Morphology Effect of Ceria on the Ammonia Synthesis Activity of Ru/CeO 2 Catalysts
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Morphology Effect of Ceria on the Ammonia Synthesis Activity of Ru/ CeO2 Catalysts Pengcheng Liu1 · Ruyue Niu1 · Wei Li1 · Shuang Wang1,2 · Jinping Li1 Received: 9 November 2018 / Accepted: 14 January 2019 / Published online: 7 February 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Three Ru/CeO2 catalysts with different morphologies of C eO2 (cube spheres, microspheres and nano rods) were used to evaluate the support-morphology-dependent ammonia synthesis activity. Catalytic experiments show that the Ru/CeO2–CS catalyst has higher catalytic activity (27,000 µmol g−1 h−1) than Ru/CeO2–MS (21,000 µmol g−1 h−1) and Ru/CeO2–NR (15,000 µmol g−1 h−1) under the reaction conditions of 450 °C, 3 MPa, H2/N2 = 3:1 (60 mL min−1). The transmission electron microscopy analysis showed that the dispersion of active metal Ru is affected by the morphology of CeO2. Brunauer– Emmett–Teller indicates that the 3–5 nm the pore size of C eO2 supports contributes to the active metal Ru enters the pores of the CeO2 support, which improves the dispersion of Ru and prevents the sintering and agglomeration of Ru in some extent. TPR studies shown that the reduction of ruthenium oxide is influenced by the morphology of CeO2. XPS and CO2-TPD demonstrated that the Ru/CeO2–CS catalyst exhibited higher surface oxygen vacancies, higher basic site density and lower Ru binding energy, indicating that Ru nanoparticles in Ru/CeO2–CS is more electron-rich and are more capable of backdonating electrons to adsorbed N 2 and subsequently activate N 2. Our results indicate that the morphology effect of the C eO2 supports on the Ru/CeO2 catalyst is related to the pore size distribution and the surface oxygen vacancies of the C eO2 supports, ratio of Run+, basic site density. Graphical Abstract
The CeO2–CS (cube spheres) morphology facilitated the dispersion of the active metal Ru and the 3 nm the pore size of CeO2–CS contributed to the Ru enters the pores of the support. And the Ru/CeO2–CS catalyst exhibited higher surface Electronic Supplementary Material The online version of this article (https://doi.org/10.1007/s10562-019-02674-1) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
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oxygen vacancies and lower Ru binding energy, which enhanced the adsorption of hydrogen and nitrogen species and thus weakened the N≡N bond. Keywords Ammonia synthesis · Ru-based catalyst · Cerium oxide morphology · Catalytic performance
1 Introduction According to the published, Ru-based catalysts are ideal for ammonia synthesis due to their more active performance under mild conditions (lower temperatures and pressures) than conventional iron-based catalysts [1–5]. Followed related studies have focused on the development of the size and shape of the active metal Ru [6], promoters [7, 8] (Cs+, K+, Ba2+) and supports [9–11]. Especially, the exploration of support has become one of
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