Effect Of Water And Carbon Dioxide On Mo-based Sulphur-resistent Methanation Catalysts

Coal to natural gas is an important way for effective conversion of coal intoclean fuel. The methanation catalyst is the key process technology of the coal tonatural gas. The research on non-sulfur-tolerant methanation catalysts has matured.However, there are many shortcomings about the Ni-based catalyst, such as thecomplex process and non-sulfur-tolerant. To save the cost of the technology, thesulfur-resistant methanation catalyst has become the focus of today’s domestic andforeign research. Sulfur-resistant methanation process is generally on themolybdenum-based catalyst, the catalyst can be directly to the convert the coal intomethane. Among the reactions, a certain amount of water and carbon dioxide arecontained. It is no reported that the effect of water and carbon dioxide on Mo-basedsulfur-resistant methanation catalysts.This paper studies that the effect of adding water and carbon dioxide onMo-based sulfur-resistant methanation catalysts, and the effects of the water-gas shiftreaction and methanation of carbon dioxide on the Mo-based catalysts. The resultsshow that adding water has promoted the water gas shift reaction, while themethanation reaction is suppressed. The CO conversion rate is not recovered to theoriginal level after the removal of water, which indicated that the partially irreversibleinactivation of catalysts is caused by the water. On the adding water conditions,adding cobalt additives can improve the stability of the Mo-based catalysts at1.2%H2S concentration, while the0.2%H2S concentration of adding cobalt is not obvious.Add carbon dioxide could inhibit the catalyst activity. With the carbon dioxide contentincrease, the degree of inactivation on the catalysts is greater. Adding carbon dioxidesignificantly reduced the selectivity of methane, the main result is the reverse watergas shift reaction more easily occur than the methanation reaction on the Mo-basedcatalysts. It consumes more hydrogen, lead to the H2/CO proportion reduced. ForCo-Mo/Ce-Al catalyst, adding10%water or10%carbon dioxide in feed gas had littleeffect on the reaction performance, while the addition of10%water and10%carbondioxide in feed gas caused an irreversible inactivation. The activity of the water gasshift reaction is high than the methanation activity on Mo-based catalysts. Theexperimental results of carbon dioxide methanation show that the methanation of carbon dioxide is very weak while the reverse water gas shift reaction is abundant; thecarbon monoxide selectivity has up to80%with the temperature increasing, while themethane selectivity was only20%.Several characterization methods, such as N2-adsorption, XRD, TPR, TEM andXPS, were applied to detect the change of Mo-based catalysts, analysis of the impactof the water and carbon dioxide on these catalysts, and discuss the cause of catalystdeactivation.