Herein we investigate the effect of graphene decoration with metal nanoparticles, namely Ag and Pd, starting from pristine graphene (GR). Decoration is directly made on graphene obtained by Liquid Phase Exfoliation of natural graphite in eco-friendly solvents. The nanoparticles are synthesized in situ via chemical reduction from metal salts promoted by microwave treatment, resulting in metal nanoparticles directly stuck onto the pristine graphene surface. Sensing layers based on graphene and metal decorated graphenes were exposed to hydrogen, nitrogen dioxide and ammonia. Pristine graphene showed a marked specificity towards NO2 gas. Palladium nanoparticles enhanced graphene response towards hydrogen, while devices based on graphene/silver nanoparticles were highly specific towards ammonia detection. This eco-friendly and straightforward preparation method of graphene and graphene hybrids demonstrates an effective modulation of the sensing properties of graphene with respect to sensitivity and selectivity.