Dehydration Activity Research Articles

A study of the catalytic hydroconversion of biocarboxylic acids to bioalcohols using octanoic acid as model reactant

The catalytic hydrodeoxygenation (HDO) of octanoic acid (C7COOH) to octene and octane was found to proceed in consecutive reaction through octyl aldehyde and octyl alcohol intermediates. Aluminosilicate and γ-alumina supported Cu and Cu,In catalysts were applied in a fixed bed flow-through reactor at 21bar total pressure in the temperature range of 330–380°C. The feed was 7.1% C7COOH/84.3% H2/He. The WHSV of the acid was 1.82h−1. The results suggested that at lower temperatures the rate of acid hydrogenation/dehydration determined the rate of the consecutive hydroconversion process and alcohol selectivity. The reduction of aldehyde was facile, thus, the aldehyde selectivity was low under most conditions. At lower temperatures and conversions the acid coverage was high hindering the catalytic dehydration of the product alcohol. At higher temperatures and acid conversions the alcohol dehydration activity of the catalyst determined the alcohol selectivity. The indium additive was found to increase the HDO activity and the alcohol selectivity of the copper catalysts significantly. The favorable effects of indium were attributed to the formation of new catalytically active Cu2In alloy phase.

Enhancement of the Promiscuous Aldolase and Dehydration Activities of 4‐Oxalocrotonate Tautomerase by Protein Engineering

Double play: The enzyme 4-oxalocrotonate tautomerase (4-OT) catalyzes not only the initial cross-coupling of acetaldehyde and benzaldehyde to yield 3-hydroxy-3-phenylpropanal, but also the subsequent dehydration of this aldol compound to yield cinnamaldehyde as the final product. Mechanism-inspired engineering provided an active site mutant (F50A) with strongly enhanced aldol condensation activity.

New insights into the development of Brønsted acidity of niobic acid

The development of Brønsted acidity and the relationship between acidity, catalytic performance and structure of niobium oxide were investigated for a series of samples prepared by calcination of niobic acid at temperatures between 423 and 823K. All solids were active for propan-2-ol dehydration. The Brønsted acidity was monitored by adsorption of lutidine and CO followed by FT-IR. Low temperature CO adsorption measurements showed that all solids exhibit essentially the same medium Brønsted acid strength. A direct relationship between the abundance of Brønsted acid sites monitored by lutidine adsorption followed by desorption at 523K and propan-2-ol dehydration activity was observed.

One-pot synthesis of 5-hydroxymethylfurfural directly from starch over [formula omitted]/ZrO2–Al2O3 solid catalyst

The synthesis of 5-hydroxymethylfurfural (HMF) directly from starch was studied in dimethyl sulfoxide–water. The effects of catalyst variation, reaction time, water content, catalyst loading and temperature on the reaction were investigated. The SO42-/ZrO2–Al2O3 catalyst was found to act as a bifunctional catalyst with high activity for both hydrolysis and dehydration of starch. HMF yield of 55% was obtained after 6h at 423K for the reaction of starch (the molar ratio of water to glucose in starch is 44/1) over the SO42-/ZrO2–Al2O3 catalyst, which bears high acidity and moderate basicity with Zr/Al molar ratio of 1:1.

Redispersion of Gold Supported on Oxides

Although many gold heterogeneous catalysts have been shown to exhibit significant activity and high selectivity for a wide range of reactions in both the liquid and gas phases, they are prone to irreversible deactivation. This is often associated with sintering or loss of the interaction of the gold with the support. Herein, we report on the use of methyl iodide as a method of dispersing gold nanoparticles supported on silica, titania, and alumina supports. In the case of titania- and alumina-based catalysts, the gold was transformed from nanometer particles into small clusters and some atomically dispersed gold. In contrast, although there was a drop in the gold particle size on the silica support following CH3I treatment, the size remained in the submicrometer range. The structural changes were correlated with changes in the selectivity and activity for ethanol dehydration and benzyl alcohol oxidation. From these observations, it is clear that this treatment provides a method by which deactivated gold catalysts can be reactivated via redispersion of the gold.

