Dehydrogenation Of Isopropanol Research Articles

The influence of plasma chemical treatment of nickel and nickel-rhenium catalysts deposited on sibunite on their activity in dehydrogenation

The dehydrogenation of isopropanol was studied at 440–680 K to find that the activity of the Ni(1 wt %)/sibunite catalyst decreased after annealings and quenchings and was stabilized after subsequent treatment with an (I) O2 glow-discharge or (II) H2 high-frequency plasma. Treatments of both kinds decreased the activity of the catalyst below the Curie point (633 K) and increased it over the paramagnetic temperature range (635–680 K). The treatment of the (1 wt % Ni–1 wt %Re)/sibunite and (2 wt % Ni–2 wt % Re)/sibunite catalysts with plasma II weakly influenced their activity, whereas treatment with plasma I substantially increased it. The kinetic reaction parameters on the (2 wt % Ni–2 wt % Re)/sibunite catalyst were found to depend on the duration of treatment with plasma II. Treatment with plasma I much more effectively changed the state of the surface of all the catalysts studied than treatment with plasma II.

Chemical, plasma chemical, and thermal modification of metallic catalysts

The role played by factors that modify the state of the surface of metals and their influence on catalytic activity are discussed. It is shown that the theoretical real gas model (two-dimensional electron gas-chemisorbed impurity particles) can be used to explain the character of the influence of nonmetallic and metallic impurities on the activity of catalysts. The influence of plasma chemical and thermal treatments of Rh, Ir, Ni, and Ag in the form of films, massive samples, and ultradisperse powders deposited on silica gel and Sibunite on their activity in the oxidation of CO, dehydrocyclization of n-C6H14, and dehydrogenation of isopropanol was studied. The influence of impurities and treatments specified was determined separately and in combination. The catalytic parameters changed because of changes in the surface electron density and the formation of structure defects on the surface of metals.

Novel improved ruthenium catalysts for the generation of hydrogen from alcohols

The dehydrogenation reaction of alcohols to generate hydrogen at ambient conditions has been studied, it is shown for the first time that ruthenium in the presence of easily available amine ligands constitutes an active catalysts for this reaction: high turnover frequencies (TOF) up to 519 h(-1) (after 2 h) and catalyst stability (>250 h) were achieved for the dehydrogenation of isopropanol with a combination of [RuCl2(p-cymene)]2/TMEDA.

Surface properties and catalytic behavior of MoO3/SiO2 in esterification of acetic acid with ethanol

AbstractA series of MoO3/SiO2 catalysts was prepared by an impregnation method with Mo loadings ranging from 1 to 50 wt%. The original and calcined samples at 400 °C were characterized by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR) spectroscopy, and nitrogen adsorption measurements. The surface acidity and basicity of the catalysts were investigated by the dehydration–dehydrogenation of isopropanol and the chemisorption of pyridine. The catalytic esterification of acetic acid with ethanol was carried out at 220 °C in a conventional fixed‐bed reactor at 1 atm using air as a carrier gas. The results clearly revealed that silica–molybdena catalysts were active and selective towards the formation of ethyl acetate. Moreover, the catalyst containing 20 wt% MoO3 was the most active and selective one. The results emphasize the importance of the surface acid sites together with the specific surface area of the prepared catalyst, towards ester formation. Copyright © 2005 Society of Chemical Industry

Stage-II-screening device for testing of heterogeneous catalysts in gas phase reactions with Fourier transform infrared analysis

The construction of a stage-II-screening device for heterogeneous catalysts in gas phase reactions under ambient pressure is described. The concentrations of the reaction products are determined by Fourier transform infrared analysis in combination with a chemometric interpretation of the obtained spectra. Thus, fast high-precision product analyses with complete mass balances are feasible, within the limits of accuracy of the measurements. The device is designed to screen up to 17 catalysts in one testing cycle. It is possible to determine temperature-conversion-selectivity dependencies as well as long-term measurements under constant conditions. With the help of the device described, the catalytic properties of new materials were parallel tested for the oxidative dehydrogenation of isopropanol.

