An emergent catalytic material: Pt/ZnO catalyst for selective hydrogenation of crotonaldehyde (original) (raw)
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Catalysis Today, 2009
Pt-ZnO catalysts prepared from different precursors, H2PtCl6 and Pt(NH3)4(NO3)2, and reduced at increased temperatures are used to achieve high selectivity towards crotyl alcohol in hydrogenation of crotonaldehyde. The ex-chloride catalyst shows a higher activity and selectivity than the ex-nitrate one. Transmission electron microscopy, electron diffraction, high-resolution imaging, energy dispersive X-ray spectroscopy and element mapping are used to characterize the catalysts in order to correlate the microstructure to the catalytic behavior. PtZn alloy formation is confirmed for both ex-chloride and ex-nitrate catalysts reduced at 673 K. The metal particles in ex-nitrate catalyst are smaller in size than those in exchloride. In most aggregates of the ex-chloride catalyst, chlorine is distributed homogeneously with low concentration (<1%). The higher chlorine concentration in some region leads to local morphology and microstructure changes. Influences of the observed structural features such as alloy formation, particle size difference, formation of ill-defined material, and chlorine distribution are discussed.
Selective hydrogenation of crotonaldehyde on Pt/ZnCl/SiO catalysts
Journal of Catalysis, 2005
5 wt% Pt deposited on two different supports made of 3 and 1/6 equivalent monolayers of ZnCl 2 deposited on silica (termed Pt30 and Pt2) were prepared and tested in the selective hydrogenation of crotonaldehyde. Pt-based catalysts were prepared starting from tetraammine platinum nitrate as a metallic salt precursor. These catalysts showed very different catalytic behaviors in terms of the activity and the selectivity during time on stream. Pt2 was more active than Pt30 but less selective toward the formation of crotyl alcohol. On the Pt30 catalyst, the selectivity to the formation of crotyl alcohol increased with the reduction temperature, whereas the activity did not change significantly. When the catalyst was reduced at 400 • C, the selectivity to crotyl alcohol was >80%. It behaved similarly to Pt/ZnO catalysts prepared from hexachloroplatinic acid precursor [F. Ammari, J. Lamotte, R. Touroude, J. Catal. 221 ]. In contrast, the Pt2 sample showed a decrease in the selectivity to crotyl alcohol and an increase in the activity with increasing reduction temperature. The catalysts were extensively characterized by BET, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and Fourier transform infrared pyridine adsorption. The higher selectivity of Pt30 is explained by a synergetic effect of Zn and chlorine. The greater amount of chlorine present on the catalyst surface led to an increase in the Lewis acidity of the support; moreover, the formation of PtZn alloy was observed. In agreement with our previous findings, we propose that modification of the electronic properties of platinum both from alloying to Zn and from the Lewis acidity of the support changes the adsorption mode of crotonaldehyde by favoring the binding of terminal oxygen of the molecule to the electronically modified platinum atoms. 2005 Elsevier Inc. All rights reserved. (R. Touroude). intramolecular selectivity have been studied. An increase in the selectivity toward unsaturated alcohol was obtained by adding promoters , by using bimetallic catalysts and by varying the nature of supports. In general, monometallic catalysts supported on Al 2 O 3 or SiO 2 led mostly to the formation of the saturated aldehyde . However, an increase in the selectivity of unsaturated alcohol was observed using TiO 2 as a support, which was able to create strong metal-support interactions (SMSIs) when Pt/TiO 2 was reduced at high temperature . The widely accepted mechanism to explain the enhancement of selectivity towards the formation of unsaturated alcohol on catalysts under an SMSI state is the activation of the C=O bond on special active sites created by the partially reduced support (TiO x ) covering Pt particles . Particle size is also consid-0021-9517/$ -see front matter
Novel polymer-supported platinum catalyst for selective hydrogenation of crotonaldehyde
Journal of Molecular Catalysis A: Chemical, 2002
Platinum catalyst was prepared by immobilizing the metal precursor on polyamide support containing a pyridine moiety, -[-CO-C 5 H 3 N-CONH(CH 2 ) 6 NH-]n , PA-py, and by reducing it with sodium borohydride solution at room temperature. The activity and selectivity of the catalyst were examined for liquid phase hydrogenation of crotonaldehyde (CAL) under 40 bar hydrogen pressure at 75 • C. Tin chloride was added to improve the reaction selectivity towards formation of unsaturated alcohol (UOL). The catalyst was characterized by X-ray diffraction (XRD). The repeated use of the Pt-Sn catalysts showed the increase of activity and selectivity of the catalyst. The maximum yield of crotyl alcohol achieved in the hydrogenation of CAL was about 55.1%, which was equivalent to 834 catalytic cycles per Pt atom. The effect of the polymer support on the reaction selectivity has been discussed.
