Sulfur resistance mechanism of PdSx catalysts in catalytic oxidation of toluene

Abstract

Toluene is a main component of volatile organic compounds (VOCs) in the refinery flue gas, and catalytic oxidation stands out as an efficient and energy-saving method for eliminating toluene. Nevertheless, the presence of SO₂ within VOCs can result in the irreversible deactivation of the catalyst. The enhancement of the catalyst's sulfur resistance is imperative. Here, we prepared PdS_x/Hβ-zeolite catalysts with exceptional sulfur resistance by using the gas-phase sulfidation method. The PdS_x/Hβ-zeolite exhibits remarkable activity under the experimental conditions of 1000 ppm toluene and 21% O₂, with a sustained conversion rate of toluene exceeding 76% even after the introduction of SO₂. Based on the characterization of catalysts and resistance experiments, the reaction mechanism and sulfur resistance mechanism were studied. Pd⁰ serves as the active catalytic center, and the catalytic oxidation mechanism follows the Mars–van Krevelen (MVK) mechanism. The high sulfur resistance of the PdS_x/Hβ-zeolite catalyst is attributed to the PdS_x species, which is considered as the sulfur resistance center. The presence of PdS_x facilitates SO₂ desorption, thereby improving the catalyst's sulfur resistance. This work will provide new insights into enhancing precious metal catalysts' resistance to sulfur.