Study of the effects of lanthanum and the iron ion on the acidic properties of Al-pillared vermiculite

Study of the effects of lanthanum and the iron ion on the acidic properties of Al-pillared vermiculite

Marcus Venicio da Silva Fernandes; Lindomar Roberto Damasceno da Silva^*

Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará – UFC, Fortaleza, CE, Brazil

ABSTRACT

The synthesis of porous materials has attracted interest for decades due to their applications in catalysis and gas adsorption. Clay obtained by insertion of mesoporous oligomer [La_xAl_13-xO_{4 (OH})₂₄ (H₂O)₁₂]⁷ + (where x equals the molar amount of lanthanum), followed by calcination, may cause variation in the acidic properties. The analyzes showed that increasing the amount of La on oligomer results in a higher acidity shown in the spectrum a characteristic band in the region of 1445 and 1545cm^–1 to Lewis and Brönsted respectively, predominantly of the last one. The Mössbauer spectroscopy results showed a relationship between increased symmetry of the octahedral site of iron (Fe³⁺) and increased lanthanum doping, and consequently a sharp increase in acidity.

Keywords: acidity, mesoporous clay, lanthanum

1. Introduction

The first reports about obtaining clays mesoporous metal oxide occurred at the beginning of the 1970s. Since then the issue has been addressed in many studies^1-5. Ions such as Keggin, also called an polycationic oligomer Al₁₃^6,7, which has the empirical formula [Al₁₃O₄₍OH)₂₄(H₂O)₁₂]⁷⁺, are interspersed in the clay lamellae such as smectites and vermiculites by ion exchange⁸, which will subsequently calcined to obtain crystalline oxides structures like pillars in the clays internal structures^9,10.

Textural and catalytic properties of the mesoporous clays are related to its intrinsic characteristics due great exposure of active sites by the presence of metal oxides or pillars in the interlayer spacing, thereby increasing the surface area and creating porosity in the material. Acidity study in pillared clays is of great importance due may help in understanding the catalytic selectivity, depending on the acid sites distribution^11,12.

Clay minerals from smectite group possess layered structure formed by tetrahedral and octahedral sheets. The tetrahedral contain mainly Si(IV) as the central atom, while the octahedral sites are occupied by Al(III), Fe(III) or Mg(II). Two types of octahedral sheets occur in clay minerals: the dioctahedral type, where two-thirds of the octahedral sites are occupied mainly by Al(III), Fe(III) or Mg(II) and the trioctahedral type, with most of the sites occupied by Mg(II) or Li(I)^13-15. Iron is another important characteristic of the clay, which is a chemical species naturally occurring clay minerals from the vermiculites group^16,17.

Generally, the pillared clays properties depends on the modifying agent position. This behavior can be well evaluated by different methods, such as IR, Mössbauer spectroscopy, NMR, and others¹⁸. Related processes due iron presence in the clay is best understood using the Mössbauer spectroscopy.

This work aims to obtain mesoporous material by intercalation aluminum oligomer ([OH^–]/[Al³⁺] = 2.4) in vermiculite previously modified, followed by pillaring by calcination at 773K, and acidity increasing studies by aluminum doping (Al₁₃) in lanthanum (12Al : 1La and 11Al : 2La ) and iron possible effects related.

1.1. Material and Methods

Precursor clay samples (vermiculite) are from the Paraiba State, Brazil. All of them were dried at 373K, crushed and sieved to 200 mesh to obtain a material with homogeneous particle size. Vermiculite treated with HNO₃ at 0.8 mol.L^-1 353K, calcined at 873K for 2 hours, was treated with oxalic acid 0.12 mol L^–1 to 353K at reflux exchangeable for iron removal, next, was added NaCl 3 mol.L^–1 to obtain the sodium form (VNa) (Table 1). Aluminum oligomer (Al₁₃) was prepared by addition of NaOH 0.2 mol.L^–1 in AlCl₃.6H₂O 0.2 mol.L^–1 at reflux. Aluminum oligomer doped lanthanum (La_xAl_13-x), were obtained from solutions of NaOH 0.2 mol.L^–1, AlCl₃.6H₂O 0.2 mol.L^–1 and LaCl₃ .6 H₂O 0.2 mol.L^–1, seeing x equals to 1 or 2. Oligomers were obtained by considering the ratio OH / (Al + La) = 2.4. Oligomer solution with stirring at 353K was added to the sample VNa dispersed in deionized water (10% m.V^–1) under stirring for 24 hours, obtaining the interleaved samples, which were washed with deionized water and dried at 373K, crushed and calcined at 773K for 3 hours.

