Short Communication Tunable ceria–zirconia support for nickel–cobalt catalyst in the enhancement of methane dry reforming with carbon dioxide Moom Sinn Aw a, ⁎, Ilja Gasan Osojnik Črnivec a , Albin Pintar a,b a Laboratory for Environmental Sciences and Engineering, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia b Centre of Excellence “Low Carbon Technologies”, SI-1001 Ljubljana, Slovenia abstract article info Article history: Received 19 February 2014 Received in revised form 31 March 2014 Accepted 1 April 2014 Available online 12 April 2014 Keywords: Glycol-thermal synthesis Ceria–zirconia Bi-metallic catalyst support Nickel–cobalt Methane dry reforming with carbon dioxide Coking Ceria–zirconia mixed oxides (CeZr) were glycol-thermally synthesised as nano-crystalline supports with tunable ratios for the anchoring of nickel–cobalt (Ni–Co) catalyst to enhance methane dry reforming (MDR) reaction with carbon dioxide. High conversion of methane (90%) and carbon dioxide (92%), good output (H 2 = 32%; CO = 44%), and selectivity and stability of syngas prove the effectiveness of the catalyst deposited on this support. 80:20 for Ce:Zr was identified as the optimal ratio to attain active and stable catalytic performance in MDR, with a low coking content of 0.47 wt.%. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Depletion in oil and natural gas summons the need for sustainable energy resources. To date, methane dry reforming (MDR) reactions are garnering much attention due to the importance of syngas for meth- anol and the Fischer–Tropsch syntheses to generate renewable fuels. As such, catalysts are continually developed for this purpose [1–3]. Howev- er, coking is a significant problem, especially for transition metals such as nickel (Ni) and (Co) metal solids. Introducing catalyst support into the reaction system is a good measure to resolve this issue, since catalyst support allows better dispersion of active metals on its surface. In pur- suit for an excellent support for Ni–Co catalyst in MDR, ceria (Ce) and zirconia (Zr) were chosen. Ce has been extensively explored for oxida- tive and three-way catalysis in fuel cells, by virtue of its high O 2 storage capacity, low cost, technical viability in industrial processes for CO 2 ac- tivation, NO removal, low temperature water–gas shift reaction and wet oxidation processes [4–7]. Zirconia (Zr) possesses attractive features, namely, high mechanical strength, chemical robustness and thermal stability for heterogeneous catalysis [8]. Since 1990s, numerous studies were dedicated to ceria–zirconia mixed oxides, CeO 2 –ZrO 2 (CeZr), whereby the incorporation of Zr into Ce species was found to induce substantial defects and mechanical strain in their nano- structure [9]. Numerous approaches have been employed to produce CeZr solid solutions, for instance, ball milling, sol–gel, co-precipitation, Pechini method and microwave-hydrothermal synthesis [10,11]. However, these strategies bear certain drawbacks, including high cost which inhibits productivity, excessively time-consuming process, or final grain size that is too large [12,13]. Based on our previous work, glycol-thermal autoclaving with ethylene glycol was found to be a sim- ple, facile, practical and inexpensive approach for stable nucleation and growth of CeZr nanocrystals with sufficiently small particle size [14,15]. These findings led us to investigate the glycol-thermally synthesised CeZr solid solutions with modifiable Ce to Zr ratios (70:30, 80:20 and 90:10), to improve the dispersion of Ni–Co metals and to identify the optimal Ce:Zr ratio (which was previously not done before) for syner- gistic support properties and better catalytic performance. Upon synthesis, physico-chemical characterisation and activity tests were conducted to examine the intrinsic properties of the fresh and spent catalysts pre- and post-22 h MDR reaction. 2. Experimental section 2.1. Synthesis of ceria–zirconia (CeZr) mixed oxide support Glycol-thermal synthesis using ethylene glycol (EG) was employed for the synthesis of ceria–zirconia solid solutions, i.e. CeO 2 –ZrO 2 (weight ratio = 70:30, 80:20, 90:10; denoted as CeZr (70:30), (80:20), (90:10), respectively) as the support for our bi-metallic Ni–Co catalyst. 1 mL Milli-Q water, 1 mL propionic acid (Merck, N 99% purity) and 15 mL Catalysis Communications 52 (2014) 10–15 ⁎ Corresponding author at: L-05, Laboratory for Environmental Sciences and Engineering, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia. Tel.: +386 (0)1/476 02 49; fax: +386 (0)1/476 04 60. E-mail address: moom.sinn.aw@ki.si (M.S. Aw). http://dx.doi.org/10.1016/j.catcom.2014.04.001 1566-7367/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom