Hydrogen-rich syngas production through partial oxidation of methane over Ni-promoted molecular sieves: Impact of reducibility and surface area

Abstract

CH4 is a potential greenhouse gas, and its fast-catalytic transformation into hydrogen-rich syngas by molecular oxygen escalates both environmental and industrial benefits. Herein, Mordenite-based molecular sieve (SiO2/Al2O3 = 13) is investigated for supporting Ni and various promoters like In, Cs, and Ga for the partial oxidation of methane reaction (POM). Catalysts are characterized by X-ray diffraction, surface area-porosity, temperature programmed studies, thermogravimetry analysis, transmission electron microscopy and X-ray photo electron spectroscopy. The stability of major active sites (metallic Ni) under oxidizing gas (O2 and CO2) is checked by Cyclic H2TPR-CO2TPD-H2TPR and Cyclic H2TPR-O2TPOH2TPR experiment where metallic Ni was found more susceptible to oxidize under oxygen. So, active sites should be deactivated but the current catalysts are found promising for achieving hydrogen rich syngas (H2/CO > 2) with high H2 yield through direct pathways and indirect pathways of POM. The co-presence of hydrogen (from hydrogen rich syngas) must stabilize the metallic state of Ni during POM. 1 wt.% Ga promotional addition over 5Ni-MOR13 brings the least crystallinity, highest surface area, and adequate population of active sites derived from NiO which is interacted with support with moderate to strong interaction. 5Ni+1Ga-MOR13 becomes coke resistance and outperforms than others. It attains 70 % CH4 conversion, a 69 % H2 yield, and a 2.5 H2/CO ratio up to 240 min time on stream.

Keywords

• Partial oxidation of methane
• Molecular sieve
• Mordenite
• Ni active sites
• Ga promoter
• Caesium promoter