Mechanochemical synthesis of ZnO.Al 2 O 3 powders with various Zn/Al molar ratios and their applications in reverse wate
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RESEARCH ARTICLE
Mechanochemical synthesis of ZnO.Al2O3 powders with various Zn/Al molar ratios and their applications in reverse water-gas shift reaction Zeinab Sakhaei 1 & Mehran Rezaei 2 Received: 8 September 2020 / Accepted: 3 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract ZnO.Al2O3 powders with various Zn/Al molar ratios were prepared via a solid-state reaction using a mechanochemical synthesis method, and the selected powder with a ZnO/Al2O3 molar ratio of 1 was used as support for the preparation of 15% Ni/ ZnO.Al2O3 catalyst. The activity of the prepared catalyst was studied in the reverse water-gas shift (RWGS) reaction. The synthesized samples were characterized by XRD, BET, TGA/DTA, TPR, FTIR, and SEM techniques. The results indicated that the prepared powders possessed mesoporous structure with pores having small diameters with crystallite sizes in the nanometer range (6.35–12.08 nm). The results showed that the increment in Zn/Al molar ratio reduced the BET area and the pure Al2O3 powder possessed the highest BET area (235.4 m2 g−1). The results also indicated that the rise of calcination temperature remarkably decreased the BET area. The prepared nickel-based catalyst also exhibited a high activity in RWGS reaction. Keywords Solid state . Mechanochemical synthesis . Reverse water-gas shift . ZnO . Al2O3
Introduction Carbon dioxide can be considered as one of the most important greenhouse gasses in the atmosphere that can accelerate the global warming and climate change (Chen et al. 2004a; Ishito et al. 2016; Chen et al. 2017). The CO2 capture and its storage in geological formations such as depleted gas reservoirs are considered as an effective method for reducing the negative impact of carbon dioxide (Chen et al. 2000; PastorPérez et al. 2018). In addition, the use of CO2 as a feedstock for the synthesis of useful chemicals such as CO, CH4, and methanol is another alternative method (Fornero et al. 2017; Wang et al. 2017). The mixture of H2 and CO, synthesis gas, can be employed for the production of long-chain hydrocarbons using the gas to liquid process (Fischer-Tropsch reaction) (Chen and Cheng 2002). To adjust the H2/CO ratio that can be used in these processes, the reforming of
hydrocarbons with steam along with water and reverse water-gas shift reactions (WGS and RWGS) can be used (Chen et al. 2003; Stone and Waller 2003; Fornero et al. 2017; Wang et al. 2017; Pastor-Pérez et al. 2018). RWGS reaction (Eq. (1)) is a key step in many hydrogenation processes of CO2 such as methanation and CH3OH synthesis reactions [10–12]. RWGS reaction is an endothermic reaction and needs high reaction temperature to achieve high conversion. However, working at high temperature decreases the CO selectivity and the development of a highly active catalyst at low reaction temperature is still a research challenge (Yang et al. 2018). In this process, the CO2 methanation reaction (Eq. (2)) competes with the RWGS, as a parallel unwanted reaction (Pettigrew et al. 1994; Pastor-Pé
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