Framework Aluminum Species Research Articles

Synergistic effect of the framework boron and Al-rich region to enhance the metal-support interaction for boosting Pd-based catalyst activity of dimethyl carbonate synthesis

Efficient production of dimethyl carbonate (DMC) from methyl nitrite (MN) carbonylation based on PdCu/NaY zeolite catalysts is highly desired for industrial applications. The introduction of boron species into the initial gels of NaY synthesis is a cost-effective modification strategy for boosting the catalytic performance. It not only introduces trace amounts of framework boron but also regulates the distribution of framework aluminum (AlF) species. Most importantly, the synergistic effect of framework boron and Al-rich region significantly enhanced the metal − support interaction, thus promoting more electrons to be transferred from metal to support. This strategy allows the palladium active species to remain in an electron-deficient state more easily. The carbon monoxide (CO) adsorption and the critical intermediate species *CH3COO are more easily formatted on PdCu/NaBY catalyst, which leads to superior weight-time yields (WTYDMC up to 1507·g·kgcat − 1·h− 1), and CO conversion to DMC (CCO up to 83 %). Our design is of great importance for developing metal-zeolites catalysts, which motivates the industrial application of Pd-based catalysts in the MN carbonation of DMC field.

Hierarchical Y zeolite with accessible intracrystalline mesopores and enhanced hydrocracking performances via sequential multi-carboxyl acid and fluoroborate post-treatments

Hierarchical Y zeolite that combines the intrinsic microporosity with mesoporosity can alleviate diffusion limitation in hydrocracking catalyst. In this study, hierarchical Y zeolites with abundant mesopores that connect the interior of the zeolite crystals to the external surface were successfully synthesized by post-synthesis dealumination using citric acid (C6H8O7) and/or ammonium tetrafluoroborate (NH4BF4) as agents. The results show that C6H8O7 can effectively extraction framework aluminum species (FALs), while NH4BF4 mainly interacts with extra framework aluminum species (EFALs). Via sequentially adopting C6H8O7 and NH4BF4 (denoted as DAY-C-F), such interconnected mesopores can be effectively introduced without sacrificing the zeolite crystallinity. The results of the scaled-up hierarchical Y zeolite reveal that the above mentioned post-treatment strategy is feasible and reproducible for potential industrial manufacturing and applications. The hydrocracking test results reveal that the naphtha yield for the catalyst derived from the C6H8O7-NH4BF4 sequentially treated USY is higher than that of the counterpart made from commercial USY.

Fast synthesis of highly crystallized LSX zeolite with boosted carbon dioxide hydrogenation activity

Fabrication of suitable zeolite-based multifunctional catalysts has been perceived as a potential method for CO2 conversion to value-added chemicals and fuels. Thus, a highly crystallized LSX zeolite was prepared directly for the first time without aging and strong alkali sodium/potassium salt. Besides, the hierarchical structure was also successfully introduced by template-free method. The resulted LSX zeolite-based catalyst can significantly boost CO2 hydrogenation with a preferential production of methanol (100% selectivity). This can be owing to the electron transfer between extra framework aluminum (EFAl) and ZnO species that drives the remarkable adsorption capability of CO2 and the formate activation pathway. Furthermore, the highly dispersive Cu nanoparticles that interplay with zeolite host and ZnO species render convenient access to the activated CO2 * species for those dissociated H after their spillover. More importantly, an exceptional stability can also be obtained, indicating the promising prospect in practical and industrial application.

Enhanced catalytic activity of phosphorus-modified SSZ-13 zeolite in the ethylene-to-propylene reaction by controlling acidity and intracrystalline diffusivity

A highly selective means of producing propylene via the ethylene-to-propylene (ETP) reaction is required to manage the supply-demand balance of light olefins. To improve the catalytic activity of the ETP reaction, a phosphorus-modified SSZ-13 zeolite (P-SSZ-13) was prepared by introducing phosphorus to the SSZ-13 zeolite via a simple impregnation method. The P-SSZ-13 catalyst exhibited increased propylene selectivity and yield compared to the pristine catalyst. According to solid-state NMR spectroscopy and STEM-EDS observation, the phosphorus species were mainly located on the outer part of the crystal as a form of polyphosphate. To reveal the effect of the phosphorus loading on the enhancement of ETP reactivity, a series of surface-modified SSZ-13 catalysts were prepared and investigated. It was found that the polyphosphate species in the P-SSZ-13 catalyst not only weakened the acidity of the zeolite by bonding with the framework aluminum species but also reduced the diffusion out of the relatively large-sized hydrocarbon species by partially blocking the pore mouths. The change in the diffusivity of the hydrocarbons over the SSZ-13 catalysts also affected the ETP reactivity. The relationship between the amount of phosphorus and the ETP reactivity of the P-SSZ-13 catalysts could also be clearly demonstrated in terms of the change in both acidity and intracrystalline diffusivity. Moreover, 13C MAS NMR measurement with isotopic switch experiment confirmed the alkyl naphthalene-based hydrocarbon pool mechanism over the P-SSZ-13 for the ETP reaction.

