DRY reforming of DRY reforming of methane over stabilized nickel-lanthanum supported on fibrous KCC-1 catalyst methane over stabilized nickel-lanthanum supported on fibrous KCC-1 catalyst

Abstract

Dry reforming of methane (DRM) is a promising technology towards production of synthesis gas (syngas) with low H2:CO ratio by utilization of gases (CO2 and CH4) with potential to cause global warming. This study entails the development of highly active and stable nickel (Ni) based catalyst supported on synthesized fibrous KCC-1 silica (KAUST Catalytic Centre number 1) by in situ one-pot method. The performance and robustness of the synthesized Ni/KCC-1(1P) catalyst to DRM reaction was evaluated and compared to other silica-based Ni catalysts supported by wet impregnation on KCC-1 (Ni/KCC-1(IM)) and conventional silica (Ni/SiO2). Furthermore, lanthanum (La) was added as a promoter to Ni/KCC-1 also in situ one-pot synthesis and compared to catalysts of single metal loadings of nickel (Ni/KCC-1(1P)) and lanthanum (La/KCC-1(1P)). Fresh and spent catalysts were characterized with the aid of X-ray diffraction, nitrogen adsorption-desorption isotherm, field-emission scanning electron microscope, energy-dispersive X-ray, transmission electron microscope, Fourier-transform infrared spectrometer, IR-pyrrole chemisorption, temperature-programmed reduction with hydrogen and X-ray photoelectron spectrometer, Raman spectrometer, thermogravimetric analysis. The effects of support morphology, synthesis mode and addition of La promoter on the activity and stability of Ni-based catalysts for DRM were studied over a temperature range of 550 – 850 oC and atmospheric pressure. From the results obtained, Ni/KCC-1(1P) produced the best performance in terms of reactants (CO2, CH4) conversions in comparison to Ni/KCC-1(IM) and Ni/SiO2 in the order: Ni/KCC-1(1P) (88 %, 92 %) > Ni/KCC-1(IM) (80 %, 92 %) > Ni/SiO2 (76 %, 82 %). From the reaction kinetics, low activation energy Ni/KCC-1(1P) at 22.7 kJ/mol facilitated its high activity in comparison to Ni/KCC-1(IM) and Ni/SiO2 with energy values of 26.5 and 40.9 kJ/mol, respectively. Enhanced surface area, mesoporosity and basicity were responsible for the increased activity of KCC-1 supported catalysts over silica. Activity of Ni/KCC-1(1P) was accompanied by an outstanding stability over 72 h time on stream with negligible activity loss, whereas Ni/KCC-1(IM) and Ni/SiO2 produced activity losses of 13.4 % and 42.5 %, respectively for CH4 conversion. The long-term stability was attributed to the confinement effect, core-shell structure and strong metal-support interaction provided by the one-pot mode of synthesis. The introduction of La promoter on Ni/KCC-1 increased its catalytic activity and selectivity for CO production due to enhancement in Ni dispersion and catalyst basicity for CO2 chemisorption. As a result, the activation energy for CO2 and CH4 conversions were reduced by a margin of 10.4 kJ/mol and 2.2 kJ/mol respectively. Based on optimization of reaction conditions for the synthesized catalyst by response surface methodology, DRM reaction temperature of 820 oC, CO2:CH4 feed ratio of 2.5 and gas hourly space velocity of 35.5 Lg-1h-1 produced an optimal CH4 conversion of 97 %. The highlight of this study is the application of the confinement effect and core-shell structure from in situ one-pot synthesis and the fibrous dendrimer morphology of KCC-1 support in the quest for a robust catalyst design for industrialization of syngas production via DRM.