Desorption Of Pyridine Research Articles

Modification of chemical vapor-phase deposition and coking resistance over HZSM-5 catalysts for toluene disproportionation

Abstract To achieve higher catalytic activity of toluene disproportionation and improve the p-xylene selectivity and stability of coking resistance on HZSM-5 catalysts, tetrabutyl titanate, ethyl orthosilicate and diethyl phosphite were used for chemical gas-phase deposition modification on HZSM-5 catalysts. The properties of acid sites on catalysts were characterized by infrared spectroscopy (IR) and temperature-programmed desorption of pyridine (TPD), respectively. The experimental results showed that the type of acid sites and density of weaker acid sites over HZSM-5 zeolites deposited by oxides containing Ti, Si and P in chemical vapor coating did not change while the density of stronger acid sites decreased, in which acid intensity on HZSM-5 zeolite deposited by oxides containing P enhanced obviously. Using HZSM-5 zeolites modified as catalysts of toluene disproportionation, HZSM-5 catalysts deposited by oxides containing Si and P can greatly improve both catalytic activity and coking resistance on catalysts.

Ruthenium Catalysts Supported on Hydrothermally Treated Carbon from Rice Husk: The Effect of Reduction Temperature on the Hydrogenation Reaction of Levulinic Acid to γ-Valerolactone

Ru catalysts supported on activated carbon obtained by hydrothermal treatment of rice husk were evaluated in the hydrogenation reaction of levulinic acid to γ-valerolactone. The hydrothermally treated carbon was characterized by nitrogen physisorption, elemental analysis, and thermogravimetric analysis, and the catalysts were characterized by FTIR spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction, and temperature-programmed desorption of pyridine (acidic properties). Prior to the reaction, the catalysts were reduced at different temperatures in the range of 100–350 °C to evaluate the effect of the reduction temperature on the performance in the hydrogenation of levulinic acid. The reaction was carried out in a batch reactor at 70 °C and 1.5 MPa. The results of conversion and selectivity to γ-valerolactone showed that the catalyst with the best performance was the sample reduced at 200 °C. After 2 h of reaction, a γ-valerolactone yield of 74% was achieved. This catalyst presented the lowest acidity value, and the ruthenium-containing phase consisted mainly of RuO2, with a small portion of Ru0. The solid catalyst can be recovered and successfully reused for three runs with the GVL yield at 56%.

Facet-Dependent selectivity of CeO2 nanoparticles in 2-Propanol conversion

CeO2 nanoshapes, cubes with dominant (100) facets and octahedra with dominant (111) facets, were synthesized to investigate the influence of surface structure on acid-base properties. An optimization of calcination temperatures, coupled with Raman and TEM, was employed to minimize the intrinsic (Frenkel-type) defect sites and their potential complications on the facet studies involved in this work. The acid-base properties of these CeO2 nanoshapes were characterized with in situ pyridine and CO2 adsorption using infrared spectroscopy and quantified using pyridine, ammonia, and CO2 temperature-programmed desorption (TPD). The (100) facet displayed weaker acid sites with lower site density than the (111) facet which had a similar density of base sites but those on the (100) facet were stronger. A strong correlation was observed between 2-propanol conversion and each facet’s acid-base properties. CeO2 cubes exhibited greater base-site catalyzed dehydrogenation to acetone while the more acidic CeO2 octahedra were more active in dehydration to propene.

Effect of support acidity during selective hydrogenolysis of glycerol over supported palladium-ruthenium catalysts.

We report the role of the acidity of support during the selectivity hydrogenolysis of glycerol over supported bimetallic palladium-ruthenium (PdRu) catalysts. The PdRu nanoparticles were supported on a series of metal oxides and zeolitic supports via the modified impregnation method and tested for the liquid-phase hydrogenolysis of glycerol using gaseous hydrogen. The relative acid site densities of selected catalysts were determined by ammonia temperature-programmed desorption and pyridine desorption experiments. Based on these studies, we report a direct correlation between the catalytic activity (conversion and 1,2 propane diol yield) and two different acid sites (strong acid sites and very strong acid sites). Besides zeolite-supported catalysts, TiO2 supported PdRu nanoparticles exhibit moderate catalytic activity; however, this catalyst shows high selectivity for the desired C-O bond cleavage to produce C3 products over the undesired C-C bond cleavage to produce < C3 products. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Tungsten oxide-based materials as effective catalysts in isopulegol formation by intramolecular Prins reaction of citronellal