Direct synthesis of HZSM-5 zeolites with enhanced catalytic performance in the methanol-to-propylene reaction

HZSM-5 zeolites were directly synthesized via a two-stage crystallization method using ammonia hydroxide as an alkaline source instead of the conventional sodium hydroxide, and their performance in the methanol-to-propylene (MTP) reaction was investigated at 470 °C. The use of ammonia hydroxide as the alkaline source can overcome the inherent drawback of requiring multiple ion exchanges for converting Na-form zeolites to NH4+-form derivatives. Bulk and surface characterization techniques were combined to study the changes in crystallinity, porosity, morphology, aluminum distribution, and acidity with the experimental conditions. It was found that ammonia hydroxide had limited effect on the crystallinity and morphology of HZSM-5 zeolites, whereas the silicon and aluminum sources affected significantly the morphology and aluminum distribution. The acid properties and aluminum distribution induced important changes in the MTP activity and selectivity. Thus, increasing the framework SiO2/Al2O3 ratios in HZSM-5, in other words, reducing the acid density and the amount of framework aluminum species in the channel intersections, could improve the selectivity to propylene by favoring the olefinic-based cycle reaction. The catalyst lifetime was found to depend on not only the acid density but also on the acid distribution (or framework aluminum distribution).

Elucidation of the versatile Brønsted acidity of nanosized ZSM-5 materials

Abstract Studying a series of nanosized and microsized H-ZSM-5 zeolites with nSi/nAl ratios of 31–88 revealed systematic differences in the crystallinity, morphology, and Bronsted acidity of these materials. While the aluminium atoms in all samples under study are tetrahedrally coordinated framework species, only 32–34% of these atoms in the nanosized materials contribute to the formation of Bronsted acidic bridging OH groups (Si(OH)Al), which are characteristic for common microsized H-ZSM-5 zeolites. The remaining framework aluminium species cause formation of silanol groups with weakly enhanced Bronsted acidity (Si(OH)⋯Al) comparable with those in amorphous aluminosilicates. These properties of nanosized ZSM-5 materials are explained by the assumption of hybrid particles consisting of internal crystalline ZSM-5 domains containing Si(OH)Al groups covered by X-ray-amorphous surface layers with Si(OH)⋯Al groups. Direct evidence for these surface layers is found with transmission electron microscopy, but the other characterisation methods are also in line with this explanation.

Effect of aluminum and sodium on the sorption of water and methanol in microporous MFI-type zeolites and mesoporous SBA-15 materials

The interaction and nature of surface sites for water and methanol sorption on MFI-type zeolites and mesoporous SBA-15 were investigated by solid-state NMR spectroscopy and correlated with the desorption enthalpies determined via TGA/DSC. For siliceous Silicalite-1, 29Si CPMAS NMR studies support stronger methanol than water interactions with SiOH groups of Q3-type. On siliceous SBA-15, SiOH groups of Q2-type are accompanied by an enhanced hydrophilicity. In aluminum-containing Na-ZSM-5, Na+ cations are strong adsorption sites for water and methanol as evidenced by 23Na MAS NMR in agreement with high desorption enthalpies of ΔH = 66–74 kJ/mol. Solid-state NMR of aluminum-containing Na-[Al]SBA-15, in contrast, has shown negligible water and methanol interactions with sodium and aluminum. Desorption enthalpies of ΔH = 44–60 kJ/mol hint at adsorption sites consisting of SiOH groups influenced by distant framework aluminum. On H-ZSM-5, Brønsted acidic OH groups are strong adsorption sites as indicated by partial protonation of water and methanol causing low-field shifts of their 1H MAS NMR signals and enhanced desorption enthalpies. Due to the small number of Brønsted acid sites in aluminum-containing H-[Al]SBA-15, water and methanol adsorption on this material is suggested to mainly occur at SiOH groups with distant framework aluminum species, as in the case of Na-[Al]SBA-15.

