Isopropanol Decomposition Research Articles

Reactions of aliphatic alcohols on the {011}-facetted Ti0 2 (001) surface

The adsorption and decomposition of ethanol, n-propanol and isopropanol were studied by means of TPD and XPS on the {011}-facetted TiO 2 (001) surface. The higher aliphatic alcohols adsorbed both molecularly and dissociatively at 200 K, but only dissociatively at 300 K. Molecularly adsorbed alcohols desorbed readily below 300 K. Adsorbed alkoxides were stable surface intermediates, and were removed at higher temperatures via two channels. Approximately 50% of surface alkoxides were removed as the parent alcohols at 365 K via recombination with surface hydroxyl species. The remaining alkoxides decomposed at temperatures higher than 500 K. The decomposition of surface alkoxides followed predominantly a net dehydration pathway to produce oleflns. For ethanol and n-propanol, net dehydrogenation to produce aldehydes was also observed. The dehydrogenation/ dehydration selectivity ratios were less than 0.25 in all cases. The peak temperatures of alkoxide decomposition products reflect the relative thermal stabilities of the alkoxides, which were in the order: isopropoxide < n-propoxide ⩽ ethoxide. No bimolecular reaction products, e.g. ethers, were observed in this study.

Photo-enhanced catalytic decomposition of isopropanol on V2O5

The effect of UV-visible photo irradiation has been investigated on the decomposition of isopropanol over V2O5. A ∼ 2.5-fold photo-enhancement in the rate of the dehydration (-H2O) reaction was observed under UV-visible photo irradiation compared to thermal heating of the catalyst. The increase in propene yield under photo irradiation is believed to be initiated from photo excitation (photo-reduction) of the V2O5 complex to [-V4+-O−] * thus, increasing surface concentration of V4+ species. The V4+ active surface species is assumed to serve as the center for adsorption of isopropanol. The observed increase in water formation along with the formation of propene suggests that the rate determining step for the dehydration reaction is desorption of water. Selectivity toward the dehydrogenation (-H2) reaction has also been measured to be ∼ 1% under UV-visible photo irradiation as compared to ∼ 15% under thermal heating of the catalyst.

Structure and reactivity of transition-metal oxide monolayers

Transition-metal oxides supported on and chemically interacting with the surface of SiO2, Al2O3, TiO2etc. form discrete monolayers of species unlike those found at the surface of the unsupported oxides, being in effect two-dimensional compounds. Areas of their application include alkene metathesis and polymerisation, selective reduction of NO by NH3, and selective oxidation of aromatics. They are readily detected by Raman spectroscopy, FTIR and EXAFS/XANES, and thermal methods and XPS assist their characterisation. They can exhibit strong acidic character, mainly of the Bronsted type; whereas isopropyl alcohol decomposition on MoO3TiO2 gives chiefly dehydration, the main product over V2O5/TiO2 is acetone. The unique ability of the latter system to catalyse the selective oxidation of o-xylene to phthalic anhydride is attributed to the ability of the surface species to undergo oxidative addition at VO groups and to effect the elimination of H atoms in adsorbed radicals as water. When the amount of supported oxide exceeds the monolayer capacity, two further forms of the oxide are detectable, both differing in their reactivity from that of the bulk oxide.

Influence of thermal activation of chalcopyrite on activity and selectivity of catalytic decomposition of isopropyl alcohol

The decomposition of isopropyl alcohol on natural chalcopyrite was studied by the microcatalytic pulse method in the region 473–673 K. The activity and selectivity of the catalyst was confronted with the temperature of its thermal activation. The apparent activation energies of decomposition were calculated for chalcopyrite activated in argon atmosphere at temperatures of 673, 773, and 873 K. The values of activation energy thus obtained are 61, 38, and 44 kJ mol−1 The liberation of sulfur from the lattice of chalcopyrite caused by thermal activation gives preference to dehydration over dehydrogenation at lower temperatures. The proportion of hydrogen and acetone in reaction products increases with temperature.

