  The present paper describes in situ preparation of Ni{\deg} nanoparticles
immobilized on acid activated montmorillonite K10 (Ni{\deg}-Mont) by
impregnation of Ni(OAc)2 into nanopores of acid activated montmorillonite K10
followed by polyol reduction. Ni{\deg} NPs was highly dispersed into the
initiated mesopores on the surface or inside swelled-interlayers of the
examined clay with average size of 10-20 nm. Acid treatment of montmorillonite
was carried out with HCl (4 M) under controlled conditions for generation of
the desired pore sizes as a host of Ni{\deg} NPs. The prepared Ni{\deg}-Mont
was used as a highly efficient heterogeneous catalyst for one-pot synthesis of
biscoumarins in 85-95% yields. The reactions were carried out via Knoevenagel
condensation of aromatic aldehydes with 4-hydroxycoumarin under microwave
irradiation. The Ni{\deg}-Mont catalyst was reused at least for seven times
without significant loss of its catalytic activity.
