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
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Introduction
250
1294
Sol-gel oxides 𝑀(𝑂𝑅)𝑥
Hydrolysis
150
412 100
50
817
0 1000
2000
3000
Raman Shift (cm-1)
Figure 2. Raman spectra of Fe/SiO2calcined at 723 K
𝑀(𝑂𝑅)𝑋 + 𝑋𝐻2 𝑂 ↔ 𝑀 𝑂𝐻 + 𝑋𝑅𝑂𝐻 Condensation
500
400
a
Experimental
300
300 200
Counts
(𝑂𝑅)𝑋−1 𝑀 − 𝑂𝑅 + 𝐻𝑂 − 𝑀 𝑂𝑅 𝑋−1 ↔ 𝑂𝑅 𝑋−1 𝑀 − 𝑂 − 𝑀 𝑂𝑅 𝑋−1 + 𝑅𝑂𝐻
b
400
Counts
(𝑂𝑅)𝑋−1 𝑀 − 𝑂𝐻 + 𝐻𝑂 − 𝑀 𝑂𝑅 𝑋−1 ↔ 𝑂𝑅 𝑋−1 𝑀 − 𝑂 − 𝑀 𝑂𝑅 𝑋−1 + 𝐻2 𝑂
200
100
100 0
0
-100
-100 20
40
60
80
20
Molar relation TEOS/Ac.Oxa: 1, T: 723 K, Fe 1.5 wt%
40
60
80
Position [°2Theta] (Copper (Cu))
Position [°2Theta] (Copper (Cu))
Structuring agent Dissolution Organic salt Dissolution
976
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
