Nature Of Acid Sites Research Articles

Enhancing the Acidity Window of Zeolites by Low-Temperature Template Oxidation with Ozone.

Revisiting the impact of the first and often deemed trivial postsynthetic step, i.e., a high-temperature oxidative calcination to remove organic templates, increases our understanding of thermal acid site evolution and Al distributions. An unprecedented degree of control over the acidity of high-silica zeolites (SSZ-13) was achieved by using a low-temperature ozonation approach. Fourier transform infrared spectroscopy of adsorbed probe molecules and solid-state NMR spectroscopy reveal the complexity of the thermal evolution of acid sites. Low-temperature activated (ozonated) zeolites maintain the original Brønsted acidity content and high defect content and have virtually no Lewis acidity. They also preserve the "as-made" Al distribution after crystallization and show a clear link between synthesis conditions and divalent cation capacity, as measured with aqueous cobalt ion uptake. The synthesis protocol is found to be the main contributor to Al proximity, yielding record high exchange capacity when ozonated. After conventional calcination at 500-600 °C, however, the presence of water leads to the gradual depletion of Brønsted acid sites, in particular, in small crystals. This work indicates that low-temperature ozonation followed by thermal activation at different temperatures can be used as a novel tool for tuning the amount and nature of acid sites, providing insights into the activity of zeolites in acid-catalyzed reactions, such as CO2 hydrogenation to dimethyl ether, and thereby expanding the possibilities of rational acidity tuning.

Tuning of the acid sites in the zeolite-alumina composite Ni catalysts and their impact on the palm oil hydrodeoxygenation reaction

The hydrodeoxygenation (HDO) of bio-oil is one of the potential approaches to produce green diesel. However, HDO catalyst requires the development of bifunctionality which translates to the simultaneous presence of acidic and metal sites for desired catalytic activity and selectivity. Zeolites and their composites are attractive candidates for the conversion of biomass to fuels. In the present work, a series of Ni-incorporated Al2O3-zeolite beta bifunctional composite catalysts with distinct Al2O3 (25–75 wt%) and Ni contents (5–15 wt%) were synthesized via a facile one-pot method directly from nickel acetate, nano-boehmite (γ-AlO(OH)) and the NH4+ form of beta zeolite (NH4+-BZ). The nano-boehmite particles, due to the positive charges on their surface, electrostatically attract negatively charged beta zeolite crystals, which leads to the assembly of a hierarchical pore structure upon calcination. Interestingly, the composite catalysts synthesized were quite homogeneous with uniform dispersion of Ni particles. All composite catalysts were thoroughly characterized using XRD, SEM-EDX, SEM-mapping, HR-TEM, H2-TPR, H2-TPD, NH3-TPD, XPS, 31P MAS NMR, 27Al MAS NMR and N2 sorption analysis. The synthesized composite catalysts with distinct Al2O3 contents showed diverse textural properties, distinct nature of acid sites and improved performance in hydrodeoxygenation of palm oil. Particularly, the Ni/BZ-Al50 (with BZ:Al2O3 = 50:50) composite catalyst significantly enhanced the conversion of palm oil (up to 90%) and yield of n-C15-C18 hydrocarbons (up to 69%) at moderate temperature of 375 °C as compared to 10Ni/BZ catalyst (Conv. = 75%, yield of n-C15-C18 = 52%). The higher catalytic performance realized with composite catalysts can be ascribed to its hierarchical pore structure, moderate acidity (chemisorption studies), tuned acid sites nature (solid state NMR) and homogeneous distribution of active Ni sites (H2 chemisorption) which helps to improve product selectivity by minimizing side reactions. The time-on-stream (TOS) experiments were carried out up to 20 h which clearly showed that composite catalysts are more stable suggesting the lower amount of coke deposition (TPO studies) and suppression of metal sintering.

Hydrolysis of Furfuryl Alcohol to Angelica Lactones and Levulinic Acid over Nb‐based Catalysts

AbstractLevulinic acid and angelica lactones are important building blocks obtained from hemicellulose. This process comprises multiple chemical reactions at which furfuryl alcohol is an intermediate, but only few studies have investigated its hydrolysis. This work studied the role played by the nature of acid sites and the impact of their strength and amount on furfuryl alcohol hydrolysis over Nb2O5 and NbOPO4. It was disclosed that production of levulinic acid is a two‐step cascade reaction at which angelica lactones are intermediates. These two hydrolysis steps were catalyzed by Brønsted acid sites with no contribution from Lewis centers. Brønsted acidity of Nb2O5 presented no activity while phosphate moieties on NbOPO4 were effective. Mixtures of organic solvent and water hindered side reactions, improving selectivity to valued bioproducts. 1,4‐dioxane was the most suitable organic solvent. This study shows that selectivity of 96 % of levulinic acid and angelica lactones can be accomplished over NbOPO4.

