Unveiling the Influence Mechanism of Impurity Gases on Cl-Containing Byproducts Formation during VOC Catalytic Oxidation

Volatile organic compounds (VOCs) emitted from industry processes are often accompanied by the discharge of impurity gases, which would affect the active sites and further pose great influence on the catalytic performance, even inducing toxic byproduct formation, bringing more serious threat to human health and the ecological environment. Furthermore, VOCs degradation byproducts would be changed with the alteration of catalysts, especially metal-organic frameworks (MOFs)-based catalysts, over which various degradation byproducts could be generated due to the precursor residual. Herein, an acid-modified Zr-MOF, UiO-67, supported Pd catalyst was synthesized and optimized as an example to explore the influence mechanism of impurity gases (H₂O and CO) on o-xylene degradation intermediates. It was found that the impurity gases had a great influence on the generation of Cl-containing byproducts, which formed due to the presence of residual Cl in the frameworks. Meanwhile, the influence mechanism was experimentally and theoretically studied. It was revealed that the introduction of H₂O weakened the formation of energy barriers for Cl-containing byproduct generation, resulting in the spontaneous generation of Cl-containing byproducts. Conversely, the addition of CO improved the energy barrier of the Cl-containing byproduct formation rate-determined step, chlorine addition reaction (*C₆H₃CH₃CH₃ + Cl → *C₆H₃ClCH₃CH₃, *C₆H₄CH₃CH₂ + Cl → *C₆H₄CH₃CH₂Cl), inhibiting Cl-containing byproducts formation. This study may provide guidance for the application of MOFs-based catalysts for VOCs elimination in actual discharge conditions.