2-propanol Dehydration Research Articles

Characterization of NiO-TiO2Modified with WO3and Catalytic Activity for Acid Catalysis

A series of <TEX>$NiO-TiO_2$</TEX>/<TEX>$WO_3$</TEX> catalysts was prepared by drying powdered <TEX>$Ni(OH)_2-Ti(OH)_4$</TEX> with ammonium metatungstate aqueous solution, followed by calcining in air at high temperature. Characterization of prepared catalysts was performed by using FTIR, Raman, XPS, XRD, and DSC and by measuring surface area. Upon the addition of tungsten oxide to titania up to 25 wt%, the specific surface area and acidity of catalysts increased in proportion to the tungsten oxide content due to the interaction between tungsten oxide and titania. Since the -<TEX>$TiO_2$</TEX>/stabilizes the tungsten oxide species, for the samples equal to or less than 25 wt%, tungsten oxide was well dispersed on the surface of titania, but for the samples containing above 25 wt%, the triclinic phase of <TEX>$WO_3$</TEX> was observed at calcination temperature above 400 <TEX>$^{\circ}C$</TEX>. The catalytic activities of 10-NiO-<TEX>$TiO_2$</TEX>/<TEX>$WO_3$</TEX> for 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method. NiO may attract reactants and enhance the local concentration of reactants near the acid sites, consequently showing the increased catalytic activities.

Selective skeletal isomerization of alkanes over partially reduced MoO3

The surface area and the pentane isomerization activity of Pt/MoO3 were enlarged by H2 reduction. The enlargements was observed only when the reduction proceeded through the formation of hydrogen molybdenum bronze, HxMoO3. The catalytic activities of H2-reduced MoO3 with different noble metals for pentane isomerization and 2-propanol dehydration depended on the ability of noble metal to produce the HxMoO3 phases. H2-reduced Pt/MoO3 was more active for pentane isomerization than Pt/Hβ, and its activity was comparable to that of Pt/HZSM-5. In heptane isomerization, H2-reduced Pt/MoO3 exhibited a lower activity than Pt/Hβ, although heptane was isomerized very selectively. Strong adsorption of heptane onto H2-reduced Pt/MoO3 is likely to be a reason for its lower heptane isomerization activity.

Effect of diffusion in catalytic dehydration of alcohol over silica–alumina with continuous macropores

Bimodal porous silica–alumina catalysts with both continuous macropores and mesopores were prepared from tetraethyl orthosilicate in the presence of polyethylene oxide, and the effectiveness of macropores in vapor-phase dehydration of 2-propanol was evaluated by the comparison with silica-alumina having no macropores. The reaction rate of dehydration varies depending on the particle size and the presence of macropores as well as reaction temperature. For more detail data processing, diffusion coefficients in pores at each reaction temperature were theoretically calculated by assuming molecular diffusion and Knudsen diffusion for catalysts with and without macropores, respectively. Then, we compare the catalyst effectiveness factors obtained experimentally with the theoretical curve. The experimental data well agree with theoretical prediction. The results clearly show that the macropores with interconnected structure effectively work as pathways for rapid diffusion and improve the reaction kinetics.

Catalytic performance of Nafion/SiO 2 nanocomposites for the synthesis of α-tocopherol

Synthesis of α-tocopherol starting from trimethylhydroquinone (TMHQ) and isophytol (IP) was performed over Nafion/SiO 2 nanocomposite catalysts (Nafion content: 5–20 wt.%) and Nafion ® NR50 resin. The nanocomposites were made by in situ hydrolysis of tetraethoxysilane in the presence of home-made Nafion solution. Nitrogen adsorption and catalytic dehydration of 2-propanol were used, respectively, to characterize the texture and acid properties of the nanocomposites. It is found that acid strength of the Nafion-based acidic sites was weakened in the nanocomposites and the weakening disappeared when the amount of Nafion exceeded 30 wt.% of the nanocomposite. The pore structure and accessibility of the Nafion-based acidic sites in the nanocomposite catalysts showed pronounced effects on the catalytic efficiency toward the desired α-tocopherol. In comparison with Nafion resin in the condensed phase (Nafion ® NR50), 5 and 13 wt.% Nafion/SiO 2 catalysts showed tenfold higher catalytic activities by turnover frequency for α-tocopherol formation owing to increased Nafion dispersion and accessibility of the Nafion-based acid sites. Though the acid sites in the 20 wt.% Nafion/SiO 2 catalyst had similar accessibility to those in the 5 and 13 wt.% Nafion/SiO 2 catalysts by the dehydration of 2-propanol, smaller pore sizes of the 20 wt.% Nafion/SiO 2 catalyst induced severe side reactions of the IP reactant, such as dehydration to form phytadienes and furan derivatives, which resulted in much lower yield (or selectivity) and turnover frequency for α-tocopherol.

