H. Zhang, Y. Alhamed, Y. Kojima, A. Al-Zahrani, H. Idriss, L. Petrov, M. Daous
King Abdulaziz University, SA
hydrogen generation, ammonia decomposition, nickel catalysts, surface groups
Functional groups on the Multi-Wall Carbon Nanotubes (MWCNTs) surfaces play an important role in anchoring metal ions. Transition metals such as Fe, Co, Ni supported on MWCNTs with surface carboxyl groups have demonstrated an excellent catalytic activity for ammonia decomposition (AD). Graphene, single-wall carbon nanotubes (SWCNTs) and several types of commercial MWCNTs, were used as supports to prepare nickel catalyst by the incipient wetness method. Catalysts were characterized using powder X-ray diffraction (XRD), Temperature programmed reduction (TPR), and X-ray Photoelectron Spectrometry (XPS). AD was performed in a fixed bed quartz microreactor at atmospheric pressure, 400-500 oC and GHSV from 6000 to 24000 h-1 Activity tests revealed that both Ni/Graphene and Ni/SWCNTs are inactive with NH3 conversion of 1.0% at 500oC and GHSV of 6000 h-1. Ni supported on MWCNTs with different surface functional groups showed that the Ni/MWCNTs-COOH catalyst was most active with ammonia conversion of 25.4 % at 500 oC and 6000 h-1. Comparable conversions were obtained with Ni/MWCNTs-OH (23.5%) and Ni/MWCNTs-NH2 (24.6%). However, Ni/MVCNTs gave much lower conversion of ammonia (13.2%). TPR measurements (Fig. 1) showed that the functionalized MWCNTs are much easier to reduce which could explain their higher activity in AD reaction.