Sustainable and selective hydrogen production by steam reforming of bio-based ethylene glycol: Design and development of Ni–Cu/mixed metal oxides using M (CeO2, La2O3, ZrO2)–MgO mixed oxides

Abstract

Hydrogen (H2) production in a clean and green manner via renewable sources is at present of great interest. Ethylene glycol, a bio-based feedstock, offers a sustainable route for high purity H2 production. In the current investigation, MgO based mixed metal oxides containing CeO2, La2O3 and ZrO2 were synthesized and used to support 20 wt% Ni–Cu (1:1). The impacts of altering support characteristics on catalytic behavior have been studied and compared in H2 synthesis via ethylene glycol steam reforming (SR), employing various characterization techniques such as XRD, SEM, EDX, TEM, H2-TPR, H2-TPD, TG-DSC and BET. Further, high resolution XPS studies were performed to explore the valence states and effectiveness of surface engineering of the catalysts. Assessment of the efficacy of catalysts was done via several parameters such as reactant conversion, H2 concentration and long-term stability. All the synthesized materials produced encouraging results with high H2 yield and conversion under the said operating conditions [T- 623 to 773 K; GHSV - 3120 to 6240 h−1; P - 0.1 MPa; S/C - 3 to 7.5 mol/mol]. Amongst the three catalysts, Ni–Cu/La2O3–MgO and Ni–Cu/CeO2–MgO exhibited superior behavior for high H2 production. Ni–Cu/La2O3–MgO was better in comparison to Ni–Cu/CeO2–MgO in terms of reactant conversion whereas Ni–Cu/CeO2–MgO showed highest H2 concentration (98 mol %) and improved stability along with absence of carbon deposition owing to its high mobile oxygen vacancies in its lattice. The highly active cubic CeO2 species and its long-term durability (up to 8 cycles) owing to its exceptional redox property further justified its efficacy. The optimized process showed that at T = 773 K, GHSV = 3120 h−1, S/C = 4.5 mol/mol for Ni–Cu/La2O3–MgO and Ni–Cu/CeO2–MgO and at T = 773 K, GHSV = 3120 h−1, S/C = 6 mol/mol and for Ni–Cu/ZrO2–MgO, maximum H2 concentration was obtained. At the end, reaction pathway followed by the catalysts was proposed.