Dehydration Activity Research Articles

In Silico Investigation of Ligand-Regulated Palladium-Catalyzed Formic Acid Dehydrative Decomposition under Acidic Conditions

In silico investigation of ligand-regulated palladium-catalyzed formic acid dehydrative decomposition to carbon monoxide under acidic conditions was conducted. The pyridyl group implanted in the pytbpx ligand is found to mainly contribute to enhancing the activity of the palladium catalyst. para-Toluenesulfonic acid (PTSA) displays a specific role for regenerating active species and suppressing dehydrogenation during HCOOH dehydration, especially when the bis-protonated Pd–pytbpx complex is formed with excessive PTSA loading. However, the Pd–dtbpx system is too complicated to elucidate the HCOOH decomposition route only by one kind of species. According to the mechanism hereby supposed, introducing electron-donating substitution at the para position of pyridyl rings may further improve the dehydration activity of Pd–pytbpx.

Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

The catalytic activity of zeolites is often related to their acid–base properties. In this work, the relationship between the value of apparent activation energy of ethanol dehydration, measured in a fixed bed reactor and by means of a temperature-programmed surface reaction (TPSR) depending on the amount of ethanol in the zeolite lattice and the value of activation energy of H/D exchange as a measure of acid–base properties of MFI and CHA zeolites, was studied. Tests in a fixed bed reactor were unable to provide reliable reaction kinetics data due to internal diffusion limitations and rapid catalyst deactivation. Only the TPSR method was able to provide activation energy values comparable to the activation energy values obtained from the H/D exchange rate measurements. In addition, for CHA zeolite, it has been shown that the values of ethanol dehydration activation energies depend on the amount of ethanol in the CHA framework, and this effect can be attributed to the substrate clustering effects supporting the deprotonation of zeolite Brønsted centers.

Sulfur-treated TiO2 shows improved alcohol dehydration activity and selectivity.

The dehydration of alcohols is an important class of reactions for the development of fossil-free fuel and chemical industries. Acid catalysts are well known to enhance the reactivity of alcohols following two main pathways of either dehydration to olefins or dehydrogenation to ketones/aldehydes. TiO2 surfaces have been well documented for primary and secondary alcohol dehydration with selectivity ranging from 1-100% towards dehydration products based on process conditions and catalyst structure. In this work we document the effects of various sulfur treatments of TiO2 surfaces which induce higher activity and, more importantly, higher selectivity for alcohol dehydration than untreated surfaces. The increase in activity and >99% dehydration selectivity is coupled with demonstrated stability for several hours on stream at high conversion. Using temperature programmed reaction studies, XPS and FT-IR spectroscopy, we identify Lewis acidic sites correlated with sulfate species on TiO2 surfaces as active sites for the reaction.

Soft-templating routes for the synthesis of mesoporous tantalum phosphates and their catalytic activity in glycerol dehydration and carbonylation reactions

The craftsmanship in catalyst synthesis becomes very fascinating when the catalytic activity of the material can be enhanced by tuning the synthesis conditions. The underlying fundamental strategy is presented here in tailoring the structural and chemical behavior of the tantalum phosphates (TaP) by using different structure directing agents (SDAs). We found that by employing appropriate template assisted pathway it is possible to tune the morphology and the nature of active sites of TaP. The synthesised catalysts were comprehensively characterised by N2-physisorption, FESEM, HRTEM, powder XRD, FTIR, UV–Vis, XPS, NH3 and CO2-TPD, Py-adsorbed IR, elemental analysis and 31P{1H} NMR techniques. The FESEM and HRTEM analysis revealed the transition of non-spherical to rod-shaped particles upon moving from ionic to non-ionic surfactants. The TPD and Py-IR studies revealed the variation in amount, strength and nature of the acidic-basic sites with the change in SDA. The resultant TaP catalysts were investigated for gas phase glycerol dehydration to acrolein and liquid phase glycerol carbonylation to glycerol carbonate. Among these catalysts, TaPC synthesized by using CTAB as SDA exhibited promising catalytic activity in both gas and liquid phase reactions. The active site elucidation in TaPC catalyst was done by adopting basic probe molecule 2,6-lutidine. The deactivation kinetic study was carried out for the gas phase glycerol dehydration reaction. The investigation on the spent catalyst showed it is stable under both gas-phase and liquid-phase reaction conditions. This study hence provides a pathway for analytical architecture and construction of highly efficient TaP catalysts for glycerol transformation reactions.