Dehydrogenation of isopropyl alcohol on carbon-supported Pt and Cu–Pt catalysts

The kinetics of isopropyl alcohol (IPA) dehydrogenation over carbon-supported Pt and three bimetallic Cu Pt catalysts were examined and compared with previous results for carbon-supported Cu. Adsorption of H 2 and CO, dissociative chemisorption of N 2O, and the titration of adsorbed O atoms by H 2 and CO were used to determine surface compositions and metal dispersion. Monometallic platinum catalysts had a higher specific activity than monometallic Cu catalysts and the bimetallic catalysts; for example, at 448 K and 14 Torr IPA, for an activated carbon heat treated at 1223 K as the support, the turnover frequency (TOF) on the Pt catalyst was 0.11 s −1, the TOF on the Cu catalyst was 0.020 s −1, and the TOFs on the three bimetallic catalysts were between 0.006 and 0.043 s −1. Reaction orders were typically between 0 and 1 2 for IPA and slightly negative for acetone and H 2. Increasing the Cu loading reduced the number of surface Pt atoms, and the kinetic behavior became similar to that of monometallic copper catalysts. The apparent activation energy for acetone production from IPA on Pt/C was 6.8 kcal mol −1, compared with 21 kcal mol −1 for the monometallic Cu/C catalysts. Apparent activation energies for the Cu Pt/C catalysts (7–9 kcal mol −1) were comparable to those of Pt/C at lower temperatures and decreased further to ∼ 3 kcal mol −1 above 443 K. This decrease is not due to diffusional limitations and can be explained by a decrease in the surface coverage of IPA. A Langmuir–Hinshelwood model invoking cleavage of the alcohol O H bond to form a surface isopropoxide species as the rate-determining step fit the data well and accounted for the shift in the apparent activation energy. Physically meaningful values of enthalpies and entropies of adsorption were obtained from the fitting parameters contained in the L-H rate expression. Additional evidence for adsorbed IPA and acetone was provided by infrared spectra of the catalysts obtained under reaction conditions.

05/00591 Highly coking resistant and stable Ni/Al 2O 3 catalysts prepared by W/O microemulsion for partial oxidation of methane

Various materials consisting of magnesium (mMgPO-1 and mMgPO-2) or aluminium phosphates (mAlPO-1 and mAlPO-2) were synthesized from microemulsions and characterized in structural terms using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), thermal analysis, and solid-state 31P and 27Al NMR spectroscopies. The morphology of the solids was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their surfaces properties were determined from N2 adsorption–desorption isotherms. The new materials thus prepared are structurally and compositionally similar to solids obtained by precipitation from solutions; their specific surface areas, however, are substantially greater and their pore size distribution more narrow. The catalytic activity of the materials in the dehydration–dehydrogenation of isopropyl alcohol was found to be similar to or greater than that of catalysts obtained by precipitation from aqueous solutions. The magnesium orthophosphates yielded acetone (the major product) and propene from 2-propanol; the aluminium orthophosphates, which possess dehydrating activity only, yielded propene alone.

Highly active Cu-based catalysts on carbon nanofibers for isopropanol dehydrogenation

Cu/CNF and Cu/CeO 2/CNF catalysts have been synthesized and characterized on different nanostructured carbon nanofibers (CNF). The samples have been tested in isopropanol dehydrogenation. Cu/CNF show similar activity to Cu catalysts supported on activated carbon. Cu/CeO 2 nanotubes have been synthesized on the CNF surfaces. The Cu/CeO 2 nanotubes exhibit much higher activity and lower activation energy than Cu/CNF. The selectivity towards acetone depends on the fraction of CeO 2 in the composites. High activity and selectivity has been achieved with a Cu 12Ce 5/CNF catalyst.

