A highly efficient catalyst of palygorskite-supported manganese oxide for formaldehyde oxidation at ambient and low temperature: Performance, mechanism and reaction kinetics

A series of palygorskite-supported manganese oxide (MnO_x/PG) catalysts were prepared by a precipitation method using different manganese precursor. The as-prepared MnO_x/PG catalysts were used to evaluate the catalytic oxidation of HCHO and characterized by BET, XRD, TG, Raman spectroscopy, TEM, H₂-TPR, XPS, and chemical titration. The results showed that the crystalline phase, distribution and Mn valence states of MnO_x on the surface of PG depended on the precursors. Birnessite-type manganese oxide (δ-MnO₂) formed and uniformly coated on the surface of PG when potassium permanganate (PP) was used as the precursor. The MnO_x/PG-PP catalyst showed the best catalytic activity for HCHO removal at low temperature among these catalysts and achieved complete HCHO conversion at 150 °C. More importantly, the dynamic single-pass removal efficiency of MnO_x/PG-PP catalyst for ppm-level HCHO oxidation was as high as 95% under high GHSV (300 L/g·h) at ambient temperature. MnO_x/PG-PP catalyst also exhibited excellent cycling stability and long-term activity at low and ambient temperature. The kinetic results of MnO_x/PG-PP catalyst showed that the oxidation of HCHO followed the Mars-van Krevelen mechanism. The possible reaction pathway of HCHO oxidation was proposed based on in situ DRIFTS and TPSR studies. The large specific surface area, highly distributed active component, a high proportion of Mn⁴⁺ species, and lattice oxygen content are responsible for the high catalytic activity of MnO_x/PG-PP for oxidation of formaldehyde. This work developed a natural mineral supported manganese oxide as an inexpensive and efficient catalyst for the purification of HCHO in industrial or indoor air environment.