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.