Fengyu Zhao

The leaching and re-deposition of metal species from and onto conventional supported palladium catalysts in the Heck reaction of iodobenzene and methyl acrylate in N-methylpyrrolidone

When supported palladium catalysts are used for Heck vinylation of iodobenzene with methyl acrylate in N-methylpyrrolidone (NMP) in the presence of triethylamine and sodium carbonate bases, the reaction proceeds homogeneously with dissolved active palladium species that are formed through coordination of NMP and triethylamine with palladium. These active species easily react with iodobenzene (oxidative addition), beginning the catalytic cycle of Heck coupling. The last step of catalyst regeneration takes place with the action of sodium carbonate. The active palladium species are not stable and deposit the metal to support when they cannot find iodobenzene to react in the reaction mixture after this substrate is completely consumed. The re-deposition of palladium occurs on the surfaces of bare support and/or palladium particles remaining on it, depending on the nature of support surface and the number and size of residual metal particles. The growth of palladium particles has been observed after the reuse of catalyst in some case. However, the supported catalysts are recyclable without loss of activity.

Influence of electronic state and dispersion of platinum particles on the conversion and selectivity of hydrogenation of an α,β-unsaturated aldehyde in supercritical carbon dioxide

Abstract The selective hydrogenation of cinnamaldehyde (CAL) was investigated using silica supported platinum catalysts in supercritical carbon dioxide. Selectivity to cinnamyl alcohol (COL) is enhanced as Pt0/Pt2+ ratio increases; namely, zero-valent metallic surface is beneficial to the formation of COL compared with less reduced surface. The influence of Pt0/Pt2+ ratio is more significant on the selectivity than on the total conversion. For the catalyst with small Pt0/Pt2+ value, the selectivity also depends on the degree of platinum dispersion. The selectivity to COL is higher for higher degree of platinum dispersion. The CO2 pressure did not affect the conversion and selectivity so much.

Hydrogenation of an α,β-unsaturated aldehyde catalyzed with ruthenium complexes with different fluorinated phosphine compounds in supercritical carbon dioxide and conventional organic solvents

Abstract The effectiveness of a series of Ru complexes with fluorinated phosphine compounds has been studied for cinnamaldehyde (CAL) hydrogenation in supercritical carbon dioxide (scCO2) and conventional organic solvents. The Ru complexes with fluorinated phosphine compounds are more active for CAL hydrogenation in scCO2 medium as well as in conventional solvents compared with that with an unfluorinated phosphine, triphenylphosphine. 1,2-bis[bis(pentafluorophenylphosphino)ethane was found to be the best among the six phosphine compounds examined for both scCO2 and organic solvents. scCO2 is a more effective, green reaction medium for homogeneous CAL hydrogenation compared with conventional organic solvents.

Completely selective hydrogenation of trans-cinnamaldehyde to cinnamyl alcohol promoted by a Ru–Pt bimetallic catalyst supported on MCM-48 in supercritical carbon dioxide

Supercritical carbon dioxide (scCO2) is a unique reaction medium for the selective hydrogenation of cinnamaldehyde using a well-defined Ru–Pt bimetallic catalyst supported on MCM-48. The reaction is completely selective to the unsaturated alcohol in supercritical carbon dioxide. The selectivity to the desired unsaturated alcohol shows a significant pressure dependence. By varying the pressure at the constant reaction temperature of 323 K, we are able to optimize the selectivity of cinnamyl alcohol to 100%. This is a particularly dramatic enhancement compared to that in organic solvents and under solventless conditions, where Ru–Pt bimetallic catalyst produces cinnamyl alcohol along with hydrocinnamaldehyde and 3-phenylpropanol. More importantly, the excellent physicochemical properties of the scCO2 medium provide a significant influence on the selectivity, which goes beyond that of simple solvent replacement only.

An effective and recyclable catalyst for hydrogenation of α,β-unsaturated aldehydes into saturated aldehydes in supercritical carbon dioxide

A carbon supported palladium catalyst (Pd/C) is successfully used in selective hydrogenation of α,β-unsaturated aldehydes in scCO2 and under solventless reaction conditions. The reactions take place very rapidly in scCO2 and the average turnover frequency values for cinnamaldehyde and crotonaldehyde at 100% conversion maximally reached 3.1 and 11.6 s−1, respectively. The catalyst can be recycled several times without loss of activity and selectivity. The products (liquid), solvent (scCO2) and catalyst (solid) can be easily separated by a simple phase separation process. The present reaction is an ideal green chemical process in the view of industrial applications.

Highly Efficient Hydrogenation of Cinnamaldehyde Catalyzed by Pt-MCM-48 in Supercritical Carbon Dioxide

In supercritical carbon dioxide medium, a platinum-containing cubic mesoporous molecular sieve was shown to promote markedly the selective hydrogenation of trans-cinnamaldehyde, giving an excellent selectivity for cinnamyl alcohol. In contrast to the other platinum-containing conventional catalysts, Pt-MCM-48 can be recycled a number of times without showing any deactivation in the studied reaction condition. The selectivity mainly depends on the pressure of carbon dioxide, while the conversion depends on the pressure of carbon dioxide as well as hydrogen pressure.

Hydrogenation of 2-butyne-1,4-diol to butane-1,4-diol in supercritical carbon dioxide

Hydrogenation of 2-butyne-1,4-diol to butane-1,4-diol has been successfully conducted in supercritical carbon dioxide at 323 K with a high selectivity of 84% for butane-1,4-diol at 100% conversion. No catalysts are needed since the reaction is promoted by the stainless steel reactor wall.

Noncatalytic Heck coupling reaction using supercritical water

Heck coupling of iodobenzene with styrene can be promoted in supercritical water without using catalyst, and the conversion reaches over 70% within 10 min in the presence of base, such as KOAc, in which case the yield of stilbene is 55.6% (both trans- and cis-stilbene).