Dehydration and Rehydration Mechanisms of Pharmaceutical Crystals: Classification Of Hydrates by Activation Energy

Dehydration strongly influences the stability of hydrate drug substances. Consequently, the ability to predict dehydration of crystalline hydrate using the intermolecular interactions of water molecules contained in the crystals is essential for drug development. The conventional method employed to predict the propensity for dehydration uses the dehydration temperature, which is related to how tightly water molecules are bound in the crystal lattice. However, it is difficult to predict the dehydration propensity of a particular hydrate using only the dehydration temperature because other kinetic factors affect dehydration behavior, such as intermolecular interactions, and drug-substance-to-water molar ratio in a hydrate. In this study, we explored the use of the dehydration activation energy Ea and rehydration behavior to classify 11 pharmaceutical hydrates into three classes according to their kinetic behavior related to the thermodynamic factors of hydrates. There is good agreement between these classes and hydrate crystal structures determined from single-crystal X-ray diffraction, and thus, the classification reflects their crystal structural features. We compared Ea to the dehydration temperatures for each class and found that Ea plays a crucial role and is better than the temperature for quantitative differentiation of the dehydration propensities in these hydrates.

Linking the Defective Structure of Boron-Doped Carbon Nano-Onions with Their Catalytic Properties: Experimental and Theoretical Studies.

Defects are widely present in nanomaterials, and they are recognized as the active sites that tune surface properties in the local region for catalysis. Recently, the theory linking defect structures and catalytic properties of nanocatalysts has been most commonly described. In this study, we prepared boron-doped carbon nano-onions (B-CNOs) by applying an annealing treatment of ultradispersed nanodiamond particles and amorphous boron. These experimental conditions guarantee doping of CNOs with boron atoms in the entire carbon nanostructure, thereby ensuring structural homogeneity. In our research, we discuss the correlations between defective structures of B-CNOs with their catalytic properties toward SO2 and tert-butanol dehydration. We show that there is a close relationship between the catalytic properties of the B-CNOs and the experimental conditions for their formation. It is not only the mass of the substrates used for the formation of B-CNOs that is crucial, that is, the mass ratio of NDs to amorphous B, but also the process, including temperature and gas atmosphere. As it was expected, all B-CNOs demonstrated significant catalytic activity in HSO3– oxidation. However, the subsequent annealing in an air atmosphere diminished their catalytic activity. Unfortunately, no direct relationship between the catalytic activity and the presence of heteroatoms on the B-CNO surface was observed. There was a linear dependence between catalytic activity and Raman reactivity factors for each of the B-CNO materials. In contrast to SO2 oxidation, the B-CNO-a samples showed higher catalytic activity in tert-butanol dehydration due to the presence of Brønsted and Lewis acid sites. The occurence of three types of boron-Lewis sites differing in electron donor properties was confirmed using quantitative infrared spectroscopic measurements of pyridine adsorption.