Importance of the Nature of Acidic Sites of Different Aluminosilicates on Fixation of Carbon Dioxide with Styrene Oxide.

The nature of acidic sites in commercially available aluminosilicates, zeolite Na-Y, zeolite NH4 + -ZSM-5, and as-synthesized Al-MCM-41 have been investigated by employing them as catalysts for capturing CO2 by styrene oxide. The catalysts, in tandem with tetrabutylammonium bromide (TBAB), produce styrene carbonate, and the yield of the product is observed to be governed by the acidity of the catalysts and hence, the Si/Al ratio. All these aluminosilicate frameworks have been characterized by IR, BET, TGA, and XRD. XPS, NH3 -TPD, and 29 Si solid-state NMR studies have been carried out to analyze the Si/Al ratio and the acidity of these catalysts. According to TPD studies, the number of weak acidic sites of these materials follow an order as NH4 + -ZSM-5 < Al-MCM-41 < zeolite Na-Y, which is just in accordance with their Si/Al ratios and the yield of the cyclic carbonates obtained, i. e., 55.3 %, 68 %, and 75.4 % respectively. The TPD data and the yield of the product carried out with calcined zeolite Na-Y indicate that not only the weak acidic sites but also the role of strong acidic sites might appear crucial in the cycloaddition reaction.

One-pot transformation of glucose into hydroxymethyl furfural in water over Pd decorated acidic ZrO2

A high surface acidic ZrO2 nanoparticle was prepared using glucose as a non-toxic reducing agent. Palladium (Pd) nanoparticles in the range of 1–2 nm are grafted in in-situ as well as ex-situ via urea deposition over pre-synthesized ZrO2 nanoparticles. Both methods are found to be useful for the one-pot transformation of glucose to HMF, and their catalytic activities towards selective production of HMF are found to be strongly dependent on the particle size and nature of acidic sites. A linear-type activity trend is observed with Pd loading in reference to the HMF selectivity and presents the best catalytic performance. The activation energy and turnover frequency (TOF) of the 1–2 nm NP catalyst are further calculated to be 44.1 kJ mol−1 and 6.011 molHMF·molPd−1·h−1, respectively. Characterization of the spent catalysts indicates that smaller-sized NPs face severe agglomeration, resulting in poor stability and activity. Hence, the high catalytic performance can be attributed to the balance between Brønsted and Lewis acid sites, in combination with Pd species intrinsic activity. Due to their improved activity and stability, 2Pd–ZrO2in-situ exhibits 55% glucose conversion with 74.0% of HMF selectivity after 3h of reaction at 160 °C.

Exploring tailor-made Br\xf8nsted acid sites in mesopores of tin oxide catalyst for \u03b2-alkoxy alcohol and amino alcohol syntheses

The generation of Brønsted (Sn–OH) and Lewis (coordinatively unsaturated metal centers) acidic sites on the solid surface is a prime demand for catalytic applications. Mesoporous materials are widely employed as catalysts and supports owing to their different nature of acidic sites. Nevertheless, the procedure adopted to generate acid functionalities in these materials involves tedious steps. Herein, we report the tunable acidic sites containing Brønsted sites with relatively varied acid strength in tin oxide by employing soft template followed by simple thermal treatment at various temperatures. The readily accessible active sites, specifically Brønsted acidic sites distributed throughout the tin oxide framework as well as mesoporosity endow them to perform with exceptionally high efficiency for epoxide ring opening reactions with excellent reusability. These features promoted them to surpass stannosilicate catalysts for the epoxide ring opening reactions with alcohol as a nucleophile and the study was extended to aminolysis of epoxide with the amine. The existence of relatively greater acid strength and numbers in T-SnO2-350 catalyst boosts to produce a high amount of desired products over other tin oxide catalysts. The active sites responsible in mesoporous tin oxide for epoxide alcoholysis were studied by poisoning the Brønsted acidic sites in the catalyst using 2,6-lutidine as a probe molecule.

