In the course of our attempts to replace the traditional but environmentally disfavored organic solvents in organic processes by water, we studied the double bond isomerization of hydrophobic allylarenes, in aqueous microemulsions. The catalyst for these reactions was the rhodium-trichloride-Aliquat (R) 336 ion pair encaged within hydrophobic silica sol-gel. During the entrapment of the rhodium compound, it was converted into supported catalytically active Rh(0) nanoparticles characterized by TEM and XPS studies. The transformations of the allylarenes to (E)- and (Z)-1-phenyl-1-propenes follows the first order rate law, and proved to be significantly affected by the electronic nature of the substrates and by the hydrophobicity of the sol-gel support. Upon completion of the isomerization the catalyst could be recovered and recycled at least six times without a decrease in the catalytic activity after the first catalytic run. (C) 2010 Elsevier B.V. All rights reserved.