Vapor-phase dehydration of 1,4-butanediol to 1,3-butadiene over Y2Zr2O7 catalyst

• Vapor-phase catalytic dehydration of 1,4-butanediol was investigated over Y 2 Zr 2 O 7 catalysts. • 1,3-Butadiene together with 3-buten-1-ol, tetrahydrofuran, and propylene was produced depending on the conditions. • 1,3-Butadiene yield of 90% or higher was achieved over the Y 2 Zr 2 O 7 calcined at 700 °C in the dehydration at 360 °C. • An unsaturated alcohol such as 3-buten-1-ol is more reactive than 1- and 2-butanol over the Y 2 Zr 2 O 7 catalyst. • It is suggested that the C=C double bond of 3-buten-1ol affects an attractive interaction to anchor the Y 2 Zr 2 O 7 catalyst. Vapor-phase catalytic dehydration of 1,4-butanediol (1,4-BDO) was investigated over Y 2 O 3 -ZrO 2 catalysts. In the dehydration, 1,3-butadiene (BD) together with 3-buten-1-ol (3B1OL), tetrahydrofuran, and propylene was produced depending on the reaction conditions. In the dehydration over Y 2 O 3 -ZrO 2 catalysts with different Y contents at 325°C, Y 2 Zr 2 O 7 with an equimolar ratio of Y/Zr showed high selectivity to 3B1OL, an intermediate to BD. In the dehydration at 360°C, a BD yield higher than 90% was achieved over the Y 2 Zr 2 O 7 calcined at 700°C throughout 10 h. In the dehydration of 3B1OL over Y 2 Zr 2 O 7 , however, the catalytic activity affected by the calcination temperature is roughly proportional to the specific surface area of the sample. The highest activity of Y 2 Zr 2 O 7 calcined at 700 °C for the BD formation from 1,4-BDO is explained by the trade-off relation in the activities for the first-step dehydration of 1,4-BDO to 3B1OL and for the second-step dehydration of 3B1OL to BD. The higher reactivity of 3B1OL than saturated alcohols such as 1-butanol and 2-butanol suggests that the C=C double bond of 3B1OL induces an attractive interaction to anchor the catalyst surface and promotes the dehydration. A probable mechanism for the one-step dehydration of 1,4-BDO to BD was discussed.

Phase transformation of ZrO2 by Si incorporation and catalytic activity for isopropyl alcohol dehydration and dehydrogenation

The synthesis of metal oxides under basic conditions can yield unexpected experimental errors, such as contamination by impurities. Here, we clarified the influence of Si on the physicochemical properties of ZrO2 by comparing intentionally synthesized silica–zirconia (SZ) with accidentally synthesized Si-containing ZrO2. While pure monoclinic ZrO2 with a low surface area (20 m2 g−1) and acidity was synthesized without Si addition, SZ was structurally transformed to a tetragonal phase with a high surface area (140 m2 g−1) and acidity with the incorporation of Si. The ZrO2 synthesized by precipitation and digestion at pH 10.0 for different periods (24 − 240 h) using glassware equipment was found to have up to 26% dissolved Si; the mixture exhibited physicochemical properties similar to those of SZ catalysts with equivalent amounts of Si. The crystallization temperature of amorphous ZrO2 increased with increasing Si content, whereas the crystal size decreased with the amount of Si in the structure. The stabilization of the tetragonal phase by the incorporation of Si was theoretically investigated using density functional theory. The catalytic performance of the SZ catalysts toward the dehydration/dehydrogenation of isopropyl alcohol (IPA) was studied and compared with that of ZrO2 catalysts prepared by the precipitation method. The Brønsted acid sites originating from Si incorporation were more advantageous for the dehydration of IPA to propylene than Lewis acids.

Experimental and Theoretical Insights into the Active Sites on WOx/Pt(111) Surfaces for Dehydrogenation and Dehydration Reactions

The catalytic upgrading of biomass is an important step toward realizing renewable chemical production. Pt/WOx and the inverse catalyst, WOx/Pt, have been shown to be highly active and selective for the C–O bond scission of various biomass-derived oxygenates. Yet, the nature of the active sites and detailed reaction mechanisms have not been well understood. In this study, carbon monoxide and isopropyl alcohol (IPA) have been used as probe molecules to study the active sites of WOx/Pt(111) model surfaces. Temperature-programmed desorption experiments identified two distinct active sites responsible for different reaction pathways: dehydrogenation over Pt sites and dehydration over WOx sites. High-resolution electron energy loss spectroscopy (HREELS) identified the surface reaction intermediates. In situ infrared reflection absorption spectroscopy and HREELS measurements confirmed the presence of hydroxyl groups on WOx, which were consumed upon the adsorption of IPA, suggesting that the hydroxyl groups were the active sites for IPA dehydration. Density functional theory (DFT) calculations further revealed the reaction mechanisms and activation barriers of the IPA dehydrogenation and dehydration reactions. The comparison of different in situ-generated hydroxyl groups on WOx by DFT calculations suggested that the most active sites for dehydration should be those with protons least strongly bound (site formation energy of −0.3 eV), with a dehydration activation barrier of 1.23 eV. The understanding from this study provides insights into the design of relevant metal/metal oxide catalysts for the upgrading of biomass-derived oxygenates.