Catalytic dehydration of glycerol to acrolein over mesoporous MCM-41 supported heteropolyacid catalysts

A series of vanadium substituted phosphomolybdic acid (VPMA) supported on mesoporous MCM-41 catalysts with varying VPMA content ranging from 10 to 50 wt% were prepared by impregnation method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy, N2 adsorption–desorption measurements to determine surface area and pore size distribution. The acidity measurements were studied by temperature programmed desorption (TPD) of NH3 and nature of acidic sites were examined by pyridine adsorbed FT-IR spectra. XRD results and N2 adsorption–desorption isotherms revealed the retention of ordered mesoporous structure of MCM-41 and the uniform pore structure with increase in HPA loading. FT-IR and Raman spectra showed that the primary structure of the Keggin units of the VPMA remains intact with the MCM-41. The TPD-NH3 showed that acidity of the catalysts increased with increase of VPMA loading. The findings of FT-IR spectra of pyridine adsorption revealed that VPMA/MCM-41 catalysts contain both the Bronsted and Lewis acidic sites and the amount of Bronsted acidic sites increased with increase of VPMA loading up to 40 wt% on the support. The catalysts were tested for the vapour phase dehydration of glycerol to acrolein. The catalyst samples were found to be highly active with 100% conversion and the acrolein selectivity changed with VPMA active phase loading on the support. In summary, the catalytic properties in terms of conversion and selectivity are attributed to the acidity, structural and textural properties of VPMA/MCM-41 catalyst.

Comparative Study of Different Acidic Surface Structures in Solid Catalysts Applied for the Isobutene Dimerization Reaction.

Dimerization of isobutene (IBE) to C8s olefins was evaluated over a range of solid acid catalysts of diverse nature, in a fixed bed reactor working in a continuous mode. All catalytic materials were studied in the title reaction performed between 50–250 °C, being the reaction feed a mixture of IBE/helium (4:1 molar ratio). In all materials, both conversion and selectivity increased with increasing reaction temperature and at 180 °C the best performance was recorded. Herein, we used thermogravimetry analysis (TGA) and temperature programmed desorption of adsorbed ammonia (NH3-TPD) for catalysts characterization. We place emphasis on the nature of acid sites that affect the catalytic performance. High selectivity to C8s was achieved with all catalysts. Nicely, the catalyst with higher loading of Brønsted sites displayed brilliant catalytic performance in the course of the reaction (high IBE conversion). However, optimum selectivity towards C8 compounds led to low catalyst stability, this being attributed to the combined effect between the nature of acidic sites and structural characteristics of the catalytic materials used. Therefore, this study would foment more research in the optimization of the activity and the selectivity for IBE dimerization reactions.

Effect of support on selective 5-hydroxymethylfurfural hydrogenation towards 2,5-dimethylfuran over copper catalysts

The production of 2,5-dimethylfuran (DMF) from 5-hydroxymethylfurfural (HMF) over different copper supported catalysts was investigated. An adequate metal dispersion and the nature of acid sites played a role in catalytic activity. Alumina containing catalysts showed the best performance in HMF hydrogenation and DMF production due to both higher acidity and copper particle size. Cu/Al2O3, Cu/Fe2O3-Al2O3, Cu/Nb2O5-Al2O3-623 and Cu/Nb2O5-Al2O3-773 showed a complete HMF conversion at 1 h of reaction and a DMF yield higher than 85% with a negligible quantity of ring-hydrogenation products (<1%). Except for Cu/Nb2O5, DMF production occurs via 2,5-bis (hydroxymethyl) furan (BHMF) as the key intermediate.

1H-31P HETCOR NMR elucidates the nature of acid sites in zeolite HZSM-5 probed with trimethylphosphine oxide.

Two-dimensional 1H-31P heteronuclear correlation NMR of trimethylphosphine oxide (TMPO) adsorbed in zeolites, in tandem with DFT calculations, challenges previous one-dimensional 31P NMR assignments, enabling the unambiguous discrimination of Brønsted and Lewis acid sites, extending the understanding of TMPO:Brønsted complexes formed with distinct stoichiometries at the HZSM-5 zeolite surface, and the proton-transfer mechanism.