Role of Al in Na-ZSM-5 zeolite structure on catalyst stability in butene cracking reaction

The Na-ZSM-5 catalysts (SiO2/Al2O3 molar ratio = 20, 35, and 50) were prepared by rapid crystallization method to investigate their performance in butene cracking reaction. The XRD, XRF, NH3-TPD, FT-IR, TPO, UV–Vis, and 1H, 27Al, 29Si MAS NMR techniques were used to identify the physical and chemical properties of Na-ZSM-5 catalysts. The silanol group (Si–OH) was the main acid site of Na-ZSM-5, and it was proposed to be the active site for the butene cracking reaction. The butene conversion and coke formation were associated with the abundance of silanol groups over the Na-ZSM-5 catalyst. The dealumination, resulting in the deformation of tetrahedral framework aluminum species was a key factor for Na-ZSM-5 catalyst deactivation, because of the Si–O–Al bond breaking and formation of Si–O–Si bond. The stability of the Si–O–Al bond was linked to the molar number of sodium since the Na atom interacts with the Si–O–Al bond to form Si–ONa–Al structure, which enhances the stability of the silanol group. Therefore, the Si–ONa–Al in zeolite framework was an essential structure to retain the catalyst stability during the reaction. The Na-ZSM-5 with the lowest SiO2/Al2O3 molar ratio showed the best performance in this study resulting the highest propylene yield and catalyst stability.

Understanding structure-function relationships in HZSM-5 zeolite catalysts for photocatalytic oxidation of isopropyl alcohol

The HZSM-5 molecular sieves are a kind of special photocatalyst with photocatalytic activity, while their relationship between structure and function has been a matter of debate. Here, we report that for HZSM-5, the distinguished transformation of coordination environment derived from the removal of tetrahedral framework aluminium by thermal treatment will result in a considerable change in photocatalytic behaviours. The established NMR analysis combined with the theoretical calculations demonstrates the formation of extra-framework aluminium (EFAL) upon calcinations. This leads to a changed reaction path of photocatalytic oxidation of isopropyl alcohol in gas-phase over calcined HZSM-5 catalysts. DFT calculation results show the formed of EFAL species can increase the interaction energy between reactant molecules and zeolites which affords an outstanding photocatalytic reactivity and a controllable photocatalytic selectivity in the oxidation of isopropyl alcohol. This clearly indicates that the framework aluminium (FAL) species are responsible for acetone formation, while the EFAL species are apt to promote the deep mineralization of isopropyl alcohol to inorganic CO2. This study provides new understanding in the issue of photocatalysis for zeolite molecular sieves.

The acidic nature of "NMR-invisible" tri-coordinated framework aluminum species in zeolites.

The unambiguous characterization of different acid sites in zeolites is of great importance for understanding their catalytic performance and the rational design of highly efficient zeolite catalysts. In addition to various well-characterized extra-framework Al species, a tri-coordinated framework aluminum species can also serve as a Lewis acid site in zeolites, which is "NMR-invisible" owing to its extremely distorted local environment. Here we provide a feasible and reliable approach to elucidate the acidic nature of the tri-coordinated framework Al in dehydrated H-ZSM-5 zeolites via sensitivity-enhanced two-dimensional (2D) multiple nuclear correlation NMR experiments coupled with trimethylphosphine oxide (TMPO) probe molecules. Two types of tri-coordinated framework Al sites have been unambiguously identified, which amount to 11.6% of the total Brønsted and Lewis acid sites. Furthermore, it was found that synergistic effects arising from the close spatial proximity between the tri-coordinated framework Al site and the Brønsted acid site lead to the generation of superacidity (with an acid strength stronger than 100% H2SO4) in the zeolite.