Catalytic properties of certain technetium compounds

1. A comparative study has been made of the catalytic properties of Tc, TcO2, and TcS2 in the decomposition reactions of isopropanol and cyclohexane. 2. In the dehydrogenation of isopropanol the oxide catalysts occur in the order for a decrease in activity: TcO2/γ-Al2O3 >TcO2/MgO > TcO2/ZrO2-TcO2/Y2 O3 > TcO2/Cr2O3. 3. The decomposition of isopropanol on the supported metallic and oxide catalysts takes place in the direction of dehydrogenation, while dehydrogenation and dehydration take place on the sulfide catalyst. 4. For catalysts based on Tc, TcO2, and TcS2 the yield of benzene in the dehydrogenation of cyclohexane depends on the nature of the supported technetium compound and the nature of the substrate. In their activity in this process the technetium compounds can be arranged in the following order Tc > TcO2 > TcS2.

Catalytic decomposition of isopropyl alcohol on iron(II) sulfide

The decomposition of isopropyl alcohol on troilite (FeS) which was thermally activated at 873, 973 and 1073 K, is described in this paper. The catalyst subjected to thermal activation exhibits improved activity, which increases with temperature of activation. It has been observed that the apparent activation energy E and the preexponential factor A have a compensating effect. The experiments involving the preadsorption of pyridine have shown that this substance is preferentially and irreversibly adsorbed on hydrogenation active centers.

Decomposition of isopropanol on V2O5 of different grain morphology and its relation to o-xylene oxidation catalysts

Decompositon of isopropanol has been studied on V2O5 samples of different morphology. It has been shown that the selectivity to acetone increases with the increase in the fraction of (010) plane of V2O5 on the sample surface, whereas the selectivity to propene decreases. The results are compared with previous data of o-xylene oxidation on the same samples and discussed in terms of the model of V2O5 surface [7].

Characterization of organically pillared zirconium phosphates

Samples of α-zirconium phosphates and of zirconium phosphates pillared by phenyl, dimethylphenyl, and diphenyl have been characterized by BET surface area, surface acidity, adsorption capacity and pore sizes, TGA, X-ray powder diffraction, and activity for isopropanol decomposition. The BET surface areas of pillared zirconium phosphates have been found to increase with the increase in size and number of organic groups in the interlayers. The total number of surface acidic sites of α-zirconium phosphates has been found to be greater than any one of the pillared catalysts. It is concluded from this study that α-zirconium phosphate pillared by diphenyl has interlayer openings large enough to sorb isopropanol, and its decomposition takes place mainly in the interlayers of this catalyst. In contrast, the phenyl and dimethylphenyl pillared zirconium phosphates have less free space between the interlayers so that the reactions of isopropanol take place on the outer surface of the catalysts. The dehydration of isopropanol to propylene has been found to be the primary reaction for all the catalysts.

Kinetic compensation effects and activated states for alcohol decomposition over alkali-modified vanadium oxides

The rate of thermal decomposition of ethanol, isopropanol and t-butanol over well-defined alkali vanadates (trivanadate, MV 3O 8, M = Li, Na, and K; and hexavanadate, M 2V 6O 16, M = Rb and Cs) were precisely measured in a closed cyclic reaction system at constant reactant vapor pressures between temperatures of 190 and 370 °C. A steady rate was evident in the initial 20 min for most of the experiments. The initial mean rate decreased in the order Li → Na → K for the trivanadate. However, the initial mean rate increased in the order Rb → Cs for the hexavanadate. The plot of rate versus alkali ion size was a U-shaped curve for each alcohol run. The activation energies ( E a) for the hexavanadates were much larger than those for the trivanadates with any alcohol tested. Despite the kinetic differences between the tri- and hexavanadates, a linear relationship was found between the preexponential factor (log V 0) and the activation energy ( E a) through the series of alkali-modified vanadates for any alcohol. The data depended on the alkali ion size. The slope of the plot increased as the size of the alkyl group on the reactants increased. This compensation effect can be explained by assuming that the activation entropy is proportional to the excitation of the internal frictional rotation of an alkyl group in the reactants. In other words, the entropy term is directly related to the strength of the interaction energy, when based on a model where the alkyl and hydroxyl groups of the reactant molecule interact with the surface VO group and the alkali metal ion, which is placed on the VOV interchains.

