Molecular Catalysis 497 (2020) 111204 Available online 20 September 2020 2468-8231/© 2020 Elsevier B.V. All rights reserved. Low-temperature formaldehyde oxidation over manganese oxide catalysts: Potassium mediated lattice oxygen mobility Abubakar Yusuf a , Yong Sun b , Colin Snape c , Jun He a, b, *, Chengjun Wang d, **, Yong Ren e , Hongpeng Jia f a International Doctoral Innovation Center, University of Nottingham Ningbo China, Ningbo, China b Department of Chemical and Environmental Engineering, University of Nottingham Ningbo China, Ningbo, China c Faculty of Engineering, University of Nottingham, University Park, Nottingham, United Kingdom d College of Resources and Environmental Science, South-Central University for Nationalities, Wuhan, China e Department of Mechanical, Materials and Manufacturing Engineering, University of Nottingham Ningbo China, Ningbo, China f Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China A R T I C L E INFO Keywords: formaldehyde manganese oxide catalyst potassium catalytic oxidation lattice oxygen ABSTRACT Manganese oxide catalysts with self-modulating K + content and tunable concentration of lattice oxygen and Mn 4+ were synthesized and investigated for HCHO oxidation. The preparation method affects the physico- chemical properties and catalytic activity of the catalysts. Herein, the role of K + in enhancing the lattice oxygen mobility of manganese oxide catalysts for enhanced formaldehyde (HCHO) is presented. The presence of K + enhances the redox properties of Mn and promotes catalytic activity by enhancing the mobility of the lattice oxygen and sustaining the availability of surface active oxygen to sustain the reaction. Catalytic activity was observed to improve with increasing K + content and the surface concentration of lattice oxygen and Mn 4+ . A drastic reduction in catalytic activity was observed in the acid-treated samples, with low K + concentration. Characterization results indicate that the presence of K + enhances activity and mobility of the lattice oxygen by the weakening the Mn-O bond in manganese oxide and promotes the redox properties of the catalyst. The absence of K + impacted the mobility of the lattice oxygen and the ability of the catalyst to supplement the consumed oxygen species, resulting into reduced catalytic activity and deactivation in the room-temperature (30 ◦ C) activity and stability test. Introduction The removal of formaldehyde (HCHO) – a known and confrmed carcinogenic substance, from the indoor environment is pertinent to improving indoor air quality and comfort. Satisfactory pieces of evi- dence have revealed that exposure to HCHO over a long period, can lead to nasopharyngeal cancer, sinonasal cancer, and leukaemia [1]. Some of its major indoor sources include wooden works, furniture and con- struction materials; others may include indoor combustion processes, such as cooking, smoking, and heating [2,3]. Amongst the HCHO removal techniques, catalytic oxidation seems more promising, as the complete conversion of HCHO into CO 2 and H 2 O can be achieved [4]. Catalysts containing noble metals are promising in this respect, and various techniques devised have enhanced their low to room temperature activity for HCHO oxidation. Alkali metals doping, mainly Na + and K + , has been demonstrated to be a very effective strategy [5–8]. Bai et al.[5] observed a promotional effect of K + addition on the activity of Ag/Co 3 O 4 catalyst for HCHO by promoting the generation of surface OH-. Zhang et al.[8] observed a phenomenal improvement in the catalytic activity of Pt/TiO 2 , after its treatment with Na. Total oxidation of HCHO was achieved at room temperature over the Na modifed Pt/TiO 2 , in contrast to 150 ◦ C for the untreated catalyst. In another study, Na + was observed to promote the stabilization and dispersion of Pd on TiO 2 support, and enhanced its activity by facilitating the acti- vation of chemisorbed oxygen and OH groups to achieve room tem- perature oxidation of HCHO (compare to 120 ◦ C for unmodifed Pd/TiO 2 ) [7]. Similar promotional effects of Na + were observed by Nie at al.[6] for HCHO oxidation on Pt supported TiO 2 catalysts. However, * Correspondence author at: International Doctoral Innovation Center, University of Nottingham Ningbo China, Ningbo, China. ** Correspondence author. E-mail addresses: jun.he@nottingham.edu.cn (J. He), cjwang@scuec.edu.cn (C. Wang). Contents lists available at ScienceDirect Molecular Catalysis journal homepage: www.journals.elsevier.com/molecular-catalysis https://doi.org/10.1016/j.mcat.2020.111204 Received 28 May 2020; Received in revised form 13 August 2020; Accepted 4 September 2020