Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Full length article Role of rubidium promotion on the nitrous oxide decomposition activity of nanocrystalline Co 3 O 4 -CeO 2 catalyst Bahaa M. Abu-Zied a,b,c, ⁎ , Soliman A. Soliman b , Abdullah M. Asiri a,c a Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia b Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt c Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia ARTICLE INFO Keywords: N 2 O decomposition Co 3 O 4 -CeO 2 catalyst Alkali metal Promoter Rb-doping Cobalt oxide ABSTRACT Rb-promoted nanocrystalline Co 3 O 4 -CeO 2 catalysts were prepared by the impregnation of the Co 3 O 4 -CeO 2 , previously prepared using the solution combustion route, with an aqueous solution of Rb 2 CO 3 (Rb/Co ratios 0.0125–0.20) and subsequent calcination at 500 °C. The obtained catalysts and the un-promoted Co 3 O 4 and Co 3 O 4 -CeO 2 catalysts have been characterized using XRD, FT-IR, SEM, TEM, XPS, H 2 -TPR and N 2 physisorption techniques. The activity of the various catalysts was tested for N 2 O direct decomposition. All the Rb-promoted catalysts exhibited better performance than the bare Co 3 O 4 -CeO 2 catalyst, where the highest activity was ob- tained using the catalyst with Rb/Co ratio of 0.025. The activity performance of the various catalysts was discussed in terms of the electronic properties modification accompanying the Rb-doping. For the optimum catalyst, further experiments were conducted in the presence of O 2 and NO in the reactor feed. 1. Introduction Nitrous oxide (N 2 O) has been recognized as a strong greenhouse gas and is said to be one of the most harmful ozone depletors [1,2]. The global warming potential (GWP) of N 2 O is 310 times higher than that of CO 2 and 21 times higher than that of CH 4 [3] emitted from both natural and anthropogenic sources. The latter, mainly, include nitric acid and adipic acid industries [3]. The catalytic decomposition process is the most effective way for the abatement of nitrous oxide emissions. For this purpose, various catalytic systems such as metals (bare and sup- ported) [4–11], metal oxides [12–20], perovskites [21,22], hydro- talcites [23–26], hexaferrites [27,28], spinels [29–44] and ion-ex- changed zeolites [45–49] have been investigated for N 2 O decomposition. Co 3 O 4 spinel has been reported as an active catalyst in many redox- reactions such as oxidation of NH 3 [50,51], CO [52,53], ethanol [54] and o-xylene [55] as well as reduction of water [56] and 4-nitrophenol H 2 O[57]. Co 3 O 4 exhibits promising activity in the oxidation of hy- drocarbons and carbon monoxide [58,59], which was attributed to the ability of cobalt oxide spinel to bind oxygen quickly and the very weak metal-oxygen bond [58]. Doping of Co 3 O 4 spinel with a small quantity of alkali [29,30,37,42–44] and alkali earth metals [39] or other oxides like lead [31], cerium [41] and zirconium [38] oxides enhance sig- nificantly the catalyst activity towards N 2 O decomposition. The promotion effect of alkali and alkali earth metals is attributed by many authors to the enhanced Co 3+ → Co 2+ reduction induced by these metals [30,40,42–45]; thus, facilitating the oxygen desorption from the catalyst surface, which is the rate determining step of N 2 O decom- position [41,48]. In this context, it was reported that promoting Co 3 O 4 with potassium ions leads to a marked reduction in the activation en- ergy, for N 2 O decomposition, from ~106 to 40 kJ/mol [60]. Asano et al. [44] ascribed the improved N 2 O decomposition of Co 3 O 4 catalyst upon doping with potassium ions to the induced oxygen desorption enhancement and the increasing number of active sites. A redox-type reaction mechanism was proposed by this research group involving the stabilization of the surface coordinately unsaturated Co 2+ species via electron donation from the highly basic oxygen, which is adjacent to potassium ions. Meanwhile, the newly-formed Co 3+ species was de- stabilized. Catalyst supports, such as alumina [58], ceria-zirconia [61] or ceria [41,58,62–64] are used to increase the catalytic activity as well as the thermal and mechanical stability of Co 3 O 4 spinel. Ceria stabilizes metal oxide supports, prevents the sintering of precious metal and stabilizes their dispersed state [64]. Addition of ceria to cobalt oxide spinel, significantly improves its activity towards N 2 O decomposition and 100% conversion, below 400 °C was exhibited by the catalyst with Ce/ Co = 0.05, as suggested by Xue et al. [41]. This improvement was as- cribed to the improved reduction of Co 3+ to Co 2+ by enhancing https://doi.org/10.1016/j.apsusc.2019.01.200 Received 28 August 2018; Received in revised form 25 December 2018; Accepted 23 January 2019 ⁎ Corresponding author at: Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt. E-mail addresses: babuzaid@kau.edu.sa, babuzied@aun.edu.eg (B.M. Abu-Zied). Applied Surface Science 479 (2019) 148–157 Available online 10 February 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved. T