The Impact of Ce-Zr Addition on Nickel Dispersion and Catalytic Behavior for CO2 Methanation of Ni/AC Catalyst at Low Temperature

Hindawi Journal of Chemistry Volume 2017, Article ID 4361056, 11 pages https://doi.org/10.1155/2017/4361056 Research Article The Impact of Ce-Zr Addition on Nickel Dispersion and Catalytic Behavior for CO2 Methanation of Ni/AC Catalyst at Low Temperature Minh Cam Le, Khu Le Van, Thu Ha T. Nguyen, and Ngoc Ha Nguyen Theoretical and Physical Chemistry Division, Faculty of Chemistry, Hanoi National University of Education, Hanoi 1000, Vietnam Correspondence should be addressed to Minh Cam Le; Received 8 November 2016; Revised 31 January 2017; Accepted 26 February 2017; Published 13 March 2017 Academic Editor: Anton Kokalj Copyright © 2017 Minh Cam Le et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The CO2 methanation was studied over 7 wt.% nickel supported on Ce0.2 Zr0.8 O2 /AC to evaluate the correlation of the structural properties with catalytic performance. The catalysts were investigated in more detail by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A sample of 7 wt.% nickel loading supported on activated carbon (AC) was also prepared for comparison. The results demonstrated that the ceria-zirconia solid solution phase could disperse and stabilize the nickel species more effectively and resulted in stronger interaction with nickel than the parent activated carbon phase. Therefore, 7% Ni/Ce0.2 Zr0.8 O2 /AC catalyst exhibited higher activity for CO2 reduction than 7% Ni//AC. It can attain 85% CO2 conversion at 350∘ C and have a CH4 selectivity of 100% at a pressure as low as 1 atm. The high activity of prepared catalysts is attributed to the good interaction between Ni and Ce0.2 Zr0.8 O2 and the high CO2 adsorption capacity of the activated carbon as well. 1. Introduction Increasing emissions of carbon dioxide arising from the widespread production of energy from fossil fuels is a critical matter regarding greenhouse gases effect and, thus, global warming [1, 2]. Technologies including possible reduction or conversion of CO2 give valuable advantages for protecting the environment by recycling CO2 effectively based on the catalytic methanation [3–5]. Conversion of carbon oxides into methane CO2 + 4H2 󴀘󴀯 CH4 + 2H2 O (1) is a exothermic reaction with ΔH∘ = −165 kJ/mol. The exothermic character of the methanation process causes problems with respect to an exact control of the reaction temperature, which can result in a further increased conversion of CO2 [6]. Therefore, the development of catalysts for methanation of carbon dioxide is the key factor. Recently, results of Beuls et al. [7] and Jacquemin et al. [8] give evidences that at low temperature (<200∘ C) and atmospheric pressure the reaction takes place with very high selectivity. Various metal-based catalysts have been studied for the CO2 methanation reaction such as Fe [9], Ru [10], Co [11], Rh [12, 13], Pd [14, 15], Pt [16], and Ni [16, 17] supported on several oxides (SiO2 [18], TiO2 [19], Al2 O3 [20, 21], ZrO2 [22, 23], CeO2 [24], and Ce-Zr mixed oxides [25, 26]) or porous materials (HZSM-5 [27], HUSY [28, 29]). Although the noble metals (Ru, Rh, and Pd) exhibit better activity, they are too expensive for a large-scale industrial application; therefore nonnoble metal-based catalysts are often preferred. Among group VIII metals, the nickel-based catalysts have covered the larger part of published works [30–35] due to their high catalytic activity, high selectivity for methane, and relatively low price. The main problems of Ni-based catalysts are the deactivation due to carbon deposition and poor stability at high temperature [29, 34]. Therefore, great efforts have been made to develop an effective promoted Ni-based catalyst which exhibits both high activity and high thermal stability in CO2 methanation. Firstly, adding catalyst promoters, Trovarelli et al. [36, 37], who compared the catalytic activity of several Rh-based catalysts using different types of supports, CeO2 , SiO2 , Ta2 O2 , 2 and Nb2 O5 , found that the catalytic activity and thermal stability of the catalyst could be improved by using CeO2 or ZrO2 as the support. Rynkowski et al. [38] reported that Ni (or Ru) supported on Al2 O3 (or SiO2 ) which is promoted with CeO2 possessed an improved activity for CO2 hydrogenation into methane. The CO2 methanation reaction using Ni supported on Ce-Zr mixed oxides catalysts was for the first time investigated by Ocampo et al. [39–41]. They found that these catalysts exhibited excellent levels of activity, selectivity, and stability for CO2 methanation. Liu et al. [34] found that CeO2 promoted the dispersion of metal Ni on the support and prevented the nickel species from sintering leading to the high activity and good stability. In addition, the presence of oxygen vacancies on the support, such as CeO2 , will create the additional driving force for the CO2 conversion to CO in reducing atmosphere. Results from [42] seem to indicate that Ce𝑥 Zr1−𝑥 O2 (0.5 < 𝑥 < 0.8) solid solution has a superior performance in terms of overall reduction and total oxygen storage. Secondly, choosing a porous support, Wei and Jinlong [43] had written an overview about methanation of carbon dioxide. The article focuses on recent developments in catalytic materials, novel reactors, and reaction mechanism for methanation of CO2 . The authors demonstrated that the different interactions that can be established between the metal and the support shall influence the catalytic properties of the active metal sites. Jwa et al. [33] who studied the hydrogenation of carbon oxides (CO and CO2 ) into methane over Ni/𝛽-zeolite catalysts have the same result. In order to increase catalytic activity of the methanation, it is necessary to enhance CO2 supply at the surface of the catalyst. Some researchers have studied nickel supported on porous alumina [44] or MCM41 [45, 46] catalysts and their results showed that the porous structure of the supports improved the dispersion of the nickel species on their surfaces and prevented the nickel species from sintering. Recently, activated carbon has been investigated by various research groups because of its large surface area, surface functionalization, and low energy requirements for regeneration. Their results indicated that activated carbon (AC) is a promising adsorbent for CO2 , at ambient conditions [47–49]. Vargas et al. [47] studied carbon dioxide adsorption at 273 K on three series of activated carbon monoliths prepared by impregnation of African palm shells. Their results showed that the carbon monoliths obtained can adsorb as much CO2 as 5.8 mmol CO2 g−1 at 1 bar and 273 K. Wickramaratne et al. [48, 49] indicated that the activated carbon spheres exhibited very high CO2 uptake of 8.9 and 4.55 mmol/g at 0∘ C and 25∘ C under atmospheric pressure, resp (...truncated)