Gas Phase Hydrogenation Of Crotonaldehyde Research Articles

Morphological and chemical influences on alumina-supported palladium catalysts active for the gas phase hydrogenation of crotonaldehyde

A series of five alumina-supported palladium catalysts have previously been prepared and characterised by a combination of CO chemisorption and infrared spectroscopy. The reactive attributes of these catalysts are examined using the hydrogenation of crotonaldehyde as a test reaction, using a modified infrared gas cell as a batch reactor. Periodic scanning of the infrared spectrum of the gaseous phase present over the Pd/Al(2)O(3) catalysts was used to construct reaction profiles. Four of the catalysts were able to facilitate a 2-stage hydrogenation process (crotonaldehyde → butanal → butanol), whilst one catalyst was totally selective for the first stage hydrogenation process (crotonaldehyde → butanal). Rate coefficients for the first and second stage hydrogenation processes are normalised to the number of surface palladium atoms for the particular catalyst. Correlation of these kinetic parameters as a function of mean particle size indicates the first stage process to be structure insensitive, whilst the second stage hydrogenation is structure sensitive. Chlorine residues associated with the preparative process of one of the catalysts is seen to selectively poison the second stage hydrogenation process for that catalyst. Structure/activity relationships are considered to explain the observed trends.

Rh/ZnO-Al2O3 Catalysts for Selective Hydrogenation of Crotonaldehyde

Gas phase hydrogenation of crotonaldehyde was performed over 1 wt% Rh/ZnO-Al2O3 catalysts with various Zn/Rh atomic ratios. Monometallic Rh/Al2O3 was also prepared for comparison. The samples were prepared by the successive impregnation of Al2O3 with chloride precursors of zinc and rhodium. The solids have been characterized by H2 chemisorption, temperature-programmed reduction, scanning electron microscopy, and cyclohexane dehydrogenation. Their catalytic behaviour in the gas phase crotonaldehyde hydrogenation reaction after reduction treatment in flowing hydrogen at 723 K was investigated. The relationship between catalytic activity, selectivity for crotyl alcohol, and physicochemical properties of the catalysts was examined. Results obtained showed that the presence of Zn clearly promotes the hydrogenation of the carbonyl bond. The catalyst with Zn/Rh atomic ratio of 5 displayed good catalytic stability and the highest selectivity for crotyl alcohol (70%) along with alloy formation.

Hydrogenation of crotonaldehyde on different Au/CeO 2 catalysts

The gas-phase hydrogenation of crotonaldehyde was carried out at 120, 150, and 180 °C over Au catalysts supported on ceria with low and medium surface areas (150 and 80 m 2 g −1, respectively). An initial deactivation period was observed, followed by a steady-state regime. Ethanol was the main product in the deactivation period, whereas crotyl alcohol, butanal, butanol, and condensation products were produced under steady-state conditions. The activity and selectivity to crotyl alcohol (in the 20–32% range) were lower than those for the high-surface area ceria catalysts studied previously [B. Campo, M. Volpe, S. Ivanova, R. Touroude, J. Catal. 242 (2006) 162]. Samples were characterized by TPR, XPS, TEM, and XRD. The analysis of catalytic and characterization results indicates that gold particles supported on low- and medium-surface area ceria were relatively large, and the promotional effect of Ce 3+ species was not achieved for the corresponding catalysts. Moreover, under reductive conditions, sintering still increased gold particle size.

Influence of the preparation method on the catalytic behaviour of PtSn/TiO2 catalysts

PtSn/TiO2 catalysts containing 2wt% Pt and a Pt:Sn atomic ratio of 2:1 and 1:1 were prepared by coimpregnation or successive impregnation method with aqueous solutions of SnCl2·2H2O and H2PtCl6·6H2O of a commercial TiO2 (P25, from Degussa). Both catalyst series, independent of the preparation method, were reduced at 473 and 773K. XPS results show that tin was in an oxidized state after reduction at 473K, and that a fraction was in the metallic state after reduction at 773K. By use of in situ FTIR spectroscopy of adsorbed CO, the presence of bimetallic Pt–Sn phases was assessed after reduction at 773K. Microcalorimetric analysis of CO adsorption enthalpy indicates that reduction at 773K causes the appearance of a more heterogeneous distribution of active sites, as well as a loss in the amount of sites. The catalytic activity for the gas phase hydrogenation of crotonaldehyde was greatly improved when the catalysts were prepared by coimpregnation, at both reduction temperatures. The selectivity toward crotyl alcohol was higher after reduction at 773K and independent of the preparation method, although it increased with the amount of tin, suggesting a promoting effect of tin on this reaction.