Lewis and Bronsted-Lowry acidity study of pillared vermiculites was carried out using pyridine as a probe molecule by infrared spectroscopy absorption (FT-IR) of samples tablets form at different temperatures (373K - 673K). Weight W (g) and diameter D (cm) of each sample were recorded for the measurement of the Brönsted and Lewis acid sites (q_B,L) using an equation:

where A is the integrated area of the band (a) and ε_{B, L}, molar extinction coefficient (µmol.g^–1)^19,20.

Mössbauer spectra were recorded in transmission mode at room temperature with a radioactive source ⁵⁷Co rhodium matrix mounted in a speed control operating mode sine ranging from –4 to +4 mm.s^–1, to observe all transitions possible energy hyperfine parameters of structural iron (⁵⁷Fe) nuclei.

2. Results and Discussion

2.1. Acidity characterization

Some authors, such as Pálkova et al.¹³ and Nunes et al.²¹ suggest that acidic properties of pillared clays are attributed to the presence of SiOH or AlOH groups. An efficient way to investigate this association is the use of organic bases such as pyridine, which second Chmielarz et al.,²² has frequently been used in the study of acidic sites.

According Akçay¹¹ and Benvenutti et al.²³, distinction between the of Lewis and Bronsted acidity is based on the position of certain vibrational modes (Table 2) of pyridine molecule known as 8a and 19b. Pyridine is a strong base and a proton transfer, resulting in the formation of ions when the pyridinium molecules interact with Brönsted acid sites.

Figures 1, 2 and 3 show pyridine spectra adsorbed on samples of the oligomers modified with vermiculite Al₁₃, LaAl₁₂ and La₂Al₁₁ respectively, at different temperatures: 373K, 473K, 573K and 673K. Stretch region in the spectra of 1580-1550 cm^–1 and 1455-1440 cm^–1 band 19b are characteristics to the Brönsted and Lewis sites (Table 2), respectively.

Gyftopoulou et al.²⁴ report the samples acidic character of pillared vermiculites derived from both Brönsted sites (proton donor) and Lewis sites (receiver pair of electrons). Brönsted acidity may be associated with the protons release during pillars and the vermiculite lamellae dehydroxylation, whereas the Lewis acidity is assigned to metal oxides pillars.

Figures 1, 2 and 3, the band at 1445cm^–1 on Lewis sites increases significantly as the amount of lanthanum incorporated increases. Layman et al.²⁵, Shimizu et al.²⁶ and Yazıcı et al.²⁷ noted that the region in 1490 cm^–1 correspond Lewis and Brönsted acid sites, who also undergo changes in their intensities. However, these changes and thermal degradation of Lewis and Brönsted acid sites (Figure 4), are not as significant, and appear to be related to the fact that the lanthanum is not in a central position in the oligomer, and also the greater stability than Lewis sites acquire when they are located in this specie.

Figure 4

2.2. Mössbauer spectroscopy

Parameter values hyperfine obtained by adjusting the Mössbauer spectra are shown in Table 3. All Mössbauer spectra (Figure 5a-d) obtained from samples in powder of natural and pillared clay with aluminum and aluminum - lanthanum, show the presence of Fe³⁺, and still observing (Figure 5a) that only natural vermiculite (VERM) presented Fe²⁺.

Mössbauer spectra (Figure 5) may elucidate doubt as iron may affect the thermal stability of the obtained material and possibly iron and interacts only with pillared aluminum oligomer (Al₁₃) and aluminum-doped lanthanum oligomers (LaAl₁₂ and La₂Al₁₁).

Al₁₃PILV, and LaAl₁₂PILV La₂Al₁₁PILV showed quadrupole splitting values (Δ) * significantly different (1.28, 1.21 and 1.14 mm. s^–1), respectively, as shown in Table 3, decreasing values show an increase in the organization octahedral site iron could be related growing pillars doping with lanthanum and increased acidity.

According Carriazo et al.²⁸ may be slight variations in the parameters δ and Δ_EQ, especially considering the chemical environment of Fe³⁺ in the mineral structure may vary slightly, and distortion may occur in the geometry sites of Fe³⁺ due loss of water or OH groups in the calcination step.

3. Conclusions

Aluminum doped lanthanum oligomer (LaAl₁₂PILV and La₂Al₁₁PILV) showed Lewis and Brönsted sites predominance at temperatures up to 373K and 573K respectively. The Brönsted sites showed greater thermal stability in all modified clay samples. Mössbauer spectra indicated a possible relationship between increased octahedral site Fe³⁺ symmetry, lanthanum/aluminum doped oligomer and higher acidity.

