Bronsted Acid Sites Research Articles

Facilely adjusting acidity features of zeolites by steaming treatment for enhanced methanol conversion to aromatics: A mechanism study

In this contribution, the effects of the steaming treatment on the acidity and aluminum structure of ZSM-5 were systematically investigated by using different types of zeolite catalysts. The relationships between the acid properties and the catalytic performance of the methanol-to-aromatics (MTA) reaction were also elucidated. The results revealed that different kinds of acid sites showed varied stability during the steaming treatment. Especially for Brønsted acid sites (BAS), the reduction of the acid site was highly related to the stability of different distributed framework Al sites (Alsingle > Alpairs) and the existence of non-framework species (“neutralization” by the EFAL and ZnO). Additionally, the presence of the extra-framework aluminum (EFAl) and metal compensation ions could enhance the stability of the zeolite framework Si-O(H)-Al. Besides, it was found that the reduction degree in the content of the Zn-LAS (LAS = Lewis acid sites) was less than the Al-LAS. The effects of steaming treatment on acid properties over zeolites with different particle sizes were also explored. Furthermore, the catalytic performance for the MTA reaction showed that the stability of the ZSM-5 catalyst was significantly enhanced after the steaming treatment. Moreover, the reduction in the proportion of the Alpairs sites may inhibit the hydrogen-transfer aromatization process of alkenes, while the increase of the Alsingle species enhanced the cracking process of higher olefins, leading to the reduction of aromatics selectivity and the increase of light olefins selectivity, respectively.

Dynamic Formation of Brønsted Acid Sites over Supported WOx/Pt on SiO2 Inverse Catalysts─Spectroscopy, Probe Chemistry, and Calculations

Platinum-tungsten oxides are among the most studied metal–metal oxide pair catalysts for C–O hydrogenolysis reactions. The Brønsted acid density and synergy between Pt and WOx, especially in the inverse structure, are critical to reactivity and selectivity. However, a clear molecular-level understanding of the formation and dynamics of Brønsted acid sites (BAS) is lacking. Here, using in situ spectroscopic characterizations (Raman and FTIR), chemical probing (CO chemisorption and pyridine titration), density functional theory (DFT) calculations, and a model reaction (tert-butanol dehydration), we demonstrate the structural evolution of WOx species and associated BAS dynamics in various environments. In situ Raman and DFT calculations show that below monolayer coverage, the WOx species stay as isolated monomers on the SiO2 support and W3Ox trimers on Pt. The W3Ox trimers on Pt are dynamic and 10× more active toward dehydration than the WOx species on the SiO2 support. H2 plays a complex role: at low temperatures (<473 K), it creates more BAS in the form of W3O7H on Pt by reversible hydrogen spillover, and at higher temperatures (>573 K), it partially reduces the W3Ox. We further show that the inverse configuration allows changes in the BAS density via catalyst pretreatments. This study provides a strategy for tuning Brønsted acid density and regenerating sites by pretreatment and catalyst composition.

Towards selective glycerol hydrodeoxygenation to 1,3-propanediol with effective Pt-WOx catalyst design: Insights from first principles

DFT simulations predicted the C-O bond cleavage in glycerol on Brønsted acidic Pt-WOx catalyst under a hydrogen atmosphere to be via a “protonation dehydration” mechanism. Interfacial Pt-WOx sites facilitate Brønsted acid (BA) site formation by hydrogen spillover and synergistic activity of Pt and WOx. At strong BA sites, selective formation of 1,3-PDO is likely due to the large difference of over 40 kJ/mol in primary and secondary C-O bond cleavage barriers. The secondary C-O bond cleavage has a linear relation with NH3 binding energy while there is a non-monotonic trend for the primary C-O cleavage. Hence, Brønsted acid strength is a potential descriptor for the catalyst activity and 1,3-PDO selectivity. Synthetic strategies enabling fine dispersion of WOx to trimeric units on the Pt nanoparticles, while preventing W doping and agglomeration of WOx to 3D WO3 on small Pt nanoparticles are desirable for high BA strength and thereby 1,3-PDO yield.

