Habibi et al., 2013, proposed a "green synthesis of formamides using the Natrolite zeolite as a natural, efficient and recyclable catalyst". "Chemoselective N-formylation of different amines was carried out with formic acid in the presence of the Natrolite zeolite as an efficient, stable and natural heterogeneous catalyst to give the corresponding formamides at room temperature under solvent-free conditions. This method has the advantages of high yields, mild conditions, simple methodology, easy work up and short reaction times. … The Natrolite zeolite was recovered and reused several times without the significant loss of its catalytic performance" .