Control of the NO–NH3 SCR Behavior of Cu-ZSM-5 by Variation of the Electronic State of Copper

The effect of NH4OH/Cu2+ in a copper-acetate solution on the properties of ion-exchanged Cu-ZSM-5 catalysts in the selective catalytic reduction of NO by NH3 (NO–NH3 SCR) has been studied. The temperature programmed desorption of ammonia (NH3-TPR) on Cu-ZSM-5 and the ammonia adsorption–desorption dynamics at 75–300 °C were studied to identify and quantify the nature of acid sites and ammonia desorption heat of Cu-ZSM-5. The Cu-ZSM-5 catalysts containing Cu-structures with extra-lattice oxygen were active in the low-temperature SCR, whereas those with isolated Cu2+ ions were active in the high-temperature SCR. It was shown that Cu-structures with extra-lattice oxygen were generated during the ion exchange of H-ZSM-5 with a water-ammonia solution of copper-acetate where the NH4OH/Cu2+ ratio was in the range of 6–15. Isolated Cu2+ ions were produced in the ion-exchange mode with the ammonia-free solution.

Novel ionic liquid-templated ordered mesoporous aluminosilicates: Synthesis, characterization and catalytic properties

Abstract Highly crystalline ordered mesoporous aluminosilicates with hexagonal AlIITM-41 and cubic AlIITM-48 pore symmetries with varying silicon-to-aluminium ratios were hydrothermally synthesized, for the first time, using long-chain ionic-liquid (IL) such as 1-hexadecyl-3-methylimidazolium chloride (HDMIC), as structure directing agent. The prepared materials were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, BET, TEM and XRF. In addition, the extent of aluminium incorporation and the nature of acid sites were deduced from 27 Al MAS-NMR and NH 3 -TPD measurements. The structural and physico-chemical properties of both AlIITM-41 and AlIITM-48 were compared with analogous AlMCM-41 and AlMCM-48, respectively prepared using hexadecyltrimethylammonium bromide (CTAB). It was found that all the ionic liquid-templated materials, viz., AlIITM-41 and AlIITM-48, and exhibited large surface area, high crystallinity and thicker pore walls. The observed superior orderness of AlIITM-41 and AlIITM-48 could attribute to a well distributed positive charge and π-π stacking of aromatic imidazolium head group of ionic-liquid. In addition, it also assisted in the incorporation of all the aluminium species exclusively in the tetrahedral silicate framework even after the calcination as confirmed by 27 Al MAS NMR. AlIITM-41 and AlIITM-48 possess more medium and strong Bronsted acid sites due to their thicker walls, high crystallinity and presence of tetrahedral aluminium in the framework, due to which they exhibited higher catalytic activity towards tertiary butylation of phenol with a good Para tertiary butyl phenol selectivity compared to commonly used aluminosilicates, H-AlMCM-41 and H-AlMCM-48.

A Mesopore-Dependent Catalytic Cracking of n-Hexane Over Mesoporous Nanostructured ZSM-5.

Herein, pore size, crystalinity, and Si/Al ratio of mesoporous ZSM-5 (MFI) nanocrystals was controlled by synthesis parameters, such as surfactant concentration ([3-(trimethoxysilyl)propyl] hexa-decyl dimethyl ammonium chloride), sodium hydroxide concentrations, synthesis temperature and time. The morphology, surface structure and composition of the MFI particles was systematically investigated. More notably, the mesopore-dependent catalytic activity of ZSM-5 was evaluated by studying the cracking of n-hexane. The findings suggest the porosity has pronounced impact on the catalytic activity, selectivity and stability of ZSM-5 nanocrystals. Critical surface attributes such as nature of acid sites (Brønsted and Lewis), concentration, and strength are obtained by the infrared study of adsorbed probe molecules (pyridine) and the temperature programmed desorption. In spite of being weaker in Si/Al ratio or acidic strength, mesoporous catalysts showed more stable and efficient cracking of n-hexane suggesting that acidity seems not the predominant factor operative in the activity, selectivity and stability.

Study of the gas-phase glycerol oxidehydration on systems based on transition metals (Co, Fe, V) and aluminium phosphate

The gas-phase glycerol (Gly) transformation in the presence of oxygen has been studied on cobalt oxide systems (10 and 20 wt% Co) supported on a synthetic mesoporous aluminium phosphate (AlPO4) calcined at 350 °C, as well as on a binary Co-Al phosphate with a Co content of 10 wt%. Synthetic binary phosphate of Al-M (M = Fe, V) have also been tested. The acidity (number and nature of acid sites) of the solids was determined by pyridine adsorption, whereas the reducibility was determined by H2 TPR. The propene oxidation was employed as a test reaction. The influence of the amount of oxidant agent and the reaction temperature on both the glycerol conversion and the yield to reaction products was studied. The formation of acrylic acid; acetic acid and carbon dioxide was favoured for values of O2/Gly ≥ 2 molar ratio and of temperatures beyond 250 °C. The Co oxide species in the supported systems that were the easiest to reduce (lower H2 desorption temperature) exhibited the highest activity to produce acrylic acid. The formation of acetic acid and carbon dioxide was also promoted, suggesting the participation of the acid sites in addition to redox sites. Among the metals investigated here, Co would form part of the required catalyst for the formation of acrylic acid from glycerol. Based on the identified products in this study, some possible reactions involved in the glycerol transformation into oxidized compounds, have been suggested.

