Abstract
In this paper, the 10 wt% Ni/Al2O3-MgO (10Ni/MA), 5 wt% Ni-5 wt% Ce/Al2O3-MgO (5Ni5Ce/MA), and 5 wt% Ni-5 wt% Co/Al2O3-MgO (5Ni5Co/MA) catalysts were prepared by an impregnation method. The effects of CeO2 and Co doping on the physicochemical properties of the Ni/Al2O3-MgO catalyst were comprehensively studied by N2 adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 temperature programmed reduction (H2-TPR), CO2 temperature programmed reduction (CO2-TPD), and thermogravimetric analysis (TGA). The effects on catalytic performance for the combined steam and CO2 reforming of methane with the low steam-to-carbon ratio (S/C ratio) were evaluated at 620 °C under atmospheric pressure. The appearance of CeO2 and Co enhanced the oxygen species at the surface that decreased the coke deposits from 17% for the Ni/MA catalyst to 11–12% for the 5Ni5Ce/MA and 5Ni5Co/MA catalysts. The oxygen vacancies in the 5Ni5Ce/MA catalyst promoted water activation and dissociation, producing surface oxygen with a relatively high H2/CO ratio (1.6). With the relatively low H2/CO ratio (1.3), the oxygen species at the surface was enhanced by CO2 activation-dissociation via the redox potential in the 5Ni5Co/MA catalyst. The improvement of H2O and CO2 dissociative adsorption allowed the 5Ni5Ce/MA and 5Ni5Co/MA catalysts to resist the carbon formation, requiring only a low amount of steam to be added.
Highlights
The combined steam and CO2 reforming of methane (CSCRM) (Equation (1)) is a process that combines steam reforming of methane (Equation (2)) and CO2 reforming of methane (Equation (3))
This work evaluated the effect of CeO2 and Co promoters over the CSCRM (using a low steam- to-carbon ratio (S/C ratio) that accompanies CO2 and H2 O oxidants) catalytic performance of the 2020, Ni/MgO-Al
The reduction peak at low temperature in the TPR profile of 5Ni5Co/MA catalyst shifted to a lower temperature compared to 10 wt% Ni/MgO-Al2 O3 (10Ni/MA)
Summary
The combined steam and CO2 reforming of methane (CSCRM) (Equation (1)) is a process that combines steam reforming of methane (Equation (2)) and CO2 reforming of methane (Equation (3)). To prevent the formation of carbon, steam in the feed must be sufficient. The development of high-performance catalysts for CSCRM operating at a low steam-to-carbon ratio could be a critical challenge of syngas production technologies. The oxygen vacancy sites can be created when Ce4+ in the oxide form of cerium (CeO2 ) transforms to Ce3+. Steam in the feed promotes the steam reforming of methane as well as the water gas shift reaction, which increases the H2 /CO ratio in the syngas product. This work evaluated the effect of CeO2 and Co promoters over the CSCRM (using a low steam- to-carbon ratio (S/C ratio) that accompanies CO2 and H2 O oxidants) catalytic performance of the 2020, Ni/MgO-Al. Ce/MgO-Al2 O3 (5Ni5Ce/MA), and 5 wt% Ni–5 wt% Co/MgO-Al2 O3 (5Ni5Co/MA) were prepared methods.
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