A carbon deposition and sulphur poisoning study of new pyrochlore catalysts for methane reforming

Abstract

Reforming of landfill gases for the production of syngas that leads to the generation of heat or electricity is a very promising pathway considering the increasing price of oil. The dry reforming technique is a very interesting approach to reduce the greenhouse effect and convert these gases into valuable syngas. A key factor for the success of the dry reforming process is selecting a catalyst that shows high stability and activity toward dry reforming conditions as well as resistance to carbon deposition and sulphur poisoning. This work aims to prepare a new pyrochlore catalyst as an alternative to Ni supported catalysts that suffer from deactivation because of carbon deposition and sulphur poisoning. Several essentials factors were changed to produce a promising catalyst for methane reforming including a) the preparation method, b) the ratio of Ni doped and c) the kind of the metal doped. The LaCeZrNiO7 was prepared by the hydrothermal and the Pechini methods. The performance of the Ni-doped pyrochlore catalysts were compared with a noble metal (Ru) pyrochlore under different dry reforming conditions.
All new prepared pyrochlore catalysts were characterized using XRD, BET, SEM and TPR techniques. The pyrochlore phase was seen in all prepared materials; however an additional La/CeZrO4 phase was also seen in all the hydrothermal Ni catalysts.
Generally, no significant carbon deposition was seen on all materials at temperatures above 750 ? C and an almost complete conversion was observed at high temperatures without deactivation for both the Ni and Ru catalysts under the conditions of stoichiometric and methane-rich dry reforming.
At low temperatures, the hydrothermal 1Ni-LCZ pyrochlore catalyst, showed a significant increase in carbon deposition compared with that synthesised by the Pechini method.
However, the low hydrothermal Ni loading pyrochlore catalyst showed low carbon deposition with high activity at 650 ? C.
The performance of the catalysts in the presence of H2S (10-30 ppm) was investigated under the methane-rich dry reforming and at temperatures between 700 and 1000 ? C. All Ni catalysts showed high resistance and complete conversion for more than 40 hours with 10 ppm of H2S at 850 ? C. The Ru catalyst was however the only one to show excellent activity without complete deactivation at 30 ppm at 700 ? C. At a temperature of 900 ? C and above, no deactivation was observed even when the H2S concentration increased for all catalysts.