Industrial coal gasification ash as a support substrate for the thermocatalytic decomposition of methane into hydrogen and carbon nanotubes

Abstract

This novel study has demonstrated an economical and sustainable solution to utilize the industrial waste of coal gasification ash (CGA) for the preparation of co-precipitated Ni and Co-based catalysts to generate COx-free hydrogen and high-end carbonaceous products in the form of carbon nanotubes (CNTs). Catalysts with different transition metal loadings were investigated at a reaction temperature of 700 degrees C and atmospheric pressure conditions in a gas-chromatograph coupled fixed-bed reactor system to decipher the impact on methane conversion and hydrogen yield performance parameters. The catalysts and the product samples were characterized using a series of complementary bulk and surface-sensitive analytical techniques consisting of X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman, and energy dispersive X-ray spectroscopy (EDX) coupled scanning electron microscopy (SEM) & field emission scanning electron microscopy (FESEM) instruments. The morphology and texture properties of the product CNTs were analyzed using high-resolution transmission electron microscopy (HRTEM) and the methods mentioned above. The thermocatalytic decomposition of methane (TDM) reaction conducted at the earlier mentioned process parameters demonstrated the Ni-CGA catalyst as the most active catalyst among the investigated Co-CGA and Ni-Co-CGA catalysts over testing on stream for almost 4 h with the highest methane conversion and hydrogen yield performance. The Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analysis results showed a remarkable rise in the specific surface area (SBET) and total pore volumes (Vt) for the prepared Ni-CGA catalyst, compared to the support CGA substrates. The EDX-assisted FESEM and HRTEM showed the formation of CNTs with external diameters of 40 nm to 125 nm and lengths from 600 nm to 1,500 nm, originating from the active Ni-Fe alloy metal sites with equivalent spherical diameters of few 100 nm.