Catalytic partial oxidation is an alternative process to steam reforming, the industrial process for production of synthesis gas from natural gas. Partial oxidation (POX) is a more energy efficient and less expensive process than steam reforming. The POX process is capable of producing syngas with a H 2 /CO ratio of about 2, which makes it favorable for methanol and hydrocarbon synthesis [1][2][3][4]. Unfortunately, most catalysts used for the POX process are poisoned, and therefore deactivated, in the presence of sulfur compounds [5].
It is well reported that noble metal catalysts (Ir, Ru, Rh, Pt, Pd, etc.) exhibit high activity, along with long-term stability, while minimizing the levels of coking [1,3]. Furthermore, the cost of these metals, in addition to the limited supply, has caused the researchers to concentrate their efforts on more readily available catalysts, particularly, Ni-based supported catalysts. However, Ni supported catalysts can be deactivated rapidly via carbon formation and sulfur poisoning. It has been reported earlier on the formation of carbon from methane over Ni-MgO in the presence of CO 2 and CO, demonstrating that carbon formed from both methane and CO 2 possibly via CO disproportionation [6].
In this paper, we are reporting on the catalytic activity and the effects of sulfur poisoning on the performance of reforming catalysts used for partial oxidation of methane into syngas.
Deactivation of reforming catalysts by sulfur has been widely studied and it is well understood that the sulfur significantly alters catalyst performance [7,8]. Sulfur poisoning and regeneration of poisoned supported noble metal catalysts have been studied for many applications including methane reforming and combustions. Deng and Nevell studied the sulfur poisoning and recovery of supported Pd, Rh, and Ir catalysts for methane oxidation. They reported that all of these catalysts were significantly affected by sulfur poisoning [9]. They reported the formation of sulfate (S 6+ ), using XPS, which its concentrations decreased with increasing temperature. Nasri et al. reported that noble metal catalysts demonstrated different activity for methane combustion when they were exposed to H 2 S [10]. They studied alumina-supported Pt, Pd, and Rh catalysts and found that the order of reactivity for the fresh and reduced catalysts is Pd > Rh > Pt but for the regenerated catalysts is Rh > Pt > Pd. Miller and Koningsberger reported that Pt catalysts supported on acidic and alkaline supports lose most of their activity due to loss of exposed Pt sites when they are exposed to hydrogen sulfide, forming adsorbed sulfur species (Pt-S) which physically block the active sites [11].
It is reported that the catalytic activity of Rh catalyst is significantly affected by the type of support, metal sintering, carbon deposition, and the presence of sulfur impurities either in feed or in