Dynamic Evolution of Mn-O Site and ROS Formation in Room-Temperature Formaldehyde Oxidation over Phase-Dependent MnO₂

Area of Science:

• Environmental Chemistry
• Materials Science
• Catalysis

Background:

• Formaldehyde (HCHO) is a significant indoor air pollutant and carcinogen.
• Manganese dioxide (MnO2) shows promise for HCHO removal, but its catalytic mechanisms at room temperature are not fully understood.
• Understanding active site dynamics and reactive oxygen species (ROS) formation is crucial for optimizing MnO2 catalysts.

Purpose of the Study:

• To investigate the catalytic performance and mechanism of various MnO2 crystal phases for formaldehyde removal.
• To elucidate the dynamic evolution of active sites and ROS formation during HCHO oxidation on MnO2 catalysts under ambient conditions.
• To provide theoretical guidance for designing advanced MnO2-based materials for air purification.

Main Methods:

• Screening of different MnO2 crystal phases for HCHO catalytic oxidation.
• In situ characterization techniques including Raman, EPR, TPD-MS, and DRIFTS to monitor reaction intermediates and species.
• Density Functional Theory (DFT) calculations to analyze electronic structure and orbital interactions.

Main Results:

• δ-MnO2 demonstrated superior catalytic activity for HCHO removal, achieving near-complete conversion.
• δ-MnO2 exhibited stable performance over 48 hours at room temperature.
• In situ studies and DFT calculations revealed the dynamic evolution of [MnO6] octahedra, ROS, and reaction intermediates, clarifying the catalytic mechanism.

Conclusions:

• δ-MnO2 is a highly effective catalyst for ambient formaldehyde removal.
• The study provides a deeper mechanistic understanding of MnO2 catalytic activity, particularly concerning active site dynamics and ROS generation.
• Findings offer valuable insights for the rational design of high-performance MnO2 catalysts for indoor air quality improvement.