Zeolite Active Sites Research Articles

Modified Zeolite in Methanol to Hydrocarbons Transformation

The work is devoted to the modification of H-ZSM-5 samples with sodium hydroxide and oxalic acid to provide the formation of the mesoporous structure of the zeolite and to obtain optimal Si/Al ratio. Moreover, zeolite active sites were modified with Co, Ni, Fe in order to decrease polyaromatic substances formation during methanol transformation into hydrocarbons. The testing of the samples was performed at 350 oC in a flow reactor, the methanol feed rate was maintained at 0.16 g(methanol)/(g(Cat)*h). Dimethyl ether transformation rate into hydrocarbons was found to be 0.055-0.1 kg(DME)/(kg(Cat)*h) for investigated catalysts. Alkali treatment of H-ZSM-5 samples results in the formation of a mesoporous structure with a mean pore diameter of 5 nm. Formation of additional mesopores results in some increase of dimethyl ether to hydrocarbons transformation rate up to 0.09 kg(DME)/(kg(Cat)*h). Zeolite treatment with oxalic acid results in decreasing of Si/Al ratio from 0.76 to 0.41 that case some decrease of dimethyl ether transformation rate from 0.07 kg(DME)/(kg(Cat)*h) to 0.05 kg(DME)/(kg(Cat)*h), however considerable decrease of polyaromatic hydrocarbons concentration in reaction media was achieved for sample with lowest Si/Al ratio. Modification of H-ZSM-5 with Co, Fe, Ni results in some increase of dimethyl ether transformation rate up to 0.07-0.1 kg(DME)/(kg(Cat)*h) and a considerable decrease of polyaromatic hydrocarbons concentration in reaction media due to active sites modification.The ZSM-5-Ni-0.001M sample showed highest activity 0.1 kg(DME)/(kg(Cat)*h).

Nanocrystals FAU-X monoliths as highly efficient microreactors for cesium capture in continuous flow

Abstract The performances of binderless FAU-X monoliths (0.5 × 3 cm) build of nanocrystals featuring hierarchical trimodal porosity (micro-/meso-/macroporosity) in decontamination Cs-containing effluents have been evaluated. They have been compared to those obtained with newly synthesized FAU-X particles (1 mm) build with nanocrystals. Data have been confronted to those recently reported for a benchmark reference Cs+ adsorbent Sorbmatech®, based on copper hexacyanoferrate nanoparticles (15 nm) immobilized into mesoporous silica particles (250–500 μm) (Cu-HCF@SiO2). FAU-X monoliths show high rate of adsorption in batch in less than 2 min, much faster than Cs+ adsorption in FAU-X particles (60 min). This result highlights the importance of a homogeneous macropore network in adsorbents to enhance mass transport and access to the zeolite active sites. FAU-X monoliths with 20 μm macropore diameter have been used in continuous flow experiments for sequestering Cs+ (0.5 mmol/L) in mineral drinking water containing competing cations (Ca2+, Mg2+, Na+, K+) with flow rates of 0.5–1 mL/min, corresponding to Darcy rates of 1.5–3 m/h. FAU-X monoliths are very efficient for Cs+ removal and show ideal steep breakthrough curves characteristic of fast diffusion. FAU-X monoliths are as excellent as Cu-HCF@SiO2 and could represent an alternative adsorbent for safer processes, avoiding the handling of powders or particles. Above all, this study reveals the unique hydrodynamic behavior of FAU-X monoliths and opens the route for process intensification using FAU-X in continuous flow.

Exploring the Synthesis of Mesoporous Stannosilicates as Catalysts for the Conversion of Mono- and Oligosaccharides into Methyl Lactate

Sn-beta zeolites are among the most promising catalysts for the conversion of biomasses due to their high Lewis acidity, which allows coordination to functionalized molecules and promotes cleavage and rearrangement reactions. For applications in biorefining zeolite porosity would ideally be optimized to avoid diffusional limitations, which otherwise may decrease reaction rates and restrict the conversion of bulky substrates. The synthesis of mesoporous zeolites can help alleviating limitations and is a central topic in heterogeneous catalysis, with many synthetic procedures for mesoporous zeolites proposed over the last decades. Here, we explore different syntheses routes to prepare Lewis acidic Sn-containing zeolites, and the main features of the prepared mesoporous materials are characterized. We investigate the correlation between different types of porosity and the activity for the conversion of sugars into methyl lactate. The monomer glucose, the dimer sucrose and the oligomer inulin are applied as model substrates for the reaction in order to probe the accessibility of molecules with different sizes to active sites in zeolites with different pore systems.

