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.