Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod Ni-doped ceria nanorods for the WGS reaction: Effect of Ni distribution in methane suppression Araceli Romero-Núñez a, ⁎ , Antonio Gómez-Cortés a , Hugo Tiznado b , Gabriela Díaz a a Instituto de Física, Universidad Nacional Autónoma de México, Circuito de la Investigación Científica s/n, Cd. Universitaria, Ciudad de México, 04510, Mexico b Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, 22860, Ensenada, Mexico ARTICLE INFO Keywords: WGS reaction Ni-doped ceria Nanorods Well-defined catalysts Methanation ABSTRACT Behavior of Ni-doped CeO 2 nanorods (NR-CeNiX) in WGS reaction is evaluated. The proposed novel system simultaneously exhibits reactive (110)-ceria facets and Ni substitution. Catalytic runs for WGS reaction show greater stability, activity and selectivity towards the shift reaction regarding the traditional Ni-supported (110)- ceria system. Analysis of the surface phenomena during the catalytic reaction, followed by in-situ DRIFTS, in- dicates a formate via mechanism where ceria-nickel interaction plays a key role in the suppression of methane formation. Further surface characterization by X-Ray photoelectron spectroscopy evidences the existence of low- coordination Ni at the ceria surface suggesting that Ni location is the reason for the improvement attained. 1. Introduction WGS reaction (CO + H 2 O ↔ CO 2 +H 2 ) is an important chemical process for H 2 production and one of the key steps involved in hydrogen purification for fuel cell applications. CeO 2 -based catalysts have been widely investigated in both high and low temperature shift reactions [1]; ceria, doped or co-doped with transition metals, represents a pro- mising non-noble component for WGS. Likewise, NiO systems have also been described as potential materials for their use in WGS reaction according to model reactivity trends and comparative catalytic activ- ities on transition metals [2,3]. Therefore, Ni-CeO 2 systems have be- come attractive materials for suitable WGS catalytic reaction; indeed, great activity has been found using ceria as support when the system has been tested in WGS, whereas other supports as SiO 2 showed higher selectivity [4]. Drawbacks in selectivity concern the methane formation via CO methanation (CO + 3H 2 ↔ CH 4 +H 2 O), which represents a competing route for the shift reaction and consumes the product of interest, H 2 [5]. This points out that despite the great activity presented by Ni as active phase, its interaction with the support makes a differ- ence in selectivity for WGS reaction. A wide number of materials has been studied to overcome hindrances related to working temperature, sintering, efficiency and sensitivity to oxygen. Poor Ni dispersion as well as high Ni loadings manage methane formation. Enhancement of these systems has been achieved using additives and co-dopants to obtain stronger Ni-CeO 2 interactions and improved oxygen mobility. Approaches as the use of bimetallic Cu-Ni, or Ni-W co-doped ceria, have also been tested in order to hinder methanation process and increase WGS activity [6–8]. An enhanced CO adsorption has been obtained because of the strong Ni-support interactions in those systems, resulting in further CO methanation suppression. Additionally, surface oxygen mobility is also improved by these modifications. The dependence of defect chemistry over ceria surface terminations has been plenty demonstrated together with the large impact of ceria particle shape on reactions involving water, as WGS [9,10]. Knowledge of the surface of materials regarding morphology and composition is essential in defining their catalytic properties. The structure-property relation in terms of CeO 2 surface terminations has been largely de- monstrated by means of both experimental and simulation methods [11–15]. Great improvements have been attained by the implementa- tion of metal loading over reactive ceria with 1D-morphology [16,17]. Previous work demonstrates that the simultaneous use of 1D mor- phology and Ni-doping, i.e. exposure of reactive (110) facets along with Ni substitution, enhances redox behavior and oxygen storage capacity in Ni-doped ceria nanorods [11]. The observed enhancement in cata- lytic-related properties is achieved by synergetic effects between the two afore-mentioned characteristics. In this work, spectroscopic (Raman and XPS) and chemical (in-situ DRIFTS) techniques were applied for the comprehension of catalytic behavior of the NR-CeNiX system for WGS reaction. Catalytic activity, selectivity and stability for the WGS reaction of this system as well as in selected reference sample using same Ni charge but different distribu- tion are compared. Insights about structure-functionality relationships https://doi.org/10.1016/j.cattod.2018.09.009 Received 14 April 2018; Received in revised form 5 September 2018; Accepted 16 September 2018 ⁎ Corresponding author. E-mail address: ara_romero@ciencias.unam.mx (A. Romero-Núñez). Catalysis Today 349 (2020) 10–16 Available online 19 September 2018 0920-5861/ © 2018 Elsevier B.V. All rights reserved. T