Features of Butene-1 Adsorption on H-Beta Zeolite

The adsorption of butene-1 on Beta zeolite (H form) is studied via flow-adsorption calorimetry. Upon feeding a mixture of 2 vol % of butene-1 in nitrogen over the pre-calcined zeolite (500°C) at room temperature, an exothermic effect is observed that is associated with the adsorption and transformations of butene, particularly its isomerization to cis- and trans-butenes-2. The thermal desorption of adsorbed butene‑1 results in formation of hydrocarbon products showing that oligomerization proceeds during adsorption. It is found that zeolite pretreated with moist nitrogen adsorbs water up to 9.2 wt %. A weak exothermic effect is observed when butene-1 is adsorbed on this rehydrated zeolite, due apparently to the physical adsorption of butene-1. When the rehydrated zeolite is held for long periods of time in a stream of a butene/nitrogen mixture, cis-butene-2 is detected at the reactor outlet, indicating the gradual replacement of water with butene-1 on the active sites of zeolite.

Fine speciation of active sites in zeolites by a CO probe: Dynamics and IR frequencies

AbstractThe influence of system dynamics onto infrared spectra calculated and measured for probe molecules weakly interacting with active sites is discussed. OH stretching frequencies for Brønsted sites in Y zeolite and their shift on CO adsorption (measured by IR spectroscopy at ca. 170 K) are simulated from AIMD trajectory, based on BO DFT calculations. We present here very good agreement between experimental and computed OH frequency red‐shift on CO adsorption in dealuminated zeolite Y. It is shown that extracting nonharmonic OH frequencies from ab initio molecular dynamics trajectory provides better estimate of experimental IR results than standard vibrational analyses due to realistic computational model and better correspondence with experimental conditions.

Diffusion of aromatic hydrocarbons in hierarchical mesoporous H-ZSM-5 zeolite

Hierarchical mesoporous zeolites exhibit higher catalytic activities and longer lifetime compared to the traditional microporous zeolites due to improved diffusivity of substrate molecules and their enhanced access to the zeolite active sites. Understanding diffusion of biomass pyrolysis vapors and their upgraded products in such materials is fundamentally important during catalytic fast pyrolysis (CFP) of lignocellulosic biomass, since diffusion makes major contribution to determine shape selectivity and product distribution. However, diffusivities of biomass relevant species in hierarchical mesoporous zeolites are poorly characterized, primarily due to the limitations of the available experimental technology. In this work, molecular dynamics (MD) simulations are utilized to investigate the diffusivities of several selected coke precursor molecules, benzene, naphthalene, and anthracene, in hierarchical mesoporous H-ZSM-5 zeolite. The effects of temperature and size of mesopores on the diffusivity of the chosen model compounds are examined. The simulation results demonstrate that diffusion within the microspores as well as on the external surface of mesoporous H-ZSM-5 dominates only at low temperature. At pyrolysis relevant temperatures, mass transfer is essentially conducted via diffusion along the mesopores. Additionally, the results illustrate the heuristic diffusion model, such as the extensively used Knudsen diffusion, overestimates the diffusion of bulky molecules in the mesopores, thus making MD simulation a powerful and compulsory approach to explore diffusion in zeolites.

Iron and Copper Active Sites in Zeolites and Their Correlation to Metalloenzymes.

Metal-exchanged zeolites are a class of heterogeneous catalysts that perform important functions ranging from selective hydrocarbon oxidation to remediation of NO x pollutants. Among these, copper and iron zeolites are remarkably reactive, hydroxylating methane and benzene selectively at low temperature to form methanol and phenol, respectively. In these systems, reactivity occurs at well-defined molecular transition metal active sites, and in this review we discuss recent advances in the spectroscopic characterization of these active sites and their reactive intermediates. Site-selective spectroscopy continues to play a key role, making it possible to focus on active sites that exist within a distribution of inactive spectator metal centers. The definition of the geometric and electronic structures of metallozeolites has advanced to the level of bioinorganic chemistry, enabling direct comparison of metallozeolite active sites to functionally analogous Fe and Cu sites in biology. We identify significant parallels and differences in the strategies used by each to achieve high reactivity, highlighting potentially interesting mechanisms to tune the performance of synthetic catalysts.

