Nickel Based Catalysts For Methane Decomposition

Methane decomposition into hydrogen and carbon nanofiber is regarded as an effective way to provide hydrogen. Nickel-based catalysts showed much more higher catalytic activity in methane cracking as compared with iron- and cobalt-based catalysts. However, most of the reported nickel catalysts were supported by oxides, such as SiO2, Al2O3, to stabilize the nickel particles, which played critical roles in determining the catalytic activity. In this works, we focused on development of novel Ni catalysts without the presence of support. Calcination (573～1073 K) of theα-Ni(OH)2 prepared in the solution of ethylene glycol resulted in the formation of nickel oxides with similar fibrous shapes and crystalline size of 3.0～8.1 nm. Metallic Ni crystalline sizes of about 11 nm and fibrous structures were obtained after reduction with hydrogen at 773 K.The effect of preparation conditions on the structure of nickel hydroxide, the morphology of nickel oxide and metallic nickel, the crystallite size and the catalytic activity of methane cracking are studied by HRTEM, XRD, FT-IR, TG etc. The catalytic activity of the pure Ni catalysts for methane decomposition was strongly related to the crystalline sizes. The metallic Ni with crystalline size of about 11 nm showed the highest carbon and hydrogen yields, and the nickel crystalline of about 20 nm gave relatively lower carbon yields. While increasing the nickel crystalline size to about 24 nm led to extremely low catalytic activity, and further increasing up to 26 nm resulted in totally deactivation towards methane decomposition. Further evolution of the metallic nickel particles during...