In-situ developed active sites of MOFs in aqueous electrocatalytic ammoxidation

doi:10.1016/S1872-2067(26)65042-5

Abstract

Abstract:

Metal organic frameworks (MOFs) are frequently employed as electrocatalysts for chemical and energy conversions, owing to their tailored structure and electronic properties. However, the stability and evolution of MOFs under electrochemical conditions remain unclear, resulting in the identification of true active sites a challenging task, thus limiting the design of high-performance electrocatalysts. Here, we follow the development of a representative Co-MOF anode in electrolyte under bias by in-situ spectroscopies, and resolve the evolution of active species for efficient electrocatalytic ammoxidation of aldehydes. A rapid dissociation of Co-MOF occurs in KOH, forming a composite electrocatalyst (e-Co) that consists of crystalline cobalt hydroxide (Co(OH)₂) and amorphous cobalt oxide (CoO_x). The active Co²⁺ sites promote the dissociative adsorption of ammonia, forming Co³⁺-NH_3-_x sites to interact with aldehyde, yielding an imine intermediate and eventually generating nitrile via dehydrogenation. The evolved e-Co electrocatalyst exhibits a satisfactory yield (83%) and Faradaic efficiency (72%) for the synthesis of nitrile at an ultra-low cell voltage of 1.0 V in aqueous electrolyte under ambient air pressure. The e-Co electrocatalyst also displays a decent stability, a broad substrate scope, and a consistent catalytic performance at higher reactant concentrations, offering a sustainable solution for ammoxidation at a practical scale.

Key words: Heterogeneous electrocatalysis, Metal organic frameworks, Active sites evolution, Electrochemical synthesis, Electrochemical ammoxidation, Cobalt electrocatalyst

Chao Wang, Kun Feng, Liangshuyu Tang, Wujun Zhang, Muyu Zhou, Jialu Li, Tianyu Shao, Flemming Besenbacher, Yanbin Shen, Jun Zhong, Ren Su. In-situ developed active sites of MOFs in aqueous electrocatalytic ammoxidation[J]. Chinese Journal of Catalysis, 2026, 86: 171-180.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)65042-5

https://www.cjcatal.com/EN/Y2026/V86/I7/171

Figures/Tables 6

Fig. 1. The fresh and transformed electrocatalysts. HRTEM (a,b), Raman (c), and XPS (d) spectra of the as-synthesized Co-MOF and e-Co. The e-Co is produced from treating Co-MOF in 0.1 mol·L?1 KOH for 30 min at 1.2 V. XANES (e) and EXAFS (f) spectra at Co K-edge for Co-MOF, e-Co, and standard materials.

Fig. 2. Evolution of the electrocatalyst. (a) The activation process of the Co-MOF and the appearance of the Co catalyst during electrochemical ammoxidation of benzaldehyde. In-situ Co K-edge XANES (b), EXAFS (c) and Raman (d) spectra in 0.1 mol·L?1 KOH upon dosing ammonia (2.6 mol·L?1) and benzaldehyde (10 mmol·L?1) under bias (1.4 V vs. RHE). The time interval is 3 min for Raman.

Fig. 3. Electrocatalytic ammoxidation. (a) Catalytic performance in comparison with other electrodes. (b) Time-course of ammoxidation using the developed e-Co under a cell voltage of 1.2 V. (c) Effect of NH3·H2O concentration on the ammoxidation. (d) Stability of e-Co for the synthesis of benzonitrile under optimum conditions. (e) Five-dimensional evaluation of the e-Co system in comparison with reported electrocatalytic ammoxidation systems. Reaction conditions: two-electrode system, benzaldehyde (0.24 mmol) and desired quantity of NH3?H2O in 12.0 mL electrolyte (0.1 mol·L?1 KOH/MeCN, v/v = 11:5).

Fig. 4. Reaction mechanisms. (a) Multi-potential i-t curves of e-Co in 0.1 mol·L?1 KOH and under ammoxidation conditions. (b) LSV of Co-MOF and e-Co with a mixture of hemiaminal and imine intermediate in a 0.1 mol·L?1 Bu4NPF6/MeCN solution. (c) Evolution of the Co-active site and the promotional mechanism for electrocatalytic ammoxidation.

Table 1 Substrates scope. Electrosynthesis of nitriles catalyzed by e-Co a.

Fig. 5. Scalability and Expandability. (a) Effect of starting concentrations of benzaldehyde for the synthesis of benzonitrile using e-Co electrocatalyst. Reaction conditions: desired quantity of benzaldehyde, 2.4 mL NH3·H2O (aq.), and 9.6 mL 0.1 mol·L?1 KOH/MeCN, e-Co as anode, NS as cathode, 1.2 V. (b) Gram-scale synthesis of nitriles using e-Co with a geometric surface area of 7.5 cm2. Reaction conditions: 10 mmol 3a, 20 mL NH3?H2O (aq.), and 80 mL KOH/MeCN, 1.4 V for 96 h. 9 mmol 3v, 3w or 3ab, 18 mL NH3?H2O (aq.) and 72 mL KOH/MeCN, 1.6 V for 120 h.

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