Role of impurity components and pollutant removal processes in catalytic oxidation of o-xylene from simulated coal-fired flue gas

Yuting Wang; Xiao Zhang; Boxiong Shen; Richard Lee Smith Jr; Haixin Guo

doi:10.1016/j.scitotenv.2020.142805

Role of impurity components and pollutant removal processes in catalytic oxidation of o-xylene from simulated coal-fired flue gas

Sci Total Environ. 2021 Apr 10:764:142805. doi: 10.1016/j.scitotenv.2020.142805. Epub 2020 Oct 8.

Authors

Yuting Wang¹, Xiao Zhang², Boxiong Shen³, Richard Lee Smith Jr⁴, Haixin Guo⁵

Affiliations

¹ School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, China; Tianjin Key Laboratory of Clean Energy and Pollution Control, Hebei University of Technology, Tianjin, China.
² School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, China; Tianjin Key Laboratory of Clean Energy and Pollution Control, Hebei University of Technology, Tianjin, China. Electronic address: zhangxiao@hebut.edu.cn.
³ School of Energy and Environmental Engineering, Hebei University of Technology, Tianjin, China; Tianjin Key Laboratory of Clean Energy and Pollution Control, Hebei University of Technology, Tianjin, China. Electronic address: shenbx@hebut.edu.cn.
⁴ Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba, Sendai 980-8579, Japan; Research Center of Supercritical Fluid Technology, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan.
⁵ Graduate School of Environmental Studies, Tohoku University, Aramaki Aza Aoba 6-6-11, Aoba, Sendai 980-8579, Japan.

PMID: 33082048
DOI: 10.1016/j.scitotenv.2020.142805

Abstract

Volatile organic compounds (VOCs) emitted from coal-fired flue gas of thermal power plants have reached unprecedented levels due to lack of understanding of reaction mechanisms under industrial settings. Herein, inhibition mechanisms for catalytic oxidation of o-xylene in simulated coal-fired flue gas are elucidated with in-situ and ex-situ spectroscopic techniques considering the presence of impurity components (NO, NH₃, SO₂, H₂O). MnCe oxide catalysts prepared at Mn: Ce mass ratios of 6:4 are demonstrated to promote 87% o-xylene oxidation at 250 °C under gas hourly space velocities of 60,000 h^-1. Reaction intermediates on the catalyst surface are revealed to be o-benzoquinones, benzoates, and formate and they were stably formed under O₂/N₂ atmospheres. When either NO or NH₃ was introduced into the simulated flue gas, the formed species shifted toward formate in minutes, which indicated that changes in catalyst surface chemistry are directly related to impurity components. Presence of NH₃ in the simulated flue gas inhibited o-xylene oxidation by reducing Mn and lowering Brønsted acidity of the catalyst. Impurity components associated with pollutant removal processes (Hg⁰ oxidation and selective catalytic reduction of NO) lowered o-xylene removal efficiency. Presence of o-xylene in the flue gas had little effect on the efficiency of pollutant removal processes. Layered catalytic beds located downstream from Hg⁰/NO pollutant removal processes are proposed to lower VOC emissions from coal-fired flue gases of thermal power plants in industrial settings.

Keywords: Coal combustion; Selective catalytic reduction of NO; Transition metal catalyst; VOC catalytic oxidation; in-situ measurement.