Acknowledgements

This work was financially supported by the CNPQ, CAPES and Policlay NT.

References

1. Huang Q, Zuo S and Zhou R. Catalytic performance of pillared interlayered clays (PILCs) supported CrCe catalysts for deep oxidation of nitrogen-containing VOCs. Applied Catalysis B: Environmental. 2010; 95:327-334. http://dx.doi.org/10.1016/j.apcatb.2010.01.011

2. Romero A, Dorado F, Asencio I, Garcia PB and Valverde JL. Ti-pillared clays: synthesis and general characterization. Clays and Clay Minerals. 2006; 54(6):737-747. http://dx.doi.org/10.1346/CCMN.2006.0540608

3. Gil A, Trujillano R,Vicente MA and Korili SA. Hydrogen adsorption by microporous materials based on alumina-pillared clays. International Journal of Hydrogen Energy. 2009; 34:8611-8615. http://dx.doi.org/10.1016/j.ijhydene.2009.08.057

4. Gil A, Korili SA, Trujillano R and Vicente MA. A review on characterization of pillared clays by specific techniques. Applied Clay Science. 2011; 53:97-105. http://dx.doi.org/10.1016/j.clay.2010.09.018

5. Yuan P, Annabi-Bergaya F, Taoa Q, Fan M, Liu Z, Zhu J et al. A combined study by XRD, FTIR, TG and HRTEM on the structure of delaminated Fe-intercalated/pillared clay. Journal of Colloid and Interface Science. 2008; 324:142-149. PMid:18502444. http://dx.doi.org/10.1016/j.jcis.2008.04.076

6. Jiménez de Haro MC, Pérez-Rodríguez JL, Poyato J, Pérez-Maqueda LA, Ramírez-Valle V, Justo A et al. Effect of ultrasound on preparation of porous materials from vermiculite. Applied Clay Science. 2005; 30(1):11-20. http://dx.doi.org/10.1016/j.clay.2005.02.004

7. Kloprogge JT, Duong LV. and Frost RL. A review of the synthesis and characterisation of pillared clays and related porous materials for cracking of vegetable oils to produce biofuels. Environmental Geology. 2005. http://dx.doi.org/10.1007/s00254-005-1226-1

8. Altunlu M and Yapar S. Effect of OH^-–/Al³⁺ and Al³⁺/clay ratios on the adsorption properties of Al-pillared bentonites. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2007; 306:88-94. http://dx.doi.org/10.1016/j.colsurfa.2006.10.071

9. Chmielarz L, Kus'trowski P, Piwowarska Z, Dudek B, Gil B and Michalik M. Montmorillonite, vermiculite and saponite based porous clay heterostructures modified with transition metals as catalysts for the DeNOx process. Applied Catalysis B: Environmental. 2009; 88:331-340. http://dx.doi.org/10.1016/j.apcatb.2008.11.001

10. Zhu L, Tian S, Zhu J and Shi Y. Silylated pillared clay (SPILC):A novel bentonite-based inorgano-organo composite sorbent synthesized by integration of pillaring and silylation. Journal of Colloid and Interface Science. 2007; 315:191-199. PMid:17659295. http://dx.doi.org/10.1016/j.jcis.2007.06.053

11. Akçay, M. FT-IR spectroscopic investigation of the adsorption pyridine on the raw sepiolite and Fe-pillared sepiolite from Anatolia. Journal of Molecular Structure. 2004; 694:21-26. http://dx.doi.org/10.1016/j.molstruc.2004.01.010

12. Hernández WY, Centeno MA, Odriozola JA, Moreno S and Molina R. Acidity characterization of a titanium and sulfate modified vermiculite. Materials Research Bulletin. 2008; 43:1630-1640. http://dx.doi.org/10.1016/j.materresbull.2007.10.018

13. Pálková H, Madejová J, Zimowska M and Serwicka EM. Laponite-derived porous clay heterostructures: II. FTIR study of the structure evolution. Microporous and Mesoporous Materials. 2010; 127:237-244. http://dx.doi.org/10.1016/j.micromeso.2009.07.012

14. Brigatti MF, Galan E and Theng BKG. Structures and mineralogy of clay minerals. In: Handbook of Clay Science. 2006. v. 1, capt. 2, p. 19-69.