Remarkable N2-selectivity enhancement of NH3-SCR over HPMo modified MnCo-BTC@SiO2 catalyst

In this work, the phosphomolybdate (HPMo) modification strategy was applied to improve the N2 selectivity of MnCo-BTC@SiO2 catalyst for the selective catalytic reduction of NOx, and further, the mechanism of HPMo modification on enhanced catalytic performance was explored. Among MnCo-BTC@SiO2-x catalysts with different HPMo concentrations, MnCo-BTC@SiO2-0.75 catalyst exhibited not only the highest NH3-SCR performance (∼95% at 200-300°C) but also the best N2 selectivity (exceed 80% at 100-300°C) due to the appropriate redox capacity, greater surface acidity. X-ray photoelectron spectrometer (XPS) and temperature programmed reduction of H2 (H2-TPR) results showed that the modification with HPMo reduced the oxidation-reduction performance of the catalyst due to electron transfer from Mo5+ to Mn4+/Mn3+ and prevent the excessive oxidation of ammonia adsorption species. NH3 temperature-programmed desorption of (NH3-TPD) results showed that the modification with HPMo could significantly improve the surface acidity and NH3 adsorption, which enhance the catalytic activity and N2 selectivity. In-situ diffused reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) revealed that modification with HPMo increased significantly the amount of adsorbed NH3 species on the Bronsted acid site and CB/CL, it suppressed the production of N2O by inhibiting the production of NH species, the deep dehydrogenation of ammonia adsorption species. This study provided a simple design strategy for the catalyst to improve the low-temperature catalytic performance and N2 selectivity.

Supported Ionic Liquid Catalysts for the Oxidation of S- and N-Containing Compounds—The Effect of Bronsted Sites and Heteropolyacid Concentration

In this article, a series of effective catalysts based on betaine and sulfuric or phosphomolybdic acids was obtained. These compositions were characterized by various physicochemical methods and tested in the oxidation of sulfur- and nitrogenous-containing compounds by H2O2. An increase in the amount of heteropolyacid (HPA) leads to a non-linear change in acidity, and the degree of removal of sulfur-containing compounds correlates with the concentration of Bronsted acid sites on the surface. On the contrary, the degree of pyridine removal is determined primarily by the content of heteropolyacids in the catalyst.

Superior adsorption and removal of toxic industrial dyes using cubic Pm3n aluminosilica form an aqueous solution, Isotherm, Kinetic, thermodynamic and mechanism of interaction

In the current work, a direct synthesis method was used to create an ordered mesocage cubic Pm3n aluminosilica nanoadsorbent with mesopores and a monolith-like shape. Rhodamine B (RB), a harmful dye for the environment, was successfully removed from wastewater using this aluminosilica nanoadsorbent. The aluminosilica nanoadsorbent's multi-directional pores (3D), mesostructural geometries, and loading amount of Bronsted acid sites were important in improving the coverage of the nanoadsorbent surfaces and intra-particle diffusion of adsorbate (RB) molecules onto the network surfaces and into the pore architectures of monoliths. The cubic Pm3n aluminosilica composite was characterized via XRD, EDX, XPS, FT-IR, HRSEM, BET, HRTEM, and pHzpc which was 4.05. The effect of pH on the adsorption process has been studied. In addition, the initial concentration approves that the reaction fitted to Langmuir. While, during the study, the effect of time the adsorption kinetic model was fitted to the pseudo-second order. On the other hand, the effect of temperature was proof that the reaction was spontaneous and endothermic. The RB was adsorbed at cubic Pm3n aluminosilica composite with high amount 1.75 mmLg−1. However, the reusability showed that the efficiency of the removal of RB using this adsorbent was more than 91 % after 6th cycle. The capability to design reversal RB adsorption systems with several reuse cycles is a key characteristic of the cubic Pm3n aluminosilica composite.

Theoretical study of the influence of H-SAPO-34 modified with Zn2+ on the formation of butadiene

In the process of methanol to olefin (MTO), dienes are the precursors of aromatic species. Experimental study showed that Zn2+ modified H-SAPO-34 (Zn@H-SAPO-34) promoted aromatics formation at the initial stage of MTO reaction. Our recent work reported the reaction mechanism of the aromatization of dienes to low methylbenzene aromatics catalyzed by Zn@H-SAPO-34. Herein, using density functional theory (DFT), the possible reaction pathways of diene formation on H-SAPO-34 with and without Zn doping were systematically investigated with propene as the initial olefin. After Zn2+ modification, the acidic strength of adjacent Brønsted acid sites (BAS) is enhanced, which is conductive to the alkene-mediated butadiene formation pathway catalyzed by B-acid, and the Lewis acid produced by Zn2+ provides catalytic site for the transfer dehydrogenation reaction of methanol with propene, which promotes the formation of formaldehyde and induces the formaldehyde-mediated mechanistic pathway. Further microkinetic calculation reveals that formaldehyde-mediated pathway is the optimal reaction pathway for butadiene formation. This study demonstrates that the synergistic effect of BAS and LAS improves the formation activity of diene on Zn@H-SAPO-34. This work will help to deepen the understanding of the role of Zn2+ in the early stage of MTO reaction.