On the Acid–Base State of the Surface of Semiconductor Components of the ZnSe–CdS System Exposed to Different Media

Using the methods of hydrolytic adsorption, mechanochemistry, and nonaqueous conductometric titration, the acid–base properties of the surfaces of binary semiconductors and solid solutions of the ZnSe−CdS system are studied. The nature of acid sites, and the extent, character, and mechanism of the surface (absorption) interaction are established. The interrelationships in the changes of the acid–base and bulk physical properties upon changing the chemical composition are determined, which make it possible to draw conclusions that are fundamentally important in scientific and practical aspects.

New insights into Cu/SSZ-13 SCR catalyst acidity. Part I: Nature of acidic sites probed by NH3 titration

In this work we investigated an unusual acidity feature of a Cu/SSZ-13 catalyst used in selective catalytic reduction of NOx with NH3 (NH3-SCR). In particular, this catalyst showed two distinct NH3 desorption peaks in NH3-TPD measurements, in contrast to single, unresolved desorption peaks observed for other Cu-exchanged zeolites conventionally used in the SCR studies, including its isostructural but chemically different analogue Cu/SAPO-34. We further observed that the intensities of the two TPD peaks, which represented the amount of stored NH3, changed in opposite directions in response to progressive mild hydrothermal aging, while the total storage capacity was preserved. We proposed an explanation for this remarkable behavior, by using model reference samples and additional characterization techniques. At least three NH3 storage sites were identified: two distinct populations of Cu sites responsible for low-temperature NH3 storage, and Brønsted acid sites responsible for high-temperature NH3 storage. Contrary to the commonly accepted mechanism that Brønsted acid site loss during hydrothermal aging is driven by dealumination, we concluded that the decline in the number of Brønsted acid sites upon mild hydrothermal aging for Cu/SSZ-13 was not due to dealumination, but rather transformation of Cu sites, i.e., gradual conversion of ZCuOH (Cu2+ singly coordinated with Zeolite) to Z2Cu (Cu2+ doubly coordinated with Zeolite). This transformation was responsible for the increased low-temperature desorption peak in NH3-TPD since each ZCuOH adsorbed ∼1 NH3 molecule while each Z2Cu adsorbed ∼2 NH3 molecules under the conditions used here. These findings were used in Part II of this series of studies to develop a method for quantifying hydrothermal aging of industrial Cu/SSZ-13 SCR catalysts.

Effect of liquid water on acid sites of NaY: An in situ liquid phase spectroscopic study

Liquid phase catalyst characterization is experimentally challenging, but it deserves consideration because solvent choice can affect catalyst structure and acidity. Thus, in vacuo spectroscopy of adsorbed probe molecules such as pyridine, while valuable, may provide incomplete information on available catalytic sites in liquid phase reactions. To this end, an Attenuated Total Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR) cell was used to detect pyridine adsorbed on sodium exchanged faujasite (NaY) in liquid water. The slow accumulation of pyridinium on NaY in the presence of liquid water was observed, suggesting water promotes the protonation of pyridine on NaY, a Lewis acidic material. Transmission FTIR and ATR-FTIR experiments revealed that pyridinium concentration increased with increasing amount of water in NaY, making the liquid phase technique more apt than the established vacuum technique for observing the effect of water on the acid sites of NaY. However, the Brønsted catalyzed ring opening of 2,5-dimethylfuran (DMF) to 2,5-hexanedione is not active on NaY in water. The lack of activity is attributed to the low basicity of DMF. This is consistent with the observation that acetonitrile, a weaker base than pyridine, was not protonated on NaY in water, while 2,6-dimethylpyridine, a stronger base than pyridine, was readily protonated. Thus, although NaY is capable of forming pyridinium in water, NaY may not be active with respect to Brønsted catalyzed pathways unless a reactant is sufficiently basic. Results presented in this work suggest that probe molecule choice can lead to different interpretations of the nature of acid sites in the presence of adsorbed, and especially liquid, water.