Zinc complexes of a macrocyclic N 3O 2 ligand for the functional modelling of alcoholdehydrogenase

The macrocyclic ligand 1,12,15-triaza-3,4:9,10-dibenzo-5,8-dioxacycloheptadecane ( L) and the zinc halides form the complexes L·ZnHal 2 ( 1a– c, Hal=Cl, Br, I) and [ L·ZnHal] 2 ZnHal 4 ( 2a, b, Hal=Cl, Br). The structure determination of 2a has shown that the oxygen donors of the macrocycle remain uncoordinated and there is tetrahedral ZnN 3Cl coordination. The complexes catalyse the hydrogenation of aromatic aldehydes with BNAH and the dehydrogenation of isopropanol with BNA +. Although the catalytic efficiency is rather small, it surpasses that of previously reported zinc complexes.

Gas phase esterification of acetic acid with ethanol over MoO3 supported on AlPO4 and the effect of modification with phosphomolybdic acid and Ce4+ ions

AbstractA series of AIPO4–MoO3 (APM) systems with various molybdena loadings (5–50) mol %, same modified with phosphomolybdic acid (PMA) and cerium ions, were prepared by an impregnation method and calcined at 400 °C, except for the samples modified with PMA which were calcined at 350 °C for 4 h. The catalysts were characterized by TG/DTG, XRD, IR spectroscopy, N2 adsorption and electrical conductivity measurements. The surface acidity and basicity of the catalysts were determined by adsorption of pyridine and the dehydration–dehydrogenation of isopropyl alcohol. The catalytic esterification of acetic acid with ethanol was carried out in a convention fixed bed reactor. The results clearly revealed that the catalyst with a composition of 10 mol % MoO3 (APM10) was the most active and selective catalyst for the production of ethyl acetate. Moreover, the yield of ethyl acetate increases on addition of PMA into APM10 while it decreases on the addition of Ce4+ ions. These results were correlated with structure, semiconductivity and the acid–base properties of the prepared catalysts. Copyright © 2003 Society of Chemical Industry

Microkinetic analysis for the selective oxidation of propylene to acetone over vanadia/titania

The reaction mechanisms for the oxidation of isopropanol and propylene to acetone over the 10% V 2O 5/TiO 2 catalyst were modeled according to the results of FTIR, microcalorimetric adsorption and microreactor kinetics. The two reaction mechanisms are closely correlated since isopropanol can be taken as the intermediate for the oxidation of propylene to acetone. The simulations revealed how the reaction conditions affect surface coverages that in turn influence the reaction activities. The abstraction of α-H from the surface isopropoxy groups by the oxidation sites (V 5+–O) is the rate-limiting step for the oxidative dehydrogenation of isopropanol to acetone, while the adsorption of propylene on surface Brönsted acid sites (V–OH) to form the surface isopropoxy groups is the rate-limiting step for the selective oxidation of propylene to acetone. Both Brönsted acid sites and oxidation sites (V 5+–O) are required for the conversion of propylene to acetone. Thus, one way to promote the rate of propylene adsorption in order to enhance the rate of propylene conversion to acetone may be to increase the strength of the Brönsted acid sites by adding some other acidic materials. The oxygen deficient vanadium sites were found to promote the dissociative adsorption of isopropanol to form the surface isopropoxy groups and the adsorption of water to form the surface Brönsted acid sites (V–OH) needed for the adsorption of propylene.

Hydrogenation/dehydrogenation reactions: isopropanol dehydrogenation over copper catalysts