Several types of mixed WO3/SiO2/Al2O3 materials were prepared using sol–gel and wet impregnation methods. Four different loadings of WO3 (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X-ray diffraction, X-ray fluorescence spectroscopy, and their acidity was measured by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in Prins reaction—intramolecular cyclization of citronellal. Influence of reaction conditions (temperature 70–90 °C, catalyst amount 1–10 wt%, catalyst type) on citronellal conversion and selectivity of isopulegol formation was monitored. The best result (90% of isopulegol, 97% selectivity of isopulegol formation, 24 h) was obtained using W25 IMP catalyst (10 wt%, 50 °C). Possibility of catalyst reuse was confirmed.

Effects of Cerium Doping on Pt–Sn/Al2O3 Catalysts for n-Heptane Reforming

A series of trimetallic Pt–Sn–Ce catalysts supported on chloride Al2O3 was prepared by a sequential impregnation method and applied for n-heptane reforming and characterized by several techniques, including N2 physiosorption, transmission electron microscopy, X-ray diffraction, hydrogen temperature-programmed reduction, CO chemisorption, ammonia temperature-programmed desorption, pyridine desorption Fourier-transform infrared spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. We have demonstrated that the introduction of Ce can promote isomerization reactions by suppressing undesirable hydrogenolysis reactions, whereas it does not significantly influence the dehydrocyclization reactions. The characterization results show that CeOx can enhance the reducibility of Pt species via enhancing the Pt dispersion. In addition, Ce increases the proportion of medium-strength acid sites, which does not only promote isomerization activity, but also suppresses the undesirable reactions such as hydrogenolysis and cracking.

Contribution to MoO3–SiO2 and WO3–SiO2 utilization—active catalysts in jasmine aldehyde, 2-hexyl-1,3-dioxolane and methyllaurate synthesis

Several types of mixed molybdenum and tungsten oxide—SiO2 materials were prepared using sol–gel and wet impregnation method. In all cases, four different loading of MoO3 or WO3 (1, 10, 25 and 40 wt%) were prepared. Materials were characterized using X-ray diffraction, X-ray fluorescence spectroscopy and its acidity was determined by temperature programmed desorption of pyridine. Catalytic activity of these materials was tested in three model reactions providing valuable fine chemicals—aldol condensation, acetalization and esterification. These reactions are usually catalyzed by homogenous catalysts. With increasing interest in environmental protection these catalysts are replaced by heterogeneous ones—offering easy separation from reaction mixture and a possibility of catalyst reuse. More specifically the chosen reactions were: aldol condensation of benzaldehyde with heptanal giving jasmine aldehyde (1), acetalization of heptanal by ethylene glycol giving 2-hexyl-1,3-dioxolane (2) and esterification of lauric acid by methanol giving methyllaurate (3). The prepared materials proved to be catalytically active in above mentioned reactions—in aldol condensation was the best result (78% heptanal conversion, 58% selectivity to jasmine aldehyde, 24 h) obtained using Mo 40 material prepared by impregnation. This material showed to be the best together with W 40 material prepared by sol–gel process in esterification (91 or 94% conversion, 24 h). Acetalization occurs very willingly, best results (heptanal conversion > 90% and selectivity > 90%, 5 h) was obtained using Mo and W 25 and 40 prepared by sol–gel and impregnation process.

Tuneable Acidity in Fluorinated Al-SBA-15 Materials for the Esterification of Valeric Acid to Alkyl Valerates.

