A catalyst, useful for the hydroformylation of allyl alcohol, is described. The catalyst comprises a rhodium complex and a 6-bis(3,5-dialkylphenyl)phosphino-N-pivaloyl-2-aminopyridine or a 3-bis(3,5-dialkylphenyl)phosphino-2H-isoquinolin-1-one. The invention also includes a process for the production of 4-hydroxybutyraldehyde comprising reacting allyl alcohol with a mixture of carbon monoxide and hydrogen in the presence of a solvent and the catalyst. The process gives a high ratio of the linear product 4-hydroxybutyraldehyde to the branched co-product 3-hydroxy-2-methylpropionaldehyde.