Combined Steam and CO2 Reforming of Methane over the Hierarchical Ni-ZrO2 Nanosheets/Al2O3 Catalysts at Ultralow Temperature and under Low Steam

This research developed hierarchical 10 wt % Ni-1 wt % ZrO2/Al2O3 catalysts for combined steam and CO2 reforming of methane (CSCRM) reaction to produce syngas for gas-to-liquid (GTL) application under the ultralow temperature and low steam condition. The hierarchical nanosheet catalysts were prepared via a novel impregnation technique assisted by ammonia vapor diffusion with various times (1, 6, and 12 h) to develop the different magnitude of hierarchical nanosheets on the surface. Then, CSCRM at 600 °C was performed on the catalysts for 6 h. The results evidenced the improvement of H2 selectivity, reaching an appropriate H2/CO ratio (1.9-2.0) in FT subunits in the GTL process when nanosheets existed on the surface due to the increase in H2O adsorption-dissociation sites. The good dispersion of hierarchical nanosheets accompanied by the ZrO2 promoter successfully enhanced the CH4 conversion and the coke prevention through the spread nanosheets because of the increase in the number of active sites and the surface interaction. The interaction of hierarchical nanosheets created the H2O activation-dissociation sites that allowed CO2 to be selective on the oxygen vacancy sites, producing more OH* and OH* on the catalyst surface to resist the carbon deposition during CSCRM operation.

The Efficiency of Carbon Conversion and Hydrogen Production from Tar Steam Reforming of Biomass Using Ni-Based Catalysts with Alkaline Earth Promoters

H2 production can be used as a clean and renewable energy source for various applications, including fuel cells, internal combustion engines, and chemical production. Using nickel-based catalysts for steam reforming biomass tar presents challenges related to catalyst deactivation, poisoning, heterogeneous composition, high process temperatures, and gas impurities. To overcome these challenges, adopting a nickel-based catalyst with selected oxide support and MgO and CaO promoter is a promising approach for improving the efficiency and sustainability of steam reforming for hydrogen production. The majority of studies conducted to date have focused on the steam reforming of particular tar compounds, most commonly benzene, phenol, toluene, or naphthalene, over a range of support catalysts. However, the actual biomass tar composition is complex, and each component impacts how well steam reforming works. In this research, a multi-compound biomass tar model including phenol, toluene, naphthalene, and pyrene underwent a steam reforming process. Various types with 10 wt.% of nickel-based catalysts were generated by the co-impregnation technique, which included 90 wt.% different oxide supports (Al2O3, La2O3, and ZrO2) and 10 wt.% of combination alkaline oxide earth promoters (MgO and CaO). Thermogravimetric analysis, Brunauer–Emmett–Teller (BET) method, N2 physisorption, temperature-programmed reduction (H2-TPR), temperature-programmed desorption (CO2-TPD), and X-ray diffraction (XRD) of ni-based catalyst characterized physiochemical properties of the prepared catalyst. The reaction temperature used for steam reforming was 800 °C, an S/C ratio of 1, and a GHSV of 13,500 h−1. Ni/La2O3/MgO/CaO (NiLaMgCa) produced the most carbon to-gas conversion (86.27 mol%) and H2 yield (51.58 mol%) after 5 h of reaction compared to other catalysts tested in this study. Additionally, the filamentous carbon coke deposited on the spent catalyst of NiLaMgCa does not impact the catalyst activity. NiLaMgCa was the best catalyst compared to other catalysts investigated, exhibiting a stable and high catalytic performance in the steam reforming of gasified biomass tar. In conclusion, this study presents a novel approach by adding a combination of MgO and CaO promoters to a ni-based catalyst with various oxide supports, strengthening the metal-support interaction and improving the acid-base balance of the catalyst surface. The mesoporous structure and active phase (metallic Ni) were successfully developed. This can lead to an increase in the conversion of tar to H2 yield gas and a decrease in the production of undesired byproducts, such as CH4 and CO.