Effect of polyaromatic tars on the activity for methane steam reforming of nickel particles embedded in silicalite-1

•Naphthalene and pyrene used a model tars during methane steam reforming.•Both Rh and Ni-based catalysts were strongly poisoned, sometimes reversibly.•Embedding Ni particles in silicalite-1 could not prevent deactivation.•Thermal cracking of bulky tars leads to small arenes able to penetrate silicalite-1.