Catalytic Decomposition Of 2-propanol Research Articles

Structure–acidity correlation of supported tungsten(VI)-oxo-species: FT-IR and TPD studies of adsorbed pyridine and catalytic decomposition of 2-propanol

Abstract The amount of 10 wt%-WO3 was supported on alumina, titania or silica by impregnation with aqueous solution of ammonium paratungstate and subsequent calcination at 500 °C for 10 h. Tungstate-related chemical and physical changes in the calcination products were resolved by ex-situ infrared (IR) spectroscopy. Nature of exposed surface acid sites were probed by in-situ IR spectroscopy of adsorbed pyridine (Py) molecules at room temperature (RT). The relative strength of the acid sites thus probed was gauged by combining results of temperature-programmed desorption (TPD) measurements of the RT-adsorbed Py with those communicated by in-situ IR spectra of residual Py on the surface after a brief thermoevacuation at high temperatures (100–300 °C). Reactivity of the surface acid sites was tested toward 2-propanal catalytic decomposition, and observed by in-situ IR gas phase spectra. Results obtained were correlated with predominant structures assumed by the supported tungstate species. Accordingly, polymerization of the supported tungstate into 2-/3-dimensional structures, was found to be relatively most advanced on favorable locations of titania surfaces as compared to the case on alumina or silica surfaces. Consequently, the Lewis acidity was strengthened, and strong Bronsted acidity was evolved, leading to a 2-propanol dehydration catalyst (tungstate/titania) of optimal activity and selectivity. Strong tungstate/support interfacial interactions were found to hamper the formation of the strongly acidic and catalytically active polymeric structures of the supported tungstate (i.e., the case on alumina or silica).

Transesterification of ethyl butyrate with methanol using MgO/CaO catalysts

A series of mixtures of MgO/CaO with different Mg/Ca molar ratios (between 3 and 15), as well as the corresponding pure oxides, was prepared by the coprecipitation method in a basic medium and subsequent calcination. Their textural and structural characterization was carried out by using XRD, FT-IR, SEM and N 2 sorption at 77 K. The alkalinity was studied by CO 2-TPD and catalytic decomposition of 2-propanol. The MgCa oxides obtained after calcination at 1073 K exhibit X-ray diffraction patterns with clearly visible signals corresponding to crystalline CaO and MgO. Textural properties are improved by the presence of Mg, with the porosity increased and the particle sizes decreased with respect to pure CaO. FT-IR spectroscopy reveals the presence of surface carbonate. These catalysts are active in the transesterification of ethyl butyrate with methanol at 333 K and atmospheric pressure, a model reaction to evaluate the potential of these basic catalysts in triglycerides transesterification for biodiesel production. The highest activity was found for a Mg:Ca molar ratio of 3, with conversion close to 60%, whereas MgO was inactive. Moreover, lixiviation of the active phase was not observed thus excluding the contribution of the homogeneous catalysis to the studied transesterification process.

Sulfated Alumina Catalysts: Consequences of Sulfate Content and Source

Consequences of the loading level of sulfate ions (3, 6, and 10-wt%) as well as the source of sulfate (H2SO4 or (NH4)2SO4) on the structural, textural, and surface acid–base properties as well as the impacts on catalytic activity towards 2-propanol conversions on γ-Al2O3 and on aluminum hydroxide gel is described. Structural investigations of the catalysts by XRD revealed that the sulfation processes do not remarkably affect the γ-phase of alumina irrespective of the sulfate content or source. N2-adsorption at 77 K indicated that sulfated gel catalysts exhibit the highest S BET areas and, in general, S BET for all catalysts were found to decrease with the increase of sulfate content, such a decrease is more pronounced for the 10% loaded catalysts. Pyridine adsorption as followed by FTIR indicated that sulfation of alumina increases the strength of its Lewis acid sites and creates Bronsted acidity in the case of highly loaded catalysts. The catalytic decomposition of 2-propanol in the gas phase indicated that, amongst all the catalysts investigated, the 6% loaded ones exhibited 100% activity (2-propanol conversion) and the highest propene (dehydration product) selectivity.

Influence of support composition on the structure and reactivity of strontium base catalysts

Strontium was supported on a variety of carriers, including silica, alumina, titania and carbon, by impregnation and decomposition of an acetate precursor at 773 K. These supported samples were characterized by surface area measurements, stepwise temperature-programmed desorption of carbon dioxide and activity for the catalytic decomposition of 2-propanol. In some cases, infrared and X-ray absorption spectroscopy were used to identify surface species. Results from these techniques suggested that strontium supported on silica forms a weakly basic surface silicate phase that had low activity for 2-propanol dehydrogenation. On alumina and titania, strontium acetate decomposed to form supported basic carbonates that were moderately active for 2-propanol dehydrogenation. When rates are normalized by the base site density determined from CO2 desorption, strontium supported on carbon was the most active sample for dehydrogenation of 2-propanol. These results suggest that the nature of supported alkaline earth catalysts is strongly dependent on the composition of the carrier.

Unsupported MoO 3Fe 2O 3 catalysts: characterization and activity during 2-propanol decomposition

The catalytic decomposition of 2-propanol (2-PrOH) was studied as probe reaction, in the gas phase, over unsupported MoO 3Fe 2O 3 mixed catalysts. The samples were prepared by mixing MoO 3 (as ammonium heptamolybdate) with different x mol% Fe 2O 3 (as ferric nitrate) and calcined at 500°C in air for 5 h. All catalysts were characterized by TPR, IR, XRD and XPS analyses. The surface area of these samples were determined using the BET method. Also, the acidity and the basicity of all catalysts were estimated thermogravimetrically using the adsorption of pyridine and formic acid as probe molecules. The catalytic decomposition of 2-PrOH was studied over the catalysts in the temperature range of 150–260°C. A correlation between the catalytic activity and the acidity or the basicity of these catalysts has been made. The activation energies for both propene and acetone formation, over MoO 3Fe 2O 3 catalysts, were calculated.

