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, H 2 -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-MnO 2) 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. Display Omitted • Crystalline phase of MnO x supported on the palygorskite depends on the precursor. • δ-MnO 2 uniformly coated on palygorskite (like a capsule) was synthesized. • δ-MnO x /PG showed excellent performance for HCHO removal at 25–150 °C. • The mechanism on HCHO removal over MnO x /PG was elucidated. [ABSTRACT FROM AUTHOR]