The influence of porosity and active sites of zeolites Y and beta on the co-cracking of n-decane and 2-ethylphenol

We investigated the cracking of n-decane and 2-ethylphenol as co-substrate in a 90/10 wt.-% mixture over zeolites Y and beta. The use of these substrates aimed to better understand the occurring chemistry in applications such as Co-FCC. We employed a number of different zeolites Y with different amounts of active sites and pore volumes. Additionally, the pore system of zeolite beta was modified by basic leaching. The materials were characterized by N2 physisorption, ICP-OES, XRD, 27Al, 1H, 13C MAS NMR, NH3-TPD, IR and TGA. It was found that the activity of the catalysts depends on the number of Brønsted acid sites as determined by NMR spectroscopy. Also most important is the mesopore volume/mesopore surface which is beneficial for the diffusion towards the micropores, especially for zeolite Y that is able to deoxygenate phenols.

A study on the effect of SiO2/Al2O3 ratio on the structure and performance of nano-sized ZSM-5 in methanol to propylene conversion

The effect of SiO2/Al2O3 ratio on high silica content nano-sized HZSM-5 stability and selectivity in conversion of methanol to propylene (MTP) has been investigated in a continuous flow isotherm fixed-bed reactor. Highly crystalline HZSM-5 zeolite samples with SiO2/Al2O3 ratios ranging 150–200 have been prepared and characterized using XRD, ICP-AES analytical techniques, NH3-TPD, BET surface area and SEM imaging for studying their physical and chemical behavior. The reaction was conducted at 480 °C and 1bar with WHSV = 1 h−1 and a solution with 1:1 wt% of methanol and water as feed. Over thoroughly monitoring the catalyst synthesis conditions, the nanocrystal ZSM-5 zeolite samples were fabricated with fairly close microstructural properties and crystal sizes in order to be able to study the effect of SiO2/Al2O3 ratio on the ZSM-5’s performance in MTP. Results show that although the crystal size does not considerably affect the elementary structure of the zeolite active sites, it seems to be an influential factor in bond strength of Si–O versus Al–O. The results have also showed that increase of SiO2/Al2O3 ratio leads to higher selectivity and stability of catalyst.

Insight into the correlation between the adsorption-transformation behaviors of methylthiophenes and the active sites of zeolites Y

Correlation between the adsorption-transformation behaviors of 2-methylthiophene and 3-methylthiophene and the active sites of NaY, HY and rare earth ion-exchanged ultra-stable Y (REUSY) zeolites have been studied by using an in situ FTIR technique and an intelligent gravimetric analyser-mass spectrometer (IGA-MS) coupling technique. The results show that the bridging hydroxyls (OH) of Si and Al atoms located in the supercage of zeolites Y are the preferred active sites, leading to the protonation and cracking reactions of the methylthiophenes. The AlO+ active sites in the HY, and the Al(OH)2+ and RE(OH)2+ active sites in the REUSY both can make the oligomerization reaction occur at 303 and 373K, and especially, the RE(OH)2+ active sites significantly improve the oligomerization abilities. Besides, the activities and selectivities of the protonated 2-methylthiophene and 3-methylthiophene play a decisive role in the oligomerization pathways. As system temperatures of >473K, the oligomerization reaction is restricted, while the cracking reaction is improved. Thereby, modulation of the key active sites in adsorbents and system temperatures will be a good prospect for ultra-deep desulfurization in the future.

Investigation of metal-exchanged mesoporous Y zeolites for the adsorptive desulfurization of liquid fuels

Removal of sulfur from transportation fuels using zeolites as sorbents is an attractive desulfurization method, because of its low energy and cost requirements. However, diffusion limitations within the micropore structure of zeolites can reduce their adsorption capacity, especially when refractory sulfur compounds are present in fuels. Moreover, the selective adsorption of sulfur compounds from a mixture of hydrocarbons can be very challenging. The objective of this study was to address the aforementioned challenges of adsorptive desulfurization of fuels using metal-exchanged mesoporous Y zeolites. Mesoporosity was introduced in the Y zeolites by two top-down methods (desilication and surfactant-assisted). Metals, Ce and Cu, were introduced via ion-exchange. The prepared metal-exchanged mesoporous zeolites were characterized and tested in terms of their sulfur adsorption capacity using a fixed-bed column and model fuels. The strength of adsorption was determined using isosteric heat of adsorption calculations. Our results demonstrated that mesoporous Y reduced diffusion limitations and were very effective sorbents for removing sulfur compounds with high kinetic diameter, such as dibenzothiophene (DBT). Metals highly increased the selectivity toward sulfur compounds. According to experimental results, the tendency of thiophenic molecules to adsorb on the zeolites increase in the order of thiophene (TP)<benzothiophene (BT)<DBT. The results of this study revealed that metal-exchanged mesoporous Y zeolites have the potential to display remarkable sulfur removal properties since the mesopores allow access to zeolite active sites while the metal cations improve the selectivity and/or capacity for sulfur compounds.