Hydroisomerization of n-hexane over metal oxides-loaded fibrous silica catalyst for cleaner fuel production

Fibrous silica (KCC-1) was impregnated with cobalt (Co), iron (Fe), and zinc (Zn) oxides which are denoted as Co/KCC-1, Fe/KCC-1 and Zn/KCC-1 for hydroisomerization of n-hexane. The characterization analysis revealed that the introduction of Co, Fe, and Zn into KCC-1 significantly altered the physicochemical properties of KCC-1 including reduced surface area, pore volume as well as crystallinity. Pyridine adsorbed IR showed that higher amount of the Lewis acid sites (LAS) and Brønsted acid sites (BAS) when introduced the Co, Fe, and Zn into KCC-1. Interestingly, a new band at 1610 cm−1 of Zn/KCC-1, corresponds to the presence of LAS by the formation of binuclear species of Zn in the form of [ZnOZn]2+. The formation of [ZnOZn]2+ was further confirmed by the presence of a band at 350 nm and higher intensity of the binding energy at 1022.8 eV from UV-DRS and XPS analysis, respectively. From temperature-programmed reduction analysis, these binuclear species were formed at a higher temperature, which has a stronger interaction with the KCC-1. The proposed formation of [ZnOZn]2+ was also discussed in this work. Based on the n-hexane hydroisomerization, the Zn/KCC-1 possessed the most excellent catalytic performance amongst the catalysts owing to the existence of the binuclear species of [ZnOZn]2+, which acts as a new acidic center in the stabilization of generated protonic acid sites by trapping of electrons, resulting in increased isomers yield of n-hexane as well as no cracking products. Zn/KCC-1 showed the lowest activation energy compared to other catalysts within 423–673 K.

Unusual Acid Sites in LSX Zeolite: Formation Features and Physico-Chemical Properties

The advanced approach for the preparation of the NH4 form of highly crystalline LSX zeolite under gentle drying conditions (40 °C, membrane pump dynamic vacuum) is discussed. Decationization of this form at moderate temperatures led to the formation of Brønsted acid sites (BASs), whose concentration and strength were characterized by IR spectroscopy. It was found that a maximum concentration of three BASs per unit cell can be achieved at 200 °C prior to the initiation of zeolite structure degradation. The proton affinity of BASs is unusual, and aspires 1240 kJ/mol, which is significantly higher compared to faujasites with higher moduli. The increase in temperature of the heat treatment (up to 300 °C) resulted in thermal decomposition of BASs and the manifestation of amorphous phase with corresponding Lewis acid sites (LASs) as well as terminal Si-OH groups. Both the destruction of BASs and formation of the LAS-containing amorphous phase are the key reasons for the significant decrease in the adsorption capacity in the micropore region revealed for the sample decationized at 300 °C.

Synthesis of etheric ester based biofuel additive over bifunctional metal/zeolite catalysts comprising NiRe nanoparticles and Beta zeolite

Biomass derived etheric ester compounds show promising applications as renewable fuel additives and solvents. In this study, we reported the preparation of bifunctional transition metal/zeolite catalysts comprising Ni-Re bimetal nanoparticles and Beta zeolites prepared via conventional wet-impregnation method. The bifunctional nature makes it possible for the synthesis of ethyl-4-ethoxy pentanoate (EEP) as etheric ester starting from ethyl levulinate (EL) in presence of H2 with good performance. The textural properties and acidity of the catalysts were characterized by several techniques: XRD, TEM, STEM-Mapping, H2-TPR and XPS. The addition of ReOx increased the dispersion and reducibility of NiO·NH3-TPD and in-situ FT-IR of pyridine adsorption confirmed that the NiReOx/Beta catalyst affords large amount of Lewis acid sites and certain amount of Bronsted acid sites. The attained Bronsted acid sites in BEA topology may be the key sites contributing to the etherification. Under optimized reaction conditions, namely 160 °C, 1 MPa H2 and reaction time of 2 h, almost full conversion of EL with 83% yield of EEP could be achieved in ethanol.

