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Controlled synthesis of fullerenes and heterofullerenes on surfaces is a preceding step towards the development of a true fullerene-based molecular electronics. Given the limitations of the current preparation techniques based on graphite vaporization, new methods are required for the rational, size-controlled synthesis of fullerenes, heterofullerenes, and endohedral fullerenes. Here we report a highly efficient (<100%) dehydrogenation mechanism leading to the formation of fullerene CB60B and for the first time triazafullerene CB57BNB3B in a one-step from their corresponding planar polycyclic aromatic precursors by a surface catalysed process [1]. We have visualized the whole process by in-situ Scanning Tunneling Microscopy (STM) and X-Ray Photoemission spectroscopy (XPS). The cyclodehydrogenation has been confirmed by the thermal desorption of HD and DB2B hexadeuterated 1-d6 precursors, and by the massspectrometric detection of CB60B in the platinum-catalysed dehydrogenation. First principles DFT calculations have been used to follow the whole process. The process is catalysed by reactive substrates, as Pt, which favours strong surface-molecule interactions. We have thoroughly studied with STM and large-scale DFT calculations (using both efficient local orbital basis methods FIREBALL [2] and OPENMX [3] and standar