Some acidity test reactions on Sn&z.sbnd;Sb&z.sbnd;O oxide systems

The decomposition of isopropanol and cumene cracking were studied on Sn&z.sbnd;Sb&z.sbnd;O oxide catalysts with different Sb contents and different calcination temperatures, examined previously in the oxidation of hydrocarbons. Dehydration of isopropanol increases with increasing antimony content in the samples, in particular in the region when the Sb2O4 phase was observed. Cumene cracking, the rate of which is very low for both component oxides (SnO2 and Sb2O4), is maximal at low Sb contents in the region of the existence of a solid solution of Sb5+ ions in SnO2. Samples with a monolayer of Sb2O4 deposited on SnO2 show a marked decrease in the dehydration rate in comparison with bulk Sb2O4.

Performance of Pt−Sn/Al2O3−Cl catalysts in isopropanol decomposition

Pt−Sn/Al2O3, Pt/Al2O3 and Sn/Al2O3 catalysts were tested for isopropanol decomposition. Dehydration activity was related to catalysts acidity. Pt/Al2O3 and bimetallic catalysts show a similar dehydrogenation activity, however, monometallic catalysts have a deactivation rate non-observable in Pt−Sn/Al2O3.

Catalytic decomposition of isopropanol over chromite spinels MCr2O4(M = Ni, Mn and Mg)

The decomposition of isopropanol over nickel, manganese and magnesium chromite spinel catalysts has been investigated in the vapour phase in an integral reactor. Its decomposition follows first-order kinetics. Kinetic and thermodynamic parameters have been calculated using the Arrhenius and Eyring equations. The activity pattern is found to be NiCr2O4 > MnCr2O4 > MgCr2O4. The chromite spinels have been characterised by X-ray studies, i.r. spectral analysis, conductivity and thermoelectric potential measurements. All three chromites were found to be p-type semiconductors in the temperature range 150–400 °C. Exclusive dehydrogenation is shown by NiCr2O4 and MnCr2O4, whereas MgCr2O4 functions as a dehydrogenation and dehydration catalyst. A linear correlation exists between the entropy of activation and the activation energy for electrical conduction for the chromite spinels studied.

Isopropyl alcohol decomposition over molybdena-alumina catalyst

The decomposition of isopropyl alcohol was chosen as a probe reaction of acid-base property of molybdena-alumina catalyst. The catalytic kinetics was examined on the oxidized catalyst. The kinetics of the dehydration (yielding propene) and the dehydrogenation (yielding acetone) obeyed the Langmuir-Hinshelwood mechanism in which the rate determining step is the desorption of water for the former and the sur face reaction for the latter, respectively. The effect of varying the extent of reduction of the catalyst was also studied. The trend of variation with the reduction was fairly consistent with the surface chemistry of the catalyst.

Catalytic behavior and surface chemistry of copper/alumina catalysts for isopropanol decomposition

Supported copper on γ-Al 2O 3 catalysts (1, 3, and 4 Cu atoms per 100 Al atoms) have been pretreated in a controlled way in oxygen and in hydrogen in order to have a known surface concentration of Cu(II), Cu(I), and Cu(0). These samples were tested as catalysts for the decomposition of 2-propanol. Below 443 K the samples showed only dehydrogenating activity which increased with the extent of catalyst reduction. A linear relationship was found between the kinetic constant and the surface area of copper metal. It is hence proposed that surface Cu(0) species are responsible for the dehydrogenation. The effect of the copper concentration on the sample stability under reaction conditions is also discussed.

