Self-heating photothermal synergy in MnO2-catalyzed n-propylamine oxidation: From photothermal activation to degradation pathway elucidation

n-Propylamine, a toxic nitrogen-containing volatile organic compound (NVOC), poses health and environmental risks alongside intense odours. Its photothermal catalytic oxidation is effective, but the synergy between photocatalysis and thermocatalysis remains unclear. This study compared five MnO 2 catalysts with different tunnel structures (α, β, γ, δ, τ) for ambient-temperature self-heating photothermal oxidation of n-propylamine. Remarkable crystal phase-dependent catalytic performance was observed, with α-MnO 2 exhibiting superior activity achieving 93.6% CO 2 yield and, notably, 100% N 2 selectivity without detectable NO x emissions. Mechanistic studies reveal a photothermal coupled catalysis mechanism: light-induced excitation weakens Mn–O bonds and activates lattice oxygen, while the photothermal effect simultaneously promotes charge transfer and drives thermocatalytic decomposition.   Furthermore, in-situ DRIFTS combined with mass spectrometry and ion chromatography elucidated a bifurcated degradation pathway: C–N bond cleavage yielding propyl radicals (undergoing stepwise oxidation to CO 2 via alcohols, aldehydes, and carboxylic acids) and amino radicals (selectively converted to N 2 via photo-iSCR or NH 3 -SCO mechanisms); concurrently, a dehydrogenation route produces propionitrile as a transient intermediate that eventually feeds into the main oxidation cascade. This work provides fundamental insights into the crystal structure-dependent photothermal catalytic performance and establishes a comprehensive mechanistic framework for n-propylamine oxidation, offering rational guidelines for designing high-performance catalysts for NVOC abatement.