ion from a primary OH group of glyc-erol. 223,231 A similar mechanism was proposed manyyears ago for alcohol oxidation on Pt/C, involving asecond step, the transfer of a hydride ion to the Ptsurface (Scheme 11). 8,87,237 We consider it more feasible that the rate-deter-mining step is the cleavage of the C-H bond at theR-carbon atom. A similar mechanism is now generallyaccepted for Au electrodes (Scheme 12). 238 Despite thestructural differences between Au nanoparticles andan extended Au electrode surface, there are alsosimilarities, such as the critical role of aqueousalkaline medium and the absence of deactivation dueto decomposition products (CO and C x H y frag-ments). 239,240 An important question is the nature of active siteson Au nanoparticles. Electrooxidation of ethanol onAu nanoparticles supported on glassy carbon re-quired the partial coverage of Au surface by oxides. 241 Another analogy might be the model proposed for COoxidation. 219,242,243 According to this suggestion, theactive site consists of an ensemble of metallic Auatoms and a cationic Au

Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

The synthesis of a large number of fine chemicals, particularly in the field of flavor and fragrance chemistry [1,2] and pharmaceuticals [3], involves the selective hydrogenation of unsaturated carbonyl intermediates as a critical step. The hydrogenation of α,β-unsaturated carbonyls into saturated carbonyls is comparatively easy to achieve because thermodynamics favor the hydro-genation of the C═C bonds; therefore, research efforts were more directed at improving the selectivity to unsaturated alcohols. When a substituent is present on the carbon atom of the carbonyl group (i.e. with ketones), there is no chance to hydrogenate selectively the C═O bond, and saturated ketones are obtained with a high yield. This review is thus mostly restricted to the hydrogenation of α, β-unsaturated aldehydes into the corresponding unsaturated alcohols.

Selective Hydrogenation of α,β-Unsaturated Aldehydes

Asymmetric catalysis at chiral metal surfaces.

The hydrodeoxygenation of furfural has been investigated over three different metal catalysts, Cu, Pd and Ni supported on SiO2, on a continuous-flow reactor under atmospheric pressure of hydrogen in the 210–290 °C temperature range. The distribution of products is a strong function of the metal catalyst used. High selectivity to furfuryl alcohol is obtained over Cu/SiO2, with the formation of only small amounts of 2-methyl furan at the highest reaction temperature studied. In contrast to Cu catalyst, the conversion of furfural over Pd/SiO2 mainly produces furan by decarbonylation. Furan can further react with hydrogen to form tetrahydrofuran (THF). Finally, on Ni/SiO2 catalysts ring opening products (butanal, butanol and butane) can be obtained in significant amounts. The different product distributions are explained in terms of the strength of interaction of the furan ring with the metal surface and the type of surface intermediates that each metal is able to stabilize.

/pdf/hydrodeoxygenation-of-furfural-over-supported-metal-3hcv4f54at.pdf

Hydrodeoxygenation of Furfural Over Supported Metal Catalysts: A Comparative Study of Cu, Pd and Ni

https://www.ou.edu/catalysis/pubs/2011-2.pdf

Kinetics and mechanism of hydrogenation of furfural on Cu/SiO2 catalysts

Spectroscopic identification of alkoxide, aldehyde, and acyl intermediates in alcohol decomposition on Pd(111)

Decarbonylation and decomposition pathways of alcohol's on Pd(111)

The adsorption and reaction of formaldehyde, acetaldehyde, and propanal were compared in temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) studies on a clean Pd(111) surface. Formaldehyde reacted upon adsorption at 170 K via decomposition to CO(a) and H(a) and polymerization to paraformaldehyde. In contrast, decomposition of the higher aldehydes required significantly higher temperatures. Acetaldehyde adsorbed on the clean surface in an /eta//sup 2/ configuration and reacted to form stable acetyl species (CH/sub 3/C/double bond/O), which decomposed above 300 K to produce CO(a), H(a), and C/sub 1/ hydrocarbon fragments. Adsorbed acetyl groups were readily identified by the characteristic frequency of their CO stretch at 1565 cm/sup /minus/1/. In competition with decarbonylation, desorption of acetaldehyde occurred at 220 and 325 K. The CO stretch of /eta//sup 2/-acetaldehyde was observed at 1390 cm/sup /minus/1/. Similarly, the adlayer produced by the adsorption of propanal on Pd(111) was a mixture of /eta//sup 2/-propanal and propanoyl species (CH/sub 3/CH/sub 2/C/double bond/O) produced by removal of the aldehyde hydrogen atom. No evidence was found for polymerization of either acetaldehyde or propanal on the clean Pd(111) surface. A kinetic isotope effect was observed in the decomposition of adsorbed acetyl intermediates, suggesting that C-H cleavage ismore » rate determining for this reaction. These results illustrate the pathways, intermediates, and energetics of aldehyde decarbonylation reactions on group VIII metal surfaces and may provide insights into the mechanism of oxygenate synthesis from CO and H/sub 2/.« less

J.L. Davis

Papers

Spectroscopic identification of alkoxide, aldehyde, and acyl intermediates in alcohol decomposition on Pd(111)

Decarbonylation and decomposition pathways of alcohol's on Pd(111)

Polymerization and decarbonylation reactions of aldehydes on the Pd(111) surface

The influence of oxygen on the selectivity of alcohol conversion on the Pd(111) surface

Reactions of carboxylic acids on the Pd(111)-(2 × 2)O surface: multiple roles of surface oxygen atoms