An Investigation on the Role of Lanthanide Promoters in Promoted γ-alumina-supported Nickel Catalysts for Dry Reforming of Methane Mohamad Hassan Amin, James Tardio, Suresh K. Bhargava Centre for Advanced Materials & Industrial Chemistry, School of Applied Sciences, RMIT University, Melbourne, VIC 3001, Australia Email: mohamadhassan.amin@rmit.edu.au Abstract— The influence of promoters (Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm) on the catalytic performance of sol-gel prepared Ni/γ-Al 2 O 3 catalysts in CO 2 reforming of methane was investigated. The catalysts investigated were characterised using the following techniques: synchrotron X-Ray diffraction, X-ray Photoemission Spectroscopy, a Temperature Programmed Reduction technique and N 2 adsorption-desorption isotherms. It was found that there was almost a linear relationship between catalyst activity and the extent to which nickel was reduced in the catalysts tested. Keywords- CO 2 reforming of methane; Ni/γ γ γ-Al 2 O 3 catalyst; Promoter I. INTRODUCTION Catalytic CO 2 /dry reforming of methane (CH 4(g) +CO 2(g) ↔ 2CO (g) +2H 2(g) ) is of significant interest due to the potential environmental benefits of utilising CO 2 and due to the increased demand for syngas (H 2 , CO), [1, 2]. Research on dry reforming of methane (DRM) has focussed mostly on the development of improved materials for catalysing this reaction. Although noble metal based catalysts are usually highly active for the DRM (and experience low carbon deposition) they have the drawbacks of high cost and limited availability, hence there has been significant interest in the development of cheaper non-noble metal based catalysts. Of the non-noble metal based catalysts Ni based catalysts in particular have received a significant amount of interest due to the promising activity and selectivity that has been achieved. Ni-based catalysts however have a larger tendency to undergo deactivation via carbon deposition and sintering, which in turn significantly reduces their stability over time [1, 2]. Therefore, significant efforts have been devoted to improvements in the aforementioned areas. Approaches to achieve improvements in the activity and stability of Ni based catalysts for the dry reforming of methane have focussed mostly on the discovery of better supports [1-9] and suitable promoters. The types of promoters for Ni based catalysts that have been studied include alkali [10, 11], alkaline earth [10, 12], transition metal [10, 13-17] and rare earth metal oxides [7, 12, 18-24]. Some lanthanides have been used as promoters in Ni based catalysts for the dry reforming of methane, with Ce and La oxides being the most widely studied [23, 25-29]. The positive effects of lanthanides on catalytic activity and stability of Ni based catalysts for the dry reforming of methane have been proposed to be mostly due to the following: (1) the high oxygen storage capacity of these oxides [26], (2) improved dispersion of Ni metal on the surface of supports [26], (3) formation of nanotube and reactive filamentous carbon on Ni-based catalysts[1, 30], (4) promotion of CO 2 adsorption on the surface of the catalyst [30], (5) positive effects on the chemical environment and electronic state of Ni at the Ni-lanthanides interface [31], and (6) reduction of the chemical interaction between nickel and the support resulting in an increase in the extent to which Ni is formed (i.e. increase in the extent at which Ni(II) in precursor material is reduced) [32]. Previous studies have not been conducted on the effects of a full series of lanthanide doped catalysts on Ni based dry reforming catalysts. This is important however as it can allow direct comparison in both activity and stability of catalysts doped with lanthanides under the same process conditions. Hence in the work reported here, the effect of 10 of lanthanide elements on the activity of a Ni/Al 2 O 3 catalyst for dry reforming of methane was studied and compared under the same conditions. The lanthanide-promoted Ni/Al 2 O 3 catalyst was chosen based on previous finding’s which showed that the introduction of 2 wt% Yb as promoter to Ni/γ-Al 2 O 3 catalyst via sol-gel method leads to superior catalytic activities and stabilities [1, 33- 36]. II. EXPERIMENTALS A. Catalyst preparation Based on previous observations [1, 34] that the optimal amount of lanthanide promoter and Ni on γ-Al 2 O 3 under the DRM conditions selected for testing were 2 and 15 wt% respectively, Ni(15wt%)/γ-Al 2 O 3 containing 2wt% of lanthanide elements (Lns) including praseodymium(Pr), neodymium (Nd), samarium(Sm), europium(Eu), gadolinium(Gd), terbium(Tb), dysprosium(Dy), holmium(Ho), erbium(Er), Thulium (Tm) and non-doped catalyst were prepared using a sol-gel method as reported earlier[1]. Materials were also subjected to a reduction process to simulate that used in the activation of Ni based catalysts prior to use in catalytic dry reforming. This process involved exposing catalysts to a mixed flow of H 2 and He (10:40 mL min -1 ) at