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

Abstract

Nickel ferrite (NiFe2O4) nanocatalysts with trace metal nickel (Ni0) as the reaction trigger were dispersedly supported by halloysite nanotubes (HNTs) to decompose toxic phosphine (PH3) 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 PH3 decomposition mechanism on Ni0@NiFe2O4/HNTs was proposed. The original plated Ni0 triggers the reaction to form active H radicals ([▾H]) contributing to the reduction of octahedral Ni(II) in NiFe2O4, and the newly generated Ni0 determines the catalytic activity and stability. In addition, the formation of Ni2P is crucial to developing the stable elemental phosphorus (P) layer as the mainly active intermediate for PH3 successive decomposition into P4, since P layer reduces the activation barrier of PH3 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 PH3 air-pollution control and P recovery from the industrial off-gas.