are consistent with the Al-O-Al vibrational modes in AlO6 octahedra [30,31]. Additional signals appearing at approximately 398, 499, 525, 612, 826, To prove this hypothesis, XRD patterns of the unsupported samples (Figure 2a) reveal no detectable differences for a γ-Al 2 O 3 sample, as found elsewhere [10,13,21].…”

Section: Structural Characterizationssupporting

confidence: 63%

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Effect of Basic Promoters on Porous Supported Alumina Catalysts for Acetins Production

et al. 2022

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A facile strategy for the design of porous supports was obtained by modifying the sol-gel method followed by the wet impregnation technique. In this respect, herein, the acidity of the γ-Al2O3 phase was modulated by adding basic MgO, La2O3 or ZnO promoters to form binary supported catalysts. The Ni and Co dispersion on the supports associated with their tunable acidity and morphologies resulted in highly porous supported alumina-based catalysts. The physicochemical properties of the solids were comprehensively investigated by XRD, textural properties, Raman and FTIR spectroscopy, SEM-EDS, TEM, EPR and XPS analyses. The catalytic performances in the esterification of glycerol in the presence of acetic acid (EG) for the acetins production were evaluated. The highly dispersed NiO and Co3O4 active species on binary porous supports produced synergistic effects appearing to be the reason for the activity of the solids in the EG reaction. Under the optimized reaction conditions, NiCo/MgO-Al2O3 was found to be a robust solid with superior catalytic performance and improved stability in four reaction cycles with 65.0% of glycerol conversion with an exclusive selectivity of 53% for triacetin. The presence of Co2+/Co3+ and Ni2+ strongly interacting with the spinel γ-Al2O3 and MgAl2O4 phases, the latter having a large number of lattice oxygen species, was considered another active component besides those of Ni and Co in the esterification of glycerol.

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

Cited by 6 publications

References 42 publications

Pseudo‐Periodically Coupling NiO Lattice with CeO Lattice in Ultrathin Heteronanowire Arrays for Efficient Water Oxidation

Pseudo‐Periodically Coupling NiO Lattice with CeO Lattice in Ultrathin Heteronanowire Arrays for Efficient Water Oxidation

Lignin Depolymerization by Catalytic Hydrodeoxygenation Performed with Smectitic Clay‐Based Materials

Effect of Basic Promoters on Porous Supported Alumina Catalysts for Acetins Production

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