Effect of the synthetic parameters on the textural properties of one-pot mesoporous Al–Ce–Cu systems

doi:10.1016/j.micromeso.2008.05.028

Microporous and Mesoporous Materials

Volume 116, Issues 1–3, December 2008, Pages 575-580

https://doi.org/10.1016/j.micromeso.2008.05.028 Get rights and content

Abstract

Various samples of the Al–Ce–Cu ordered mesoporous oxide system were prepared by a single-step synthesis using n-propanol as solvent, aluminum sec-butoxide as Al precursor, metal stearates and/or metal nitrates as Cu and Ce sources. Different reagent types and reagents ratios were used in order to explore the role of these synthetic parameters in determining the chemical, textural and structural properties of the resulting materials. The study was carried out using nitrogen physisorption at 77 K, X-ray powder diffraction (XRPD), temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of ammonia (NH₃-TPD) and FT-IR spectroscopy of adsorbed pyridine.

Introduction

Among the non-silica mesoporous oxides, alumina is of particular interest due to the large field of applications ranging from catalysis to ceramics. Nowadays, the preparation of alumina with a porous structure comparable to that of M41S mesoporous silicas can generally be well controlled using both non-ionic and ionic surfactants [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11] or ionic liquids [12] as chemical templates. One of the most interesting anionic routes toward the synthesis of mesoporous alumina involves the reaction of aluminum alkoxides with various long chain carboxylic acids employed as structure-directing agents, in the presence of controlled amount of water [13], [14], [15], [16], [17].

Non-siliceous ordered mesoporous materials find more and more practical applications, due to their often unique catalytic, magnetic, electronic and optical properties, and many synthetic strategies have been described for their preparation [18], [19], [20]. Catalytically active noble metals are usually supported on a mesoporous oxide by impregnation with solutions of the metal salts, followed by calcination, but a more convenient solution, in order to obtain a well dispersed and closely interacting metal-support system, can be represented by the direct incorporation of the noble metal salts into the synthesis gel (one-pot), used to prepare the organized mesoporous oxide [21], [22], [23], [24].

It is well known that the association of two or more active metals or oxides can be beneficial for the performances of the resulting catalytic system [25]. Because the final properties of these multi-component systems are strictly related to the degree of intimacy of the interaction of the components [25], the one-pot methodology can be applied also to the preparation of a multi-component catalyst.

In previous papers, [26], [27] we demonstrated that is possible to prepare, in a single synthetic step, alumina-based multi-component systems with ordered mesoporosity. Following our studies on Cu/Ce/Al based catalysts [27], [28], here we report the synthesis of a series of nanostructured Al–Ce–Cu oxide materials with high surface area and uniform pore size prepared by a one-pot method, using aluminum tri-sec-butoxide as alumina precursor and Cu and Ce stearates and/or nitrates as metal sources. For comparison, a Al–Ce–Cu oxide sample was synthesized in the same reaction conditions, using aluminum tri-sec-butoxide and Cu and Ce nitrates, without the assistance of any surfactant.

Section snippets

Sample preparation

All the materials used in this paper are Aldrich products and no further purification was carried out.

Thermogravimetric analysis

Thermogravimetric analyses were performed from 25 to 1000 °C under air flow, in order to determine the thermal treatment necessary to completely remove the organic phase of the surfactant and/or the inorganic one due to nitrates. Thermal analyses of AlCe_SCu_S, AlCe_SCu_N, AlCe_NCu_S and AlCe_NCu_N are reported in Fig. 1.

As to the sample AlCe_SCu_S, the weight loss up to ca. 250 °C can be attributed to the removal of residual organic solvent and physisorbed and bulk water, while that starting at 250 °C and

Conclusions

Mesoporous Al–Ce–Cu oxide materials were prepared by a one-pot method, using aluminum tri-sec-butoxide as Al precursor in the presence of Cu and Ce stearates and/or nitrates. The long chain carboxylate salts appear to act both as metal sources and structural directing agents.

The N₂ physisorption measures showed that the material, obtained using both Cu and Ce stearates, AlCe_SCu_S, exhibits very high surface area (499 m² g⁻¹) and uniform pore size. NH₃-programmed temperature desorption indicated

Acknowledgments

The Ministero dell’Università e Ricerca (MiUR) (PRIN 2006) is gratefully acknowledged for financial support.