The acidity of Al-SBA-15 materials functionalized by ball milling with several niobium loadings (0. 25–1 wt.%) as well as with several fluorine loadings (by wet impregnation using NH4F as a precursor) was characterized and materials investigated in the esterification of valeric acid to alkyl valerates. The parent Al-SBA-15 support as well as the modified materials loaded with Nb and/or F have been catalysts synthesized characterized by X-ray diffraction (XRD), N2 physisorption measurements, and diffuse reflection infrared spectroscopy (DRIFT) among others. A special interest was paid on the acidity of the materials that was investigated by temperature-programmed desorption of pyridine. Interestingly, the characterization results for the materials containing fluorine showed up an increase in the acidity strength despite of a reduction in the number of acid sites. The catalytic performance of the as-prepared catalysts was investigated in the microwave-assisted esterification reaction of valeric acid to valerate esters. Thus, while the materials modified with niobium exhibited a lower catalytic activity as compared with the catalytic support (Al-SBA-15), the materials loaded with fluorine either onto Al-SBA-15 or on Nb1%/Al-SBA-15 materials presented enhanced conversion values of valeric acid. Therefore, it can be said that the new acid sites with enhanced strength formed by the incorporation of fluorine boost the esterification of valeric acid with alcohols to form the respective valerate ester.

Kinetics of the isomerization of α-pinene epoxide over Fe supported MCM-41 and SBA-15 materials

A kinetic study for the isomerization of α-pinene epoxide over Fe/SBA-15 and Fe/MCM-41 catalysts was developed using a pseudo-homogeneous (polynomial law) and heterogeneous (LHHW formalism with one and two actives sites) models. TEM analysis of Fe/SBA-15 and Fe/MCM-41 showed that the materials have the typical hexagonal organization; FTIR adsorption–desorption of pyridine revealed the presence of Lewis acidity in both Fe/SBA-15 and Fe/MCM-41 catalysts. The presence of Fe3+ and Fe2+ species was concluded from XPS analysis; however, active site for α-pinene epoxide isomerization was attributed to Fe3+. With toluene as solvent, it was found that in both catalysts, the more adequate kinetic model was the unimolecular LHHW model with two active sites of the same type. Apparently, α-pinene epoxide isomerization is much faster over Fe/MCM-41 (5.78 L h−1 gFe−1) than over Fe/SBA-15 (1.14 L h−1 gFe−1). The activation energy for both Fe catalysts was evaluated using solvents of different polarity. In the case of Fe/MCM-41, the less energetic barrier was observed with toluene (30.99 kJ mol−1), while tert-butanol (13.76 kJ mol−1) was more favorable in the case of Fe/SBA-15 catalyst. Fe/MCM-41 is a very robust catalyst because it can be used up to four times without a significant loss of catalytic activity in comparison with Fe/SBA-15 that only can be used two times. Finally, a reaction mechanism was proposed for the isomerization of α-pinene epoxide over both Fe/SBA-15 and Fe/MCM-41 catalysts.

Zirconium Exchanged Phosphotungstic Acid Catalysts for Esterification of Levulinic Acid to Ethyl Levulinate

Zirconium exchanged phosphotungstic acid catalysts were prepared and studied for esterification of levulinic acid with ethanol. The catalysts were characterized by powder XRD, BET surface area, Raman spectroscopy, FT-infrared spectroscopy, Temperature programmed desorption of NH3 and Pyridine adsorbed FT-IR analysis. The presence of Zr resulted in the generation of strong Lewis acidic sites. Among all the catalysts the catalyst with partially exchanged Zr (Zr0.75TPA) showed higher activity due to the present of stronger Bronsted and Lewis acidic sites. The Zr0.75TPA catalyst exhibits amazing reusability with constant activity. Zr exchanged TPA is active in the esterification of levulinic acid into ethyl levulinate.

Porosity Design of Shaped Zeolites for Improved Catalyst Lifetime in the Methanol-to-Hydrocarbons Reaction

Additional porosity, such as meso- and macropores, was introduced in zeolite extrudates with the intention intuit of improving the effective diffusivity of the catalysts. The samples were characterized in depth by nitrogen adsorption-desorption, mercury intrusion porosimetry, ammonia temperature programmed desorption and adsorption of pyridine followed by infrared spectroscopy. The results revealed no significant change in the acidity but an increase of the pore volume. According to significant improvement in the effective diffusivity, the samples were tested in the methanol-to-hydrocarbons reaction. The catalytic stability was greatly enhanced with an increase in the pore volume, demonstrating a relation between effective diffusivity and resistance to deactivation by coke formation. Further experiments also revealed a higher toluene adsorption capacity and a raise in the breakthrough time over the most porous samples due to better accessibility of toluene molecules into the active sites of the zeolite.