For accurate catalyst comparisons and kinetic modeling, data free of mass and heat transfer effects must be acquired over a range of temperature and reactant concentrations using well-characterized heterogeneous catalysts. For semibatch reactors operated at constant pressure, selectivity vs conversion profiles at several temperatures, preferably obtained with catalysts reduced in situ, are required to allow complicated reaction networks to be defined. Vapor-phase isopropyl alcohol (IPA) dehydrogenation over carbon-supported Cu catalysts in a differential fixed-bed reactor was studied and compared to UHP Cu powder and a Cu chromite catalyst. Low dispersions of Cu (ca. 0.02–0.17) were obtained in all these catalysts. Cu dispersed on an activated carbon heat-treated at 1223 K had the highest turnover frequency (0.052 s−1 at 448 K) of all the Cu/C catalysts, more than double that on an industrial Cu chromite catalyst; thus the rate with this 5.0% Cu/C catalyst (6.0 μmol s−1g−1) was close to that of the chromite catalyst containing 41% Cu (10.6 μmol s−1g−1). The steady-state selectivity to acetone was 100% for all catalysts except those containing the nitric-acid-treated carbon. In the absence of Cu, the nitric-acid-treated carbon produced propylene under steady-state reaction conditions, and reduction at 573 K decreased activity compared to reduction at 423 K. This dehydration reaction is associated with the presence of oxygen-containing acidic groups on the C surface. The apparent activation energy for acetone formation was typically near 20 kcalmol−1 for all the Cu/C catalysts and the Cu powder, but it was near 12 kcalmol−1 for the Cu chromite catalyst. A DRIFT spectrum under reaction conditions indicated the presence of an isopropoxide species and molecularly adsorbed IPA on the surface. A Langmuir–Hinshelwood mechanism, which assumed removal of the first hydrogen atom as the rate-determining step and incorporated adsorbed IPA, hydrogen, acetone, and a surface isopropoxide species into the site balance, fit the kinetic data well and gave physically meaningful values for the enthalpies and entropies of adsorption.

Microemulsion-assisted synthesis of catalysts based on aluminium and magnesium phosphates

Various materials consisting of magnesium (mMgPO-1 and mMgPO-2) or aluminium phosphates (mAlPO-1 and mAlPO-2) were synthesized from microemulsions and characterized in structural terms using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), thermal analysis, and solid-state 31P and 27Al NMR spectroscopies. The morphology of the solids was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their surfaces properties were determined from N 2 adsorption–desorption isotherms. The new materials thus prepared are structurally and compositionally similar to solids obtained by precipitation from solutions; their specific surface areas, however, are substantially greater and their pore size distribution more narrow. The catalytic activity of the materials in the dehydration–dehydrogenation of isopropyl alcohol was found to be similar to or greater than that of catalysts obtained by precipitation from aqueous solutions. The magnesium orthophosphates yielded acetone (the major product) and propene from 2-propanol; the aluminium orthophosphates, which possess dehydrating activity only, yielded propene alone.

Isopropyl Alcohol Dehydrogenation on Modified Porous Membrane Reactor.

Isopropanol (IPA) dehydrogenation was carried out at 388-423 K in Vycor glass-based modified porous membrane reactor (MPMR) to confirm the result previously obtained for cyclohexane dehydrogenation. The result reveals that the phenomenon of organic product concentrating in MPMR's sweep side as observed on cyclohexane dehydrogenation also occurs in IPA dehydrogenation. In addition, the overall IPA conversion in MPMR also lay between Local Fixed Bed Reactor (LFBR) and Global Fixed Bed Reactor (GFBR). However, at lower temperatures, the difference of conversion in GFBR and MPMR is almost negligible. This is due to the effect of surface diffusion and the characteristics of IPA dehydrogenation.

Microkinetic analysis of isopropanol dehydrogenation over Cu/SiO 2 catalyst

The reaction of isopropanol dehydrogenation to acetone over the Cu/SiO 2 catalyst was studied using the method of microkinetic analysis. This analysis provided a picture about the coverage of different surface species and their influences on the reaction rate. Specifically, the analysis reinforced the previously proposed mechanism and added some new findings for the reaction. It was found that under the normal reaction conditions, the catalyst surface is mostly covered by the isopropoxyl groups and the overall reaction rate is controlled by the elimination of α-H of the isopropoxyl groups. In addition, the elimination of the α-H is significantly affected by the availability of surface Cu sites. At the low hydrogen partial pressure, the number of bare surface Cu sites increases with the increasing of hydrogen partial pressure, leading to the increased overall reaction rate and thus the positive reaction order with respect to hydrogen. Thus, hydrogen can enhance the rate of this reaction via some kinetic factors under the specific coverage regime, although it is thermodynamically unfavorable for the reaction.