References (50)

W. Deng et al.
Micropor. Mesopor. Mater.
(2002)
S. Valange et al.
Micropor. Mesopor. Mater.
(2000)
J. Čejka
Appl. Catal. A
(2003)
T.J. Pinnavaia et al.
Stud. Surf. Sci. Catal.
(2005)
J. Čejka
Stud. Surf. Sci. Catal.
(2005)
N. Žilková et al.
Micropor. Mesopor. Mater.
(2006)
Y. Kim et al.
J. Non-Cryst. Solids
(2005)
P. Kim et al.
J. Mol. Catal. A: Chem.
(2004)
A. Taguchi et al.
Micropor. Mesopor. Mater.
(2005)
A. Vinu et al.
Sci. Technol. Adv. Mater.
(2006)

M. Jacquin et al.

J. Catal.

(2004)

P. Kim et al.

Appl. Catal. A

(2004)

P. Kim et al.

J. Mol. Catal. A: Chem.

(2005)

B. Coq et al.

J. Mol. Catal. A: Chem.

(2001)

E. Moretti et al.

J. Colloid Interf. Sci.

(2007)

E. Moretti et al.

Appl. Catal. A

(2008)

E. Moretti et al.

Appl. Catal. B

(2007)

E.P. Parry

J. Catal.

(1963)

M. Turco et al.

J. Catal.

(2004)

C. Morterra et al.

Catal. Today

(1996)

L.J. Kundakovic et al.

J. Catal.

(1998)

A. Pintar et al.

J. Colloid Interf. Sci.

(2005)

D. Gamarra et al.

J. Power Sources

(2007)

P.K. Cheekatamarla et al.

J. Power Sources

(2005)

W.-P. Dow et al.

Appl. Catal. A

(2000)

Cited by (11)