A new route for the synthesis of self-acidified and granulated mesoporous alumina catalyst with superior Lewis acidity and its application in cumene conversion

Self-acidified and granulated mesoporous alumina (SAGMA) with dendritic-like microscopic shape was prepared by a new route that involves: (a) direct dehydration of AlCl3 (in the presence of capping petroleum wax), and (b) oxidation of intermediary AlCl3-nanorods. The AlCl3 solution dispersed in petroleum wax (capping media) was firstly dehydrated at 100 °C under inert atmosphere for manufacturing anhydrous AlCl3-nanorods (length: 50–100 nm; diameter: 5–10 nm). In a second step, this support was oxidized into γ-alumina at 300 °C, under air atmosphere. In the course of the manufacturing process, released chlorine was deposited at the surface of the nanorods (more specifically during the oxidation step). The binding of chlorine (5.35%, w/w at the surface) onto γ-alumina was demonstrated by both electron dispersive X-ray analysis (SEM–EDX) and Fourier-transformed infrared spectroscopy. Specific surface area reached 230 m2 g−1; the average pore size was 7.8 nm. Material characterization was completed by measuring the surface acidity through both temperature-programmed desorption and pyridine desorption. The morphology and the phase structure were investigated using scanning electron microscopy and X-ray diffraction analysis, respectively. SAGMA (γ-alumina) can be described as a strong Lewis (1.713 mmol g−1; i.e., about 93% of total acid sites) and Bronsted acid catalyst supported on a mesoporous structure (self-granular size of 177–250 µm). Cumene conversion (through a dealkylation pathway) was tested on SAGMA: maximum catalytic activity reached 87% at 300 °C. The conversion is highly selective: the reaction produces benzene and only traces of ethylbenzene (mass fraction below 4% compared to benzene). Apart from this good catalytic efficiency, the material is characterized by its strong stability in terms of both catalytic activity (loss less than 2%, for optimum conditions) and surface acidity (loss less than 3%), even for long reaction times (i.e., 24 h) under severe conditions (i.e., T 300 °C). This new material, easily manufactured, is characterized by high efficiency and selectivity in cumene conversion into benzene, associated with high acidity and good stability.

Catalytic activity of sulfated niobium oxide for oleic acid esterification

In this work, very high acidity niobium oxide was obtained by surface modification with sulfate groups. This modification increased the Brønsted acidity of niobium oxide and the functionalized material showed noticeable activity in the biodiesel production using the esterification of oleic acid as a reaction model. The characterization of the functionalized materials by nitrogen adsorption/desorption, scanning electron microscopy (SEM), and X-ray diffraction (XRD) showed the amorphous morphology and high surface area of these materials. Temperature programmed reduction (TPR) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of sulfate groups on the niobium oxide surface, and the acid surface sites on the catalyst were evaluated by adsorption of pyridine and Temperature-programmed desorption of ammonia (NH3-TPD). Reactions of methyl oleate production from oleic acid with methanol were evaluated by 1H-NMR and the sulfated niobium oxide exhibited a conversion up to 92% for esterification depending on the oleic acid/methanol ratio, as well as the catalyst amount. In addition, kinetic studies showed that the sulfated niobium oxide was able to promote a significant reduction in the activation energy of the esterification reaction from 68.4 kJ mol−1 to 34.7 kJ mol−1. The direct reuse of the catalyst was also evaluated up to five cycles with minimal activity loss.

Temperature-Programmed Desorption of Pyridine on Zeolites in the Presence of Liquid Solvents

Selecting the proper solvent is a major challenge involved in biomass conversion processes as there is little predictive understanding of how solvent choice will affect reaction rates. To date, most attempts to understand solvent behavior are on a case by case basis, through catalytic activity testing and screening multiple solvent choices. There is a need for characterization techniques aimed toward fundamental understanding of solvent behavior in a simple and systematic fashion. In this work, the effect of solvent on the Bronsted acid site–pyridine interaction was isolated to improve understanding of a solvent’s ability to stabilize charge in nonideal environments like zeolite micropores. Pyridine temperature-programmed desorption (TPD) was applied to zeolites ZSM-5, Beta, and Y in back-pressurized, flowing solvent. The desorption temperatures of pyridine from Bronsted acid sites in vacuum were compared in liquid water, acetonitrile, and n-heptane. For H/ZSM-5 (Si/Al = 12), the pyridine desorption tempe...

