A supported aq.-phase (SAP) 0.14 or 0.16% Rh catalyst was prepd. by dissolving a hydrophilic phosphinic ligand, tri-Na salt of tri(m-sulfophenyl)phosphine (TPPTS-Na), and a H2O-sol. [RhH(CO) (TPPTS-Na)(3)] complex in 5.5, 9.8 or 16.2 wt.% (=100 degrees C) H2O layered on 100-200-mesh silica gel, and examd. in hydroformylation of 1-hexene run in cyclohexane or 3-hydroxy-2,2,4-trimethylpentyl 2-methylpropionate as solvent. The 16.2% H2O, 0.14% Rh, P/Rh 2.1 (by moles) catalyst was active and selective toward aldehydes (88.2 and 96.6% in resp. solvents); the 9.8% H2O, 0.16% Rh, P/Rh 6.0 catalyst was active in isomerization of 1- to 2-hexene. Catalyst prepn. and structure studies (FTIR and P-31 NMR) are described.