Promotional effect of Cu additive for the selective catalytic oxidation of n-butylamine over CeZrO<inf>x</inf> catalyst
2022, Chinese Chemical Letters
The catalytic elimination of nitrogen-containing volatile organic compounds (NVOCs) still encounters bottlenecks in NO_x formation and low N₂ selectivity. Here, a series of Cu-promoted Ce-Zr mixed oxide catalysts were synthesized using a simple precipitation approach, and n-butylamine was adopted as the probe pollutant to evaluate their catalytic performance. The CeCu_10%ZrO_x catalyst exhibited the best catalytic activity, with 100% n-butylamine conversion and 90% N₂ selectivity at 250 °C. Concurrently, this sample also displayed good water resistance. A detailed characterization of the catalyst was performed through a series of experimental studies and theoretical calculations. The addition of Cu increased the redox property and promoted the production of oxygen vacancies, all of which were favorable for the greatest n-butylamine selective catalytic oxidation performance. The changes of oxygen vacancies over CeCu_10%ZrO_x in reaction process were studied by in situ Raman spectra. Moreover, in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) and theoretical calculations were employed to explore the reaction mechanism of n-butylamine selective oxidation. The high activity and selectivity of this catalyst confirm the practical feasibility of the selective oxidation of n-butylamine to CO₂ and N₂, and the exploration of the reaction mechanism provides new insights into the further design of catalysts.
Liquid phase selective oxidation of benzene over nanostructured Cu <inf>x</inf>Ce<inf>1-x</inf>O<inf>2-δ</inf> (0.03 ≤ x ≤ 0.15)
2014, Journal of Molecular Catalysis A: Chemical
Citation Excerpt :
However, these catalysts are prone to copper leaching during oxidation, which can be controlled by adopting specific preparation procedure and by incorporation with other metals [3]. Association of two or more active metals can perform well in a reaction system with enhanced degree of interaction of the components over a support with new redox and acid properties [21]. Ceria is well known for its oxygen storage/release capacity due to the oxygen vacancies and changes in the redox state of cerium (4+/3+).
Liquid phase direct oxidation of benzene to phenol was carried out over copper loaded on oxides such as ceria, alumina, magnesia, ferric oxide, zinc oxide with 30% H₂O₂ as oxidant under atmospheric pressure. Of all the catalytic formulations prepared via a novel solution combustion synthesis, the ceria based catalysts showed highest activity. Particularly, over the Cu_0.10Ce_0.90O_2−δ catalyst, 43% conversion of benzene with 100% selectivity was observed at 70 °C and atmospheric pressure. The activity of this combustion synthesized catalyst is also higher than the corresponding catalyst prepared by incipient wetness impregnation and coprecipitation methods. Powder XRD, TEM and XPS studies show ionically substituted copper over ceria as the predominant phase in the combustion derived catalyst whereas on the impregnated and coprecipitated catalysts copper is present in the dispersed copper oxide form. Influences of temperature and time, H₂O₂ concentration and solvent have also been investigated. Enhanced activity over the combustion synthesized catalyst wherein Cu²⁺ ion is present as substitutional ion in ceria has been attributed to Cu–O–Ce ionic interaction. Ionic substitution also brings stability to the active copper ion component in the combustion synthesized catalyst with lower risk of Cu-leaching as compared to the corresponding impregnated and coprecipitated catalysts as evidenced from the recycling experiments.
Preparation, characterisation and testing of CuO/Ce<inf>0.8</inf>Zr<inf>0.2</inf>O<inf>2</inf> catalysts for NO oxidation to NO<inf>2</inf> and mild temperature diesel soot combustion
2014, Applied Catalysis B: Environmental
Citation Excerpt :
The profiles of samples with low copper content consist of a combination of three broad contributions, denoted as α, β and γ. According to literature [53,54] and to our analysis, the attribution of the TPR contributions is as follows: the first peak (α) can be attributed to the reduction of highly dispersed copper oxide species, strongly interacting with ceria-zirconia [53]. The third peak (γ) is always quite intense and can be ascribed to the presence of CuO, with less interaction with the support, as well as the simultaneous Ce4+ reduction and H2 spill over.
CuO/ceria-zirconia catalysts have been prepared, deeply characterised (N₂ adsorption–desorption isotherms at −196 °C, XRD, Raman spectroscopy, XPS, TEM and H₂-TPR) and tested for NO oxidation to NO₂ in TPR conditions, and for soot combustion at mild temperature (400 °C) in a NO_x/O₂ stream. The behaviour has been compared to that of a reference Pt/alumina commercial catalyst. The ceria-zirconia support was prepared by the co-precipitation method, and different amounts of copper (0.5, 1, 2, 4 and 6 wt%) were loaded by incipient wetness impregnation.
The results revealed that copper is well-dispersed onto the ceria-zirconia support for the catalysts with low copper loading and CuO particles were only identified by XRD in samples with 4 and 6% of copper. A very low loading of copper increases significantly the activity for the NO oxidation to NO₂ with regard to the ceria-zirconia support and an optimum was found for a 4% CuO/ceria-zirconia composition, showing a very high activity (54% at 348 °C). The soot combustion rate at 400 °C obtained with the 2% CuO/ceria-zirconia catalyst is slightly lower to that of 1% Pt/alumina in terms of mass of catalyst but higher in terms of price of catalyst.
Preferential CO oxidation (CO-PROX) catalyzed by CuO supported on nanocrystalline CeO<inf>2</inf> prepared by a freeze-drying method
2014, Applied Catalysis A: General
Citation Excerpt :
According to the literature, CeO2 is reduced by H2 at temperatures higher than 350 °C. Therefore, peaks in 150–250 °C range can be associated to the reduction of oxidized copper species [40–44]. The TPR profiles of all the catalysts show three reduction peaks (see inset of Fig. 2) and this multiple-step reduction profile has been attributed to the existence of different copper species in the sample.