Promotional effects of Ag on catalytic combustion of cyclohexane over PdAg/Ti-SBA-15

Recently, PdM bimetallic nanoparticle-supported catalysts have attracted considerable attention as superior catalysts for VOC combustion due to the promotional effect rendered by the added second metal. However, the promotional effect is rarely investigated. In this study, Ti-SBA-15-supported bimetallic PdAg nanoparticle catalysts with different molar ratios were prepared. Compared to Pd/Ti-SBA-15 and Ag/Ti-SBA-15, Pd13Ag1/Ti-SBA-15 with a loading amount of 0.63 wt% exhibited superior activity. Furthermore, Pd13Ag1/Ti-SBA-15 exhibited outstanding stability in the on-stream reaction. The excellent catalytic performance of Pd13Ag1/Ti-SBA-15 was mainly ascribed to the synergistic effect of Pd and Ag in promoting the key steps of cyclohexane combustion. The reaction pathways of cyclohexane over the samples were proposed on the basis of the analysis of the key intermediates generated during catalytic combustion by in situ DRIFTS and PTR-TOF-MS. Higher concentrations of cyclohexene, benzene, and light olefins were generated over Pd13Ag1/Ti-SBA-15 in comparison with those generated over Pd/Ti-SBA-15 at a temperature range of 180–220 °C, demonstrating that the addition of Ag to Pd/Ti-SBA-15 promotes the key steps of the oxidative dehydrogenation of cyclohexane to benzene and catalytic cracking of cyclohexane to olefins due to the increase of Lewis and Bronsted acid sites over Pd13Ag1/Ti-SBA-15. Revealing the promotional effect of bimetallic catalysts on catalytic VOC combustion would be beneficial for the design of bimetallic catalysts with high efficiencies and cost-effectiveness.

Ni2P/Beta@SBA-16 core-shell catalyst with tunable shell thickness for the hydrodenitrogenation of quinoline

A series of core-shell structural hydrodenitrogenation (HDN) catalyst supports, using H-Beta zeolite nanoparticles as the core and tunable mesoporous materials SBA-16 thin film thickness as shell, were designed and controllably synthesized. The corresponding Ni2P catalyst were prepared, and their catalytic performances were tested for quinoline HDN. It was found that the high external surface area provided by the mesoporous shell layer of the core-shell catalyst favored the formation of Ni2P nanoparticles with more uniform particle size. The Py-IR result indicates that the SBA-16 shell thickness plays an important role in influencing the ratio of the amount of Bronsted and Lewis acid sites on the catalyst. The H2-TPR results indicates that the introduction of core-shell structure can adjust the metal-support interactions (MSI) of materials. The core-shell support with suitable shell thickness (70 nm) exhibits a wide pore structure, large surface area and sufficient amounts of Lewis and Bronsted acid sites. These properties contribute to the formation of tiny and size homogeneous (4.6 nm) Ni2P nanoparticles. Smaller Ni2P particles present more active sites, which increases catalytic activity. The Ni2P/H-Beta@SBA-16–2 catalyst with the most suitable shell thickness exhibited a higher reaction rate constant and TOF for HDN reaction of quinoline.

Comparing the effects of hollow structure and mesoporous structure of ZSM-5 zeolites on catalytic performances in methanol aromatization

Comparing the effects of hollow and mesoporous structures over ZSM-5 zeolites on catalytic behaviors in methanol aromatization was done. Hollow zeolites possessing larger voids, increasing Bronsted acid sites and more framework Al in channel crossings promoted higher benzene, toluene and xylene (BTX) selectivity. Zero-length column (ZLC) desorption of cyclohexane stated that higher diffusion rate was observed over mesopores zeolite and hollow zeolite. However, lower effective diffusion constants (Deff) and higher activation energy of hollow zeolite demonstrated that mass transfer was not only limited by microporosity but by surface barriers resulting from surface defects and pore blockage. The highest diffusion rate of cyclohexane over hollow zeolite was presented indicating that surface barrier was not dominant in diffusion limitation. The stability of hollow ZSM-5 was lower compared to mesoporous ZSM-5 as a result of more strong acid sites and higher external silanol groups, which favored to carbon deposition. Additionally, the collapse of hollow structures with thinner shells also contributed to higher deactivation rate.

