silicon precursor

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4 Cuerpo Académico de Energía y Sustentabilidad, Universidad Politécnica de Chiapas. 5 Cuerpo Académico de Investigación y Desarrollo Agroindustrial, ...
Influence of the structuring agent/silicon precursor ratio on the properties of iron catalytic materials obtained by the sol-gel method. W.G. Cortés-Ortiz 1, J.M. López Nieto 2, C.A. Guerrero-Fajardo 3 B.Y. Pérez-Sariñana 4, S. Saldaña-Trinidad 5 1,3 Research Group: Aprovechamiento Energético de Recursos Naturales; Science Faculty, Universidad Nacional de Colombia 1 Ad-honorem professor, Science Faculty, Universidad El Bosque 2 Instituto de Tecnología Química, Universidad Politécnica de Valencia, (UPV-CSIC) 4 Cuerpo Académico de Energía y Sustentabilidad, Universidad Politécnica de Chiapas 5 Cuerpo Académico de Investigación y Desarrollo Agroindustrial, Universidad Politécnica de Chiapas

[email protected]

Introduction

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1294

Sol-gel oxides 𝑀(𝑂𝑅)𝑥

Hydrolysis

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412 100

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817

0 1000

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Raman Shift (cm-1)

Figure 2. Raman spectra of Fe/SiO2calcined at 723 K

𝑀(𝑂𝑅)𝑋 + 𝑋𝐻2 𝑂 ↔ 𝑀 𝑂𝐻 + 𝑋𝑅𝑂𝐻 Condensation

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a

Experimental

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Counts

(𝑂𝑅)𝑋−1 𝑀 − 𝑂𝑅 + 𝐻𝑂 − 𝑀 𝑂𝑅 𝑋−1 ↔ 𝑂𝑅 𝑋−1 𝑀 − 𝑂 − 𝑀 𝑂𝑅 𝑋−1 + 𝑅𝑂𝐻

b

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Counts

(𝑂𝑅)𝑋−1 𝑀 − 𝑂𝐻 + 𝐻𝑂 − 𝑀 𝑂𝑅 𝑋−1 ↔ 𝑂𝑅 𝑋−1 𝑀 − 𝑂 − 𝑀 𝑂𝑅 𝑋−1 + 𝐻2 𝑂

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-100 20

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Molar relation TEOS/Ac.Oxa: 1, T: 723 K, Fe 1.5 wt%

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Position [°2Theta] (Copper (Cu))

Position [°2Theta] (Copper (Cu))

Structuring agent Dissolution Organic salt Dissolution

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484

𝑀(𝑂𝑅)𝑋 + 𝐻2 𝑂 ↔ 𝐻𝑂 − 𝑀(𝑂𝑅)𝑋−1 + 𝑅𝑂𝐻

Or

Bands at ca. 1294 , 484 and 412 cm-1 are attributed to hematite (Li et al., 2010) Bands at ca. 817 and 976 cm-1 are attributed to Si-O bond extension vibrations (Balachandran et al., 2017)

200

Raman Intensity (cps)

Alkoxides

1/723K/1.5 wt% 3/723K/1.5 wt%

Molar relation TEOS/Ac.Oxa: 3, T: 723 K, Fe 1.5 wt%

Figure 3a and 3b. XRD pattern of Fe/SiO2 calcined at 723 K

Gelification Calcination

Silicon Precursor

Non-crystalline structure. A broad peak at ca. 2ϴ = 23.0° (fig. 3a and 3b) corresponds to amorphous silica (PDF Card No. 00-002-0242) (Guerrero & Sánchez, 2009). Peaks at ca. 2Ө = 32.6° and 36.0° (fig. 3a) were attributed to hematite (JCPDS: 00-024-0072). Absence of other peaks (fig. 3b) suggests no formation of big iron oxide agglomerates or that iron ions were well dispersed on the surface of the amorphous silica

Conclusions Characterization

Results and discussion 3456 cm-1: SiO-H extension vibration. 1637 cm-1: Vibration of trapped water. 1091 cm-1: Asymmetric (stretching) vibration of structural siloxane bond (Si-O-Si) 800 and 472 cm-1: Symmetric extension and flexion modes of the Si-O-Si bond (Adam & Iqbal, 2011). Figure 1. FT-IR spectra of Fe/SiO2 calcined at 723 K

It was obtained iron catalytic materials supported on silicon oxide by sol-gel method of a single step, evaluating two structuring agent/silicon precursor ratio The single-step sol-gel method allowed obtaining catalytic materials with high dispersion of active phase as confirmed by X-ray diffraction (DRX) and Raman spectroscopy. Structuring agent/silicon precursor ratio influences physical properties of materials like iron dispersion. Catalytic materials were obtained with a specific area of 693 m2·g-1 (relation 1) and 366 m2·g-1 (relation 3) due to role of the structuring agent.

Acknowledgements The authors thank to Agencia Mexicana de Cooperación Internacional para el Desarrollo (AMEXCID), Universidad Politécnica de Chiapas and Instituto de Física – UNAM.

References Adam, F., & Iqbal, A. (2011). Silica supported amorphous molybdenum catalysts prepared via sol-gel method and its catalytic activity. Microporous and Mesoporous Materials, 141(1–3), 119–127. https://doi.org/10.1016/j.micromeso.2010.10.037 Li, Y. S., Church, J. S., Woodhead, A. L., & Moussa, F. (2010). Preparation and characterization of silica coated iron oxide magnetic nano-particles. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, 76(5), 484–489. https://doi.org/10.1016/j.saa.2010.04.004 Balachandran, C., Muñoz, J. F., & Arnold, T. (2017). Characterization of alkali silica reaction gels using Raman spectroscopy. Cement and Concrete Research, 92, 66–74. https://doi.org/10.1016/j.cemconres.2016.11.018 Guerrero, C., & Sánchez, J. (2009). Síntesis de catalizadores de Fe-Mo soportados sobre sílice para la oxidación selectiva de metano hasta formaldehído. Ingeniería E Investigación, 29(1), 53–59