Selective dehydration of methanol to dimethyl ether on ZSM-5 nanocrystals

The effects of crystal size and mesoporosity on the performance of various synthesized ZSM-5 zeolites in catalytic dehydration of methanol to dimethyl ether (DME) reaction have been investigated. The reactions were carried out in a continuous flow fixed-bed reactor at temperatures between 180 and 320°C and 1.1bar. It was found that methanol conversion enhances by decreasing crystal size and increasing the reaction temperature. Uniform nanocrystal catalysts showed highest activity and stability for methanol dehydration to dimethyl ether in the temperature range studied. On the other hand, both the activity and selectivity of large crystals were low. The high activity and DME yield for the nanocrystals is due to smaller mass transport resistance for the Nano-ZSM-5 sample, due to the small crystal size. Furthermore, it was found that the selective dehydration of methanol to dimethyl ether on ZSM-5 catalyst is based on the product selectivity inside the pore channels; in other words, the selectivity to dimethyl ether should be 100% if there is no acid site on the external surface. From this evidence, it is concluded that in methanol dehydration to DME, the reaction activity is related to the crystal size, whereas the DME selectivity is determined by the uniformity of Al distribution, which determines acidity of external surface and low mass transport resistance of small crystal size. Therefore, a decrease in the number of acid sites on the external surface and reduction in crystal size are key ways to enhance catalytic selectivity and activity, respectively.

Simultaneous glycerol dehydration and in situ hydrogenolysis over Cu–Al oxide under an inert atmosphere

Among various catalysts screened, the Cu–Al oxide catalyst, prepared by a co-precipitation method, exhibited excellent activity for simultaneous glycerol dehydration and its hydrogenolysis without external hydrogen. Detailed characterization by XRD, XPS, HR-TEM, TPR, etc., showed evidence of Cu2+ in the form of CuO and CuAl2O4, along with Cu0 and Cu1+ species, which are responsible for their multifunctional roles in glycerol APR, dehydration and hydrogenolysis reactions under inert conditions. This catalyst also presented consistent activity for a duration of 400 h for autogeneous hydrogenolysis of refined glycerol with 36% selectivity to 1,2-propanediol (1,2-PDO). Manipulating the temperature and feed flow rate conditions, meant that the selectivity to acetol and 1,2-PDO could be tailored as desired. Substantial enhancement in 1,2-PDO selectivity (75%) was achieved for an aqueous bio-glycerol feed over the same catalyst for 50 h of testing.

Synthesis of AlOOH slurry catalyst and catalytic activity for methanol dehydration to dimethyl ether

AlOOH slurry catalysts were prepared by complete liquid-phase technology from aluminum iso-propoxide (AIP). Dehydration of methanol to dimethyl ether (DME) over these catalysts was investigated in slurry reactor. The catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption, temperature-programmed desorption of ammonia (NH 3–TPD). The results showed that the slurry catalysts had high specific surface area and pore volume, and the specific surface area and the strength of weak acidic sites were influenced considerably by the molar ratio of H 2O/AIP and HNO 3/AIP. Activity tests indicated that AlOOH slurry catalysts had excellent catalytic activity and stability in slurry reactor for the dehydration of methanol to dimethyl ether, and the activity correlated well with the strength of weak acidic sites of catalysts, which can be controlled by changing the H 2O/AIP and HNO 3/AIP molar ratios. The average methanol conversion at even stage reaches nearly 80% and DME selectivity almost 100% over CAT-P1 catalyst. No deactivation was found during the reaction of 500 h. It is also expected that CAT-P1 becomes a promising methanol dehydration catalyst for the STD process based on CuZuAl methanol synthesis catalyst.

Methanol dehydration to dimethyl ether in a platelet milli-reactor filled with H-ZSM5/SiC foam catalyst

Milli-structured reactors and process miniaturization have received an over increasing scientific interest during the last decades for the development of new generation of catalytic systems, which can find application in several catalytic processes. Here we report the development of a platelet milli-structured reactor filled with ceramic SiC foam with open porosity, high mixing efficiency, fully accessible surface area and low pressure drop. The SiC support was coated with a homogeneous layer of H-ZSM5 zeolite acting as an active phase for the catalytic dehydration of methanol into dimethyl ether. This hybrid catalyst shows an excellent and stable dehydration activity even at high space velocity due to the foam structure with high reactants mixing efficiency and better effective surface area. The low diffusion length of the foam strut also provide a high escaping of the product reducing secondary reaction and also carbonaceous residue deposit the catalyst and thus, no deactivation was observed for a long-term test.

