Applied Catalysis A: General 514 (2016) 114–125 Contents lists available at ScienceDirect Applied Catalysis A: General jou rn al hom epage: www.elsevier.com/locate/apcata Effect of nitric oxide on the formation of cobalt–aluminum oxide structure from layered double hydroxide and its further transformation during reductive activation Alexander A. Khassin a,b,∗ , Irina I. Simentsova b , Alexander N. Shmakov a,b , Natalia V. Shtertser b,a , Olga A. Bulavchenko b,a , Svetlana V. Cherepanova b,a a Novosibirsk National Research University, 2, Pirogova str., Novosibirsk, Russia b Boreskov Institute of Catalysis SB RAS, 5, Lavrentieva pr., Novosibirsk, Russia a r t i c l e i n f o Article history: Received 23 October 2015 Received in revised form 9 January 2016 Accepted 11 January 2016 Available online 14 January 2016 Keywords: Cobalt Layered double hydroxide Nitric oxide Fischer–Tropsch synthesis a b s t r a c t The presence of nitric oxide NO in the gas phase was shown to decrease the decomposition rate of the hydrotalcite-like Co–Al LDH phase in the catalysts prepared by co-precipitation or deposition on Al 2 O 3 under the condition of urea hydrolysis. The decrease in LDH decomposition rate is related to the formation of a more crystallized phase of the spinel-like Co–Al oxide due to the ability of nitric oxide to transfer oxygen in consecutive reactions of the oxidation to NO 2 and reduction to NO. The difference in the coherent scattering domain size of the catalyst samples precalcined in the presence of NO or in a pure inert gas is retained at all consecutive steps of the reductive heat treatment in hydrogen: after the formation of a cubic phase of the (Co, Al)O oxide and its reduction to metallic cobalt. The observed changes in the degree of crystallinity and dispersion of the active metal exert only a slight effect or even no effect on the activity of the catalysts in Fischer–Tropsch synthesis. Noteworthy are a lower selectivity for methane and a greater fraction of olefins in the products obtained on the catalysts precalcined in a flow of inert gas containing 3% NO. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Cobalt-containing catalysts, in particular the cobalt–aluminum ones, have attracted considerable attention over several decades primarily due to their activity in Fischer–Tropsch synthesis (FTS). The active component of cobalt-containing FTS catalysts is repre- sented by metallic cobalt nanoparticles. The optimal size of metallic cobalt particles providing maximum activity and selectivity of a cat- alyst in the process ranges from 5 to 10 nm [1–5]. In this connection, many researchers are searching for the methods of stabilizing such cobalt particles on the oxide supports. The search is hindered by the ability of cobalt cations to form difficultly reducible mixed oxides with aluminum and silicon cations. For example, Co 2+ cations in cobalt metasilicate CîSiO 3 can be reduced in flowing hydrogen only at 900–920 ◦ C, in cobalt orthosilicate Co 2 SiO 4 at 970–980 ◦ C [6,7], and Co 2+ cations in the tetrahedral positions of stoichiomet- ric cobalt aluminate CoAl 2 O 4 are reduced at temperatures above 950 ◦ C [8]. At the same time, although the presence of a small ∗ Corresponding author at: Novosibirsk National Research University, 2, Pirogova str., Novosibirsk, Russia. E-mail address: khassinaa@mail.ru (A.A. Khassin). amount of impurity Al 3+ cations in cobalt oxide decreases the frac- tion of cobalt reduced to a metallic state, it may also facilitate the stabilization of disperse metal particles due to their decoration with the oxide Al 3+ -containing clusters [9]. In this connection, the prob- lem is not to completely prevent the formation of mixed cobalt and aluminum species but rather to diminish the dissolution of cobalt cations in the support oxide, which leads to the formation of a mixed oxide enriched with aluminum. The formation of mixed cobalt–aluminum oxide can occur not only during the deposition/precipitation of cobalt species from a solution but also at the subsequent calcination of the catalyst precursor. The formation of mixed cobalt–aluminum oxide upon calcination of Co–Al hydroxocarbonates is accompanied by the oxi- dation of a substantial part of Co 2+ cations to Co 3+ , which proceeds even if calcination is performed in a flow of inert gas [10,11]. In this connection, regulation of the oxidation state of cobalt cations dur- ing calcination of the catalyst precursor can be an efficient way for controlling the phase composition of oxide precursor, the degree of cobalt reduction to metallic state, and the dispersion of active component after catalyst reduction. It was shown in [12–15] that the presence of nitric oxide, NO, strongly affects the decomposition of cobalt nitrate and hence the size of Co 3 O 4 cobalt oxide crystallites and the degree of their inter- http://dx.doi.org/10.1016/j.apcata.2016.01.012 0926-860X/© 2016 Elsevier B.V. All rights reserved.