Properties of sol–gel derived mesoporous aluminas as metal traps

The performance of fluid catalytic cracking (FCC) catalysts for processing heavy feedstocks is often determined by the tolerance of the catalyst to metal contaminants. Different approaches are used to manage contaminant metals. In this paper, the mesoporous sol–gel derived alumina properties are studied with respect to its behavior in the presence of nickel, after different thermal and steaming treatments. The samples were characterized by X-ray diffraction, BET surface area measurements, NH 3-TPD, TPR, FTIR and tested in the 2-propanol dehydration reaction. The results obtained show that sol–gel derived γ- and η-aluminas of well defined mesoporous structure can be an alternative of FCC catalysts with improved efficiency and selectivity for processing heavy feedstocks with high nickel concentration.

Design and Optimization of Hybrid Separation Processes for the Dehydration of 2-Propanol and Other Organics

The dehydration and recycling of industrial solvents often requires complex processes due to azeotropes and pronounced pinch-points. Combined processes consisting of distillation and pervaporation/vapor permeation might overcome these thermodynamic limitations and offer economically attractive alternatives by simplifying process structure, reducing energy consumption, and avoiding entrainers. The technical and economical feasibility of organic solvent dehydration by pervaporation and vapor permeation with inorganic membranes was evaluated. A survey of the process industry revealed the most attractive applications. The separation of 2-propanol and water was studied in detail. For all process calculations the commercial software Aspen Plus was used. Compatible Fortran routines were developed to incorporate membrane units into the program. Different process configurations to integrate pervaporation and vapor permeation with distillation are compared to conventional separation by extractive distillation. A hy...

Kinetics and thermodynamics of 2-propanol dehydration in supercritical water

Kinetics and thermodynamics of 2-propanol dehydration in supercritical water (SCW) and the effect of density on this reaction have been investigated in a batch reactor. The studies were performed at water densities between 0.24 and 0.58 g/cm 3 and temperatures between 654 and 686 K. The main reaction products of 2-propanol dehydration were propene and water. Rate of the reaction was found to depend essentially on the water density. Two models are used to predict the effect of SCW density on the rate constant of 2-propanol dehydration reaction: a thermodynamic model (the model of activated complex) and a model of acid-catalyzed reaction. Redlich–Kwong–Soave equation of state was used for calculation of the partial molar volumes of the reaction participants in SCW including a transition state and activation volume of the reaction. Application of the activated complex model demonstrated that the calculated values of the activation volume depend strongly on pressure at fixed temperature, which contradicts the experimental data where the activation volume is independent of pressure. At the same time, the mechanism of 2-propanol dehydration reaction in SCW was shown to correlate well with the acid-catalyzed mechanism in solutions. Rate of the reaction is directly proportional to the concentration of 2-propanol and H 3O + ions. An increase in the H 3O + concentration in SCW with density correlates unequivocally with an increase in the reaction rate.

Acidic properties of nickel sulfate supported on TiO 2–ZrO 2 and catalytic activity for acid catalysis

A series of catalysts, NiSO 4/TiO 2-ZrO 2, was prepared by the impregnation method using an aqueous solution of nickel sulfate. Calcination at 300–600 °C of co-precipitated Ti(OH) 4–Zr(OH) 4 resulted in the formation of an amorphous phase and further heating at 700 °C and above resulted in the formation of crystalline ZrTiO 4 compound. For NiSO 4/TiO 2-ZrO 2 sample, no diffraction line of nickel sulfate was observed up to 30 wt.%, indicating good dispersion of nickel sulfate on the surface of TiO 2–ZrO 2. The addition of nickel sulfate to TiO 2–ZrO 2 shifted the phase transition of ZrTiO 4 from amorphous to orthorhombic to higher temperature because of the interaction between nickel sulfate and ZrTiO 4, and the acid amount of NiSO 4/TiO 2-ZrO 2 increased in proportion to the nickel sulfate content up to 20 wt.% of NiSO 4. The high catalytic activity of NiSO 4/TiO 2-ZrO 2 was related to the increases of acid amount and acid strength due to the addition of NiSO 4. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation, were correlated with the acid amounts of catalysts measured by on ammonia chemisorption method. The asymmetric stretching frequency of the SO bonds for NiSO 4/TiO 2-ZrO 2 samples was related to the acidic properties and to the catalytic activity for acid catalysis. That is, the higher the frequency, the larger the acid amount and catalytic activities for 2-propanol dehydration and cumene dealkylation.