The role of ruthenium on the acidity of mixed alumina and silica phases and its impact on activity for ethanol dehydration

AbstractRuthenium catalysts anchored on three distinct supports (γ‐Al2O3, γ‐χ‐Al2O3, and silica [SiO2]) are tested for ethanol dehydration at 250°C. The catalytic materials were characterized using X‐ray diffraction (XRD), N2 physisorption, ammonia temperature programmed desorption (NH3‐TPD), FTIR, UV‐Vis spectroscopy, in situ UV‐Vis spectroscopy, H2 temperature programmed reduction experiments (H2‐TPR), and thermogravimetric analysis (TGA) after reaction. The activity was correlated to the number of acid sites present in the support. However, the addition of Ru increased the activity for alumina supported catalysts. Product selectivity depends on the nature of the acid sites present on the catalytic material, with ruthenium playing a critical role on the acid properties of the catalysts.

Hydrophobicity and co-solvent effects on Meerwein-Ponndorf-Verley reduction/dehydration cascade reactions over Zr-zeolite catalysts

Trans-anethole is an important ingredient in many flavors, fragrances and pharmaceutical formulations. Heterogeneous catalysis provides the opportunity for its green synthesis from 4′-methoxypropiophenone via a cascade of Meerwein-Ponndorf-Verley reduction followed by dehydration. Zr-containing zeolites were especially active catalysts. Surprisingly, Zr-HY was more active than Zr-Beta or mesoporous Zr-MSU. The effect of pore size, hydrophobicity and co-solvent has been investigated. Pyridine poisoning revealed that weak Lewis acid sites can catalyze the MPV reduction but stronger acid sites are required for the dehydration. The hydrophobicity and the ratio of open/closed Zr sites were higher for Zr-HY than Zr-Beta. Adding a moderately polar co-solvent like p-xylene more than doubled the reaction rate compared to only 2-pentanol as solvent. For an efficient cascade reaction, a hydrophobic catalyst with large micropores is required which combines hydrogen transfer and dehydration activities, together with an inert co-solvent that balances the concentration of both substrates inside the zeolite.

Insight into Active Centers and Anti-Coke Behavior of Niobium-Containing SBA-15 for Glycerol Dehydration

Niobium containing SBA-15 was prepared by two methods: impregnation with different amounts of ammonium niobate(V) oxalate (Nb-15/SBA-15 and Nb-25/SBA-15 containing 15 wt.% and 25 wt.% of Nb, respectively) and mixing of mesoporous silica with Nb2O5 followed by heating at 500 °C (Nb2O5/SBA-15). The use of these two procedures allowed obtaining materials with different textural/surface properties determined by N2 adsorption/desorption isotherms, XRD, UV-Vis, pyridine, and NO adsorption combined with FTIR spectroscopy. Nb2O5/SBA-15 contained exclusively crystalline Nb2O5 on the SBA-15 surface, whereas the materials prepared by impregnation had both metal oxide and niobium incorporated into the silica matrix. The niobium species localized in silica framework generated Brønsted (BAS) and Lewis (LAS) acid sites. The inclusion of niobium into SBA-15 skeleton was crucial for the achievement of high catalytic performance. The strongest BAS were on Nb-25/SBA-15, whereas the highest concentration of BAS and LAS was on Nb-15/SBA-15 surface. Nb2O5/SBA-15 material possessed only weak LAS and BAS. The presence of the strongest BAS (Nb-25/SBA-15) resulted in the highest dehydration activity, whereas a high concentration of BAS was unfavorable. Silylation of niobium catalysts prepared by impregnation reduced the number of acidic sites and significantly increased acrolein yield and selectivity (from ca. 43% selectivity for Nb-25/SBA-15 to ca. 61% for silylated sample). This was accompanied by a considerable decrease in coke formation (from 47% selectivity for Nb-25/SBA-15 to 27% for silylated material).

