Assessing the effect of acid and alkali treatment on a halloysite-based catalyst for dry reforming of methane

Abstract

Dry reforming of methane (DRM) has recently received wide attention owing to its outstanding performance in the reduction and conversion of CH₄ and CO₂ to syngas (H₂ and CO). From an industrial perspective, nickel (Ni)-supported catalysts have been deemed among the most suitable catalysts for DRM owing to their low cost and high activity compared to noble metals. However, a downside of nickel catalysts is their high susceptibility to deactivation due to coke formation and sintering at high temperatures. Using appropriate supports and preparation methods plays a major role in improving the activity and stability of Ni-supported catalysts. Halloysite nanotubes (HNTs) are largely utilized in catalysis as a support for Ni owing to their abundance, low cost, and ease of preparation. The treatment of HNTs (chemical or physical) prior to doping with Ni is considered a suitable method for increasing the overall performance of the catalyst. In this study, the surface of HNTs was activated with acids (HNO₃ and H₂SO₄) and alkalis (NaOH and Na₂CO₃ + NaNO₃) prior to Ni doping to assess the effects of support treatment on the stability, activity, and longevity of the catalyst. Nickel catalysts on raw HNT, acid-treated HNT, and alkali-treated HNT supports were prepared via wet impregnation. A detailed characterization of the catalysts was conducted using X-ray diffraction (XRD), BET surface area analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), solid-state nuclear magnetic resonance (ssNMR), H₂-temperature programmed reduction, (H₂-TPR), CO₂-temperature programmed desorption (CO₂-TPD), and Ni-dispersion via H₂-pulse chemisorption. Our results reveal a clear alteration in the structure of HNTs after treatment, while elemental mapping shows a uniform distribution of Ni throughout all the different supports. Moreover, the supports treated with a molten salt method resulted in the overall highest CO₂ and CH₄ conversion among the studied catalysts and exhibited high stability over 24 hours testing.