Synthesis Of Unsupported Nickel-based Catalysts And Their Performances On Methane Decomposition

Methane decomposition is a promising process for the production of CO_x-free hydrogen and carbon nanomaterial.In this work,unsupported nickel-based catalysts were synthesized by a facile precipitation metod using anhydrous sodium carbonate as the precipitant and were used for the methane decomposition.The surfactants(PVA,CTAB and SDBS)appear to be the good candidates for obtaining smaller average particle size of catalyst samples.The crystal structure and microscopic morphology of the resulting powders have been characterized by XRD,SEM and TEM characterization methods.The main results are as follows:(1)The addition of surfactant can change the particle size of unsupported Ni by affecting the particle size of NiO,and the morphology of NiO synthesized under different surfactants are all nanosheets.Among the three types of surfactants,PVA can regulate the particle size of the samples more effectively,and the particle size of Ni-PVA sample(additive amount was0.1wt%,precipitation temperature is 120℃)is the smallest.The sequence of catalytic performance of the prepared catalysts for methane decomposition under conventional performance test conditions is Ni-PVA>Ni-CTAB>Ni-SDBS.(2)Both microscopic morphology and particle size of Ni-PVA were strongly affected by rinsing solvent.Compared with Ni-PVA-et(nanoparticle-like aggregates,>100 nm),Ni-PVA-wt(nanoparticle-like,26.5 nm)exhibited higher activity for methane decomposition.(3)The particle size of metal Ni can be effectively controlled by using multi-stage temperature decomposition method.Thus,multi-stage temperature decomposition can significantly enhance the activity and stability of the unsupported Ni catalysts for methane decomposition.(4)Carbon nanofibers are formed on the surface of the catalyst during methane decomposition.The formation mechanism of carbon nanofibers derived from methane follows tip-growth mechanism.