Sulfonic Derivatives as Recyclable Acid Catalysts in the Dehydration of Fructose to 5-Hydroxymethylfurfural in Biphasic Solvent Systems.

Biphasic systems have received increasing attention for acid-catalyzed dehydration of hexoses to 5-hydroxymethylfurfural (HMF) because of their high efficiency in in situ extraction and stabilization of HMF. Different organic solvents and acid catalysts were applied in these systems, but their effects on the dehydration activity and HMF yield, and the recycling of homogeneous acid catalysts remain largely unexplored. Here, we tested different solvent systems containing a wide range of organic solvents with low boiling points to study the effects of their chemical structures on fructose dehydration and provided stable H2O–dioxane and H2O–acetonitrile biphasic systems with high HMF yields of 76–79% using water-soluble sulfonic derivatives as homogeneous acid catalysts under mild conditions (383 K). By analyzing the partition coefficients of HMF and sulfonic derivatives, 94.3% of HMF and 87.1% of NH2SO3H were, respectively, restrained in the dioxane phase and aqueous phase in the H2O–dioxane biphasic system and easily divided by phase separation. The effects of the adjacent group in sulfonic derivatives and reaction temperature on fructose conversions and HMF yields suggest that in a specific biphasic system, the catalysts’ acidity and reaction conditions significantly affect the fructose dehydration activity but hardly influence the optimal yield of HMF, and an almost constant amount of carbon loss was observed mainly due to the poor hydrothermal stability of fructose. Such developments offer a promising strategy to address the challenge in the separation and recycling of homogeneous acid catalysts in the practical HMF production.

Thermodynamic and kinetic studies on the polymorphic transformations of puerarin hydrates

Puerarin (PUE), a bioactive flavonoid from the plant Pueraria lobata, exists in two hydrated forms: monohydrate (PUEMH) and dihydrate (PUEDH). The aim of the present work was to explore the thermodynamic and kinetic mechanism of the polymorphic transformation of PUE, including the solvent-mediated polymorphic transformation (SMPT) of PUEMH to PUEDH and the solid-state polymorphic transformations (SSPTs) of PUEMH and PUEDH. PUEMH and PUEDH were identified as isolated and channel hydrate, respectively. The thermodynamic parameters (ΔG < 0, ΔH < 0, and ΔS < 0) indicated that the SMPT was a spontaneous, exothermic and entropy-decreased reaction. The facilitating roles of stirring rate and temperature on the SMPT were favored by the primary and secondary nucleation process of PUEDH. In addition, the results of SSPTs suggested that PUEMH and PUEDH would transform to two different anhydrates (PUEAH-I and PUEAH-II) upon heating, respectively. The dehydration rate of PUEMH was slower than that of PUEDH due to the stronger hydrogen bond interactions. The rate-limiting step for the dehydration of PUEMH was the diffusion of water molecules, resulting in the increased dehydration activation during the dehydration process, while the dehydration activation energy of PUEDH showed opposite trend due to the complicated crystallization process of PUEAH-II.

