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 CH4 to produce pure H2 with near-zero COx emissions and fine quality carbon nanofibers. The 27Al 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 H2 and N2O pulse titration techniques. NH3-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 H2 yields of 270 Nm3/(molNi)−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, H2-temperature-programmed reduction, Brunauer–Emmett–Teller—surface area, 27Al and 29Si MAS NMR, NH3-TPD, X-ray photoelectron spectroscopy, transmission electron microscopy, H2 and/or N2O titration, and Raman spectroscopic techniques.