The influence of surface composition of Ag 3PW 12O 40 and Ag 3PMo 12O 40 salts on their catalytic activity in dehydration of ethanol

The aim of this work was to investigate the influence of relative humidity of air on the catalytic activity of Ag 3PW 12O 40 and Ag 3PMo 12O 40 salts in the vapor-phase dehydration of ethanol. The reaction was performed in air of relative humidity of 2% or 9% and in the temperature range of 373–493 K. The catalytic activity of Ag 3PW 12O 40 salt was much higher than the one obtained for Ag 3PMo 12O 40 salt and strongly dependent on relative humidity of air. The XRD measurements showed that the structure of Ag 3PW 12O 40 salt loses the water hydrating silver in the range of 473–573 K whereas Ag 3PMo 12O 40 salt in 373–473 K. The FT-IR spectra demonstrated the stability of Keggin structure of Ag 3PW 12O 40 salt after reaction, independently of relative humidity of air. However, the XPS spectroscopy exhibited the changes in surface composition of this salt after reaction in air of 2% of relative humidity whereas the SEM imaging displayed the formation of silver nanostructures on its surface. The Ag 3PW 12O 40 salt remained stable after reaction in air of 9% of relative humidity. In case of Ag 3PMo 12O 40 salt analyzed before and after ethanol dehydration, a very limited difference in surface composition was found by XPS that was supported by SEM imaging.

Control of surface acidity and catalytic activity of γ-Al 2O 3 by adjusting the nanocrystalline contact interface

Densification of 2–2.5 nm nanocrystals assemblies in the three-level hierarchical structure of γ-Al 2O 3 aerogel significantly increases the surface acidity, as determined using indicator titration, NH 3–TPD, and FTIR of adsorbed pyridine. Thermal treatment at 1073 K and insertion of additional alumina inside the aerogel pores eliminated the slit micropores with shrinkage of nanocrystals assemblies (N 2-adsorption, HRTEM, SEM) increasing the contact interface by a factor of 2. It caused a fivefold increase in alumina surface acidity and the strength of Lewis acid sites with no measurable dehydration (weight loss, TGA). This was attributed to the formation of additional low-coordinated aluminum ions with higher charge in the areas with atomic disorder of high-angle grain boundaries, detected by 27Al MAS NMR, HRTEM, XPS, and XRD. Densification of nanocrystalline alumina aerogel yielded a higher catalytic activity in dehydration of isopropanol; it was 10-fold more active compared with commercial γ-alumina on the catalyst weight basis.

Ethanol dehydration activity on hydrothermally stable LaPxOy catalysts synthesized using CTAB template

Nanocrystalline LaPxOy with various starting P to La ratios from 0.5 to 2.0 catalysts were prepared by a sol–gel method using cetyl trimethylammonium bromide (CTAB) as template. The catalysts were thoroughly characterized by N2 physisorption, powder X-ray diffraction (XRD), temperature programmed desorption (TPD) of NH3, solid state 31P and 1H nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM) techniques. XRD results indicate the presence of predominantly monazite LaPO4 with minor amounts of (≤3.0 wt%) rhabdophane LaPO4 phase in the samples with starting P/La ratios of 1.0 and 1.5. NH3-TPD results show an increasing trend in the total acidity with increase in P/La ratio. These catalysts were tested in the selective ethanol dehydration in the temperature range between 250 and 400 °C. The catalyst activity (μmol/h/m2) is increased with P/La ratio and the catalyst with highest P/La ratio of 2.0 exhibiting the highest ethanol dehydration activity. The ethanol conversion increased with reaction temperature, reaching 100% at 350 °C and remains unchanged at higher temperatures. On the other hand, the ethylene selectivity is also increased up to 350 °C and then decreased with further increase of reaction temperature. At a P/La ratio of 2, the CTAB templated LaPxOy catalyst showed higher catalytic activities compared to the LaPxOy by hydrothermal method without any template.

The influence of reagent used for the precipitation of Cs 2HPW 12O 40 salt on its textural and catalytic properties

The series of Cs 2HPW 12O 40 samples was prepared using various reagents, namely Cs 2CO 3 and CsCl, as the precipitating agent. Moreover, the modification of preparation procedure consisting of HCl addition to the colloidal solution of Cs 2HPW 12O 40 salt, precipitated previously with Cs 2CO 3 and H 3PW 12O 40, was also studied. The aim of present research was to recognize the role of precipitating agent in the physicochemical and catalytic properties of Cs 2HPW 12O 40 samples. The samples were characterized by number of techniques, BET, FT-IR, 31P NMR, XRD, XPS, TPD-MS, laser diffraction, NH 3 sorption. It was observed that the lattice parameters and the environment of phosphorous were the same in all studied samples. The Cs 2HPW 12O 40 salt prepared by Cs 2CO 3 exhibited very low specific surface area of about 1 m 2/g. In contrast, the usage of CsCl yielded the sample of remarkably higher surface area (∼78 m 2/g) and dramatically higher catalytic activity for dehydration of ethanol. Thus, an effect of precipitating agent can be ascribed to its influence on the size of colloidal particles formed upon preparation procedure. It has been postulated that the adsorption of HCl/chloride ions on the surface of primary particles of Cs 2HPW 12O 40 salt facilitated the formation of mesoporous structure, which determined its sorption and catalytic properties.