Pt/ZrO2/TiO2 catalysts for selective hydrogenation of crotonaldehyde: Tuning the SMSI effect for optimum performance

Gas phase hydrogenation of crotonaldehyde was performed over Pt/ZrO2/TiO2 catalysts with different zirconia loadings, subjected to low- and high-temperature calcination (200 and 400 °C) and a range of reduction temperatures (200–600 °C). Pt/TiO2 was used as reference system. The catalysts were characterised by TPR, XPS, SEM, HR TEM, TOF-SIMS and H2, O2 and CO chemisorption after different stages of thermal pretreatments. The relationship between catalytic activity, selectivity towards crotyl alcohol and physicochemical properties of the catalysts was examined. The catalyst containing 30% ZrO2 in the support, calcined at 200 °C and reduced at 500 °C showed the highest selectivity (50%) while retaining good activity. The explanation of those properties was proposed, involving the mutually opposing action of two factors – presence of ZrO2 and ‘permeability’ of Pt phase for TiOx migration – in controlling of the SMSI effect.

Selective hydrogenation of crotonaldehyde on Au/HSA-CeO 2 catalysts

The gas-phase hydrogenation of crotonaldehyde was carried out over Au supported on high-surface area (HSA) CeO 2, previously reduced at 120 °C. The products analyzed during the initial, nonequilibrium stage showed the formation of large amounts of ethanol, which rapidly decreased with time on stream and were replaced by a combination of condensation products (mainly 2,4,6-octatrienal) under equilibrium conditions. The production of crotyl alcohol largely exceeded that of butanal at any time on stream. Under steady-state conditions, the crotyl alcohol-to-butanal ratio was equal to 1.7. When the catalyst was recalcined in air at 300 °C, just before the reduction treatment, the formation of ethanol in the initial stage and that of condensation products under steady state decreased. Besides, notable increase in the production of crotyl alcohol was observed, whereas butanal formation was unaffected. Finally, Au/HSA-CeO 2 is a highly selective catalyst for C O bond hydrogenation when crotyl alcohol/butanal ratio is equal to 3 under a steady-state regime. These results were compared to those obtained for Au/TiO 2 [R. Zanella, C. Louis, S. Gorgio, R. Touroude, J. Catal. 223 (2004) 328]. The role of acid–base sites, as well as that of the redox centers of HSA-CeO 2, is evaluated. Even though ceria sites are engaged in the reaction, the catalytic properties of Au/HSA-CeO 2 are attributed mainly to the gold nanoparticles.

Palladium-based alloy and monometallic catalysts for gas phase hydrogenation of crotonaldehyde: effects of alloying and alloy crystallite size

Gas phase hydrogenation of crotonaldehyde has been investigated with supported Pd catalysts using different supports. The overall conversion and product distribution significantly depend on the supports used. Crotyl alcohol is formed along with butyraldehyde as the chief products in comparable quantities with Pd/ZnO, while little crotyl alcohol is formed with such catalysts as Pd/Al 2O 3 and Pd/SiO 2. The difference in the product distribution is due to the difference in the active species, which is PdZn alloy in Pd/ZnO but is Pd in the other catalysts. The activity of Pd/ZnO decreases slightly with the size of PdZn alloy crystallites, but the selectivity to crotyl alcohol increases and that to butyraldehyde decreases.