The bifunctional catalytic properties of a partially H 2-reduced MoO 3

XPS–UPS techniques were employed in order to identify the different Mo suboxides produced by hydrogen reduction of bulk MoO 3 at different temperatures. A bifunctional MoO 2(H x ) ac phase is formed on the surface of MoO 2 produced by this reduction process at temperatures between 623 and 673 K. Dehydration of 2-propanol and the hydroisomerization of 1-hexene and n-hexane were interpreted using these dual (metal–acid) functions of MoO 2(H x ) ac.

Improved catalytic activity upon Ge incorporation into ZSM-5 zeolites

The catalytic stability of ZSM-5 can be greatly improved by the isomorphous substitution of some Si atoms by Ge. The catalytic properties of Ge-ZSM-5 zeolites have been compared to ZSM-5 in a series of acid-catalysed test reactions (the dehydration of 2-propanol and 2-butanol, the isomerisation of isobutyraldehyde to 2-butanone, and the Friedel–Crafts acylation of anisole). The propene yield in the 2-propanol dehydration reaction at 180 °C is as high as 98% for Ge-ZSM-5 and only 40% for ZSM-5. For the other investigated reactions similar differences are observed. The presence of a considerable amount of mesopores in Ge-ZSM-5 (compared to ZSM-5) is proposed to be the main explanation for the difference. These mesopores are formed upon synthesis and reduce the effect of pore blocking by coke residues that are formed at high reaction temperatures.

Synthesis and characterization of packed mesoporous tungsteno-silicates: application to the catalytic dehydrogenation of 2-propanol

The synthesis of highly ordered mesoporous tungsteno-silicas in which a high percentage of tungsten is introduced into a silica framework is reported hereafter. Powder XRD and TEM have been used to characterize the materials synthesized at room temperature. The materials are shown to be homogeneous as there is no evidence for any crystalline species other than the silica framework. The pore diameter and the surface area of the materials, evaluated from the nitrogen adsorption isotherms and unit cell parameter indicate a pore diameter of about 2 nm and a surface area of 1400 m 2 g −1 for a content of 10% tungsten. Catalyzed dehydration of 2-propanol has been investigated and the activity of the materials synthesized is significant, even for low tungsten content W-MCM-41 materials.

Hydroisomerization of n-heptane and dehydration of 2-propanol on bulk and supported WO 2(H x) ac on TiO 2

Characterization by XPS–UPS and XRD of commercial bulk WO 2 enabled us to identify the presence of four to five layers of WO 3 on the sample surface with an equal amount of W 5+, possibly W 20O 58 in the interface. The presence of these WO 3 and W 20O 58 on the WO 2 surface were not detected by XRD. Exposure of commercial bulk WO 2 to hydrogen at temperatures higher than 673 K results in the reduction of surface WO 3 to WO 2 and the formation of the bifunctional WO 2(H x ) ac phase on its surface. A complete conversion of surface WO 3 to WO 2(H x ) ac has been obtained following the exposure of the sample to hydrogen for at least 6 h at 773 K. A conversion of 52% of n-heptane at 573 K reaction temperature and a selectivity of 90% in isomerization products, mainly 2,3-MH and multibranched molecules were obtained. The isomerization products distribution is in agreement with the statistical and thermodynamic equilibrium of the methyl-shift mechanism. The stability of the active WO 2(H x ) ac phase has been tested under prolonged exposure to hydrogen and the reaction mixture. Similar results were obtained in the case of bulk WO 3 and WO 3/TiO 2 systems. Dehydration and dehydrogenation of 2-propanol were studied on these systems at 393 K reaction temperature.

