Two-step, oxygen-free conversion of methane over supported NiB amorphous alloy catalysts

NiB amorphous alloy and Ni catalysts supported on HMCM-22, HZSM-5, HY, γ-Al₂O₃ and SiO₂ were prepared, respectively, by the chemical reduction method and the standard incipient wetness impregnation method. These catalysts were examined for catalytic performance in the two-step conversion of CH₄ to produce hydrogen and higher hydrocarbons. All catalysts give similar methane conversion and yields of hydrogen and H-deficient carbon-containing species in step I. In the subsequent hydrogenation step (step II), they have similar carbon conversion, however, the yield of C₂ and C₃ hydrocarbons depends greatly on the nature of the metal particles and support acidity. Supported NiB amorphous alloy catalysts offer higher yield of C₂ and C₃ hydrocarbons than the corresponding Ni catalysts, due to their unique properties: nanoscale size, long-range disorder in structure, and electron-deficiency. Of the zeolite supported catalysts, HMCM-22 and HZSM-5 supported catalysts produce higher yield of C₂ and C₃ hydrocarbons than the zeolite HY supported catalyst because of stronger acidity of the supports. A NiB/HMCM-22 catalyst shows a rather slow deactivation during a multiple reaction cycles test. High temperature favors CH₄ decomposition and H₂ production in step I, but makes the subsequent hydrogenation of carbon formed from CH₄ decomposition difficult. The nature of the carbons formed from CH₄ decomposition was also studied by XPS and TEM combined with H₂-TPSR.