Computational Insights into the Role of Metal and Acid Sites in Bifunctional Metal/Zeolite Catalysts: A Case Study of Acetone Hydrogenation to 2-Propanol and Subsequent Dehydration to Propene

We employ electronic structure calculations to elucidate the catalytic pathways on bifunctional metal/zeolite catalysts by modeling a HZSM-5-supported nickel tetramer cluster (Ni4-ZSM-5). Hydrogenation of acetone to 2-propanol followed by dehydration to propene have been investigated as model reactions. In Ni4-ZSM-5, we observe reverse hydrogen spillover, whereby the Brønsted hydrogen migrates from the zeolite active site to the metal cluster. Consequently, the zeolite-supported metal cluster becomes electron-deficient, facilitating the hydrogenation reaction. In contrast, studies conducted on the dehydration reaction pathways indicate that the Brønsted acid catalysis in HZSM-5 is preferred over the metal catalyzed pathway in the Ni4-ZSM-5 system, again as a result of the electron-deficient nature of the metal species.

Role of zeolite in the synthesis of liquid hydrocarbons from CO and H2 on a composite cobalt catalyst

It is found that the main role of zeolite in Fischer–Tropsch synthesis on a composite Co catalysts is to reduce the average molecular weight of hydrocarbons produced from CO and H2 on acid sites. Secondary transformations of hydrocarbons on zeolites seem to occur via a carbocation mechanism. The total composition of synthesis products depends on the zeolite properties and the mutual arrangement of zeolite and cobalt active sites. It is shown that in some cases, introducing H-form zeolite into the Co catalysts for Fischer–Tropsch synthesis increases the productivity and the selectivity to synthetic oil and lowers the selectivity to methane.

Impact of the Desilication Treatment of Y Zeolite on the Catalytic Cracking of Bulky Hydrocarbon Molecules

Mesoporosity was induced on a USY zeolite by means of an alkaline leaching process. Samples were immersed in 0.05, 0.10 and 0.20 M NaOH solutions during 15 min at room temperature and then were exchanged with NH4 + ions and calcined to yield the acid forms. The formation of mesopores with size ranging from 20 to 100 A increased with the concentration of NaOH. The modified zeolites were used at 30 wt% to formulate cracking catalysts with an inert SiO2 matrix. The catalytic performance of these catalysts in the conversion of 1,3,5-tri-isopropylbenzene was evaluated in a batch, fluidized bed reactor at 450, 500 and 530 °C, with a catalyst to oil relationship of 4.7 and contact times up to 16 s. The catalysts with the modified zeolites were more active in the cracking of these bulky molecules than the one with the parent, unmodified zeolite; moreover, the selectivity to the products of primary cracking reactions increased. These results reveal an enhanced diffusion of the reactant molecules to the zeolite active sites and of the products out of the catalyst particles.

On the Rational Design of Zeolite Clusters

We have applied density functional theory calculations to systematically investigate zeolite cluster-size convergence for two acid-zeolite-catalyzed processes related to the conversion of biomass: (1) the keto–enol tautomerization of acetone in HZSM-5 and HY and (2) the protonation and ring opening of furan in HZSM-5. We have used these reactions as platforms to study two different approaches for constructing successively larger cluster models of zeolites, with the aim of determining a protocol that converges the energy differences with minimal system size. One approach for cluster design involves counting framework bonds from the Brønsted acid-site aluminum atom. Another approach involves applying multicentered spherical cutoffs based on geometries of the zeolite active site, the adsorbed reactant, and the adsorbed product. We have investigated the convergence of reaction energies using single-point calculations on clusters containing as many as 166 tetrahedral (T) atoms and geometry optimizations on clusters with as many as 78 T atoms. For all reactions studied, convergence rates of single-point reaction energies agree well with those from geometry-optimized clusters. In addition, converged and optimized reaction energies agree well with previously published values for all reactions. Our central finding is that clusters generated with multicentered spherical cutoffs yield converged reaction energies with smaller system sizes than clusters generated by counting framework bonds. This method, employing a single length scale (5 Å), converges reaction energies with respect to system size to within chemical accuracy (±1 kcal/mol), and it includes between 15 and 34 T atoms in the cluster depending on the process and zeolite framework under investigation. We suggest a general protocol for generating such clusters for subsequent use in computational studies of zeolites and other heterogeneous catalysts.