Physiological and biochemical characteristics of some therophyllous species of the Ficus genus in water stress conditions

The relevance of the search for physiological and biochemical parameters associated with the implementation of plant adaptation mechanisms to the combined action of high temperatures and water stress is dictated by frequent summer droughts in southern regions. For this purpose, every month during the dry period under the conditions of a laboratory experiment a number of physiological and biochemical parameters were determined in the leaves of species F. palmata, F. virgata, and F. carica (Sabrutsia Rozovaya variety) that grow in the collection plots of the Nikitsky Botanical Gardens. In studied genotypes were assessed leaves tissue water сut, water deficit, moisture retaining ability, resistance to dehydration, proline content, peroxidase and polyphenol oxidase activity. It was defined that during the summer season physiological and biochemical parameters in the leaves of the studied species varied unequally. There was revealed the functional relation between the activity of peroxidase, polyphenol oxidase, proline content and the level of drought resistance of the studied species of the Ficus genus. The drought resistance of these varieties is most closely related to the proline content.

Methanol Dehydration to Dimethyl Ether over Modified γ-Al2O3 with Acid, Base and Zeolite (NaA and NaX)

The effect of acids, bases, zeolite NaA and zeolite NaX impregnation to g-Al2O3 on the catalyst characteristics and activity against methanol dehydration reaction were investigated. The catalyst characteristics include N2 physisorption, X-ray diffraction (XRD), and temperature-programmed desorption of ammonia (NH3-TPD) in addition to catalytic dehydration of methanol performed in a micro fixed-bed reactor at 270°C and 1 atm. The results of XRD characterization showed no changes related to the modification of alumina over acids, bases, and zeolite NaA and zeolite NaX. Therefore, the modification did not have any effect on the crystalline structure of alumina. The textural and surface acidity of g-Al2O3 changed post addition of acids, bases, zeolite NaA and zeolite NaX. NH3-TPD analysis results demonstrated that synthesized g-Al2O3 has three types of acid sites: weak, medium, and strong; however, the weak acid sites were not observed on alumina catalysts modified phosphate, KOH, zeolite NaA, and zeolite NaX. Furthermore, the concentration of strong acid sites increased in the catalyst containing KOH. The catalytic test results showed that the untreated g-Al2O3 catalyst gave prominent activity in dehydration of methanol compared to the treated catalyst following the number and strength of acid sites.

Effect of crystalline phases and acid sites on the dehydration of 1-octadecanol to 1-octadecene over TiO2–ZrO2 mixed oxides

TiO2–ZrO2 mixed oxides with different amounts of TiO2 were prepared by co-precipitation method and used to synthesize 1-octadecene from 1-octadecanol. The results show that the doping of TiO2 leads to the formation of Lewis acid sites and Bronsted acid sites on the TiO2–ZrO2 mixed oxides. For catalysts with TiO2 doping < 3 wt.%, the catalysts are in an intermediate state from the monoclinic and tetragonal zirconia crystalline phases to the amorphous form, and no Ti–O–Zr bond is formed. For catalysts with TiO2 doping ≥ 3 wt.%, an amorphous structure and Ti–O–Zr bond are formed. The crystalline phase of metal oxides, amount and type of acid sites simultaneously affect the performance of the catalysts. The acid sites on TiO2–ZrO2 mixed oxides with monoclinic and tetragonal zirconia crystalline phases have much lower dehydration activity than those with an amorphous form. Lewis acid sites are responsible for both the dehydration of 1-octadecanol to form 1-octadecene and the double carbon bond migration of 1-octadecene to form 2-octadecene. Bronsted acid sites mainly catalyze the double carbon bond migration of 1-octadecene.

Modeling of a membrane integrated catalytic microreactor for efficient DME production from syngas with CO2

