Download PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... Pyrroles may be prepared by condensation of alkyl and aryl amines and 1,4-diketones (Paal–Knorr reaction) under potassium exchanged layered Zirconium phosphate and zirconium sulfophenyl phosphonate catalyst in solvent free conditions. ... Pyrroles may be prepared by ...