Molecular Aspects of Glucose Dehydration by Chromium Chlorides in Ionic Liquids

A combined experimental and computational study of the ionic-liquid-mediated dehydration of glucose and fructose by Cr(II) and Cr(III) chlorides has been performed. The ability of chromium to selectively dehydrate glucose to 5-hydroxymethylfurfural (HMF) in the ionic liquid 1-ethyl-3-methyl imidazolium chloride does not depend on the oxidation state of chromium. Nevertheless, Cr(III) exhibits higher activity and selectivity to HMF than Cr(II) . Anhydrous CrCl(2) and CrCl(3)⋅6 H(2)O readily catalyze glucose dehydration with HMF yields of 60 and 72%, respectively, after 3 h. Anhydrous CrCl(3) has a lower activity, because it only slowly dissolves in the reaction mixture. The transformation of glucose to HMF involves the formation of fructose as an intermediate. The exceptional catalytic performance of the chromium catalysts is explained by their unique ability to catalyze glucose to fructose isomerization and fructose to HMF dehydration with high selectivity. Side reactions leading to humins by means of condensation reactions take predominantly place during fructose dehydration. The higher HMF selectivity for Cr(III) is tentatively explained by the higher activity in fructose dehydration compared to Cr(II) . This limits the concentration of intermediates that are involved in bimolecular condensation reactions. Model DFT calculations indicate a substantially lower activation barrier for glucose isomerization by Cr(III) compared to Cr(II) . Qualitatively, glucose isomerization follows a similar mechanism for Cr(II) and Cr(III) . The mechanism involves ring opening of D-glucopyranose coordinated to a single Cr ion, followed by a transient self-organization of catalytic chromium complexes that promotes the rate-determining hydrogen-shift step.

Titanium-doped alumina for catalytic dehydration of methanol to dimethyl ether at relatively low temperatures

Mesoporous Al–Ti oxide composites with molar %Ti of 3, 5, 10, and 20 as well as pure γ-alumina were prepared using a template-free sol–gel method in the absence of a catalyst. The prepared composites were characterized by powder XRD, FTIR spectroscopy and N 2 adsorption for BET surface area and porosity measurements. The composites and the pure alumina possessed relatively high surface areas, 350–410 m 2/g, and high porosities after calcination at 500 °C. FTIR spectroscopy was employed to study the products of the catalytic dehydration of methanol to dimethyl ether, DME, over the prepared catalysts at reaction temperatures between 180 and 300 °C. Compared with pure γ-alumina, the Ti-modified alumina with %Ti < 10 showed higher catalytic activity in the methanol dehydration and better selectivity to DME. Composites with %Ti of 3 and 5 showed the highest activity at relatively lower temperatures than the other catalysts where they showed their highest activity at 190 and 200 °C, respectively. The activity of all studied catalysts slightly decreased as the temperature was raised to 300 °C and dropped considerably when the temperature was decreased to 180 °C. However, the activity of Al–Ti-3 dropped only slightly at both temperatures. The selectivity to DME was dependent on the reaction temperature where 100% DME selectivity was obtained at temperatures ⩽220 °C and as the temperature was raised to 300 °C, some CH 4 and CO 2 formed on the account of DME.

The hierarchical effects of zeolite composites in catalysis

A series of zeolite composites with hierarchically porous structures and tunable acidities were prepared. The structural, crystalline, and textural properties of the as-synthesized materials, as well as the reference Y and β zeolite samples, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/transmission electron microscopy (TEM) analyses, Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption/desorption techniques. The acidic properties of the surface were determined by in situ FTIR of adsorbed pyridine. The hierarchy factor is an appropriate tool to classify hierarchically structured materials, and the hierarchical pores of the as-synthesized zeolite composite samples were investigated during the catalytic cracking of isopropylbenzene. The results show that the catalytic activity of isopropylbenzene cracking over the catalysts has a linear dependence with their hierarchy factor (HF). The tunable acidities were tested by methanol dehydration to dimethyl ether (DME), and the dehydration activity of methanol over the catalysts shows a linear decrease with the increased Lewis/Brönsted ratio, while the selectivity of DME shows a linear increase with the enhanced Lewis/Brönsted ratio.

