Study Of Methanation Catalysts For Coal To Synthetic Natural Gas

Synthetic natural gas?SNG? production from coal is under investigation again due to the desire for less dependency from imports and the opportunity for increasing coal utilization and reducing greenhouse gas emission. Notably, the production of SNG is a relatively reasonable and clean way to utilise coal adequately. Methanation is a key reaction for producing SNG from syngas. According to the recent catalysts for SNG production from coal, in this report, we attempt to investigate the NiO/CeO₂ methanation catalyst and Mo-based sulphur-resistant methanation catalyst.The effect of NiO loading amount and preparation methods on the activity and selectivity of the NiO/CeO₂ catalysts for synthetic natural gas production was systematically investigated. The prepared catalysts were subsequently characterized by N₂-physisorption, X-ray diffraction, temperature programmed reduction, transmission electron microscopy and thermogravimetric analysis. With the increase of NiO loading amount, the NiO/CeO₂ catalysts displayed a decrease of specific surface area, a poor NiO dispersion and agglomerated NiO particles on ceria support, which thereby significantly impacted their catalytic activity. The 10%NiO/CeO₂ catalyst exhibits the best catalytic performance for SNG production. Among the different preparation methods, the NiO/CeO₂ prepared by solution combustion method demonstrates a narrow size distribution and homogeneously dispersed over the support surface. The main advantages of solution combustion method are the simplicity, control of the final stoichiometry and the economic feasibility for a large scale production.The effect of the sulphidation temperature on the activity and selectivity of a NiO-MoO₃/?-Al₂O₃ catalyst for sulphur-resistant methanation was systematically investigated. The prepared catalysts were subsequently characterised by N₂-physisorption, temperature-programmed sulphidation, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The results obtained from characterisation demonstrated that the NiMoO₄ species in the NiO-MoO₃/?-Al₂O₃ catalyst would be sulphided when the sulphidation temperature was at or above 300 °C. Evaluation of the catalysts in sulphur-resistant methanation from syngas indicated that the sample sulphided at 400 °C has the highest catalytic activities likelihood of possessing greater NiMoS type I structure. The catalytic activity decreased when the sulphidation temperature was above 400°C. This decrease was primarily caused by the formation of MoS₂ crystals and the progressive transformation of the Ni MoS phase with increasing the sulphidation temperature. The NiMoS type II structure did not display good performance for sulphur-resistant methanation because it resulted in the over-sulphidation of the NiMoS structure to form crystalline MoS₂, which exhibited lower methanation activity.The phosphorus introduction step markedly influenced the properties of P-doped alumina, such as pore structures, surface acidity and thermal stability. These differences attribute to not only the interaction between phosphorus species and alumina but also the location of phosphorus atoms. In order to enhance the stability of Mo based catalyst for SNG production, we attempted to investigate the effect of phosphorus introduction on MoO₃/Al₂O₃ catalysts' structure and catalytic performance. The introduction of phosphorus caused the formation of Mo₇O₂₄^6- heteropoly anion, and then the formation of larger crystalline Al₂?MoO₄?₃, which further reduced the number of Mo-S active sites.