A series of narrowly dispersed Pt nanoparticles of 1.5–2.2 nm in size stabilized by bulky terphenylphosphane ligands has been synthesized by the organometallic method using [Pt(dba)2] as platinum source. These nanoparticles are highly efficient catalysts for hydrogen generation by methanolysis of ammonia borane (H3N ⋅ BH3), providing notable TOF values of up to 284 min−1 at 30 °C and low catalyst loadings (0.14–0.19 mol %). Furthermore, catalyst separation (after distillation of the H2-depleted ammonium tetramethoxyborate (NH4B(OMe)4) and methanol) and recycling were proven to be feasible, although an erosion of the catalytic activity was observed after three catalytic runs. These Pt nanoparticles have also been used as catalysts for tandem dehydrogenation of ammonia borane and hydrogenation of N-heterocycles, providing the reduction products of quinoline, phenanthridine, 2-methylquinoxaline and acridine in >90 % yields under mild reaction conditions.