Catalytic decomposition of toxic phosphine gas on the developed nickel ferrite nanocrystals supported by Halloysite nanotubes

Nickel ferrite (NiFe 2 O 4 ) nanocatalysts with trace metal nickel (Ni 0 ) as the reaction trigger were dispersedly supported by halloysite nanotubes (HNTs) to decompose toxic phosphine (PH 3 ) into yellow phosphorus and hydrogen. The mixed spinel catalyst greatly reduced the temperature to 400 °C for 99% conversion and underwent no obvious deactivation after 2 h compared with magnetite. The as-synthesized and spent catalysts were characterized by Transmission electron microscope, X-ray powder diffraction and X-ray photoelectron spectroscopy. In combination with density functional theory calculations, the PH 3 decomposition mechanism on Ni 0 @NiFe 2 O 4 /HNTs was proposed. The original plated Ni 0 triggers the reaction to form active H radicals ([ ▾ H]) contributing to the reduction of octahedral Ni(II) in NiFe 2 O 4 , and the newly generated Ni 0 determines the catalytic activity and stability. In addition, the formation of Ni 2 P is crucial to developing the stable elemental phosphorus (P) layer as the mainly active intermediate for PH 3 successive decomposition into P 4 , since P layer reduces the activation barrier of PH 3 decomposition. Particularly, the mixed crystal spinel with specific coordination (with octahedral coordinated Fe(II) and tetrahedral coordinated defects) facilitates the electron transfer among the active species to recycle the catalytic reaction. This work provides a promising approach for PH 3 air-pollution control and P recovery from the industrial off-gas.