Superbase derived from zirconia-supported potassium nitrate

Superbasic sites can be generated on ZrO 2 by loading with KNO 3. The spontaneous dispersion capacity of KNO 3 on ZrO 2 was 8.1 K + nm −2 and the KNO 3 starts to decompose near 350°C, much lower than that for the decomposition of unsupported KNO 3. KNO 3/ZrO 2 samples exhibited a high activity in both dehydrogenation of isopropanol at 400°C and isomerization of cis-but-2-ene at 0°C. Moreover, they possessed the base strength of H −=26.5, which is the characteristic of solid superbase.

Characterization and Catalytic Activity of Cr2O3–Al2O3/AlPO4 Catalysts

Five samples of Al2O3/AlPO4 (Al/P = 1.75) and Cr2O3-loaded Al2O3/AlPO4 (wt% Cr2O3 = 5–25) were prepared. The catalysts were obtained by thermal treatment of the corresponding samples in air at 823 K and were characterized using XRD and DTA techniques. The textural properties (surface area, total pore volume and mean pore radius) were determined from nitrogen adsorption data obtained at 77 K. The acidic properties of all the samples were measured calorimetrically. The catalytic conversion of isopropanol was studied using a microcatalytic pulse technique. No spinel structure was detected by both XRD and DTA techniques and only Cr2O3 was detected for samples containing ≥ 15 wt% chromia. Loading Al2O3/AlPO4 with Cr2O3 led to significant changes in the texture, surface acidity and catalytic activity of the prepared catalysts. Al2O3/AlPO4 catalysts exhibit no dehydrogenation activity, whereas loading with Cr2O3 favoured the dehydrogenation of isopropanol to acetone.

On the acidity and/or basicity of USY zeolites after basic and acid treatment

The isopropanol decomposition reaction was used to evaluate the catalytic activity of ultrastable (USY) zeolites with different degrees of dealumination, treated in strongly alkaline medium at various temperatures and contact times. This treatment resulted in the reinsertion of non-framework aluminium, a result of the ultrastabilization process. The samples obtained were also submitted to an acid treatment, leaching the non-framework aluminium that had not been reinserted. The results obtained at 723K showed a large reduction in the acidic activity of the alkaline-treated zeolite, as the treatment conditions became more severe (the longer the treatment time or the higher the temperature, the higher the degree of dealumination). On the other hand, treated samples displayed some isopropanol dehydrogenation activity (basic sites). However, this activity was not very significant and did not depend on the alkaline treatment or ultrastabilization conditions used. The effect of reaction temperature and acid leaching on activity is also shown.

Structure, texture and catalytic activity of ZnO/Al 2O 3 catalysts

The structural and phase changes occurring in coprecipitated zinc–aluminum hydroxide system were studied by thermoanalytical and X-ray diffraction techniques. The textural properties of the calcined samples were determined by low temperature nitrogen adsorption. Surface acidities were determined from the adsorption of n-butylamine. The crystal structure, surface area, pore volume and surface acid character were found to be dependent on the chemical composition and calcination temperature. The heating of the samples at different temperatures led to the formation of ZnO, γ-Al 2O 3 and ZnAl 2O 4 with various degree of crystallinity. The results of nitrogen adsorption revealed that S BET values of the different solids decrease progressively on increasing precalcination temperature and ZnO content due to sintering. The same was found true for the surface acidities. The conversion of isopropanol over the investigated catalysts was determined using a pulse microcatalytic technique. The dehydrogenation of isopropanol was found to be dependent on the chemical composition. The dehydration of isopropanol is independent of the surface area but related to the surface acid density.

ChemInform Abstract: Selective Dehydrogenation of Isopropanol on Low‐Percentage Supported Bimetallic Rhenium‐Containing Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.