Study of a catalytic technology for syngas/H2 production from raw biogas self-reforming in presence of sulphur

Abstract

A synthetic biogas stream was effectively reformed in the presence of dimethyl sulphide (used as a model sulphur-containing molecule) by a multi-metallic catalyst main composed by Ni and Ce, with Sn and Rh as promoters, supported over high surface alumina. Prior to reaction, a thermodynamic equilibrium calculation indicated that dimethyl sulphide decomposes to H2S and CO2 at the reaction temperature inside the reactor. This sulphur, that strongly attaches to Ni catalyst causing deactivation, was overcome during 35 h by the studied catalyst when a moderate content was fed, 15 ppm (30 ppm of dimethyl sulphide DMS). The obtained H2/CO was close to 2/1 and methane conversion almost reached 60%. On the other hand, in the case of a higher concentration present at the reaction atmosphere, 50 ppm of sulphur (90 ppm of DMS), it was observed a continuous decay in activity. The analysis of the used catalysts by TEM, XRD, Raman and TGA indicated that sulphur promoted the formation of graphitic carbon, mostly nanotubes, removing the isolated nickel particles of the alumina surface, whilst a long time on stream favoured the sintering of the active phase, indicating a combination of different deactivation effects. In fact, the case of feeding 50 ppm of sulphur, different deactivation mechanisms were observed: sintering, coke deposition, fouling and leaching, whilst in the case of moderate concentration the catalyst was capable of tolerating the sulphur presence.