The oxidative cleavage of styrenes to benzaldehydes by an environmentally benign heterogeneous catalytic method is described. The commercially available, inexpensive KSF montmorillonite was applied as a catalyst for the cleavage reaction at moderate temperatures using air as a sustainable oxidant in aqueous medium. The approach has been thoroughly optimized by testing several commercially available heterogeneous catalysts, including supported Pd and Rh catalysts, acidic montmorillonites and other common oxides such as silica or alumina. A broad variety of reaction conditions were assessed, including catalyst/reactant/solvent ratios, temperature, solvent and reaction time. The optimized conditions yielded benzaldehyde from styrene with high yield and exclusive selectivity. The scope of the reaction has also been investigated by using substituted styrenes as substrates. The data indicate that KSF is an excellent and at the same time sustainable catalyst for the oxidative cleavage. When also considering the simplicity of this method, it makes for a good alternative that can serve as a green replacement for the traditional ozonolysis reaction.