Vapor-phase Hydrogenation Of Crotonaldehyde Research Articles

A comparative study on Pt/CeO2 and Pt/ZrO2 catalysts for crotonaldehyde hydrogenation

Vapor-phase hydrogenation of crotonaldehyde was carried out over Pt/CeO2 and Pt/ZrO2 catalysts. It was found that both catalysts suffered deactivation, with the conversion of crotonaldehyde decreasing from 31 to 6% over the Pt/CeO2 catalyst and 20 to 7% over the Pt/ZrO2 catalyst, which was due to the formation of organic compounds on the catalyst surface as revealed by temperature programmed oxidation technique on the spent catalysts, and the poisoning effect of CO chemisorptions on Pt atoms via decarbonylation reaction. For the Pt/ZrO2 catalyst, selectivity to crotyl alcohol reached 48% and kept stable during the reaction, while for the Pt/CeO2 catalyst, the selectivity to crotyl alcohol decreased dramatically from 51 to 33%. The decrease of selectivity for the Pt/CeO2 catalyst was attributed to carbon deposit formed on the catalyst surface by the reaction between CO and reduced Ce3+ ion in CeO2. However, for the Pt/ZrO2, no carbon deposit was formed on the catalyst surface, which could account for the stable selectivity during the reaction process.

Effect of the metal precursor on the properties of Ru/ZnO catalysts

The effect of the ruthenium precursor (chlorinated or chlorine-free) on the properties and the catalytic behaviour of Ru/ZnO catalysts in the vapour phase hydrogenation of crotonaldehyde (2-butenal) has been studied. Two catalysts were prepared, using ruthenium (III) chloride (Ru(Cl)/ZnO) and ruthenium (III) acetylacetonate (Ru(A)/ZnO) as the metal precursors. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), H 2 temperature-programmed desorption (H 2-TPD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), and their catalytic behaviour has been evaluated in the title reaction after reduction at low (473 K) and high (623 K) temperatures. Ru(Cl)/ZnO showed better catalytic behaviour after both reduction treatments, what has been explained on the basis of a well controlled metal-support interaction. For Ru(A)/ZnO this interaction is too high, resulting in a dramatic lost of active sites that yields worse catalytic behaviour. It is important to remark that both catalysts were very active and selective to the desired product, the unsaturated alcohol (crotyl alcohol, 2-buten-1-ol).

Enhancing the catalytic performance of Pt/ZnO in the vapour phase hydrogenation of crotonaldehyde by the addition of Cr to the support

Abstract An impressive enhancement of the catalytic performance of platinum in the vapour phase selective hydrogenation of crotonaldehyde (2-butenal) has been achieved by modifying a ZnO support by addition of Cr(III) cations. The addition of chromium enhances the structural properties of the support (larger surface area) and increases its reducibility. The presence of chromium in the support enhanced the catalytic activity and the selectivity towards the unsaturated aldehyde in such a way that the Pt/Cr–ZnO catalyst showed the best results (in terms of yield and stability) published until now. The improved behaviour of this catalyst has been explained on the basis of the high support reducibility and a proper metal-support interaction.

Effect of the support composition on the vapor-phase hydrogenation of crotonaldehyde over Pt/Ce xZr 1− xO 2 catalysts

Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde (2-butenal) have been performed at 333 K over Cl-free Pt/ZrO 2 and Pt/Ce x Zr 1− x O 2 catalysts ( 0.2 ⩽ x ⩽ 0.8 ) after reduction under H 2 at low (473 K) and high (773 K) temperatures. The catalysts were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed reduction, and X-ray photoelectron spectroscopy after each reduction treatment. An important effect of the support composition on the catalytic activity was observed for both reactions. The catalytic behavior of Pt in the two test reactions studied was strongly dependent on the support composition and on the reduction temperature. For toluene hydrogenation, after reduction at 473 K, catalytic activity was higher for catalysts with no or low ceria content. Furthermore, whereas the increase in the reduction temperature hardly modified the activity of Pt/ZrO 2, it strongly deactivated the catalysts with high cerium content in the support. For crotonaldehyde hydrogenation, on the other hand, increased reduction temperature produced a general increase in activity (except for the catalyst with the highest cerium content), along with an increase in selectivity toward the hydrogenation of the carbonyl bond to yield crotyl alcohol. The results are explained on the basis of the effect of partial reduction of Ce(IV) in the support.

