Formaldehyde Ambient-Temperature Decomposition over Pd/Mn<sub>3</sub>O<sub>4</sub>–MnO Driven by Active Sites’ Self-Tandem Catalysis
Xiaohe Liu, Tong Lu, Xinguo Jiao, Zeyu Jiang, Changwei Chen, Yadi Wang, Yanfei Jian, Chi He
Abstract
The widespread presence of formaldehyde (HCHO) pollutant has aroused significant environmental and health concerns. The catalytic oxidation of HCHO into CO 2 and H 2 O at ambient temperature is regarded as one of the most efficacious and environmentally friendly approaches; to achieve this, however, accelerating the intermediate formate species formation and decomposition remains an ongoing obstacle. Herein, a unique tandem catalytic system with outstanding performance in low-temperature HCHO oxidation is proposed on well-structured Pd/Mn 3 O 4 –MnO catalysts possessing bifunctional catalytic centers. Notably, the optimized tandem catalyst achieves complete oxidation of 100 ppm of HCHO at just 18 °C, much better than the Pd/Mn 3 O 4 (30%) and Pd/MnO (27%) counterparts as well as other physical tandem catalysts. The operando analyses and physical tandem investigations reveal that HCHO is primarily activated to gaseous HCOOH on the surface of Pd/Mn 3 O 4 and subsequently converted to H 2 CO 3 on the Pd/MnO component for deep decomposition. Theoretical studies disclose that Pd/Mn 3 O 4 exhibits a favorable reaction energy barrier for the HCHO → HCOOH step compared to Pd/MnO; while conversely, the HCOOH → H 2 CO 3 step is more facilely accomplished over Pd/MnO. Furthermore, the nanoscale intimacy between two components enhances the mobility of lattice oxygen, thereby facilitating interfacial reconstruction and promoting interaction between active sites of Pd/Mn 3 O 4 and Pd/MnO in local vicinity, which further benefits sustained HCHO tandem catalytic oxidation. The tandem catalysis demonstrated in this work provides a generalizable platform for the future design of well-defined functional catalysts for oxidation reactions.