Iridium-Katalysatoren für die Selektivhydrierung kurzkettiger α, β-ungesättigter Aldehyde: Widersprüche zwischen Theorie und Experiment?

Schimpf, Sabine; Lucas, Martin; Hönicke, Dieter; Claus, Peter

doi:10.1002/1522-2640(20021115)74:11<1564::aid-cite1564>3.0.co;2-z

Cited by 6 publications

(1 citation statement)

References 16 publications

(12 reference statements)

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“…Although in homogeneous catalysis Ir(I) compounds [52] and heterogenized Ir complexes [53] were successfully applied for the relatively simple selective hydrogenation of α, βunsaturated aldehydes with bulky substituents at the C=C group (cinnamaldehyde), the latter seems to be a prerequisite for the formation of unsaturated alcohols in the case of heterogeneous Ir catalysts. An experimental hint for the formation of allyl alcohol with Ir under technological aspects (high yields) can be found in much earlier work [54] where a yield of 60% was reported over a 5 wt.% Ir/C catalyst in liquid-phase hydrogenation (solvent EtOH) at 0.1 MPa and 298 K. However, a reexamination of acrolein hydrogenation in the liquid phase over different supported Ir catalysts clearly showed that the preferred hydrogenation of the C=O group is not possible (selectivity <15%, saturated aldehyde is the main product) [55]. with acrolein as educt, maximum selectivities of 27-37% towards allyl alcohol were observed over Ir/Al 2 O 3 but at very low conversions (0.2-0.5%) [43].…”

Section: Scheme 10mentioning

confidence: 69%

Regioselective Hydrogenations

Claus¹,

Önal²

2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Generalities in Regioselectivity with Heterogeneous Catalysts Definitions General Factors Determining Selectivity Reaction Engineering and Selectivity Selective Hydrogenation of α, β‐Unsaturated Aldehydes Physicochemical Basics and Reaction Mechanism Metal Specificity and Structure Sensitivity Influence of Support Materials, Zeolites and Surface Modifiers Influence of a Second Metal on Selectivity Regioselective Hydrogenation in the Presence of Green Solvents Kinetic Modeling Selective Hydrogenation of Polyenes Selective Hydrogenation of Ketones Selective Hydrogenation of Polycyclic Aromatics and Derivatives Selective Hydrogenation of Nitroaromatics

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Section: Scheme 10mentioning

confidence: 69%

Regioselective Hydrogenations

Claus¹,

Önal²

2008

Handbook of Heterogeneous Catalysis

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Carbon‐Carbon Double Bond versus Carbonyl Group Hydrogenation: Controlling the Intramolecular Selectivity with Polyaniline‐Supported Platinum Catalysts

et al. 2008

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The use of polyaniline (PANI) as catalyst support for heterogeneous catalysts and their application in chemical catalysis is hitherto rather poorly known. We report the successful synthesis of highly dispersed PANI-supported platinum catalysts (particle sizes between 1.7 and 3.7 nm as revealed by transmission electron microscopy, TEM) choosing two different approaches, namely (i) deposition-precipitation of H 2 PtCl 6 onto polyaniline, suspended in basic medium (DP method) and, (ii) immobilization of a preformed nanoscale platinum colloid on polyaniline (sol-method). The PANI-supported platinum catalysts were applied in the selective hydrogenation of the a,b-unsaturated aldehyde citral. In order to benchmark their catalytic performance, citral hydrogenation was also carried out by using platinum supported on the classical support materials silica (SiO 2 ), alumina (Al 2 O 3 ), active carbon and graphite. The relations of the structural characteristics and surface state of the catalysts with respect to their hydrogenation properties have been probed by EXAFS and XPS. It is found that the DP method yields chemically prepared PtO 2 on polyaniline and, thus, produces a highly dispersed and immobilized Adams catalyst (in the b-PtO 2 form) which is able to efficiently hydrogenate the conjugated C=C bond of citral (selectivity to citronellal = 87%), whereas reduction of the C=O group occurs with polyanilinesupported platinum (selectivity to geraniol/nerol = 78%) prepared via the sol-method. The complete reversal of the selectivity between the preferred hydrogenation of the conjugated C=C or C=O group is not only particularly useful for the selective hydrogenation of a,b-unsaturated aldehydes but also unveils the great potential of conducting polymer-supported precious metals in the field of hitherto barely investigated chemical catalysis.

