Catalytic gas conditioning is a key step in producing clean syngas via gasification of heterogeneous materials. Our work has focused on the steam re-forming of naphthalene and orthodichlorobenzene as prototypes of polyaromatic hydrocarbons (PAHs) and halogenated aromatics. Subsequently, we have studied the conversion of tar present in the syngas derived from biomass and waste gasification. Steam re-forming of naphthalene was initially studied over a UCI GB-98 commercial catalyst in a fixed bed reactor operated at atmospheric pressure, in the temperature range 873-1123 K, with residence times of 0.31-0.82 s and steam to naphthalene molar ratios of 10-22. Although the catalyst is efficient, it suffers from a progressive drop in activity due to coke formation as well as weight loss (35% weight loss after 24 h on stream). To overcome deactivation and catalyst weight loss, a robust catalyst formulation has been developed. It has demonstrated excellent activity as well as reasonable time-on-stream and easy regeneration without significant loss of activity. Total conversion of naphthalene and dichlorobenzene has been observed at 1023 and 1123 K, respectively. The yields of dry gas in both cases have been higher than 90%. After 60 h on stream, the catalyst weight loss is less than 5%. This catalyst has also performed efficiently in the conversion of tar present in the producer gas from air gasification of biomass and mixed wastes.