Brönsted and Lewis acid ZSM-5 zeolites for the catalytic dehydration of glucose into 5-hydroxymethylfurfural

Three different acid ZSM-5 zeolites (H-, Fe- and Cu-ZSM-5) have been prepared and tested in the catalytic dehydration of glucose into 5-hydroxymethylfurfural (HMF). A commercial NH4-ZSM-5 zeolite (MFI) was modified by thermal or ion-exchange treatments in order to create Brönsted and Lewis acid sites. The zeolitic structure is preserved, and the resulting acid zeolites have demonstrated to be active in the glucose dehydration. The influence of different experimental variables, such as reaction time and temperature, substrate:catalyst molar ratio, volume of the organic solvent and aqueous phase, as well as the density and nature of acid sites, on the catalytic behaviour was investigated. Under the optimal reaction conditions, by using a biphasic NaCl (20wt%) aqueous solution/methyl isobutyl ketone (MIBK) system, a glucose conversion of 80% and a HMF yield of 42% were achieved at 195°C, after only 30min, using H-ZSM-5, which has the lowest Lewis/Brönsted molar ratio among the prepared zeolites. The reutilization of this catalyst was also examined.

Alkali-metal-modified ZSM-5 zeolites for improvement of catalytic dehydration of lactic acid to acrylic acid

Various ZSM-5 zeolites modified with alkali metals (Li, Na, K, Rb, and Cs) were prepared using ion exchange. The catalysts were used to enhance the catalytic dehydration of lactic acid (LA) to acrylic acid (AA). The effects of cationic species on the structures and surface acid-base distributions of the ZSM-5 zeolites were investigated. The important factors that affect the catalytic performance were also identified. The modified ZSM-5 catalysts were characterized using X-ray diffraction, temperature-programmed desorptions of NH3 and CO2, pyridine adsorption spectroscopy, and N2 adsorption to determine the crystal phase structures, surface acidities and basicities, nature of acid sites, specific surface areas, and pore volumes. The results show that the acid-base sites that are adjusted by alkali-metal species, particularly weak acid-base sites, are mainly responsible for the formation of AA. The KZSM-5 catalyst, in particular, significantly improved LA conversion and AA selectivity because of the synergistic effect of weak acid-base sites. The reaction was conducted at different reaction temperatures and liquid hourly space velocities (LHSVs) to understand the catalyst selectivity for AA and trends in byproduct formation. Approximately 98% LA conversion and 77% AA selectivity were achieved using the KZSM-5 catalyst under the optimum conditions (40 wt% LA aqueous solution, 365 °C, and LHSV 2 h−1).

Vapor Phase Dehydration of Glycerol to Acrolein Over SBA-15 Supported Vanadium Substituted Phosphomolybdic Acid Catalyst.

Vapor phase dehydration of glycerol to acrolein was investigated over heteropolyacid (HPA) catalysts containing vanadium substituted phosphomolybdic acid (H4PMo11VO40) supported on mesoporous SBA-15. A series of HPA catalysts with HPA loadings varying from 10-50 wt% were prepared by impregnation method on SBA-15 support. The catalysts were characterized by X-ray diffraction, Raman spectroscopy, Fourier Transform infrared spectroscopy, temperature-programmed desorption of NH3, pyridine adsorbed FT-IR spectroscopy, scanning electron microscopy, pore size distribution and specific surface area measurements. The nature of acidic sites was examined by pyridine adsorbed FT-IR spectroscopy. XRD results suggest that the active phase containing HPA was highly dispersed at lower loadings on the support. FT-IR and Raman spectra results confirm that the presence of primary Keggin ion structure of HPA on the support and it was not affected during the preparation of catalysts. Pore size distribution results reveal that all the samples show unimodel pore size distribution with well depicted mesoporous structure. NH3-TPD results suggest that the acidity of catalysts increased with increase of HPA loading. The findings of acidity measurements by FT-IR spectra of pyridine adsorption reveals that the catalysts consist both the Brønsted and Lewis acidic sites and the amount of Brønsted acidic sites are increasing with HPA loading. SBA-15 supported vanadium substituted phosphomolybdic acid catalysts are found to be highly active during the dehydration reaction and exhibited 100% conversion of glycerol (10 wt% of glycerol) and the acrolein selectivity was appreciably changed with HPA active phase loading. The catalytic functionalities during glycerol dehydration are well correlated with surface acidity of the catalysts.