O-xylene oxidation on the V 2O 5-TiO 2 oxide system : I. Dependence of catalytic properties on the modification of TiO 2

O-xylene oxidation and isopropanol decomposition have been studied on V 2O 5-TiO 2 oxides prepared by decomposition of a vanadia phase on anatase and rutile modifications of titania under conditions in which the solid state reactions involving formation of solid solutions of vanadium in rutile are excluded. It has been shown that anatase-containing catalysts show higher activity and selectivity in o-xylene oxidation, lower reduction degree of the catalyst in the stationary state of catalytic reaction, and lower dehydration/dehydrogenation ratio as compared with rutile-containing samples. Properties of the rutile-containing catalysts resemble those of pure vanadia: the modifying action of anatase is observed even at low vanadia concentration (XXX 1.0 mole %) and it is ascribed to the formation of a special structure of vanadia of possibly a monolayer type on the anatase surface which exhibits the isopropanol dehydrogenation centres and has low acidity.

Studies of the structural stability of Sn-Sb mixed oxide in the decomposition of isopropyl alcohol

Typical Sn-80at.%Sb mixed oxide undergoes structural reduction during the decomposition of isopropyl alcohol in the absence of gas phase oxygen, and the active phase may contain metallic tin and Sb 2O 3. However, in the presence of oxygen the catalyst retains its structural stability and acetone is the major product together with small amounts of CO 2 and propylene. Product inhibition studies with acetone reveal that oxidation of the acetone to CO 2 occurs in preference to oxidation of isopropyl alcohol. The effect of the partial pressure of isopropyl alcohol and the partial pressure of oxygen on the decomposition of isopropyl alcohol was investigated. The presence of a large excess of oxygen favours CO 2 formation, whereas smaller amounts of oxygen favour acetone formation. A possible mechanism for the reaction in the presence of gas phase oxygen is proposed.

Studies on the decomposition of isopropyl alcohol on Mg Al 2-xFe xO 4

Decomposition of isopropyl alcohol was carried out on the solid solution system MgAI 2−xFe xO 4 (x = 0 to 2). The system exhibited both dehydrogenation and dehydration activities. The selectivity for dehydration did not vary monotonically with change in x, but reached a minimum at x = 0.40. Mechanistic studies were made with a view to identifying the rate-determining step. The nature of the active sites was predicted by means of specific poisoning experiments and interesting correlations were obtained between activity for dehydrogenation and certain physicochemical properties of the system. The important conclusion drawn is that dehydrogenation of the alcohol, as well as the electrical and magnetic properties, are basically influenced by a fundamental property of the spinel system, namely, the symmetry of the catalytically acive Fe 3+ site.

Catalytic activity of the CaO−CaF2 system

Cao−CaF2 catalysts containing 0–100%CaF2 have been studied concerning their activity in different reactions. Maxima of activity for butene isomerization and isopropanol decomposition as well as selectivity for the alcohol dehydration were found for the sample with equimolar ratio of the components. No sample was active in cumene cracking. Suggestions are made concerning the reaction mechanisms and the active centers involved.

Modifications of the surface reactivity of Ni(100) by structured overlayers of sulfur: Selectivity changes for ethanol and isopropanol decomposition

The reactions of ethanol and isopropanol were studied on Ni(100), Ni(100) p(2 × 2) S and Ni(100) c(2 × 2) S by temperature programmed reaction spectroscopy (TPRS). On both Ni(100) and Ni(100) p(2 × 2) S decomposition to adsorbed CO and atomic hydrogen dominated the reaction. Methane was also formed by the reaction of adsorbed hydrogen atoms with fragments of the decomposition, most likely carbon atoms. On both surfaces evidence for a COH complex was observed, similar to previous results with methanol. On Ni(100) c(2 × 2)0 S the selectivity of the reactions changed dramatically. Formation of aldehydes was enhanced at the expense of CO and H 2; methane was not observed. From these results it appears that alkoxy intermediates formed on all three surfaces by dehydrogenation and that their further decomposition to CO, h (a) and C (a) was limited by adsorbed sulfur.

Modifications of the surface reactivity of Ni(100) by structured overlayers of sulfur: Selectivity changes for ethanol and isopropanol decomposition

Modifications of the surface reactivity of Ni(100) by structured overlayers of sulfur: Selectivity changes for ethanol and isopropanol decomposition