Synergistic Catalysis of Brønsted Acid, Al-Lewis Acid, and Zn-Lewis Acid on Steam-Treated Zn/ZSM-5 for Highly Stable Conversion of Methanol to Aromatics

The development of stable and selective ZSM-5 catalysts for methanol aromatization remains an ongoing challenge. Here, we demonstrate highly stable aromatization on ZSM-5 by preliminary steam treatment before Zn introduction. Steam treatment destroyed part of frameworks, which decreased acid density from 0.5 to 0.25 mmol g–1 and increased Al-Lewis acid sites (Al-LAS) at the expense of Brønsted acid sites (BAS). However, aromatization activity was further increased and the lifetime was still kept at 100 h. A comparative experiment found that increasing the SiO2/Al2O3 ratio from 60 to 240 also decreased acid density to 0.25 mmol g–1, but BAS-based acid sites aggravated coke formation and reduced lifetime to 50 h. This reflected that Al-LAS and BAS on steam-treated ZSM-5 provided synergistic catalysis for stable aromatization. Introducing Zn into steam-treated ZSM-5 further transformed part of BAS to Zn-LAS but not changed acid density, which determined increased aromatics selectivity and a quite different well-maintained stability.

Bifunctional zirconium-based metal-organic frameworks as chemoselective catalysts for the synthesis of γ-valerolactone from furfural via a one-pot cascade reaction

The transformation of lignocellulosic biomass to platform compounds (γ-valerolactone, GVL) was a significant component in biomass development. Herein, sulfonated Zr-based metal-organic frameworks (MOF-808), a bifunctional heterogeneous catalyst with Lewis and Bronsted acid sites, were prepared to catalyze the one-pot cascade reaction of furfural (FUR) to GVL. The successful modification of the sulfonic group on MOF-808 was substantiated by multiple characterization methods. By adjusting the sulfuric acid concentration to balance the Lewis acid and Bronsted acid sites of the catalyst, S-808–2.37 was confirmed as the preferred catalyst and a 60.4 % GVL yield was achieved with 99.1 % carbon balance under the optimal conditions. Moreover, the 72.8 % GVL yield reached in the 40x magnification experiment also boded well for the catalyst’s application potential. The work in this paper opened up new perspectives for the application of MOF-808 porous materials in the field of selective catalytic conversion of biomass involving multi-step reactions.

Fluorescence color transformation of trans-4-[4-(N,N′-dimethylamino)styryl]pyridine-loaded UiO-66 for monitorable drug release

Fluorescent molecules confined into the nanopores of metal-organic frameworks generally display alterant luminescence properties, which exhibits broad application prospects. Herein, trans-4-[4-(N,N′-dimethylamino)styryl]pyridine (DMSP) was confined in the nanocavities of UiO-66, and the concomitant fluorescence color change made this host-guest material capable to act as a drug carrier that monitored drug release with luminescence. DMSP radiated green fluorescence with excitation and emission wavelengths at 381 and 478 nm, respectively. While after DMSP was confined in UiO-66, the excitation and emission wavelengths respectively red-shifted to 528 and 579 nm, accompanied by orange fluorescence emission. This luminescence color transformation was confirmed to be associated with the interaction of pyridine N-atom in DMSP with Bronsted acid sites in UiO-66, enhancing the electron push-pull effect of DMSP. This host-guest material remained the biocompatibility, porosity and degradability of UiO-66, and moreover the fluorescence color transformation from orange to green occurred after its decomposition by PO43−. On this basis, this host-guest material was capable to serve as a drug carrier that monitored drug release with the fluorescence signal, which facilitated the visual tracking of drug release in vivo.

Conjugate acid-base bi-functional polymeric ionic liquids (CAB-PILs) as efficient catalysts for CO2 capture and subsequent glycidol cycloaddition reaction

Conjugate acid-base bi-functional PILs (CAB-PILs) with carboxylate and carboxyl branches were synthesized and used as catalysts for the cycloaddition reaction of glycidol with CO2. Two functional ionic monomers, 3-(carboxymethyl)-1-vinyl-1H-imidazol-3-ium chloride (CEImCl) and 2-(1-vinyl-1H-imidazol-3-ium-3-yl) acetate (CCIm), were introduced into the CAB-PILs skeleton. In this case, we proved the excellent characteristics of the catalyst containing both Lewis base and Bronsted acid sites for converting CO2 to cyclic carbonate under mild conditions. The catalyst showed good reusability and remained excellent activity after five reaction cycles. Combined with XPS, FTIR and DFT calculations, it is proved that the CCIm ionic monomer not only play the role of CO2 absorption center, but also has synergistic effect with CEImCl in CAB-PILs to promote cycloaddition reaction.