Tuning the material and catalytic properties of SUZ-4 zeolites for the conversion of methanol or methane

This work describes the synthesis and investigation of improved SUZ-4 catalysts (SZR framework) and their application in methanol-to-olefins and methane-to-methanol conversion. We report boron containing, dealuminated and desilicated SUZ-4 catalysts. Ammonia and pyridine probe molecules enabled the assignment of acid site densities to the 10-MR and 8-MR pores, respectively. The difference in between the theoretically expected and the for the probes accessible acid site density is a good descriptor for the accessibility of pores and acid sites. The access to the 8-MR SUZ-4 pores is sterically hindered by counter ions as well as extra framework aluminum (EFAl) species that account for up to 15% of the aluminum. Dealumination and desilication were successfully applied to optimize the diffusion properties and resulted in outstandingly high BET surface area, nSi/nAl-ratios and potassium exchange degrees. The improved accessibility led to an up to 2-fold increased MTO conversion capacity of the catalysts. Cu-exchanged SUZ-4 was applied in the selective oxidation of methane to methanol. By operando X-ray absorption spectroscopy (XAS) we showed that CuII ions are mainly coordinated in 2Al sites of 6-MR motifs and inhibited for redox-reactions.

Influence of Levulinic Acid Hydrogenation on Aluminum Coordination in Zeolite-Supported Ruthenium Catalysts: A 27 Al 3QMAS Nuclear Magnetic Resonance Study.

The influence of a highly oxygenated, polar protic reaction medium, that is, levulinic acid in 2‐ethylhexanoic acid, on the dealumination of two zeolite‐supported ruthenium catalysts, namely Ru/H‐β and Ru/H‐ZSM‐5, has been investigated by 27Al triple‐quantum magic‐angle spinning nuclear magnetic resonance spectroscopy (3QMAS NMR). Upon use of these catalysts in the hydrogenation of levulinic acid, the heterogeneity in aluminum speciation is found to increase for both Ru/H‐ZSM‐5 and Ru/H‐β. For Ru/H‐ZSM‐5, the symmetric, tetrahedral framework aluminum species (FAL) were found to be mainly converted into distorted tetrahedral FAL species, with limited loss of aluminum to the solution by leaching. A severe loss of both FAL and extra‐framework aluminum (EFAL) species into the liquid phase was observed for Ru/H‐β instead. The large decrease in tetrahedral FAL species, in particular, results in a significant decrease in strong acid sites, as corroborated by Fourier transform infrared spectroscopy (FT‐IR). This decrease in acidity, evidence of the inferior stability of the strongly acidic sites in Ru/H‐β relative to Ru/H‐ZSM‐5 under the applied conditions, is considered as the main reason for differences seen in catalyst performance.

Mechanisms of the AlCl3 Modification of Siliceous Microporous and Mesoporous Catalysts Investigated by Multi-Nuclear Solid-State NMR

Solid-state NMR spectroscopy was utilized for investigating the post-synthetic formation of surface acid sites via AlCl3 modification of dealuminated zeolite Y (DeaY) and siliceous mesoporous SBA-15 and subsequent thermal treatment. Upon calcination at 723 K, aluminum atoms introduced by the AlCl3 modification coordinate at Q2 (Si(2Si,2OH)) and Q3 (Si(3Si,1OH)) sites and form tetrahedrally coordinated (AlIV) framework aluminum species. Most of the spectroscopically observed pentacoordinated (AlV) and octahedrally coordinated (AlVI) aluminum atoms are extra-framework species, partially acting as Lewis acid sites (LAC). The aluminum coordination at the framework is accompanied by the formation of Bronsted acidic SiOH groups with weak acid strength. The weak Bronsted acidity of these SiOH groups is explained by neighboring framework aluminum atoms with strongly disturbed tetrahedral oxygen coordination. For zeolite DeaY, in addition to the aluminum incorporation into silanol nests, also the aluminum incorporation via surface reactions of AlCl3 with the intact SiO2 framework occurs. In the case of mesoporous SBA-15, with a fivefold higher density of SiOH groups of the parent material compared with that of the parent zeolite DeaY, the aluminum incorporation into silanol nests is the dominating mechanism. By solid-state NMR spectroscopy of the dehydrated samples loaded with probe molecules, significantly larger densities (factor of 3–8) of LAC compared with those of Bronsted acid sites were determined for the AlCl3-modified and calcined zeolite DeaY and mesoporous SBA-15.