Modification of the catalytic behaviour of platinum by zinc in crotonaldehyde hydrogenation and iso-butane dehydrogenation

The effect of the presence of zinc on the catalytic behaviour of platinum in the vapour phase hydrogenation of crotonaldehyde (2-butenal) and in iso-butane dehydrogenation has been determined in activated carbon-supported catalysts prepared using H 2PtCl 6 and Zn(NO 3) 2 as the metal precursors. The catalysts have been characterised by temperature-programmed reduction (TPR), adsorption microcalorimetry of CO at room temperature and X-ray photoelectron spectroscopy after in situ reduction at 773 K. The bimetallic catalyst, with a bulk Zn/Pt atomic ratio of 13.7, showed a much higher initial activity in crotonaldehyde hydrogenation, although it deactivated more strongly with time on stream. Lower activation energy for this reaction was also obtained, as well as a higher selectivity towards the unsaturated alcohol. On the other hand, the catalytic behaviour for iso-butane dehydrogenation was greatly improved by the presence of zinc, the bimetallic catalyst being more active than its monometallic counterpart and showing 100% selectivity to iso-butene.

Crotonaldehyde Hydrogenation on Rh/TiO2 catalysts: In situ DRIFTS studies

The surface and catalytic properties in the vapor-phase hydrogenation of crotonaldehyde on Rh/TiO2 has been studied. It was found that a partial reduction of the support produces a surface decoration of the metal component. Thus, interfacial sites are created, which are responsible of an increase in the selectivity to crotyl alcohol, via enhancement of the polarization of the C=O bond. Photoelectron spectra revelead that rhodium is in different oxidation states, with a contribution of ca. 20 % Rhd + and 80 % Rho species for LTR catalyst and only a slight increase of Rhd + for HTR catalyst. TEM studies revelead that Rh has metal particle size close 3 nm with small increases in the catalyst reduced at high temperature. DRIFTS essayed carried out under reaction conditions allowed to identify crotonaldehyde species strongly adsorbed through the C=C bond and weakly coordinated through both the C=C and C=O bonds. After reduction at 723 K an increase in the peak at 1660 cm -1 ascribed to an interaction between the carbonyl group and the surface, was observed. This peak seems to be stabilized at interfacial Rh/TiOx sites The deactivation in crotyl alcohol formation can be ascribed to the generation of strongly chemisorbed asymmetric carboxylate species detected by band at 1740 cm -1 . This band grows at expense of crotonaldehyde O s - bonded intermediate chemisorbed on coordinatively unsaturated sites (Lewis acid sites) responsible of the crotyl alcohol obtaintion (detected by a band at 1653 cm -1 ). Additionally, a small band at 2068 cm -1 assigned to CO adsorbed on transition metals, which increases with time on-stream may explain the deactivation of the catalysts in flow systems.

Vapor-Phase Hydrogenation of Crotonaldehyde on Titania-Supported Pt and PtSn SMSI Catalysts

Vapor-phase hydrogenation of toluene and selective hydrogenation of crotonaldehyde have been performed after reduction at low (523 K) and high (773 K) temperatures over Pt/TiO 2 and PtSn/TiO 2 catalysts prepared from the metal precursors tin(II) oxalate and H 2PtCl 6. A sequential impregnation method was used to prepare the bimetallic catalyst, wherein the tin precursor was loaded first. The surface characteristics of both catalysts were evaluated with X-ray photoelectron spectroscopy (XPS) after the reduction treatments. It was shown in this analysis that tin was mainly in an oxidized state in the bimetallic catalyst (about 80%) even after reduction at 773 K. The presence of tin and the increase in the reduction temperature strongly decreased the catalytic activity for toluene hydrogenation, but the opposite effect was observed for crotonaldehyde hydrogenation. After reduction at low temperature, the bimetallic catalyst was more active than the monometallic catalyst, but it was less selective toward hydrogenation of the carbonyl bond to yield the unsaturated alcohol. However, reduction at 773 K yielded a bimetallic catalyst that showed an initial activity five times higher than that of the Pt/TiO 2 catalyst reduced at the same temperature and a high selectivity (around 50%) toward the unsaturated alcohol, which was stable with time on reaction. Furthermore, the catalytic behavior of the bimetallic catalysts was also evaluated after reduction at even higher temperatures. Reduction at 873 K increased the catalytic activity in crotonaldehyde hydrogenation while the selectivity to crotyl alcohol remained at about 50% molar fraction; however, reduction at 973 and 1023 K caused a loss of catalytic performance in terms of both activity and selectivity.

