Site-Selective Nitrogen-Doped α‑MnO₂ for Catalytic Oxidation of Carcinogenic HCHO in Indoor Air

Abstract

Developing high-efficiency formaldehyde\n(HCHO) catalytic oxidation\ncatalysts is of significance and practicability for indoor air decontamination.\nIt is generally considered that anionic doping is a traditional strategy\nto regulate the reaction activity of catalyst materials. However,\none of the concerns worth exploring is the recognition of doping sites\nand their impact on catalytic performance. Herein, nitrogen atoms\nare successfully introduced into the MnO₂ structure by\nhigh-temperature calcination with urea as the nitrogen source for\nthe first time. By regulating the usage of urea, nitrogen atoms are\nselectively and successfully doped into the interstitial sites and\nsubstitutional sites. Furthermore, the effect of nitrogen-doped MnO₂ on the catalytic oxidation of HCHO is studied in detail.\nResults indicate that nitrogen doping can promote the formation of\noxygen vacancies, strengthen the activation of adsorbed O₂, and enhance the adsorption of HCHO, which is conducive to catalytic\ndecomposition of HCHO. Importantly, nitrogen doping at various doping\nsites has a considerable effect on catalytic decomposition activity.\nAlthough both interstitial and substitutional nitrogen doping can\nboost the decomposition performance of HCHO, the interstitial sites\nare the most suitable doping sites in the α-MnO₂ lattice.\nThe chemical environment around the interstitial sites is favorable\nfor the creation of oxygen vacancies, as well as the adsorption/activation\nof HCHO and O₂. Interstitial nitrogen doping can dramatically\nincrease the HCHO catalytic activity of α-MnO₂, and\nthe complete catalytic decomposition temperature is reduced from 130\nto 90 °C at the condition of GHSV = 90 L/g_cat·h.\nThis study provides a facile and effective method for site-selective\nnitrogen-doping and an in-depth understanding of its effect on catalytic\nactivity.