Study of the catalytic decomposition of 2-propanol induced by CW−CO2 laser

The decomposition of 2-propanol induced by CW−CO2 laser with and without catalyst has been studied. In the presence of catalyst the threshold laser energy for stimulating decomposition is decreased. The reaction products depend on the adsorption states of 2-propanol on the catalyst surface. The mechanism of laser induced surface reaction is discussed.

The catalytic decomposition of 2-propanol on calcined chromia: the nature of the active sites

The effect of foreign ion incorporation and/or calcination on the activity of chromia catalysts towards simultaneous dehydrogenation and dehydration of 2-propanol is investigated. Data are presented for kinetic parameters of the reactions, the surface content of both Cr 6+ ions and hydroxyl groups for the catalysts and the selectivity factors. A mobile-electron Zener phase on the surface (couples Cr 3+-Cr 6+) is suggested to optimize the dehydrogenation activity. The dehydration activity is found to depend on surface hydroxylation and on porosity.

Effect of γ-irradiation on the catalytic decomposition of 2-propanol

70 kGy of γ-irradiation enhances the catalytic transformation of 2-propanol into acetone and propylene on transition metal oxides. Fragment products are formed and for TiO 2, V 2O 5 and Fe 2O 3 the selectivity of 2-propanol decomposition is shifted towards dehydration by the irradiation. Both catalytic and radiocatalytic transformation of 2-propanol correlate with the adsorption capacity of metal oxides, which suggests, that irradiation acts mainly on the adsorbed 2-propanol. Possible changes in the catalyst's chemical properties due to the irradiation are discussed.

The formation of propane, propylene, and acetone from 2-propanol over vanadium pentoxide and modified vanadium pentoxide catalysts

The catalytic decomposition of 2-propanol has been studied in a flow System from 200 to 280 °C on vanadium pentoxide and modified vanadium pentoxide catalysts. Results were obtained with separate melts of the oxide containing 9.09 mol% of each of the alkali metal sulfates and with individual preparations of the pentoxide containing 1.01, 2.00, and 4.98 mol% potassium sulfate, respectively. In addition to expected dehydration and dehydrogenation reactions, propane was formed over the entire temperature range and became a dominant product at higher temperatures.Kinetic experiments showed that the dehydration and dehydrogenation reactions were zero order with respect to ail components while the propane-forming reaction gave a rate order of 0.3 with respect to 2-propanol concentration. Elimination-type mechanisms have been proposed to explain the results and some evidence of a relationship between catalyst activities and surface acidity is presented. The observed kinetic compensation effect bas been shown to compare well with previous work on 2-propanol decomposition on metal oxides.

Isotope effect studies of the decomposition of 2-propanol on hafnium(IV) oxide

The catalytic decomposition of 2-propanol on hafnium dioxide has been investigated over the temperature range 355–397 °C by a micropulse reactor technique. The major reaction is one of dehydration to propene but dehydrogenation also occurs to a small extent. Isotope effect measurements with deuterio-2-propanols indicate that the rate-limiting step in dehydration involves cleavage of the β-carbon-hydrogen while in the dehydrogenation reaction it is cleavage of the α-carbon-hydrogen bond.

The Catalytic Decomposition of 2-Propanol on Magnesium Oxide

The catalytic decomposition of 2-propanol on powders of "pure" and lithium oxide doped magnesium oxide has been investigated in the temperature range 300–450 °C by a pulse reactor technique. With the "pure" magnesium oxide samples the selectivity for dehydrogenation decreases with increasing temperature with an abrupt change in the region of 375 °C. The effect of the lithium oxide dopant is to depress the selectivity for dehydrogenation at the lower temperatures. The dopant does not appear to affect the dehydration activity and the decrease in selectivity is ascribed to the strong chemisorption of acetone at anion vacancies.

The Catalytic Decomposition of 2-Propanol over the Silica-Manganese(II), -Zinc(II) and -Magnesium(II) Prepared by the Homogeneous Method

The catalytic dehydration and dehydrogenation of 2-propanol over thesilica-manganeset (II), -zinc(II)and-magnesium(II), which were prepared by the method of precipitation from homogeneous solution were compared with those over usual coprecipitated metals.Dehydration took place to a large extent over the catalysts prepared by the homogeneous method, while dehydrogenate did only toa small extent at 300Cover the catalysts prepared by the both methods. The catalytic dehydration activities on the homogeneous catalysts were much higher than those on the coprecipitated catalysts, and the order of activity was Mg(II) Zn(II) Mn(II).Kinetics studies using a fiow reactor indicated that the dehydration and the dehydrogenation were of both first-order irreversible reactions. From theArrhepius plots the activation energies for the dehydration Over the homogeneoussilica-manganese(E), -zinc(II) and -magnesium(E), were found to be 16.0, 17.9 and20.6kcal/mol.m2, respectively.From the consideration, of the changes of relative activities by adding various amounts of KOH and of the differences of thepH titration curves for the catalysts and silica gel, it was concludedthat the active sites of the dehydration were. Lewis acid site, vi2., the metals with the vacant orbitals which combined with the silica gel and those of the dehydrogenation were the electron pair donor or the oxygen atom of the metallic oxide bended to the silica gel.