Oxalic acid-mediated regeneration strategy and mechanism of phosphorus poisoned CeO₂/TiO₂ catalysts for selective catalytic reduction of NO_x with NH₃

The development of the regeneration strategies can extend the service life of deactivated catalysts and improve resource efficiency. In this work, an acid treatment method was proposed to regenerate the P-poisoned CeO₂/TiO₂ (PCeTi) catalyst for ammonia selective catalytic reduction (NH₃-SCR) of NO_x. Catalytic activity test results showed that acid treatment could achieve the efficient regeneration of PCeTi catalyst, the regenerated PCeTi mediated with oxalic acid (PCeTi-OA) catalyst showed a 90% mineralization temperature (T₉₀) of 236 °C (T₉₀ for fresh CeTi was 232 °C) and retained the promotional effect of P species at the high temperature (>350 °C). The characterization results showed that most of the P species on the PCeTi catalyst were removed after regeneration, which restored the majority of the original Ce-O active structure, thereby promoting the Ce⁴⁺/Ce³⁺ redox cycling and inducing the formation of new oxygen vacancies. At the same time, the residual P-O structures and new oxygen vacancies could provide a large amount of acid sites, which was favorable for the adsorption and activation of NH₃. The recovered redox properties and the increased surface acidity of the PCeTi-OA catalyst were responsible for its recovered low temperature activity and superior high temperature activity, respectively.