Formaldehyde Ambient-Temperature Decomposition over Pd/Mn₃O₄–MnO Driven by Active Sites’ Self-Tandem Catalysis

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 lowtemperature 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.

Sepiolite-Supported Manganese Oxide as an Efficient Catalyst for Formaldehyde Oxidation: Performance and Mechanism

“…However, the Mn 3 O 4 structure’s diffraction reflections were seen in MnO x /Sep-H, indicating that it might produce a Mn 3 O 4 structure. The existence of Mn 3 O 4 might promote the formation of Mn-vacancies (Mn v ) or manganese defects [ 25 , 26 ]. The formation of a Mn v is conducive to the adsorption and activation of oxygen molecules, producing the reactive oxygen species [ 45 , 46 , 47 ].…”

“…The AOS of the surface Mn for MnO x /Sep-I was close to the typical oxidation state of Mn in Mn 3 O 4 (2.67), whereas MnO x /Sep-H catalysts had a lower AOS of surface Mn (2.31), suggesting that it may form the Mn-vacancies or O-vacancies. The Mn 2p3/2 spectra, which were fitted into two peaks ( Figure 7 C) at around ∼642.1 eV and ∼643.2 eV, which can be attributed to Mn 3+ and Mn 4+ species, respectively [ 21 , 25 , 26 , 48 ]. According to the XPS-41 software’s fitting results, MnO x /Sep-P, MnO x /Sep-H, and MnO x /Sep-I have Mn 3+ /Mn 4+ fractions of 1.15:1, 1.67:1, and 1:1, respectively.…”

“…Many non-noble metal oxide catalysts (such as Ce, Mn, Co, Fe, and Cu) have been produced to date for the complete oxidation of HCHO at low temperature [ 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Among them, manganese-based catalysts with various supports, plentiful valence states, structural flexibility, and functional design have garnered the most interest because of their superior catalytic activity at lower temperatures [ 6 , 22 , 23 , 24 , 25 , 26 , 27 ]. But the low catalytic activity remains a barrier that these catalysts urgently need to overcome.…”

“…These visualizations suggest a robust interaction between the active ingredients and the carrier, which is advantageous for the dispersion of active components and the formation of new bonds.Three different types of oxygen species were found in the core level O 1s spectra (Figure7B) for MnO x /Sep-H, MnO x /Sep-P, and MnO x /Sep-I. These species include the following: (i) O L or O ads (530.0-530.8 eV); (ii) surface hydroxyl species (O OH , 532.6-532.8 eV); and (iii) surface water (O H2O , 534.5-534.9 eV)[26,48,53]. Furthermore, according to the XPS-41 software's fitting results, the proportions of O L or O ads surface O OH and O H2O in MnOx/Sep-P were 6.7%, 89.6%, and 3.8%, were 10%, 85.6%, and 4.3% in MnO x /Sep-H, and were 16.4%, 80%, and 3.7% in MnO x /Sep-I, respectively.…”

Formaldehyde dissipation mechanism of active alginate gel and its application in deep air purification

“…More and more attention had been focused on ambient air quality because of the change of people's lifestyle (Peng et al, 2022). Formaldehyde (HCHO), as a most frequently detected pollutant in ambient air and a key carcinogen (Hu et al, 2024;Li et al, 2024;Sundararaman et al, 2024), has caused widespread concern (Liu et al, 2024;Xu et al, 2023).…”