Enhancing Catalytic Performance in Oxidative Steam Reforming of Ethanol: The Role of Ruthenium ion Substitution in Layered Perovskite La2Ti2–xRuxO7±δ Catalysts

Abstract

Layered perovskite oxides of La₂Ti_2–xRu_xO_7±δ, where x ranges from 0.1 to 0.4 (LTR01–04), demonstrate significant catalytic efficiency and stability in the oxidative steam reforming of ethanol (OSRE). The LTR03 catalyst (0.50 wt % Ru) achieves optimal performance, achieving complete ethanol conversion and an exceptional hydrogen selectivity rate of 100.0(5)% under conditions of C/O = 0.6, GHSV = 120,000 h^–1, and a furnace temperature of 400 °C. When paired with La₂Zr₂O₇ as a support material, the LTR03 catalyst maintains a stable hydrogen selectivity of 98(1)% and an ethanol conversion rate of 99(1)% at a C/O ratio of 0.6, without any noticeable carbon deposition, over a 120 h OSRE activity test. Investigations using X-ray photoelectron Spectra (XPS), X-ray absorption spectroscopy (XAS), temperature-programmed reduction (TPR), synchrotron, and neutron powder diffraction indicate that the partial substitution of ruthenium cations leads to the emergence of multivalence of Ruⁿ⁺/Ru⁴⁺ ions and triggers the creation of oxygen vacancies and boosting the OSRE performance of La₂Ti_2–xRu_xO_7±δ. Rietveld analyses of powder diffraction data disclose a site-specific preference for Ruⁿ⁺ and Ti⁴⁺ ions within the metal lattice. In-situ powder X-ray diffraction (PXRD) and neutron powder diffraction studies on both the regular and reduced forms of La₂Ti_1.7Ru_0.3O_7±δ (LTR03) reveal that oxygen vacancies predominantly form at the top and bottom regions of the [M₂O₇]ⁿ⁻ layer. These vacancies are crucial for effectively converting ethanol and hydrocarbons in the OSRE process. These findings pave the way for further research into metal-substituted layered perovskites as catalysts and La₂Zr₂O₇ as a supporting material for efficient hydrogen production via ethanol conversion in the OSRE process.