Spectroscopic Studies on ZrO2Modified with MoO3and Activity for Acid Catalysis

Zirconia modified with MoO 3 was prepared by impregnation of powdered Zr(OH) 4 with ammonium heptamolybdate aqueous solution followed by calcining in air at high temperature. Spectroscopic studies on prepared catalysts were performed by using FTIR, Raman, XRD, and DSC and by measuring surface area. Upon the addition of molybdenum oxide to zirconia up to 15 wt%, the specific surface area increased in proportion to the molybdate oxide content, while acidity measured by irreversible chemisorption of ammonia exhibited a maximum value at 3 wt% of MoO 3 . Since the ZrO 2 stabilizes the molybdenum oxide species, for the samples equal to or less than 30 wt%, molybdenum oxide was well dispersed on the surface of zirconia and no phase of crystalline MoO 3 was observed at any calcination temperature above 400 °C. The catalytic activities for cumene dealkylation were roughly correlated with the acidity of catalysts measured by ammonia chemisorption method, while the catalytic activities for 2-propanol dehydration were not correlated with the acidity because weak acid sites are necessary for the reaction.

Preparation of new solid superacid catalyst, zirconium sulfate supported on γ-alumina and activity for acid catalysis

Zirconium sulfate supported on γ-Al 2O 3 catalysts were prepared by impregnation of powdered γ-Al 2O 3 with zirconium sulfate aqueous solution followed by calcining in air at high temperature. For Zr(SO 4) 2/γ-Al 2O 3 samples, no diffraction line of zirconium sulfate was observed up to 50 wt.%, indicating good dispersion of Zr(SO 4) 2 on the surface of γ-Al 2O 3. The acidity of catalysts increased in proportion to the zirconium sulfate content up to 40 wt.% of Zr(SO 4) 2. 40-Zr(SO 4) 2/γ-Al 2O 3 calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method.

Characterization of zirconium sulfate supported on TiO2 and activity for acid catalysis

A series of Zr(SO4)2/TiO2 catalysts were prepared by impregnation of powder TiO2 with an aqueous solution of zirconium sulfate. No diffraction line of zirconium sulfate was observed up to 30 wt%, indicating good dispersion of Zr(SO4)2 on the surface of TiO2. The high catalytic activities of Zr(SO4)2/TiO2 for both 2-propanol dehydration and cumene dealkylation were related to the increase of acidity and acid strength due to the addition of Zr(SO4)2. Zr(SO4)2/TiO2 containing 25% zirconium sulfate and calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for these reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method.

Hydroisomerization of n-heptane and dehydration of 2-propanol on MoO 2(H x) ac. catalysts

Catalytic hydroisomerization of n-heptane was carried out following the reduction by hydrogen of bulk MoO 3, MoO 3/TiO 2, as well as MoO 3 were present on the surface of commercial bulk MoO 2. A conversion of 55% and a selectivity of more than 90% in isomerization products, mainly 2- and 3-methyl hexanes, were obtained at 573 K using the supported system. The major hydrocracking products obtained are C3 and C4 with a ratio C3/C4=1.2. Modifications of the reactant flow rate as well as the catalyst mass, enabled us to increase the conversion to 74% with a selectivity of 82% in isomerization products at 573 K reaction temperature. The catalytic active phase is attributed to the bifunctional MoO 2(H x ) ac. single phase. The metallic function is assured by MoO 2 delocalized π electrons as identified by XPS–UPS in terms of density of state (DOS) at the Fermi-level. The Brönsted acidic functional group(s), (H x ) ac. were deduced from the adsorption of ammonia, the isomerization of olefins at relatively low reaction temperatures in comparison to alkanes and the dehydration of 2-propanol.

Influence of Carbon−Chlorine Surface Complexes on the Properties of Tungsten Oxide Supported on Activated Carbons. 2. Surface Acidity and Skeletal Isomerization of 1-Butene

Chlorinated activated carbons and the respective tungsten oxide catalysts supported on them were tested as catalysts in the decomposition reaction of 2-propanol and characterized by measurement of their pHPZC. Supported catalysts were also used in the skeletal isomerization of 1-butene. Results found show that an increase in the chlorine content of the support increases the total surface acidity, as measured by the pHPZC, of both the support and the supported catalysts. However, there is also a decrease in their Bronsted type acidity, as determined from the results obtained from the dehydration reaction of 2-propanol. Thus, it seems that the effect of chlorine is to increase Lewis type acidity in both the support and the supported catalyst. In addition, during the dehydration of 2-propanol there was a partial reduction of W(VI) to W(V) in most of the catalysts, which brought about a restructuring of the metal oxide particles. Isomerization of 1-butene gives only isobutene and trans-2-butene. Selectivity t...

