Dual Promotional Effects of TiO2-Decorated Acid-Treated MnO x Octahedral Molecular Sieve Catalysts for Alkali-Resistant Reduction of NO x

Lijun Yan; Yundong Gu; Lupeng Han; Penglu Wang; Hongrui Li; Tingting Yan; Sanchai Kuboon; Liyi Shi; Dengsong Zhang

doi:10.1021/acsami.9b01291

Dual Promotional Effects of TiO₂-Decorated Acid-Treated MnO _x Octahedral Molecular Sieve Catalysts for Alkali-Resistant Reduction of NO _x

ACS Appl Mater Interfaces. 2019 Mar 27;11(12):11507-11517. doi: 10.1021/acsami.9b01291. Epub 2019 Mar 12.

Authors

Lijun Yan¹, Yundong Gu¹, Lupeng Han¹, Penglu Wang¹, Hongrui Li¹, Tingting Yan¹, Sanchai Kuboon², Liyi Shi¹, Dengsong Zhang¹

Affiliations

¹ Department of Chemistry, School of Environmental and Chemical Engineering, Research Center of Nano Science and Technology, College of Sciences , Shanghai University , Shanghai 200444 , P. R. China.
² National Nanotechnology Center , National Science and Technology Development Agency , 111 Thailand Science Park , Khlong Luang , Pathum Thani 12120 , Thailand.

PMID: 30817117
DOI: 10.1021/acsami.9b01291

Abstract

Alkali metals generated during waste incineration in power stations are not conducive to the control of nitrogen oxide (NO _x) emission. Hence, improved selective catalytic reduction of NO _x with ammonia (NH₃-SCR) in the presence of alkali metals is a major issue for practical NO _x removal. In this work, we developed a novel TiO₂-decorated acid-treated MnO _x octahedral molecular sieve (OMS-5(H)@TiO₂) catalyst with improved alkali-resistant NO _x reduction at low temperature, and the dual promotional effects of OMS-5(H)@TiO₂ catalysts were clarified. It was found that the special structure of the acid-treated MnO _x octahedral molecular sieve (OMS-5(H)) was responsible for the trapping of alkali metals and high deNO _x activity at low temperature. Subsequently, the decoration by TiO₂ further improved the redox properties by accelerating the high ratio of Mn⁴⁺ and O_α on the surface of the highly active (OMS-5(H)@TiO₂) catalyst. Moreover, a thorough mechanism study via in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTs) demonstrated that the acid treatment led to remarkable increment of acid sites, which enabled the catalyst to resist alkali metals in the form of ion exchange. Meanwhile, the decoration of TiO₂ further increased the strength of the Lewis acid sites, assisting more active intermediate species to effectively take part in the deNO _x reaction. Besides, a "fast SCR" process was observed to certify that the decoration of TiO₂ promoted the improvement of low-temperature activity in the presence of alkali metals. The dual effects combining OMS-5(H) with TiO₂ decoration in terms of alkali metal resistance and high catalytic activity at low temperature proved that the high-performance deNO _x catalyst was successfully developed in this work. The work paves a way for the development of superior low-temperature SCR catalysts with improved NO _x reduction efficiency in the presence of alkali metals.

Keywords: TiO2 decoration; alkali resistant; environmental catalysis; octahedral molecular sieves; selective catalytic reduction.