Co-based heterogeneous catalysts from well-defined α-diimine complexes: Discussing the role of nitrogen

Abstract

‡ These authors contributed equally to this work.Abstract: Ar-BIANs and related α-diimine Co complexes were wet impregnated onto Vulcan® XC 72 R carbon black powder and used as precursors for the synthesis of heterogeneous supported nanoscale catalysts by pyrolysis under argon at 800 °C. The catalytic materials feature a core-shell structure composed of metallic Co and Co oxides decorated with nitrogen-doped graphitic layers (NGr). These catalysts display high activity in the liquid phase hydrogenation of aromatic nitro compounds (110 °C, 50 bar H2) to give chemoselectively substituted aryl amines. The catalytic activity is closely related to the amount and type of nitrogen atoms in the final catalytic material, which suggests a heterolytic activation of dihydrogen.Keywords: cobalt, hydrogenation, nitro compounds, kinetic, heterolytic activation IntroductionCatalysis is a key-technology for the manufacturing of all kinds of bulk and fine chemical products. It allows for producing chemicals avoiding the formation of undesired and useless stoichiometric side products which leads to additional cost and energy consumption [1][2][3]. Many of the industrially relevant catalytic processes in the fine chemical industry are still based on expensive and rare late transition metals such as Pd, Pt, Rh, Ru and Ir [4,[1][2][3][4][5]. Although these metals exhibit very good catalytic performance for advanced organic substrates, the decreasing availability of these elements requires the development of efficient alternative metal-based catalysts [6]. In this regard, the design of catalytic systems based on abundant and biocompatible metals is an important goal for the implementation and progress of green and sustainable chemistry. Hence, transition metals such as Fe, Co and Cu are ideal candidates, which meet these requirements [7][8][9][10]. As a matter of fact, these elements are among the most abundant metals in the Earth's upper crust, thus being readily accessible [11]. Recently, heteroatom-doped carbon materials attracted major interest in the field of metal supported heterogeneous catalysts for both chemical synthesis [12][13][14] and/or energy-relevant transformations [15,16]. Indeed, doping graphene with heteroatoms such as N, B, P, or S leads to a radical modification of the electronic properties of both the support and the supported metal [17][18][19]. Consequently, it is possible to modify the activity and adjust the selectivity of the final catalytic material towards the desired transformation. Among the various dopants, nitrogen attracted most interest [15,[20][21][22]. and applications of transition metal/N-doped graphene (NGr) based catalytic systems ranges from oxygen reduction reactions (ORR) [23][24][25][26], hydrogen evolving reactions (HER) [27,28], photocatalysis [29,30], oxidation [31][32][33][34][35][36][37][38], and reduction [39][40][41][42][43][44] reactions of organic

Single cobalt sites in mesoporous N-doped carbon matrix for selective catalytic hydrogenation of nitroarenes

“…Interestingly, the catalytic activity of Co@mesoNC is superior to the behavior of other recently reported supported cobalt catalysts (Table S3), such as Co@N-doped carbon [29], CoOx@NCNTs [30], Co-SiCN [31], and Co-Co3O4/NGr@C [42]. The stability and reusability of the Co@mesoNC catalyst was also investigated.…”

“…Recently, tremendous efforts have led to the development of cheaper first-row transitionmetal-based hydrogenation catalysts (i.e. Fe, Co, and Ni) [15,[29][30][31][32][33][34][35][36][37][38][39][40][41]. Among these catalysts, N-doped carbon supported cobalt materials prepared by the carbonization of metal-organicframeworks (MOFs) or a mixture of cobalt salts and organic complex exhibited good activity and chemoselectivity in the hydrogenation of nitroarenes [29-32, 36, 39-46].…”

A Reusable Cobalt Catalyst for Reversible Acceptorless Dehydrogenation and Hydrogenation of N‐Heterocycles

“…[12a-b] It is noteworthy that the activity of non-noble metal nanoparticles can be controlled by M : L composition, nature of carbon support, pyrolysis temperature and finally the microstructure of the nanomaterial. [23] Gratifyingly, the newly synthesized cobalt nanocatalyst showed superior activity in the ADH reaction of partially saturated Nheterocycles to N-heteroaromatics with the liberation of H 2 gas. The present nano-catalyst performs excellently with a five-run recycling test.…”

“…Notably, a seminal work reported by the research group of Beller and Stahl for the oxidative dehydrogenation of N‐heterocycles to N ‐aromatics using air/oxygen as the oxidant –. It is noteworthy that the activity of non‐noble metal nanoparticles can be controlled by M : L composition, nature of carbon support, pyrolysis temperature and finally the microstructure of the nanomaterial . Gratifyingly, the newly synthesized cobalt nanocatalyst showed superior activity in the ADH reaction of partially saturated N‐heterocycles to N‐heteroaromatics with the liberation of H 2 gas.…”

Accessing Frustrated Lewis Pair Chemistry through Robust Gold@N-Doped Carbon for Selective Hydrogenation of Alkynes

“…24 This type of H 2 activation at N-doped carbon supports was previously described for Pd, 48 boron− nitrogen codoped graphene, 57 and Co catalyst. 49 The introduction of N atoms might affect the properties of the supported catalyst, such as tunable acid−base character at the support surface, which could cause a better interaction of metal−support−reactant, as well as charge transfer phenomena at the metal−support junction. 44 In order to gain more insight into the mechanism of the reaction, we conducted a Hammett correlation study using the developed catalyst and Lindlar catalyst to verify the influence of various para substituents on aromatic alkynes.…”