Effect of Irradiation Sources and Oxygen Concentration on the Photocatalytic Oxidation of 2-Propanol and Acetone Studied by in Situ FTIR

The photocatalytic oxidation (PCO) of 2-propanol and acetone was studied on TiO2 powder at high coverage (>2 monolayers) at various oxygen concentrations using in situ FTIR. Two UV irradiation sources, either a continuous-wave UV lamp or an excimer laser, were applied to investigate the effect of the UV source on the PCO. It was found that higher oxygen concentrations increased the PCO rate of 2-propanol and acetone. The excimer laser source accelerated the PCO rate of 2-propanol while decelerating that of acetone as compared to the continuous-wave source. This effect was found to be larger at higher oxygen concentrations. Factors such as multiphoton adsorption or a pulsed irradiation were excluded as possible explanations for the irradiation source effect. More likely, the laser source changes the reaction mechanism by introducing an abrupt temperature increase, and hence the thermal decomposition, that is, dehydration of 2-propanol to propene, is effectively initiated on the surface. The PCO of 2-propanol was found to proceed along two routes: one was through the chemisorbed species, 2-propoxide, to form CO2 directly; the other was through conversion of H-bonded 2-propanol to acetone, followed by thermal fragmentation of mesityl oxide (aldol condensation product of acetone) to form formate species, and finally to CO2. It was also found that the acetone decay rate during acetone PCO was much faster than that of acetone formed as an intermediate during 2-propanol PCO at the same oxygen concentration. This was likely due to the presence of other species competing for reaction sites on the catalyst surface.

Exfoliated nanosheets as a new strong solid acid catalyst.

Two-dimensional metal oxide sheets in HTiNbO(5) and HSr(2)Nb(3)O(10), cation-exchangeable layered metal oxides, were examined as solid acid catalysts. Exfoliation of HTiNbO(5) and HSr(2)Nb(3)O(10) in aqueous solutions formed colloidal single-crystal TiNbO(5)(-) and Sr(2)Nb(3)O(10)(-) nanosheets, which precipitated under an acidic condition to form aggregates of HTiNbO(5) nanosheets and HSr(2)Nb(3)O(10) nanosheets. Although esterification of acetic acid, cracking of cumene, and dehydration of 2-propanol were not catalyzed by original HTiNbO(5) because of the narrow interlayer distance, which prevents the insertion of organic molecules, HTiNbO(5) nanosheets functioned as a strong solid acid catalyst for the reactions. Nanosheets of HSr(2)Nb(3)O(10) exhibited no or slight catalytic activity for these reactions. NH(3) temperature-programmed desorption and (1)H magic-angle spinning nuclear magnetic resonance spectroscopy revealed that HTiNbO(5) nanosheets have strong Brønsted acid sites, whereas HSr(2)Nb(3)O(10) nanosheets do not.

Aluminum incorporation in mesoporous MCM-41 molecular sieves and their catalytic performance in acid-catalyzed reactions

Mesoporous aluminosilicate molecular sieves, Al-containing MCM-41, with different Si/Al ratios were synthesized by four different methods: sol–gel, hydrothermal, template cation exchange and grafting. The catalysts prepared by sol–gel, grafting and template cation exchange methods are effective for the incorporation of large amounts of aluminum into the framework of MCM-41. The catalytic activities of the resulting Al-containing MCM-41 samples were tested in the cracking of cumene and the dehydration of 2-propanol, as model acid-catalyzed reactions, and then compared with the results obtained from microporous H-ZSM-5 and HY zeolites. The Al-containing MCM-41 catalysts prepared by different methods behaved differently in acting as acidic catalysts; the catalyst (having almost same Si/Al ratio) prepared by sol–gel method showed higher cracking activity, whereas that prepared by template cation exchange method showed higher dehydration activity. Moreover, these Al-containing MCM-41 catalysts are more catalytically active than microporous HY zeolite for cumene cracking and 2-propanol dehydration reactions.