On the performance of a highly loaded Co/SiO 2 catalyst in the gas phase hydrogenation of crotonaldehyde : Thermal treatments—catalyst structure–selectivity relationship

This paper reports on the performance and its relation with the structure of a highly loaded (41 wt.%) Co/SiO 2 catalyst in the gas phase hydrogenation of crotonaldehyde when varying the thermal treatments to which the catalyst precursor has been subjected. The optimum calcination and reduction temperatures were identified where the highest selectivity to crotyl alcohol (around 90%) was obtained with the catalyst calcined at 400 °C and reduced at 350 °C even at conversions as high as 60%. Higher temperature of calcination was found to lower the crotyl alcohol selectivity. Both, lower and higher reduction temperatures will not favour the crotyl alcohol formation. These results were interpreted and correlated with the surface structure of the catalyst which was shown by temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) analysis. Depending on the thermal conditions imposed, the surface consisted of either Co metal, or coexisting metal and its oxide; structure which favours the high crotyl alcohol selectivity. By TEM analysis, large particles (diameter exceeding 50 nm) were identified after reduction at 350 °C. A global activation energy of 44 kJ/mol was obtained with this catalyst. In the light of the obtained results a discussion on the reaction mechanism involving metal, metal-oxide double sites has been put forward. It was emphasised that, for selective hydrogenation of crotonaldehyde into unsaturated alcohol, Co catalysts compete favourably with platinum based catalysts.

Hydrogenation of Crotonaldehyde over Sn/Pt(111) Alloy Model Catalysts

Gas-phase hydrogenation of crotonaldehyde (CH3CHCHCHO) was studied over the (2×2) Sn/Pt(111) and (□3×□3) R30° Sn/Pt(111) surface alloys which were used as model catalysts. The influence of the alloy structure, hydrogen pressure, and temperature on activity and selectivity toward 2-butenol (CH3CHCHCH2OH) formation was investigated. The results were compared to those obtained for the pure Pt(111) surface. All catalysts were characterized prior to use by X-ray photoelectron spectroscopy and low-energy electron diffraction to ensure proper alloy formation. The hydrogenation activity was about two times higher for the bimetallic Pt–Sn catalysts compared to that for Pt(111); however, little change in selectivity was observed. Butyraldehyde was formed as the main product in all cases. Therefore, alloy formation improves hydrogenation activity toward CC and CO functional groups and cannot solely explain the improvement in selectivity toward the formation of the unsaturated alcohol that has often been reported for supported Pt–Sn catalysts versus pure Pt catalysts. Both alloys investigated had similar catalytic activity and selectivity. An attempt was made to create oxidic tin species on the Pt(111) surface, because these species have been suggested to improve selectivity to the unsaturated alcohol product. However, the oxidic species formed by heating the alloys in 5 Torr O2 for 5 min at 600 K were not stable under reaction conditions and were reduced to form a surface with low catalytic activity, probably consisting of metallic Sn rafts over the Pt(111) surface.

Performance of Pt/SnO 2 catalyst in the gas phase hydrogenation of crotonaldehyde

Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO 2 catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H 2PtCl 6 and Pt(NH 3) 4(NO 3) 2 as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn 2 formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity.

Surface Structures of Rh−Cu Sol−Gel Catalysts and Performance for Crotonaldehyde Hydrogenation

Rh−Cu/SiO2 catalysts prepared by the sol−gel method by mixing solutions of Rh(acac)3 in acetone and/or of Cu(NO3)2 in water with tetraethoxysilane (TEOS) in ethanol at 318 K at pH 3. The influence has been studied of the copper content on the surface and catalytic properties were analyzed. It was found that the addition of Cu to Rh/SiO2 catalysts increases the rhodium dispersion and modifies the rhodium clusters, either by alloy formation and/or by electron transfer from copper to rhodium metal clusters in intimate contact. X-ray photoelectron spectroscopy results indicate that copper(I) species remain trapped in the support matrix, changing the metal−support interaction. Support for these interactions was provided by testing their reactivity in the gas-phase hydrogenation of crotonaldehyde at 373 K. A significant enhancement in both activity and selectivity to crotyl alcohol was observed depending on these interactions. Selectivity to the unsaturated alcohol higher than 60% was obtained for Rh−Cu catalys...