Interfacial Properties of an Ir/TiO2 System and Their Relevance in Crotonaldehyde Hydrogenation

Titania-supported iridium catalysts were prereduced in a hydrogen flow at 473 K (LT) and 723 K (HT). Metal particle sizes determined by H2 chemisorption and by direct observation of metal particles by transmission electron microscopy were quite similar for LT treatment, and close to 3.0 nm. For the HT case, a large difference in particle size between both techniques is obtained, as a consequence of the H2 chemisorption suppression (SMSI effect). Photoelectron spectra revealed that iridium is in different oxidation states, with a contribution of 19% Irδ+ and 81% Ir° species for the LT sample and only a slight increase in Irδ+ species (26%) for the HT catalyst. Further insights into the surface structures developed by LT and HT treatments were derived from the catalytic performance in the vapor-phase hydrogenation of crotonaldehyde. Activity, expressed as turnover frequency, was more than one order of magnitude higher for the HT catalyst than for its LT counterpart. The interfacial metal–TiOx moieties, created upon reduction treatment, appeared to be responsible for the increase in activity and in selectivity to crotyl alcohol, via the formation of a [–CO…surface] σ-bonded complex (detected by in situ DRIFTS as a band at 1650 cm−1) stabilized at the metal–TiOx interface. HT treatment enhances the metal–TiOx contact, which results in an improvement in catalyst performance. The catalysts deactivate slowly with the time of reaction. Two reasons are advanced to explain the catalyst deactivation: (i) the formation of a strongly chemisorbed asymmetric carboxylate (band at 1740 cm−1); and (ii) the formation of heavy products with conjugated CO and CC bonds (band at 1720 cm−1). Both complexes are formed at the expense of the σ-complex and progressively block the active sites responsible for crotonaldehyde hydrogenation.

Vapour phase hydrogenation of crotonaldehyde over magnesia-supported platinum–tin catalysts

Magnesia-supported bimetallic Pt–Sn catalysts with various metal contents and Pt/Sn atomic ratios were prepared using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)2] or the monometallic complex cis-[PtCl2(PPh3)2] and SnCl2 as metal precursors. Catalysts were characterised by X-ray diffraction, transmission electron microscopy techniques and X-ray photoelectron spectroscopy. The bulk and surface composition of the catalysts was related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). It is shown that the various preparation methods produce catalysts with distinct properties and catalytic behaviour. For catalysts prepared with the bimetallic complex, the highest selectivity for the unsaturated alcohol (but-2-en-1-ol) was achieved for the catalyst containing larger bimetallic particles, which are associated with a higher surface concentration of oxidised tin species. The catalyst prepared with separate metal precursors contains a higher amount of residual chlorides, which significantly affect the catalytic activity but only slightly alter the selectivity for the hydrogenation of the carbonyl bond.

Crotonaldehyde hydrogenation on Ir supported catalysts

Iridium supported catalysts prepared by the sol–gel and impregnation methods have been studied in the vapour-phase hydrogenation of crotonaldehyde. The influence of different preparation variables on the surface and catalytic properties was analysed. It was found that the porosity of the support has an effect on the selectivity to the unsaturated alcohol and the presence of partially reducible supports such as ZrO 2 and TiO 2 increases the selectivity to crotyl alcohol. This increase may be attributed to an enhancement of the polarisation of the CO bond as a result of surface decoration of the metal component. The presence of chlorine ions in the metal-support interfacial region also allows, in a certain extension, a polarisation of the carbonyl bond. The effect of the reaction temperature has also been studied. It was found that a decrease in the reaction temperature led to a decrease in the crotonaldehyde conversion and in an improvement on the selectivity of the allylic alcohol.

CROTONALDEHYDE HYDROGENATION ON Rh SUPPORTED CATALYSTS

The vapor-phase hydrogenation of crotonaldehyde on Rh supported catalysts has been studied. The effect of some variables of preparation in catalysts prepared by the sol-gel and impregnation methods on the surface and catalytic properties were analyzed. It was found, that the porosity of the support has a small effect on the selectivity to the unsaturated alcohol and the presence of partially reducible supports such as ZrO2 and TiO2, may increase the selectivity to crotyl alcohol via an enhancement of the polarization of the C=O bond as a result of surface decoration of the metal component. The presence of chlorine ions in the metal-support interfacial region, also allows, in a certain extension, a polarization of the carbonyl bond.