Phosphatation of Zeolite H‐ZSM‐5: A Combined Microscopy and Spectroscopy Study

A variety of phosphated zeolite H-ZSM-5 samples are investigated by using a combination of Fourier transfer infrared (FTIR) spectroscopy, single pulse (27)Al, (29)Si, (31)P, (1)H-(31)P cross polarization (CP), (27)Al-(31)P CP, and (27)Al 3Q magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, scanning transmission X-ray microscopy (STXM) and N2 physisorption. This approach leads to insights into the physicochemical processes that take place during phosphatation. Direct phosphatation of H-ZSM-5 promotes zeolite aggregation, as phosphorus does not penetrate deep into the zeolite material and is mostly found on and close to the outer surface of the zeolite, acting as a glue. Phosphatation of pre-steamed H-ZSM-5 gives rise to the formation of a crystalline tridymite AlPO4 phase, which is found in the mesopores of dealuminated H-ZSM-5. Framework aluminum species interacting with phosphorus are not affected by hydrothermal treatment. Dealuminated H-ZSM-5, containing AlPO4 , retains relatively more framework Al atoms and acid sites during hydrothermal treatment than directly phosphated H-ZSM-5.

Application of NMR crystallography to the determination of the mechanism of charge-balancing in organocation-templated AlPO STA-2

The combination of solid-state MAS NMR spectroscopy and first-principles calculations is used to elucidate the structure of an as-prepared microporous AlPO (STA-2), in which the organocation template (bis-diazabicyclooctane-butane) is charge balanced by hydroxyl groups coordinated to framework aluminium species. 27Al MAS NMR spectra show Al exists in both tetrahedral and five-fold coordination, with the latter directly coordinated to hydroxyl O atoms as well as framework O atoms. The relative intensities of these resonances can be used to determine that the hydroxyls bridge between the two types of Al. Calculation of NMR parameters using a periodic density functional theory approach are able to suggest assignments for the resonances in both 27Al and 31P NMR spectra. 31P chemical shifts are shown to depend not only on the topologically-distinct sites in the SAT framework but also on whether or not the P atoms form part of a six-membered P(OAl)2OH ring, where OH is a bridging hydroxyl. By diffraction six possible sites for the charge-balancing hydroxyls have been identified, but all are refined with an average occupancy of 0.33. However, predicted peak positions in two-dimensional J-HETCOR NMR spectra indicate that only one hydroxyl is found in each cancrinite cage, and suggest that the most likely arrangements are those that avoid the close approach of bridging hydroxyl groups in adjacent cages. We show that the use of a combination of NMR spectroscopy and calculation to elucidate structure, often referred to as “NMR Crystallography”, offers a promising route for the future study of as-made and substituted microporous materials.

Effects of hydrothermal aging on NH3-SCR reaction over Cu/zeolites

The effects of hydrothermal treatment on model Cu/zeolite catalysts were investigated to better understand the nature of Cu species for the selective catalytic reduction of NOx by NH3. After hydrothermal aging at 800°C for 16h, the NOx reduction performance of Cu-ZSM-5 and Cu-beta was significantly reduced at low temperatures, while that of Cu-SSZ-13 was not affected. When the zeolite framework aluminum species were probed using solid state 27Al MASNMR, significant reduction in the intensities of the tetrahedral aluminum peak intensity was observed for Cu-ZSM-5 and Cu-beta, although no increase in the intensities of the octahedral aluminum peak was detected. When the redox behavior of Cu species was examined using H2-TPR, it was found that Cu2+ could be reduced to Cu+ and to Cu0 for Cu-ZSM-5 and Cu-beta catalysts, while Cu2+ could be reduced only to Cu+ in Cu-SSZ-13. After hydrothermal aging, CuO and Cu-aluminate species were found to form in Cu-ZSM-5 and Cu-beta, while little changes were observed for Cu-SSZ-13.

Framework and extra-framework aluminium in wet ion exchanged Fe-ZSM5 and the effect of steam during the decomposition of N 2O

The role of extra-framework and framework aluminium in wet-ion exchanged Fe-ZSM5 has been studied using 29Si NMR and 27Al triple quantum magic angle spinning (3QMAS) NMR. A series of samples were studied, the parent material, the wet ion exchanged Fe-ZSM5 and Fe-ZSM5 that has been used in the decomposition of N 2O with varying reaction conditions. Various framework and extra-framework aluminium species have been identified. It was found that cationic Fe species prefer to replace the Brønsted acid protons in their charge balancing role at those aluminium sites associated with the largest quadrupolar product. The framework aluminium atoms that pertain to the smaller quadrupolar product, which are either charge balanced by extra-framework aluminium or a proton, are much less prone to exchange. In the catalytic decomposition of N 2O it seemed that water present in small amounts enhances the catalytic activity. However, water also decreases the long term stability and performance by dealuminating the zeolite framework. With a high amount of water present, Fe-ZSM5 was destabilised and catalytically inferior.

