CH4 Cracking over the Cu–Ni/Al-MCM-41 Catalyst for the Simultaneous Production of H2 and Highly Ordered Graphitic Carbon Nanofibers

The Cu–Ni bimetallic catalysts dispersed on various silica supports were examined for catalytic cracking of CH 4 to produce pure H 2 with near-zero CO x emissions and fine quality carbon nanofibers. The 27 Al magic angle spinning (MAS) NMR spectra of Al-containing MCM-41 samples revealed the existence of a framework- and an extra framework-decorated Al species. Insertion of Al species into the framework of MCM-41 significantly improved the accessible active surface Ni sites, which was confirmed from the simultaneous H 2 and N 2 O pulse titration techniques. NH 3 -temperature-programmed desorption (TPD) measurements demonstrated a high ratio of moderate and strong acid sites upon Al insertion into the silica matrix. The framework tetrahedral Al in MCM-41 stabilized the surface Cu–Ni alloy sites and protected them from the sintering and fragmentation of Ni; consequently, the enhanced H 2 yields of 270 Nm 3 /(mol Ni ) −1 were obtained with a Si/Al ratio of 150 with the catalyst. The better performance of Cu–Ni/Al-MCM-41 (Si/Al = 150) was rationalized using the physicochemical characteristics of the catalyst analyzed by X-ray diffraction, H 2 -temperature-programmed reduction, Brunauer–Emmett–Teller—surface area, 27 Al and 29 Si MAS NMR, NH 3 -TPD, X-ray photoelectron spectroscopy, transmission electron microscopy, H 2 and/or N 2 O titration, and Raman spectroscopic techniques.