Effect of Oxygenate Impurities on the Conversion of Alcohols to Olefins

This Article is focused on the study of the effect of oxygenate impurities like esters and acids in the mixed methanol and ethanol feed stream on the conversion of methanol and ethanol to light olefins. The conversion of such components at 450 °C over ZSM-5 was investigated. Furthermore, the effect on conversion and selectivity of adding yttrium oxide to the catalyst was studied. It was shown that the presence of relatively small amounts of esters in the alcohol feed stream has a significant effect on catalyst lifetime. These esters will decompose on the zeolite surface leading to additional methanol or ethanol (depending on the type of ester) and to a carboxylic acid. The additional methanol or ethanol will react according to the alcohol to olefins mechanism, leading to either an increase or a decrease in the propylene/ethylene (P/E) selectivity ratio, respectively. The acid that is released upon decomposition of the ester is responsible for the decrease in lifetime of the zeolite by adsorption on the zeolite active sites. Addition of metal oxides, specifically yttria, to ZSM-5 limits this decrease in catalyst lifetime. The proposed pathway is by a stronger adsorption of the acid on yttria than on the active site of the zeolite. Removal of the acid by yttria can in some cases (typically when the ester conversion is not 100% without the yttria present) lead to a higher conversion of the ester and thereby indirectly to an effect on the P/E selectivity ratio due to the additional methanol or ethanol released.

Role of Acidic Proton in the Decomposition of NO over Dimeric Cu(I) Active Sites in Cu-ZSM-5 Catalyst: A QM/MM Study

The influence of protons on the mechanism of the direct decomposition of NO over adjacent dimeric Cu(I) active sites in zeolite is theoretically investigated by using ONIOM (QM/MM) calculations with two dicopper model systems 1T and 2T, where the Cu(I) atoms are separated by one and two SiO4 tetrahedra, respectively. The reaction proceeds through the formation of N2O as a reaction intermediate and further its decomposition into oxygen and nitrogen. The present study shows that the presence of proton plays an important role in the production of N2O from two NO molecules. In the proton-free mechanism, this process requires a large activation barrier of 56.3 and 55.3 kcal/mol on 1T and 2T, respectively, while the inclusion of protons reduces it to 31.4 and 17.3 kcal/mol. The significant decrease in the activation barrier is due to the strengthening of the N–N bond of the formed NO dimer upon protonation, which facilitates the formation of N2O. On the other hand, the presence of protons disfavors the decomposition of N2O and needs an activation barrier of 6–9 kcal/mol higher than that of the corresponding reaction in the absence of protons. The stable intermediate Cu–OH+–Cu formed in the proton-assisted mechanism is responsible for the larger activation energy for N2O decomposition. The proton-assisted NO decomposition mechanism is in agreement with the experimental observation that the decomposition of N2O as well as O2 desorption are the governing reaction steps in the decomposition of NO. The present study explains the role of the Cu–O–Cu species in the NO decomposition reaction. The results disclosed herein will also pave a way to understanding the mechanism of the reductive N–N coupling of NO molecules catalyzed by metalloenzymes and transition-metal catalysts.

Natural zeolite reactivity towards ozone: The role of compensating cations

Among indoor pollutants, ozone is recognised to pose a threat to human health. Recently, low cost natural zeolites have been applied as alternative materials for ozone abatement. In this work, the effect of compensating cation content of natural zeolite on ozone removal is studied. A Chilean natural zeolite is used here as starting material. The amount of compensating cations in the zeolite framework was modified by ion exchange using an ammonium sulphate solution (0.1molL−1). Characterisation of natural and modified zeolites were performed by X-ray powder diffraction (XRD), nitrogen adsorption at 77K, elemental analysis, X-ray fluorescence (XRF), thermogravimetric analysis coupled with mass spectroscopy (TGA-MS), and temperature-programmed desorption of ammonia (NH3-TPD). Ozone adsorption and/or decomposition on natural and modified zeolites were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results show that the zeolite compensating cation content affects ozone interaction with zeolite active sites. Ammonium ion-exchange treatments followed by thermal out-gassing at 823K, reduces ozone diffusion resistance inside the zeolite framework, increasing ozone abatement on zeolite surface active sites. Weak and strong Lewis acid sites of zeolite surface are identified here as the main active sites responsible of ozone removal.

