The hydroformylation of I-hexene in supercritical carbon dioxide is catalyzed with a heterogeneous rhodium catalyst that is active, selective, and stable for the formation of heptanal. The aldehyde yield and regioselectivity can be affected through changes in catalyst support structure, CO2 solvent pressure, and reaction temperature. A complex reaction pathway model is described that allows determination of rate constants, which are in turn, evaluated as a function of temperature and pressure. Analysis reveals an activation volume of -474 cm(3)/Mol and activation energy of 31.9 kJ/mol for the hydroformylation pathways. (C) 2002 Elsevier Science B.V. All rights reserved.