Controlled silylation of MoVTeNb mixed oxide catalyst for the selective oxidation of propane to acrylic acid

Acrylic acid is an important industrial chemical, and efficient catalysts for its direct preparation by propane oxidation are highly desirable. For this purpose, neutral silica networks were introduced on the surface of MoVTeNb mixed oxide catalysts by controlled silylation using a methyl silicate oligomer (MS-51). The modified catalysts gave ∼56.5% yield of acrylic acid with a selectivity of 77.1% in the oxidation of propane at 380°C. The catalysts were characterized by X-ray fluorescence, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller specific surface area, X-ray diffraction (Rietveld analysis), pyridine desorption, and scanning electron microscopy. MoVTeNb mixed oxide was found to be composed of 90.9% M1 phase and 2.3% M2 phase, and upon silylation, the surface was uniformly covered by a thin SiO2 layer with 0.14 molar ratio with respect to Mo and an estimated thickness of 2.4nm. The amount of acid sites decreased after the first three silylation cycles, but was not affected by repeated cycles. The results of the kinetic study based on the comparison of the simulated contribution of each side reaction were consistent with those of the model reactions using acrylic acid and other reactants: the controlled silylation effectively suppressed acrylic acid oxidation, especially after repeated silylation cycles, which is responsible for the superior performance of the silylated catalysts. Considering the relatively large size of acrylic acid compared to propane and the efficient propane activation by silica-covered catalysts, the controlled silylation was proposed to have two roles, by which further consecutive oxidation is prevented effectively to exhibit excellent performance in oxidation of propane: i) to block the unfavorable acidic sides, ii) to generate a silica layer with pore mouth openings on the surface of MoVTeNb mixed oxide, which allow the entrance of propane but inhibit re-entrance of the produced acrylic acid.

Aluminum doped mesoporous silica SBA-15 for glycerol dehydration to value-added chemicals

A series of Al-grafted mesoporous SBA-15 silica was synthesized and tested as catalysts in the gas-phase dehydration of glycerol to acrolein. Different Si/Al molar ratios were employed to tune the structure, texture and acidity of catalysts in order to analyze their effect on the catalytic performance. Different characterization techniques, such as powder X-ray diffraction, X-ray photoelectron spectroscopy, 27Al MAS NMR, N2 adsorption–desorption at −196 °C, ammonia temperature programmed desorption (NH3-TPD) and adsorption of pyridine coupled to Fourier transform infrared spectroscopy were employed. All materials were active in glycerol dehydration, being acrolein the main product in all cases. The catalyst with the highest Al content (AlSBA-2.5) showed the highest acrolein yield (27.6%) after 8 h of time-on-stream. A clear relationship between the effective production of acrolein and the acidity of catalysts could be established. Catalysts suffered from deactivation by coke deposition on the surface, but they can be reused, at least during three catalytic cycles, after regeneration at 550 °C in air during 4 h after each cycle.

Conversion of protonic magadiite to PLS-1 zeolite: thermal stability and acidity

AbstractA synthetic protonic magadiite was used as a silica source to prepare zeolitic material (PLS-1) in the presence of tetramethylammonium hydroxide and water. The conversion of the protonic magadiite to the PLS-1 phase was achieved at 150°C after 5 days, or at 170°C after 3 days for SiO2: TMAOH:H2O molar ratios of 2.54:1:4.4. The synthesis of the pure PLS-1 phase depended also on the amounts of tetramethylammonium hydroxide and water used. Analysis by 29Si magic angle spinning nuclear magnetic resonance spectroscopy confirmed the layered character of the PLS-1 phase with a resonance at −93 ppm, and its dehydroxylation-condensation process. The chemical formula of (TMA)2Si18O33(OH)6 for PLS-1 was refined with the Rietveld method and the tetrahedron-splitting model. The later model has been proposed to describe the presence of silanol defects in the layered structure of PLS-1. Upon calcinations of the PLS-1 phase at temperatures &gt;400°C, the removal of TMA cations and dehydroxlyation of PLS-1 layers resulted in a three-dimensional structure phase identified as the CDS-1 phase, with a chemical formula of Si18O36. The CDS-1 phase exhibited a large specific surface area of 288 m2/g and microporous character, as indicated by the nitrogen adsorption isotherms. The temperature-programmed desorption profile of ammonia indicated that CDS-1 exhibited one weak type of acid sites, confirmed, by pyridine desorption studies, as weak Lewis acid sites.