Decomposition of nitrous oxide over Co-zeolite catalysts: role of zeolite structure and active site

A series of Co exchanged zeolites with ZSM-5, BEA, MOR and USY structures were prepared and investigated for N2O catalytic decomposition under identical reaction conditions. It is found that Co-zeolites with different structures show dramatically different catalytic activities, which could be attributed to various Co species formed in them. Co-ZSM-5, Co-BEA and Co-MOR exhibit much higher activities than Co-USY catalysts, which is attributed to the predominant formation of active isolated Co2+ ions in the ion exchange positions; while in Co-USY Co mainly exists as less active Co oxides. Moreover, it is observed that the activities of Co2+ ions in ZSM-5, BEA and MOR zeolites are quite different and are related to the specific Co ion sites presented in each zeolite structure. In Co-ZSM-5, the most active sites are the α-type Co ions, which are weakly coordinated to framework oxygens in the straight channel. On the other hand, in Co-BEA and Co-MOR, the most active sites are β-type Co ions, which are coordinated to the framework oxygens of the elongated six-membered ring of BEA and the interconnected small channel of MOR, respectively. The main factors affecting the activities of these individual Co ions are indicated to be their location in the zeolite structure, their chemical coordination and the distances between the Co ions. The highest activity of the α-type Co ions in ZSM-5 could be attributed to their favorite location in the zeolite and weak coordination to framework oxygens, which make them easily accessible and coordinated to reactants. The large number of β-sites and their structural arrangement in MOR allow the formation of two unique adjacent β-Co ions in Co–Co pairs, which cooperate in N2O splitting, consequently yielding the high activity of β-Co ions in MOR.

Direct synthesis of DME from syngas on hybrid CuZnAl/ZSM-5 catalysts: New insights into the role of zeolite acidity

A commercial HZSM-5 zeolite (Si/Al = 16) was submitted to mild acid treatment and partial exchange of H + by Na + and Co 2+ cations in order to produce samples with different amounts and strengths of Brønsted and Lewis acid sites. The acid properties of the zeolites were determined by both FTIR of adsorbed pyridine and NH 3-TPD. Then, hybrid catalysts comprising a CuO/ZnO/Al 2O 3 (CZA) methanol synthesis catalyst and the original and treated zeolites were prepared in order to analyze the impact of the zeolite acidity in the efficiency of the hybrids for the direct syngas-to-DME process. Independent methanol dehydration experiments on the bare zeolites and syngas-to-DME runs under methanol dehydration-controlled conditions were performed using hybrids with low zeolite concentration (CZA:zeolite mass ratio of 10:1) prepared by mixing the pre-pelletized CZA and zeolite components. The results revealed that both strong Brønsted and EFAL-related strong Lewis acid sites are the likely zeolite active sites for methanol dehydration at the typical syngas-to-DME temperature of 260 °C. Interestingly, we have found that different conclusions regarding the effect of zeolite acidity may be reached depending on the specific method used for preparing the hybrid catalysts when the overall syngas-to-DME process becomes controlled by the methanol synthesis rate on the Cu-based catalyst (i.e. using hybrids with a CZA:zeolite mass ratio of 2:1, that is, with an “excess” of acid sites). Thus, for hybrids prepared by mixing the pre-pelletized components, the same CO conversion and product selectivity (with values approaching those predicted by the thermodynamic equilibrium at the studied conditions) with no signs of deactivation during at least 50 h on stream was attained irrespective of the zeolite acidity. By contrast, significant differences in catalyst stability were found for hybrids prepared by grinding the component powders prior to pelletizing. This fact points towards the occurrence of detrimental interactions between the CZA and zeolite components during the grinding preparation stage. The kind and extent of such detrimental interactions are tightly related to the properties (i.e. acidity, chemical composition) of the ZSM-5 zeolite.