Conversion of syngas (CO + CO2 + H2) to dimethyl ether (DME) with in–situ steam separation is modeled in a membrane integrated, isothermal catalytic microchannel reactor. Reaction channel, involving washcoated form of physically mixed Cu–ZnO/Al2O3 and HZSM–5 catalysts, is separated from the permeate channel by a supported sodalite (SOD) membrane layer. Conservation of momentum and mass within the porous washcoat and the channels, and cross–membrane material transport are modeled in two dimensions at steady–state to elucidate the effects of temperature, pressure, syngas composition and permeate flow properties. Dosing syngas to both channels at 523 K, 50 bar, CO2/COx (COx: CO + CO2) = 0.5 and H2/COx = 2.0 gives CO and CO2 conversions, and DME yield of 33.2, 12.4 and 15.3 %, respectively, which are 29.9, 7.2 and 12.7 % without membrane. These findings are coherent with relaxed thermodynamic limitations on methanol synthesis and dehydration upon selective H2O removal. Higher permeate syngas flow rates promote steam efflux and H2 influx across the membrane and further elevate CO2 conversion and DME yield up to 15.8 and 17.4 %, respectively. These metrics can be improved up to 23.4 and 22.9 %, respectively upon dosing pure H2 as the permeate fluid. However, a positive pressure gradient from reaction to permeate channel does not improve reactor performance. Coherent with its higher dehydration activity, HZSM–5 responds to membrane assistance stronger than γ–Al2O3.

Mesoporous silica supported phosphotungstic acid catalyst for glycerol dehydration to acrolein

Conversion of glycerol to acrolein is a useful reaction for value-added application of biodiesel-derived glycerol and bioenergy development. The high-performance solid acid catalyst is essential to this dehydration reaction. In this paper, tungsten-based heteropolyacids (HPA) were supported on non-ordered mesoporous silica (MSU-x) to increase their dispersion and used as catalysts for glycerol dehydration to acrolein. Aiming to reveal the surface structure of HPA and resulting acidic properties, as well as the relationship between acidic properties and dehydration activity, different loadings of H3PW12O40 were supported on MSU-x (10–50 wt%) and the catalysts were characterized by X-ray diffraction (XRD), BET, SEM/TEM, UV–vis diffuse reflectance spectra (DRS), Raman and FT-IR techniques. Their acidic properties were studied by NH3-Temperature Programmed Desorption (NH3-TPD) and Pyridine adsorption methods. The molecular structure and dispersion of H3PW12O40 supported on the catalysts was revealed. The Keggin unit preserved well but with different hydration level for various loadings. The total acid concentration and respective Brønsted/Lewis acid identification were calculated. The acrolein yield increased with H3PW12O40 loading until 30 wt% and showed less change with higher loadings. Based on the correlation of acrolein formation rate with acidic properties, the active role of Brønsted acid and the cooperative role of Brønsted/Lewis acid sites for glycerol dehydration to acrolein were discussed. This work provides new insight into the structure evolution of heteropolyacids and the catalyst design for the glycerol to acrolein.

Effect of Ba impregnation on Al2O3 catalyst for 1-octene production by 1-octanol dehydration

This study investigated the effect of impregnating Ba into an Al2O3 catalyst on the acid-base property and catalytic activity in the dehydration of 1-octanol to produce 1-octene. The Ba/Al2O3 catalysts were prepared by the incipient wetness method with different Ba contents of 0.0–3.0 wt%, and characterized by ICP-MS, BET-BJH, XRD, pyridine-FTIR, and CO2-TPD. The catalytic activity in 1-octanol dehydration was evaluated at 300, 350, and 400 °C with liquid hourly space velocity (LHSV) of 7–56 h−1. As the amount of Ba increased, the density of the basic site on Ba/Al2O3 increased, and the strength distribution of the Lewis acid site (LAS) was changed. Under the reaction condition of 400 °C and LHSV = 7 h−1, Ba/Al2O3 showed higher 1-octene selectivity and 1-octene purity compared with the pure Al2O3 even though the 1-octanol conversion was similar. This is because the added Ba eliminated the strong LAS, which, in turn, inhibited the side-reaction originating from the re-adsorption of 1-octene. When LHSV > 21 h−1, Ba/Al2O3 catalysts showed decreased 1-octanol conversion but maintained high 1-octene selectivity and 1-octene purity. As the Ba content reached 2.0 wt%, 1-octene selectivity was decreased as the formation of dioctyl ether became more active than olefin production. Therefore, 1.5 wt% Ba/Al2O3 is the optimal catalyst for producing 1-octene from 1-octanol in terms of 1-octanol conversion, 1-octene selectivity, and 1-octene yield.