| Abstract
| - The reaction pathways and kinetics of C1 aldehydes, formaldehyde (HCHO) and formic acid (HCOOHHOCHO), are studied at 400 °C in neat condition and in supercritical water over a wide range of waterdensity, 0.1−0.6 g/cm3. Formaldehyde exhibits four reactions: (i) the self-disproportionation of formaldehydegenerating methanol and formic acid, (ii) the cross-disproportionation between formaldehyde and formic acidgenerating methanol and carbon dioxide, (iii) the water-independent self-disproportionation of formaldehydegenerating methanol and carbon monoxide, and (iv) the decarbonylation of formaldehyde generating hydrogenand carbon monoxide. The self- and cross-disproportionations overwhelm the water-independent self-disproportionation and the formaldehyde decarbonylation. The rate constants of the self- and cross-disproportionations are determined in the water density range of 0.1−0.6 g/cm3. The rate constant of thecross-disproportionation is 2−3 orders of magnitude larger than that of the self-disproportionation, whichindicates that formic acid is a stronger reductant than formaldehyde. Combining the kinetic results with ourformer computational study on the equilibrium constants of the self- and cross-disproportionations, the reactionmechanisms of these disproportionations are discussed within the framework of transition-state theory. Thereaction path for methanol production can be controlled by tuning the water density and reactant concentrations.The methanol yield of ∼80% is achieved by mixing formaldehyde with formic acid in the ratio of 1:2 at thewater density of 0.4 g/cm3.
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