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Chapter 3 Adsorption and Hydrogenation of Carbonyl and Related Compounds on Transition Metal Catalysts

1986; Elsevier BV; Linguagem: Inglês

10.1016/s0167-2991(08)65349-5

2542-6613

Kazunori Tanaka,

Catalysis for Biomass Conversion

This chapter discusses the adsorption and hydrogenation of carbonyl and related compounds on transition metal catalysts. The hydrogenation of aldehydes and ketones to the corresponding alcohols resembles the hydrogenation of olefins to alkanes in that two hydrogen atoms are added across a C=O or C=C double bond. Olefin hydrogenations catalyzed by transition metals are a stepwise addition of two adsorbed hydrogen atoms to the adsorbed olefin. Two stereoisomers are formed in the hydrogenation of substituted cycloalkanones to the corresponding alcohols—the axial and the equatorial alcohols. The adsorption states and hydrogenation mechanism of ketones and aldehydes on transition metals depend upon the environmental conditions under which the catalyst is operating—that is, the temperature, pressure, reaction phase and solvent. The molecular adsorption and hydrogenation to the corresponding alcohol is favored in the liquid phase and at low temperatures and high pressures, whereas dehydrogenation and decarbonylation are liable to occur in the gas phase and at high temperatures and low pressures. Deuterium tracer studies have shown that on Ru, Os, Ir and Pt the hydrogenation to alcohols proceeds by simple hydrogen addition to the molecularly adsorbed ketones.