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

Abstract

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, Al2O3 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 (H2-TPR), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), and N2 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 Cr2O3 into the Ni/Al2O3 catalyst improved metal dispersion and reduction behavior compared to the un-promoted catalyst. As a result, the Ni-Cr/Al2O3 catalyst exhibited exceptional activity in terms of hydrogen yield throughout the whole reaction periods. Furthermore, the Cr2O3 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 Al2O3 support was the primary cause of deteriorating the activity of Ni/Al2O3 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/Al2O3 and Ni-Cr/Al2O3 catalysts, respectively. In addition, the addition of Cr2O3 raised the accumulated carbon yield from 9.2 to 13.5 gC/gNi for both catalysts, respectively. SEM images showed that thin carbon nanotubes were deposited on the Ni-Cr/Al2O3 catalyst, whereas large-diameter carbon nanotubes were grown on the Ni/Al2O3 catalyst.