Journal of Catalysis, 2006
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.
Pt/Ga2O3 catalysts of selective hydrogenation of crotonaldehyde
Journal of Catalysis, 2007
Hydrogenation of crotonaldehyde in a gas phase at atmospheric pressure over Pt/Ga 2 O 3 catalysts was studied. Two types of platinum precursors [Pt(acac) 2 and H 2 PtCl 6 ] and two gallia supports (α-Ga 2 O 3 [60.7 m 2 /g] and β-Ga 2 O 3 [2.2 m 2 /g]) were used for catalyst preparation. The catalyst 5 wt% Pt/α-Ga 2 O 3 prepared from Pt(acac) 2 precursor showed very high and stable selectivity to crotyl alcohol (91% and 63% at 10% and 70% crotonaldehyde conversion, respectively). Because Pt-supported catalysts, showing a high selectivity, usually have relatively low activity, the most interesting finding of this study is that the use of gallium oxide as a support for platinum makes it possible to obtain catalysts with significantly increased C=O bond hydrogenation selectivity while maintaining high activity.
Applied Catalysis A-general, 2006
The effect of the reduction temperature has been studied on ceria-supported bimetallic platinum–zinc catalysts prepared from H2PtCl6 and Pt(NH3)4(NO3)2 as the platinum precursors and Zn(NO3)2 as the zinc precursor. The catalysts have been characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS), and their catalytic behavior has been evaluated in the vapor-phase hydrogenation of toluene and
Applied Catalysis A: General, 2005
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 2 PtCl 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. # 2005 Published by Elsevier B.V.
Journal of Molecular Catalysis A: Chemical, 2015
Pt/SBA-15 catalysts, modified by zinc addition (at different Zn/Pt atomic ratios) via the co-impregnation method, were tested for the liquid phase hydrogenation of citral. The influence of the Zn insertion on the Pt monometallic catalyst properties was evaluated by different physico-chemical techniques, including X-ray diffraction, N 2-physisorption, transmission electron microscopy, hydrogen chemisorption, and cyclohexane dehydrogenation as model reaction for platinum accessibility and zinc covering evaluation. On the catalysts, the hexagonal periodic structure of SBA-15 framework was maintained indicating that neither Pt and Zn impregnations, nor thermal treatments affect the organized structure of the support. A decrease of the platinum metallic accessibility was observed with the increase in the Zn concentration in the materials, which was explained, on the basis of the TEM analysis, by a poisoning of the platinum accessible sites by zinc species. For the citral hydrogenation, Pt/SBA-15 monometallic catalyst is very active, with 100% conversion obtained after 30 min reaction time, but very poorly selective in unsaturated alcohols. Zinc addition led to an inhibition of the hydrogenating activity, in agreement with the decrease of the active surface, but contributed to an increase in the selectivity to unsaturated alcohols. Selectivity in unsaturated alcohol was observed to reach a maximum of 75%, for a Zn content equal to 0.3 wt.%, that is a very interesting value if compared to performances obtained with other more classical dopant including titania and germanium.