Role of the residual chlorides in platinum and ruthenium catalysts for the hydrogenation of α,β-unsaturated aldehydes

The gas-phase hydrogenation of crotonaldehyde has been performed over platinum and ruthenium catalysts supported over graphites with a tailored content in surface oxygen groups and prepared with different metal precursors. It is found that the selectivity to the unsaturated alcohol is independent of the amount of oxygen groups on the surface of the graphite supports. Notwithstanding this, their presence has an effect when a metal chloride precursor is used in the catalyst preparation since they act as anchoring sites of the chloride ions and the latter in residual amounts promote the hydrogenation of the carbonyl group. The addition of tin to platinum enhances also the selectivity to crotyl alcohol.

Promoting Effect of Ceria on the Gas Phase Hydrogenation of Crotonaldehyde over Platinum Catalysts

The platinum-ceria interaction, induced after high temperature reduction of platinum based catalysts, has been used to improve the selectivity towards crotyl alcohol in the gas phase hydrogenation of crotonaldehyde. Three catalysts have been used in this study, Pt/SiO2, Pt/CeO2, and Pt/CeO2/SiO2. They have been characterized by X-ray diffraction and temperature-programmed reduction, and their catalytic behavior in the gas phase benzene hydrogenation and crotonaldehyde hydrogenation reactions have been determined after reduction treatments in flowing hydrogen at 473 and 773 K. Results obtained in the gas phase hydrogenation of crotonaldehyde show that the presence of ceria clearly promotes the hydrogenation of the carbonyl bond when the sample is reduced at high temperature, this being attributed to the presence of oxygen vacancies or Ce3+cations in the neighbourhood of platinum particles, induced by the thermal treatment under hydrogen. The promoting effect is more important for Pt/CeO2; crotonaldehyde hydrogenation on this catalyst yields up to 80% crotyl alcohol after reduction at 773 K, whereas it produces 100% butanal after reduction at only 473 K.

Deactivation and Selectivity Pattern in Crotonaldehyde Hydrogenation

Gas phase hydrogenation of crotonaldehyde to crotyl alcohol, butyraldehyde, and butanol was studied in a differential microreactor at atmospheric pressure and 353 K over a supported Pt catalyst. The reaction rate was seen to be dependent on the catalyst pre-treatment mode. Rapid deactivation has been observed and the deactivation rate differed for differently treated samples. Kinetic modelling was based upon reaction a network, which apart from conventional dehydration steps included parallel hydrogenolysis to hydrocarbons. Deactivation phenomena were assumed to occur as a result of the formation of surface deposits, which block active catalyst sites. An adequate description of experimental data has been achieved via parameter estimation.

Reaction Induced Selectivity Improvement in the Hydrogenation of Crotonaldehyde over Sn–Pt/SiO2Catalysts

Silica-supported Sn–Pt catalysts, prepared by controlled surface reactions between hydrogen adsorbed on platinum and tin tetraethyl, showed high activity and selectivity in the gas phase hydrogenation of crotonaldehyde to crotyl alcohol. The selectivity of the formation of crotyl alcohol (SCO) had a strong dependence of the Sn/Pt ratio. The highest SCOselectivity (around 70%) was obtained at Sn/Pt=3. The characteristic feature of the Sn–Pt/SiO2catalyst in the given reaction is the development of the SCOselectivity during the time-on-stream period. The observed phenomenon was described as a reactant induced catalyst activation.

Gas phase hydrogenation of crotonaldehyde over platinum supported on oxidized carbon black

The effect of a previous oxidation treatment of the carbonaceous support on the catalytic behavior of platinum in the gas phase hydrogenation of crotonaldehyde ( trans-2-butenal) over Pt/carbon black catalysts has been analyzed. Two heat-treated carbon blacks, one of them subjected to an oxidizing treatment with hydrogen peroxide, have been used as supports for platinum, which was introduced using H 2PtCl 6 as metal precursor. The catalysts were characterized by H 2 chemisorption at room temperature and temperature-programmed desorption, and their catalytic behavior in the gas phase hydrogenation of crotonaldehyde was determined under differential conditions. Both the specific catalytic activity and the selectivity towards the formation of the unsaturated alcohol (crotyl alcohol) in the title reaction have been found to be higher for the catalyst with the oxidized support, and they are enhanced after reduction at increasing temperatures.

