Impact of Cr doping on the performance of Ni/Al2O3 catalyst through methane decomposition into COx-free hydrogen and carbon nanomaterials

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The co-production of clean hydrogen and nanostructured carbon materials via methane decomposition is a desirable alternative route for energy savings and environmental considerations. In the current study, Al 2 O 3 supported monometallic 50%Ni and bimetallic 40%Ni-10%Cr catalysts were prepared and evaluated for this reaction. The as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature programmed reduction (H 2 -TPR), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), and N 2 physisorption, and Raman spectroscopy. Meanwhile, the spent catalysts were characterized by XDR, SEM, and Raman spectroscopy. According to XRD, TPR, and SEM results, the incorporation of Cr 2 O 3 into the Ni/Al 2 O 3 catalyst improved metal dispersion and reduction behavior compared to the un-promoted catalyst. As a result, the Ni-Cr/Al 2 O 3 catalyst exhibited exceptional activity in terms of hydrogen yield throughout the whole reaction periods. Furthermore, the Cr 2 O 3 inclusion enhanced catalyst stability by preventing the aggregation of active metal sites during the decomposition process. In contrast, the presence of agglomerated NiO particles on the surface of the Al 2 O 3 support was the primary cause of deteriorating the activity of Ni/Al 2 O 3 catalyst over a long reaction period. Both catalysts produced 79 % hydrogen at the start of the reaction (10 min), but by the end of the reaction (180 min), the hydrogen yield was 57 % and 76 % for Ni/Al 2 O 3 and Ni-Cr/Al 2 O 3 catalysts, respectively. In addition, the addition of Cr 2 O 3 raised the accumulated carbon yield from 9.2 to 13.5 g C /g Ni for both catalysts, respectively. SEM images showed that thin carbon nanotubes were deposited on the Ni-Cr/Al 2 O 3 catalyst, whereas large-diameter carbon nanotubes were grown on the Ni/Al 2 O 3 catalyst. • Methane decomposition into hydrogen and CNTs over Ni and Ni-Cr/Al 2 O 3 catalysts was examined. • The impact of Cr addition on the performance of Ni/Al 2 O 3 catalyst was studied in detail. • The Ni-Cr/Al 2 O 3 catalyst exhibited higher catalytic activity and stability than Ni/Al 2 O 3 catalyst. • The performances of the catalysts were correlated well with all characterization results.