A novel organometallic catalyst (PSNP-CA) has been prepared by post synthesis grafting of -COOH functionalized organosilane on porous silica nano particle by using surface hydroxyl groups as anchor point. It was characterized by using an array of sophisticated analytical techniques like 13C CP MAS NMR, 29Si MAS NMR, CHN analysis, BET, HR TEM, XRD, TGA, FTIR and pH measurement. The leaching of the active site is greatly avoided as the organic moieties are covalently attached to the inorganic support. This is the first example of organocatalysis promoted by a -COOH functionalized porous silica nano particle for the chemoselective synthesis of densely substituted imidazoles. The molecular scaffolds which assimilate bio-active imidazole moiety may be worthwhile molecule from the biological point of view. All the other reported procedures led to the mixture of tri and tetra substituted imidazoles and their proportions were successfully evaluated from crude H-1 NMR spectra. Greenness of the process was well instituted as water was exploited as reaction medium. This catalyst retained its activity after having it exposed to ambient atmosphere for 10 days. There was no deteriorating effect of aerial oxygen or moisture towards the activity of the catalyst. (C) 2013 Elsevier B.V. All rights reserved.