Nanocrystalline CeO₂ with a regular size of 9.5 nm was prepared by a freeze-drying method, and subsequent impregnated with a Cu(II) acetate solution, varying the loading of Cu (3, 6, 12 wt.%). The resulting CuO/CeO₂ materials were characterized by N₂ physisorption at −196 °C, HRTEM, H₂-TPR, X-ray diffraction, Raman spectroscopy and XPS and tested as catalysts in the preferential CO oxidation in a H₂-rich stream (CO-PROX) in the temperature range 40–190 °C. In spite of their low specific surface areas the catalysts exhibited a good catalytic performance, resulting active and selective in the CO-PROX reaction at low temperatures. The inhibiting effect of the simultaneous presence of CO₂ (15 vol.%) and H₂O (10 vol.%) in the reaction mixture on the performance of CuO-CeO₂ catalysts was also investigated. The addition of CO₂ and water in the gas stream depressed CO oxidation up to 160 °C, its effect being negligible at higher temperatures. Nevertheless, despite these expected deactivation phenomena, a CO conversion value higher than 90% and a CO₂ selectivity of about 90% was achieved for all the samples at 160 °C. The excellent performance, especially shown by the catalyst with 6 wt%. of copper, has been related to the wide dispersion of the copper active sites associated with the high amount of Ce⁴⁺ species before reaction.
Influence of synthesis parameters on the performance of CeO<inf>2</inf>-CuO and CeO<inf>2</inf>-ZrO<inf>2</inf>-CuO systems in the catalytic oxidation of CO in excess of hydrogen
2013, Applied Catalysis B: Environmental
Citation Excerpt :
In general it appears to be widely accepted in the literature that the addition of even small amounts of copper species to ceria strongly modifies the redox properties of both constituents of the catalytic system, compared to the pure materials. The H2-TPR profile of some of the Cu/Ce and Cu/Zr/Ce oxide systems described in the literature [17,21,43,45,49,50] is usually composed by two well-separated reduction peaks assignable to the reduction of at least two different kind of copper components. Because H2-TPR measurements are strongly dependent on the experimental conditions, in this work, we will focus only on the temperature range and on the quantitative comparative evaluation of hydrogen consumption between the samples, in an homogeneous series of experiments.
Ce–Cu and Ce–Zr–Cu oxide systems with a flower-like morphology were prepared by slow co-precipitation in the absence of any structure directing agent. For the sake of comparison, Ce–Cu and Ce–Zr–Cu oxide samples were also prepared by a classic co-precipitation method. All the samples were calcined in air flow at 650 °C. The materials were characterized by SEM and TEM microscopy, quantitative X-ray diffraction, N₂ physisorption, H₂-TPR, O₂-TPD and XPS. The catalytic activity of the prepared samples was evaluated in the preferential oxidation of CO in excess of H₂ (CO-PROX), in the 40–190 °C temperature range.
Effect of ceria on the MgO-γ-Al<inf>2</inf>O<inf>3</inf> supported CeO<inf>2</inf>/CuCl<inf>2</inf>/KCl catalysts for ethane oxychlorination
2011, Applied Catalysis A: General
Citation Excerpt :
This fact demonstrates that both dispersed ceria species and small aggregated crystalline ceria species can decrease the strength of weak acidic sites on the catalyst. The promotional effect is that dispersed ceria can forbid the combination of Al3+ with OH− or Ce3+ has a weak force to combine OH− due to its larger radius, which is responsible for the decrease of the amount of Lewis acidic sites [29,30]. However, the increase of the intensity of peak at 200 °C is attributed to the increase of the amount of surface capping oxygen species (O2−, O−), which plays a key role for the formation of weak acidic sites on the catalyst.
A series of CeO₂-doped CuCl₂-KCl/MgO-γ-Al₂O₃ catalysts were prepared and characterized by BET, XRD, H₂-TPR, FTIR-pyridine adsorption, NH₃-TPD and XPS techniques. XRD, BET and TPR results show that three types of ceria species exist on the surface of catalysts: dispersed ceria, small aggregated crystalline CeO₂ species and large ceria particles. It was found that copper-based catalysts modified with small aggregated crystalline ceria species exhibited higher conversion of ethane and selectivity to vinyl chloride compared to copper-based catalysts with dispersed ceria or large ceria particles. The promotional effects may be originated from the formation of large amount of surface capping oxygen species (O₂⁻ or O⁻) due to structural defects and electronic properties of nonstoichimetric ceria. Moreover, these surface capping oxygen species accelerate oxidation of part of Cu⁺ to Cu²⁺, which are responsible for the increase of intermediate Cl₂ species in the process of ethane oxychlorination. NH₃-TPD results show that the catalysts modified with small aggregated crystalline ceria species have a large amount of weak acidic sites on the surface, and these weak acidic sites benefit dehydrochlorination of dichloroethane. The activity tests revealed that the copper-based catalyst with cerium content x = 5 wt.% exhibited the highest activity due to the excellent coordination effect between ceria and copper species and the largest amount of weak acid sites for breaking C–H bonds and dehydrochlorination of dichloroethane.

View all citing articles on Scopus

View full text

Effect of the synthetic parameters on the textural properties of one-pot mesoporous Al–Ce–Cu systems

Abstract

Introduction

Section snippets

Sample preparation

Thermogravimetric analysis

Conclusions

Acknowledgments

Micropor. Mesopor. Mater.

Micropor. Mesopor. Mater.

Appl. Catal. A

Stud. Surf. Sci. Catal.

Stud. Surf. Sci. Catal.

Micropor. Mesopor. Mater.

J. Non-Cryst. Solids

J. Mol. Catal. A: Chem.

Micropor. Mesopor. Mater.

Sci. Technol. Adv. Mater.

J. Catal.

Appl. Catal. A

J. Mol. Catal. A: Chem.

J. Mol. Catal. A: Chem.

J. Colloid Interf. Sci.

Appl. Catal. A

Appl. Catal. B

J. Catal.

J. Catal.

Catal. Today

J. Catal.

J. Colloid Interf. Sci.

J. Power Sources

J. Power Sources

Appl. Catal. A