15. Maqueda C, Perez-Rodriguez JL, Šubrt J and Murafa N. Study of ground and unground leached vermiculite. Applied Clay Science. 2009; 44:178-184. http://dx.doi.org/10.1016/j.clay.2009.01.019

16. Marcos C and Rodriguez I. Expansion behaviour of commercial vermiculites at 1000 ºC. Applied Clay Science. 2010; 48:492-498. http://dx.doi.org/10.1016/j.clay.2010.02.012

17. Zhang K, Xu J, Wang KY, Cheng L, Wang J and Liu B. Preparation and characterization of chitosan nanocomposites with vermiculite of different modification. Polymer Degradation and Stability. 2009; 94:2121-2127. http://dx.doi.org/10.1016/j.polymdegradstab.2009.10.002

18. Pálinkó I, Lázár K and Kiricsi I. Cationic mixed pillared layer clays: infrared and Miissbauercharacteristics of the pillaring agents and pillared structures in Fe,Al and Cr,Al pillared montmorillonites. Journal of Molecular Structure. 1997; 410-411:547-550. http://dx.doi.org/10.1016/S0022-2860(96)09516-6

19. Del Rey-Perez-Caballero FJ and Poncelet G. Microporous 18Å Al-pillared vermiculites: preparation and characterization. Microporous and Mesoporous Materials. 2000; 37:313-327. http://dx.doi.org/10.1016/S1387-1811(99)00274-7

20. Del Rey-Perez-Caballero FJ and Poncelet G. Preparation and characterization of microporous 18Å Al-pillared structures from natural phlogopite micas. Microporous and Mesoporous Materials. 2000; 41:169-181. http://dx.doi.org/10.1016/S1387-1811(00)00284-5

21. Nunes CD, Pires J, Carvalho AP, Calhorda MJ and Ferreira P. Synthesis and characterisation of organo-silica hydrophobic clay heterostructures for volatile organic compounds removal. Microporous and Mesoporous Materials. 2008; 111:612-619. http://dx.doi.org/10.1016/j.micromeso.2007.09.008

22. Chmielarz L, Kustrowski P, Drozdek M, Dziembaj R, Cool P and Vansant EF. Selective catalytic oxidation of ammonia into nitrogen over PCH modified with copper and iron species. Catalysis Today. 2006; 114:319-325. http://dx.doi.org/10.1016/j.cattod.2006.01.020

23. Benvenutti EV, Gushikem Y and Davanzo CU. Pyridine Used as a Probe for Internal Brönsted Acid Sites in Pyrochlore Antimony (V) Oxide: An Infrared Spectroscopy Study. Applied Spectroscopy. 1992 46(10):1474-1476. http://dx.doi.org/10.1366/000370292789619179

24. Gyftopoulou ME, Millan M, Bridgwater AV, Dugwell D, Kandiyoti R and Hriljac JA. Pillared clays as catalysts for hydrocracking of heavy liquid fuels. Applied Catalysis A:General. 2005; 282:205-214. http://dx.doi.org/10.1016/j.apcata.2004.12.012

25. Layman KA, Ivey MM and Hemminger JC. Pyridine Adsorption and Acid/Base Complex Formation on Ultrathin Films of ç-Al₂O₃ on NiAl(100). Journal of Physical Chemistry B. 2003; 107:8538-8546. http://dx.doi.org/10.1021/jp030046p

26. Shimizu K-I, Higuchi T, Takasugi E, Hatamachi T, Kodama T and Satsuma A. Characterization of Lewis acidity of cation-exchanged montmorillonite K-10 clay as effective heterogeneous catalyst for acetylation of alcohol. Journal of Molecular Catalysis A: Chemical. 2008; 284:89-96. http://dx.doi.org/10.1016/j.molcata.2008.01.013

27. Yazıcı DT and Bilgic C. Determining the surface acidic properties of solid catalysts by amine titration using Hammett indicators and FTIR-pyridine adsorptionmethods. Surface and Interface Analysis. 2010; 42:959-962. http://dx.doi.org/10.1002/sia.3474

28. Carriazo JG, Centeno MA, Odriozola JA, Moreno S and Molina R. Effect of Fe and Ce on Al-pillared bentonite and their performance in catalytic oxidation reactions. Applied Catalysis A: General. 2007; 317:120-128. http://dx.doi.org/10.1016/j.apcata.2006.10.009

Received: September 9, 2012

Revised: May 20, 2013

Publication Dates

• Publication in this collection
  05 July 2013
• Date of issue
  Oct 2013

History

• Received
  09 Sept 2012
• Accepted
  20 May 2013