Novel Complex Titanium NASICON-Type Phosphates as Acidic Catalysts for Ethanol Dehydration

The conversion of ethanol towards ethylene and diethyl ether in the presence of catalysts requires special consideration from the perspective of green chemistry. Ethanol dehydration was studied on a complex titanium phosphate MAlTiP (M0.5(1+x)AlxTi2-x(PO4)3 with M = Ni, Mn (x = 0; 0.2)) catalysts, alongside a NASICON-type structure synthesized by the sol–gel method. The initial catalysts were characterized by N2 gas sorption, SEM, XRD and spectroscopic methods (Raman and DRIFT of adsorbed CO and C6H6). The results revealed that all catalysts exhibited high activity and selectivity at 300–420 °C. The conversion of ethanol increases with the reaction temperature, reaching 67–80% at 420 °C. The MnAlTiP exhibited the highest ethylene selectivity among other catalysts, with 87% at 420 °C. The aluminum modification improved the acid properties of the catalysts, due to the appearance of Lewis acid sites (LAS) and the strength moderate Brønsted acid sites (BAS). It was shown that the activity of complex phosphates in ethanol dehydration increases with the strength of the Brønsted acid sites (BAS).

Design of Nickel Supported Hierarchical ZSM-5/USY Zeolite Bifunctional Catalysts for One-Pot Menthol Synthesis via Liquid-Phase Citral Hydrogenation.

Nickel-supported hierarchical zeolite catalysts were prepared through a desilication reassembly process under optimized conditions and applied in one-pot menthol synthesis. In this work, the hierarchical zeolite-supported metal bifunctional catalysts were prepared with the help of desilication re-assembly and wetness impregnation techniques and applied in menthol synthesis via citral hydrogenation. The prepared catalysts were characterized using PXRD, BET, FE-TEM, NH3-TPD, H2-TPR, pyridine adsorption, and ICP-OES techniques. As a result, the physicochemical and acidic properties, such as mesopore surface area, metal dispersion, acidity, catalytic activity, and strong Lewis acid sites of pure microporous ZSM-5/USY zeolites, were significantly improved. Consequently, with the occurrence of superior physicochemical and acidic properties, the Ni/HZ-0.5 M catalyst exhibited outstanding catalytic activity (100% conversion, TOF 7.12 h-1) and menthol selectivity (83%, 4 h) with uniform stability at 100 °C, 1.0 MPa hydrogen. Similarly, the cracking rate decreased with the decrease in Bronsted acid sites.

Impact of the Si/Al ratio on the ethanol/water coadsorption on MFI zeolites revealed using original quantitative IR approaches.

Advanced IR vibrational spectroscopic techniques, e.g., using a coupled gravimetric-IR surface analyzer (AGIR) and a high-throughput in situ IR cell (Carroucell), have been used for the quantitative studies of the adsorption and coadsorption of ethanol and water on MFI zeolites with different Si/Al ratios. The AGIR coupling is a powerful tool for the accurate determination of the molar adsorption coefficients during coadsorption experiments since their evaluation is based on the measurement of the exact amount of adsorbed species. The use of the Carroucell set up allows characterizing all the samples simultaneously, strictly in the same gaseous and temperature environment. The molar absorption coefficients of pure adsorbed ethanol and water are determined: their values are constant whatever the Si/Al ratio of the MFI zeolites. Moreover, these coefficients are found to be identical in the case of the water-ethanol coadsorption experiments. Their use allows obtaining the exact quantity of each adsorbate specie in the binary system. At low partial pressures, the unary water adsorption experiments suggest that the amount of adsorbed water results mainly from the preferential adsorption on Brønsted acid sites in tetrameric clusters. In contrast, the adsorption of EtOH occurs on both silanol groups and Brønsted acid sites (BASs). The effect of the Si/Al ratio is only observed at relatively low partial pressures. The effect of the Si/Al ratio on the ethanol adsorption capacity is also investigated. This study directs the choice of an appropriate zeolite once it is used in membranes for drying ethanol.