Crotonaldehyde hydrogenation over alumina- and silica-supported Pt–Sn catalysts of different composition. In situ DRIFT study

Alumina- and silica-supported bimetallic Pt–Sn catalysts with different Pt/Sn atomic ratios have been prepared by using the bimetallic complex cis-[PtCl(SnCl3)(PPh3)2], the monometallic complex cis-[PtCl2(PPh3)2] and SnCl2 as metal precursors. Catalysts have been characterised by X-ray diffraction and transmission electron microscopy techniques, including energy-dispersive X-ray microanalysis, electron diffraction experiments and lattice-fringe microanalysis. The phase composition of the different catalysts has been related to the catalytic behaviour in the vapour phase hydrogenation of crotonaldehyde (but-2-enal). Results show that catalysts containing platinum–tin alloy phases with large particles are more selective towards the hydrogenation of the carbonyl bond to yield crotyl alcohol. The presence of oxidised tin species on the surface of the large alloy particles promotes the hydrogenation of the carbonyl bond. In situ diffuse reflectance infrared spectroscopy studies of crotonaldehyde adsorption under He or H2 reveal differences between bimetallic catalysts and monometallic, and these differences have been related to the different catalytic behaviour of the catalysts.

Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the preparation method

The effect of the preparation method on the catalytic behavior of bimetallic Pt Sn C catalysts in the vapor phase hydrogenation of crotonaldehyde has been determined. Nine Pt Sn C bimetallic catalysts have been prepared by coimpregnation and by successive impregnations of the support with solutions of the metal precursors, with Sn Pt atomic ratios ranging from 0 to 1.43. The effect of these variables on the surface characteristics of the catalysts has been analyzed by hydrogen and carbon monoxide chemisorption at room temperature and by X-ray photoelectron spectroscopy (XPS), and they have been related to the catalytic behavior in the title reaction. Results show that both metallic and oxidized tin species are present in the reduced catalysts (hydrogen, 623 K, 12 h) and their relative amounts depend on the preparation method and on the Sn Pt ratio. The overall activity for the title reaction increases with tin content, with a maximum for Sn Pt of about 0.8, and then decreases for higher tin loadings. The selectivity for the hydrogenation of the carbonyl bond in competition with the reduction of the olefinic CC bond seems to be related to the relative amount of oxidized surface tin species. The best results in terms of activity and selectivity are achieved with catalysts in which the tin precursor has been loaded first.

Metal-support effects on the intramolecular selectivity of crotonaldehyde hydrogenation over platinum

The vapor-phase hydrogenation of crotonaldehyde (CROALD) was studied at low temperature and low conversions over Pt powder and Pt dispersed on SiO 2, η)-Al 2O 3, and TiO 2 after either a high or a low-temperature reduction, HTR and LTR, respectively. The hydrogenation of butyraldehyde (BUTALD) and crotyl alcohol (CROALC) to butanol (BUTNOL) and the isomerization of CROALC to BUTALD were also investigated to obtain additional information about this network of reactions. The typical Pt catalysts produced 100% BUTALD, as expected from previous studies of CROALD and the awareness of the high hydrogenation activity of Pt for CC double bonds. However, the TiO 2-supported Pt produced both CROALC and BUTNOL, and the best catalyst, sol (HTR) Pt TiO 2 , gave a selectivity of 37% CROALC with no BUTNOL formation. In addition to this marked enhancement in selectivity, the turnover frequencies on the sol (HTR) Pt TiO 2 samples, based on sites counted by hydrogen chemisorption near reaction temperatures, were more than an order of magnitude higher than the catalysts displaying normal adsorption behavior. Activation energies were somewhat higher on the sol Pt TiO 2 catalysts, however. This behavior is very similar to that observed previously for CO and acetone hydrogenation over these same catalysts, and it is consistent with the proposal that sites created at the Pt-titania interface are responsible for the activation of carbonyl bonds. Previous studies of liquid-phase hydrogenation of CROALD and other molecules with conjugated CC and CO double bonds support this model and indicate that a 1,4 diadsorbed species, rather than 1,2 and 3,4 diadsorbed species (counting the oxygen atom as 1), is formed in polar solvents. By analogy, defect sites on the titania at the metal-support interface may interact with the O atom, polarize the CO bond, and favor this intermediate which can react with hydrogen to give CROALC.

Single-stage vapor-phase hydrogenation of crotonaldehyde to n-butyl alcohol

Single-stage vapor-phase hydrogenation of crotonaldehyde to n-butyl alcohol