In many chemical industries, syngas, a mixture of carbon monoxide and hydrogen gases, plays a crucial role as an important feedstock for numerous desirable chemical processes such as hydroformylation, ammonia synthesis and the Fischer-Tropsch reaction. There are three eminent methane processes that have been widely used for the production of syngas, namely: the partial oxidation of methane, stream reforming of methane and dry reforming of methane. Recently, combination of the three reactions in a reactor (tri-reforming of methane) has attracted considerable attention due to the many desirable attributes associated with it.
Nickel catalysts have already been highlighted as the most promising desirable catalysts for the tri-reforming process. However, the stability of the nickel catalysts at elevated temperatures and coke generation are the main obstacles hampering their widespread application. Consequently, transition metal carbides, such as molybdenum carbide or tungsten mono-carbide, have been proposed as potential substitutes for noble metals due to their low cost and superior performance in the methane reforming process.
Researchers led by professor Hanbo Zou from the Department of Chemistry and Chemical Engineering at Guangzhou University in China investigated the effect of additives on the attributes of nickel and molybdenum carbides for the tri-reforming of methane gas. Their main objective was to synthesize a series of promoted nickel molybdenum carbides and observe the effects of the varying additives on their catalytic performance for the tri- reforming of methane gas. Their work is now published in International Journal of Hydrogen Energy.
The team found out that the presence of nickel species in the nickel-molybdenum series carbides stimulated the dissociation of methane and supplied the active carbon for the carburization process. Cerium and cobalt additives were observed to deteriorate the activities of the nickel-molybdenum carbides due to the larger particle size. Magnesium additive was observed to favor the coke generation. They then noted that the addition of potassium suppressed the carburization process of molybdenum oxide species and caused the phase transformation of active γ-aluminum oxide to less active θ- aluminum oxide. They realized that the oxidation of carbidic species and the agglomeration of small particles and the carbon deposition decreased the catalytic activities of nickel molybdenum series carbides for the tri-reforming of methane.
Doping the nickel-molybdenum series with different additives has presented a platform for thorough analysis of each additive element individually. Of most concern is that the lathanum additive which has been seen to facilitate the topotactic transformation of the oxidic precursors and refine the particles. The aggregation of the fine particles, reduction of carbidic species and the carbon deposition would all deteriorate the activities of the nickel molybdenum series carbides. The effects of each individual doping additive are therefore critical for the realization of better tri-reforming of methane process.
Hanbo Zou, Shengzhou Chen, Jiangnan Huang, Zhaohui Zhao. Effect of additives on the properties of nickel molybdenum carbides for the tri-reforming of methane. International journal of hydrogen energy volume 41(2016) pages 16842-16850.Go To International journal of hydrogen energy