Gas phase hydrogenation of crotonaldehyde over Pt/Activated carbon catalysts. Influence of the oxygen surface groups on the support

Three activated carbons were prepared with different content of oxygen surface complexes and impregnated with aqueous solutions of [Pt(NH 3 4]Cl 2. The catalysts were characterized by H 2 and CO chemisorption at room temperature, temperature-programmed decomposition (TPD) and X-ray photoelectron spectroscopy, and their catalytic behavior in the vapor phase hydrogenations of benzene and crotonaldehyde ( trans-2-butenal) was determined. Metal dispersion is highly dependent on the degree of support oxidation, being lower for the catalyst support containing the highest amount of surface acidic complexes. This is attributed to the decomposition of the surface complexes, which act as anchoring centers for the platinum precursor, upon the reduction treatments at which the catalysts are subjected. The specific catalytic activity in the gas phase hydrogenation of crotonaldehyde is higher as the starting support is more oxidized, and the activity per gram of platinum increases with reduction temperature. The selectivity for the hydrogenation of the carbonilic CO bond instead of the olefinic CC bond is also improved when an oxidized support is used, and the production of the unsaturated alcohol, crotyl alcohol, is enhanced when catalysts are reduced at higher temperature, especially those prepared with oxidized supports.

Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the Sn/Pt atomic ratio

Three bimetallic PtSn/C catalysts have been prepared by successive impregnation of pregraphitized carbon black with an aqueous solutions of hexachloroplatinic acid and tin(II) chloride. One monometallic Pt/C sample was also prepared and studied for comparison. All catalysts were characterized by hydrogen and carbon monoxide chemisorption at room temperature and X-ray photoelectron spectroscopy and their behaviour in the gas phase hydrogenation of crotonaldehyde, at atmospheric pressure, determined. The amount of surface platinum is greatly reduced by the addition of tin, as deduced from chemisorption measurements and XPS. Both Pt 0 and Pt II are detected by XPS in the fresh bimetallic catalysts; after reduction in flowing hydrogen at 623 K platinum is completely reduced to the metallic state and, although a high proportion of tin remains in an oxidized state, a relatively important amount is reduced to Sn 0, this allowing the possibility of PtSn alloys formation. The catalytic activity in the gas phase hydrogenation of crotonaldehyde is greatly improved by the presence of tin, in spite of the fact that the amount of surface platinum is reduced. Tin has also a very important effect on the selectivity towards the hydrogenation of the CO bond, increasing the production of crotyl alcohol in respect to the hydrogenation of the CC bond that would lead to the production of butyraldehyde. The observed results are explained on the basis of a promoting effect of oxidized tin species for the hydrogenation of the CO group, whereas the formation of a PtSn alloy or the dilution of surface platinum by metallic tin would hinder the hydrogenation of the olefinic CC bond.

Improvement of the selectivity to crotyl alcohol in the gas-phase hydrogenation of crotonaldehyde over platinum/activated carbon catalysts

Pt/activated carbon catalysts were prepared by using [Pt(NH 3) 4]Cl 2 as the metal precursor, and characterized by a number of techniques. The selectivity of these catalysts towards crotyl alcohol in the gas-phase hydrogenation of crotonaldehyde was considerably increased when the activated carbon support was slightly oxidized before the metal incorporation.

Selective Hydrogenation of Crotonaldehyde Over Cobalt Based Self-Supported Catalysts

ABSTRACTComplex cobalt-carbonyl ligand based clusters of clusters are used as molecular precursors for self-supported model catalysts. These precursors consist of two metal layers: an outer of the complex Co-carbonyl ligands, and a core of metal (e.g. Co or Zn) carboxylate groups. Partial thermolysis at low temperature (LT) of these materials under hydrogen results in almost completely decarbonylated material with a mainly unchanged carboxylate metal core. Complete pyrolysis at higher temperatures (HT) in hydrogen leads to mixed metal environment. These materials were used as a heterogenous catalyst in the gas phase hydrogenation of crotonaldehyde. The maximum yield of 27 % of desired product crotyl alcohol was observed when HT-CoCo was used as the catalyst at 423 K. The catalyst activity and the crotyl alcohol selectivity remained unchanged over 2 days of operation. The bimetallic ZnCo catalysts showed lower selectivity to crotyl alcohol than the CoCo catalysts.