Hydrogenation of Carboxylic Acids and Synergistic Catalysts

Trivedi, B. C.; Grote, Dace; Mason, Thomas O.

doi:10.1007/bf02666046

Cited by 16 publications

(6 citation statements)

References 4 publications

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“…After the inspiring report of Trivedi et al., [181] which demonstrated for the first time the activity enhancement promoted by the synergic effect of the addition of other metals in Re 2 O 7 , Re‐based catalysts have been intensively explored [45,134,182–187] . Neurock et al.…”

Section: Mechanistic Insightsmentioning

confidence: 99%

Rhenium – A Tuneable Player in Tailored Hydrogenation Catalysis

et al. 2021

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Although rhenium may not be the most common choice of active species in catalysis, it has been reported as a highly active and selective catalyst over a wide range of reactions. Its applications include hydrogenation reactions of great relevance in the field of renewable materials and bio‐derived platform molecules, such as valorization of lignin, CO2, and carboxylic acids. Different from several transition metals, rhenium presents oxidation numbers varying from −3 to +7. Such diversity in the coordination chemistry of rhenium is reflected in the variety of known rhenium compounds, since this metal can form stable structures such as ligand‐bridged multinuclear and organometallic compounds as well as inorganic oxides, metal‐organic frameworks, and clusters. The exceptional flexibility in rhenium speciation yields numerous selective catalysts; however, it also makes the characterization of rhenium catalysts challenging, and its influence on the catalytic activity is not trivial. This review will outline the most established rhenium‐based materials used in hydrogenation catalysis and shed some light on the relation of rhenium species to catalyst selectivity based on advanced characterization techniques. Finally, our perspectives on the use of rhenium catalysts to produce value‐added products will be given.

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Section: Mechanistic Insightsmentioning

confidence: 99%

Rhenium – A Tuneable Player in Tailored Hydrogenation Catalysis

et al. 2021

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“…The performance of these Re catalysts is superior to the copper-based catalysts. Moreover, bimetallic catalysts containing Re have been reported to be more effective to hydrogenation of carboxylic acids than the corresponding monometallic catalysts. ,,− In particular, the combination of Re species (Re metal or ReO x ) with noble metals (Pd, Rh, Pt or Ru) has been significantly efficient. ,,,,, For example, the combination of Re 2 O 7 with M/C (M = Pd, Rh, Pt, and Ru, Re/M = 0.36–1.1) (17 MPa, 443 K, in the mixture solvent of dioxane + water) showed about 2–3 times higher activity than Re 2 O 7 alone in the hydrogenation of octanoic acid . Regarding the hydrogenation of levulinic acid to 1,4-pentanediol, the modification of monometallic catalysts (Ru/C, Pt/C, and Pd/C) with Re species was effective, and for example, the Pt–Re/C catalyst provided high 1,4-pentanediol yield (82%) in water solvent .…”

Section: Introductionmentioning

confidence: 99%

“…On these reported catalysts, the amount of Re was smaller than or comparable to that of noble metals on a molar basis. Therefore, Re species is regarded as a cocatalyst in these reaction systems ,,, and also in other systems for hydrogenolysis of C–O bonds in polyols or ethers using Re-modified noble metal catalysts …”

Section: Introductionmentioning

confidence: 99%

Characterization of Re–Pd/SiO₂Catalysts for Hydrogenation of Stearic Acid

et al. 2015

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Silica-supported Re−Pd bimetallic catalysts (Re−Pd/SiO 2 ) with a high molar ratio of Re/Pd, which were reported to be effective for selective hydrogenation of carboxylic acids to the corresponding fatty alcohols in 1,4-dioxane solvent, were characterized by means of X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and CO adsorption. Various kinds of Re species (hexagonal closed packing (HCP) and face-centered cubic (FCC) Re 0 metals, Re 3+ , Re 4+ , and Re 6+ ) were detected on the catalysts after reaction or reduction, and the ratio of these Re species was estimated by the combination of characterization results. The activity of these catalysts is sensitive to air because of the high oxophilicity of Re, and the catalysts must be handled without contact to air. Pd addition and catalyst activation method (liquid-phase reduction and gas-phase reduction) influenced the ratio of the Re species. Liquid-phase reduced Re−Pd/SiO 2 (Re/Pd = 8), which is the most effective catalyst, has Pd 0 , Re 0 , and Re n+ (Re 3+ and Re 4+ ) species on the catalyst, and the metal surface (Pd 0 , Re 0 (HCP), Re 0 (FCC)) is modified with Re n+ species. This structure will be responsible for the high hydrogenation activity. Combined with kinetic studies with Re−Pd/SiO 2 (Re/Pd = 8) and Re/SiO 2 catalysts, Pd plays a role in promoting the reduction and dispersion of Re species, as well as strengthening the interaction of stearic acid with the catalytic surface, and on the other hand, Re n+ plays a role in promoting the heterolytic dissociation of H 2 .

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“…However, these catalysts are expensive, since most of them are based on a platinum group metal (PGM) or/and Re, and easily overreduce the carboxylic acid towards unfunctionalized alkanes. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The second pathway involves the formation of an amide, which is dehydrated towards a nitrile at temperatures above 250°C, typically with a ZnO catalyst, and reduced afterwards (lower pathway Figure 1). This is the most common synthesis method for fatty amines.…”

Section: Introductionmentioning

confidence: 99%