Study on sulfur-resistant Pd-based catalysts for high-efficiency oxidation of VOCs

Sulfur-resistant stability of palladium-based catalysts is important for the long-time and efficient VOCs oxidation. Therefore, palladium-based catalysts with bimetallic alloy system could be designed to regulate the dynamic behavior of ethane (the representative of the VOCs) on active sites in the presence of H₂S. Results showed that Pd-Mo/Al₂O₃ catalyst kept a high-efficient and stable conversion of ethane (ca. 100 %) for 160 h at 500°C, indicating its excellent sulfur resistance. The sulfur-poisoning and sulfur resistance mechanism of Pd-Mo alloy was revealed by XPS, SO₂-TPD, and DFT et al. Compared with metal Pd, Pd-Mo alloy performed relatively low desorption energy of SO₂. Herein, SO₂ was prone to be removed from the surface of Pd-Mo alloy easily, resulting in the inhibition of sulfates formation. This could explain the result that the sulfur-resistant stability of 1 %Pd-Mo/Al₂O₃ catalyst was much higher than that of 1 %Pd/Al₂O₃ catalyst at 500°C. It can be uncovered that the introduction of Mo could regulate the ratio of Pd⁰ to Pd²⁺ species, which could regulate catalytic performance of catalysts in the complex catalytic oxidation-sulfur resistance system. And only when the ratio of Pd⁰/(Pd⁰+Pd²⁺) was 50 % roughly, 1 %Pd-Mo/Al₂O₃ catalyst performed the strongest sulfur resistance and exhibited significant oxidation activity towards ethane. The reaction route of H₂S could follow: Hydrogen sulfide→Organic sulfur (Sulfide)→Sulfur→Sulfur dioxide→Sulfite→Sulfate. The study revealed in this paper is crucial for the development and practical application of sulfur resistant catalysts.