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Hydrogenations over Silver: A Highly Active and Chemoselective Ag‐In/SiO₂ Catalyst for the One‐Step Synthesis of Allyl Alcohol from Acrolein

Lucas

Claus

2005

Chem Eng & Technol

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A highly active, chemoselective and environmentally friendly Ag-In catalyst which enables the extremely difficult selective hydrogenation of acrolein to allyl alcohol is described. The catalyst performance far exceeds the space-time yield for the industrially performed synthesis of allyl alcohol by the isomerization of propene oxide, and can be regarded as a basis for a one step hydrogenation process of acrolein. The ProblemThe preferred hydrogenation of a C=O group in the presence of a C=C bond in a,b-unsaturated aldehydes is of special interest for the chemical industry because the partially hydrogenated products, namely unsaturated alcohols of the allyl type, are used for the production of fine chemicals, pharmaceuticals, and perfumes [1]. At present, however, the most simple unsaturated alcohol, allyl alcohol, is not produced by hydrogenation of acrolein but by expensive multistep manufacturing processes [1, 2] based on allyl chloride, propene oxide or allyl acetate using basic substances and catalysts, some of them being environmentally polluting. This applies as well to cadmium containing catalysts which are said to have selective hydrogenation properties in the production of allyl alcohol from acrolein in the gas phase [3]. These disadvantages could be avoided by succeeding in selectively producing allyl alcohol with high space-time yields in a one step synthesis by selective hydrogenation of acrolein in the presence of environmentally friendly heterogeneous catalysts.The development of active and selective hydrogenation catalysts for these reactions is not only important from an industrial point of view, but is also of fundamental scientific interest for catalysis because thermodynamic and kinetic reasons favor the formation of the non-desired saturated aldehyde (free reaction enthalpy for the hydrogenation of the C=C bond is more negative by 30 kJ mol ±1 , and higher reactivity of a C=C bond compared to the C=O group [4]). While homologous a,b-unsaturated aldehydes such as cinnamaldehyde, citral or prenal can be selectively hydrogenated to the corresponding allyl alcohols (cinnamyl alcohol, geraniol/nerol, prenol) over new Pt, Rh or Ru catalysts (conditions: large (5±200 nm) metal particles; bimetallic particles modified by organic ligands; immobilized metal particles cages of zeolite Y [5]), the selective hydrogenation of C 3 -and C 4 -a,b-unsaturated aldehydes (acrolein, crotonaldehyde) is much more difficult. It has to be noted that acrolein is the a,b-unsaturated aldehyde which is the most difficult to hydrogenate at the carbonyl group: When using monometallic supported catalysts with typical Group VIII elements useful for hydrogenations, the selectivity to allyl alcohol is smaller than 10 % [5, 6]. Even the bimetallic Rh-Sn/SiO 2 catalysts developed by our research group, which still selectively hydrogenate crotonaldehyde in the gas phase under optimal reaction conditions to crotyl alcohol (S = 68 %), exhibit lower turnover frequencies (TOF) by a factor of two to three during the acrolein hydrogenat...

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Iridium-Katalysatoren für die Selektivhydrierung kurzkettiger α, β-ungesättigter Aldehyde: Widersprüche zwischen Theorie und Experiment?

Cited by 6 publications

References 16 publications

Regioselective Hydrogenations

Regioselective Hydrogenations

Carbon‐Carbon Double Bond versus Carbonyl Group Hydrogenation: Controlling the Intramolecular Selectivity with Polyaniline‐Supported Platinum Catalysts

Hydrogenations over Silver: A Highly Active and Chemoselective Ag‐In/SiO₂ Catalyst for the One‐Step Synthesis of Allyl Alcohol from Acrolein

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Iridium-Katalysatoren für die Selektivhydrierung kurzkettiger α, β-ungesättigter Aldehyde: Widersprüche zwischen Theorie und Experiment?

Cited by 6 publications

References 16 publications

Regioselective Hydrogenations

Regioselective Hydrogenations

Carbon‐Carbon Double Bond versus Carbonyl Group Hydrogenation: Controlling the Intramolecular Selectivity with Polyaniline‐Supported Platinum Catalysts

Hydrogenations over Silver: A Highly Active and Chemoselective Ag‐In/SiO2 Catalyst for the One‐Step Synthesis of Allyl Alcohol from Acrolein

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Hydrogenations over Silver: A Highly Active and Chemoselective Ag‐In/SiO₂ Catalyst for the One‐Step Synthesis of Allyl Alcohol from Acrolein