13C Chemical Shift of Adsorbed Acetone for Measuring the Acid Strength of Solid Acids: A Theoretical Calculation Study

Adsorption of basic probe molecules is one of the widely used methods to characterize the acid strength of solid acids. In this contribution, the adsorptions of acetone on various Brønsted and Lewis acid sites (from weak acid to superacid) are theoretically studied, in order to elucidate the quantitative relationships between 13C chemical shifts of acetone and intrinsic acid strength of solid acids. The Brønsted acid sites are represented by a series of 8T zeolite models with varying terminal Si−H bond lengths, and the different extents of acidic proton transfer from these acid sites to acetone are revealed explicitly. We found that three adsorption conformations (hydrogen-bonded, proton-shared, and ion-pair) exist for acetone, and concurrently, a correlation of three-broken lines is obtained for the 13C chemical shift of acetone versus the deprotonation energy (DPE). The correlation can be used as a scale for quantitatively measuring the Brønsted acid strength of solid acids. A threshold of 245 ppm is determined for superacidity, in good agreement with the experimental value (244 ppm). The Lewis acid sites are modeled by tricoordinate framework aluminum species and various extra-framework aluminum cations or neutral species such as Al3+, AlO+, AlOH2+, Al(OH)2+, Al(OH)3, and AlOOH. We found that acetone is coordinately adsorbed on the aluminum atoms of Lewis acid sites and that the 13C chemical shift of acetone is almost linear to the lowest unoccupied molecular orbital (LUMO) energy of the acid sites.

NH 3-TPD and FTIR spectroscopy of pyridine adsorption studies for characterization of Ag- and Cu-exchanged X zeolites

Pure crystalline NaX zeolites with Si/Al = 1.2 is prepared by the hydrothermal method. The modification is achieved by following the conventional ion-exchange technique to obtain Ag- and Cu-exchanged forms of NaX zeolite with different metal loadings ranging from low to high exchange. Compositional and structural investigations of all samples are performed by atomic absorption spectrometry, elemental analysis, powder XRD, and nitrogen adsorption porosimetry. The acidity of all exchanged zeolites is investigated using both the ammonia temperature-programmed desorption (NH 3-TPD) carried out by microbalance, and the pyridine adsorption performed via Fourier transform infrared spectroscopy (FTIR). XRD analysis shows the global conservation of the zeolitic structure after ionic exchange. The crystallinity loss is more important for zeolites exchanged at high degree of copper. Porosity measurements indicate a decrease of the porous volumes and the specific surface areas when the Ag or Cu exchange degree is raised. Mesopores particularly appear at high exchange degree of copper. NH 3-TPD indicates that the increase of Ag and Cu-exchange degrees leads to an increase of the global acidity, which is more pronounced for Cu-exchanged zeolites. The strength of acid sites for Ag-exchanged zeolites is weaker than for Cu-exchanged zeolites. The FTIR spectroscopy analysis by pyridine adsorption confirms the formation of extra framework aluminum (EFAL) species, inducing an increase in the concentration and the strength of the Lewis acidity. The formation of EFAL is more important for Cu-exchanged zeolites.

Nature and location of cerium in Ce-loaded Y zeolites as revealed by HRTEM and spectroscopic techniques

Different methods were used to introduce cerium in a HUSY zeolite. The samples obtained from ion-exchange, precipitation and wetness impregnation procedures were characterized both before and after hydrothermal deactivation in order to determine and compare the nature of the cerium species and their location in the catalyst. A variety of techniques were used: XRD, HRTEM, XPS, infrared and Raman spectroscopy and catalytic test of dehydration of 2-propanol. The presence of amorphous phases of extra framework aluminium species (EFAL) depends on the preparation method as was evidenced by TEM. The presence of CeO 2 and exchanged cerium was determined in catalysts prepared by precipitation and impregnation methods. The quantification of both types of cerium species was accomplished by Rietveld refinement. For the catalyst prepared by impregnation, it is suggested that cerium species interact with EFAL species. This interaction determines the cerium dispersion.