Methane oxidation with low Pt2+ catalyst: High activity and stability against SO2, NO, and H2O poisoning

Abstract

We report the exceptional performance of a Pt/ZrO₂ catalyst with highly dispersed 3.5 at % Pt loading for methane oxidation, demonstrating its outstanding resistance to deactivation in lean exhaust conditions, which contain SO₂, NO, and H₂O. X-ray photoelectron spectroscopy analysis of fresh and used catalysts revealed the presence of Pt²⁺and Pt⁴⁺ surface species, even under these challenging reaction conditions. A mechanism is proposed to highlight the synergistic roles of Pt⁴⁺ species for oxygen adsorption and the Pt²⁺/ZrO₂ interface for methane adsorption, reducing the competition between the reacting molecules. Despite an increase in apparent activation energy in the presence of SO₂, NO, or H₂O, the catalyst retains its high activity. The high methane oxidation activity of the catalyst is attributed to the higher velocity of methane molecules, resulting in more frequent and successful collisions at Pt²⁺/ZrO₂ interface compared to other species in engine exhaust. The enhanced stability of the Pt²⁺ surface species is further explained by the energy-level alignment at the Pt²⁺/ZrO₂ interface, which is driven by the interfacial work function values of Pt²⁺ surface species and n-type semiconductor ZrO₂. The results highlight the potential of Pt/ZrO₂ catalyst for efficient and stable methane oxidation in real-world exhaust environments of natural gas engines.