Catalytic conversion of xylose to furfural over the solid acid [formula omitted]/ZrO 2–Al 2O 3/SBA-15 catalysts

Al-promoted SO 4 2 - /ZrO 2/SBA-15 catalysts were prepared and characterized by XRD, BET, ICP and NH 3–TPD techniques. The influence of introducing aluminum on the structure and surface properties of the catalyst and the catalytic activity for dehydration of xylose to furfural has been investigated. The introduction of the Al stabilizes the tetragonal phase of the ZrO 2 and thus increases the number and intensity of acid sites. Based on the characterization of the deactivated catalyst, the accumulation of byproducts is the main reason for the deactivation of the catalyst. Regeneration with H 2O 2 can completely recover the catalytic activity of the deactivated catalyst.

Solid acid catalysts based on H 3PW 12O 40 heteropoly acid: Acid and catalytic properties at a gas–solid interface

Solid acid catalysts prepared by supporting 15 wt%H 3PW 12O 40 heteropoly acid (HPA) on TiO 2, ZrO 2 and Nb 2O 5 with a sub-monolayer HPA coverage were characterised at a gas–solid interface, regarding their acid properties and chemical structure of HPA on the catalyst surface and compared to “standard” HPA catalysts such as bulk and silica-supported H 3PW 12O 40 and Cs 2.5H 0.5PW 12O 40. In contrast to the parent acid, H 3PW 12O 40, possessing strong Brønsted acid sites, the catalysts supported on TiO 2, ZrO 2 and Nb 2O 5 have both Brønsted and Lewis acid sites, with the latter mainly originating from the oxide support. The strength of acid sites in these catalysts is weaker than that in H 3PW 12O 40 and Cs 2.5H 0.5PW 12O 40. The catalytic activity (turnover frequency) in gas-phase isopropanol dehydration decreases in the order: H 3PW 12O 40 > Cs 2.5H 0.5PW 12O 40 > 15%H 3PW 12O 40/SiO 2 > 15%H 3PW 12O 40/TiO 2 > 15%H 3PW 12O 40/Nb 2O 5 > 15%H 3PW 12O 40/ZrO 2, which is in line with the acid strength as determined by NH 3 adsorption calorimetry. Ammonia adsorption calorimetry, 31P{ 1H} MAS NMR and FTIR indicate increasing interaction between support and HPA in the following order of supports: SiO 2 < TiO 2 < Nb 2O 5 < ZrO 2.

Conversion of biomass into 5-hydroxymethylfurfural using solid acid catalyst

5-Hydroxymethylfurfural (HMF) was produced from monosaccharide (fructose and glucose), polysaccharide (inulin) and the Jerusalem artichoke juice by a simple one-pot reaction including hydrolysis and dehydration using solid acid under mild condition. Hydrated niobium pentoxide (Nb(2)O(5)·nH(2)O(2)) after pretreatment showed high catalytic activities for dehydration of mono- and polysaccharide to HMF at 433 K in water-2-butanol (2:3 v/v) biphasic system, giving high HMF yield of 89% and 54% from fructose and inulin, respectively. The HMF yield was up to 74% and 65% when inulin and Jerusalem artichoke juice were hydrolyzed by exoinulinase. The solid acid made the process environment-friendly and energy-efficient to convert carbohydrates into bio-fuels and platform chemicals.

Correlation between acidity and catalytic activity for the methanol dehydration over various aluminum oxides

Dehydration of methanol into dimethyl ether (DME) was carried out over aluminum oxides with different crystalline phases, viz. η-Al2O3, γ-Al2O3, θ-Al2O3, (χ + γ)-Al2O3, δ-Al2O3, α-Al2O3, and κ-Al2O3. The catalytic activity decreased in the following order: η-Al2O3 > γ-Al2O3 ≫ θ-Al2O3 ≫ (χ + γ)-Al2O3 ≫ δ-Al2O3 > α-Al2O3 ≈ κ-Al2O3. Several techniques: N2 physisorption, X-ray diffraction (XRD), temperature-programmed desorption (TPD) of NH3, and FT-IR spectroscopy after pyridine adsorption were employed to characterize these solid acid catalysts. The good correlation can be found between the catalytic activity and the amount of Lewis acid site determined by the FT-IR spectra after pyridine adsorption.