Titanate nanotubes as acid catalysts for acetalization of glycerol with acetone: Influence of the synthesis time and the role of structure on the catalytic performance

A series of titanate nanotubes (TNTs) have been prepared by a simple hydrothermal procedure (e.g., sodic and protonic TNTs). Investigations on the influence of the material type as well as the synthesis time conditions were examined. The as-synthesized and spent catalysts were characterized by XRD, Raman spectroscopy, TEM, SEM-EDS, N2 adsorption-desorption isotherms and acidity measurements through thermoprogrammed desorption of pyridine (pyridine-TPD). Catalytic results towards acetalization of glycerol with acetone was determined by varying the reaction conditions. A screening of the physicochemical properties revealed differences in the tubular structures of the TNTs with interwall distances varying from 1.07 to 1.11nm, depending on the synthesis time applied. Sodic TNTs synthesized with times as high as 24h possessed the Na2Ti3O7 phase whereas the protonic solids had H2Ti3O7 ones. These phases changed, depending on the synthesis time. Longer hydrothermal treatment times such as 72h at 160°C exerted potent effects of decreasing the structural order of the TNTs, but lead to high textural properties and acidities of the solids as well. Most sodic TNTs did not show glycerol conversion, under relatively mild reaction conditions. On the contrary, glycerol was readily converted to solketal and acetal products with high selectivity, depending on the synthesis time of the prepared material. The best performance towards glycerol conversion was achieved by the HTNT synthesized at 72h, whose glycerol conversion was 44.4% and selectivity toward the desired products more than 98% and only 2% side products (mostly cyclic products) at 50°C and acetone glycerol molar ratio of 1.

Characterization and catalytic properties of porous clay heterostructures from zirconium intercalated clay and its pillared derivatives

The insertion of zirconium or aluminium species into porous clay heterostructures has traditionally been performed in two steps. The first step prepares the porous clay heterostructures, and then adding the metal elements during the synthesis constitutes the second step. Here, a novel method is described that reduced the use of organic surfactants and inserted zirconium directly into the silica framework of the porous clay heterostructures in one step. It consisted of preparing the zirconium tetrameric species intercalated clay mineral as a precursor followed by co-intercalation of dodecylamine and the silica source (TEOS). The derived pillared zirconia clays were used as well as the precursor to prepare PCH materials. The materials were characterized by XRD, FTIR, TGA, 29Si MAS NMR and XRF. The XRF technique confirmed the presence of Zr in the PCH material prepared from the intercalated clay. Improvements in specific surface area (918 m2/g) and pore volume (0.801 cc/g) were achieved. The concentration of Brønsted acid sites was deduced from the thermal desorption of cyclohexylamine and reached a value of 0.989 mmol of protons/g. This value was higher than the concentration for either the starting intercalated clay mineral or the derived pillared clays. Stronger Brønsted acid sites were developed into the PCH materials, in addition to Lewis sites, even at 500 °C, as indicated by the desorption of pyridine as a probe molecule. These acid sites were strong enough to convert n-heptane to isomers and cracking products.

Acidity and Characterization of 12-Tungstophosphoric Acid Supported on Silica-Alumina

This work deals with preparation and characterization of H3PW12O40 (H3PW) supported on silica-alumina. Impregnation of H3PW (15, 20, 30 and 40 wt.%) on commercial silica-alumina support in acidic aqueous solution is effective for preparing this catalyst keeping its Keggin structure, according to different methods of characterization. The catalysts were tested in a model reaction of acetic acid with ethanol and 30 wt.% H3PW/SiO2-Al2O3 had the highest activity under the conditions: catalyst calcination at 300 oC, temperature of 100 oC, acetic acid:ethanol molar ratio of 2:1 and catalyst:acetic acid mass ratio of 10 wt.%. The reaction yield was 79 and 100% selectivity for ethyl acetate over three reutilizations, for reaction time of 2 h. The calculated total acid site distribution was 0.299 mmol g-1 (97% of the theoretical probed by pyridine), and most of these (0.236 mmol g-1) were Bronsted weak-medium strength (pyridine desorption between 300 and 500 oC).