Co-Mg Synergistic Carbon Nano Onions Catalyst: Preparation and Low-temperature Catalytic Hydrogen Production from Ammonia Decomposition

doi:10.15541/jim20250211

Abstract

Abstract:

Decomposition of ammonia for hydrogen production is a promising method, but still needs developing low-cost, highly active and selective catalysts which can operate at moderate temperatures. In this study, carbon nano-onions (CNOs), a byproduct of methane pyrolysis at 850 ℃, were used as a support for loading active metal cobalt (Co) via a uniform deposition-precipitation method. Additionally, magnesium oxide (MgO) was introduced as a promoter to prepare a high-performance ammonia decomposition catalyst. An investigation was conducted on the effects of acid washing and potassium (K) activation treatments on morphology of the CNOs support and catalyst performance with in-depth exploration of their influence mechanisms. Various characterization and chemical adsorption experiments confirmed a positive correlation between basicity strength of the catalyst and its ammonia decomposition performance. It was revealed that incorporation of CNOs significantly enhanced electronic conductivity of the catalyst and facilitated uniform dispersion of Co₂MgO₄ nanoparticles on the support. This uniform dispersion increased the exposure of basic active sites, thereby enhancing the catalyst's ability to adsorb ammonia molecules. The acid washing treatment introduced more oxygen-containing functional groups on the CNOs surface which acted as anchoring sites to form strong chemical bonds (coordination or ionic bonds) with Co²⁺ or Mg²⁺, thus stabilizing Co₂MgO₄ particles. These strong chemical bonds increased the reduction difficulty of the metal oxides, leading to an elevated reduction temperature. Catalytic performance tests demonstrated that the synergistic effect of CNOs, MgO, K, and Co significantly optimized structural characteristics, metal particle size and catalytic performance of the catalyst. Among a series of synthesized catalysts, Co₂Mg/K-CNO’ exhibited the best catalytic activity for ammonia decomposition, achieving a conversion rate of 99.6% at 550 ℃ and a space-time yield of 12000 mL·g_cat^-1·h^-1.

Key words: ammonia decomposition, catalyst, carbon nano-onion, acid washing, alkalinity, metal-support interaction

CLC Number:

O643

XUE Xinyan, ZHANG Xiaowei, LU Heng, LI Shijie, ZHANG Weike, CHAN Siewhwa. Co-Mg Synergistic Carbon Nano Onions Catalyst: Preparation and Low-temperature Catalytic Hydrogen Production from Ammonia Decomposition[J]. Journal of Inorganic Materials, 2026, 41(4): 500-508.

Figures/Tables 11

Fig. 1 N2 adsorption-desorption isotherms (a) and pore size distributions (b) of different catalysts

Table 1 Specific surface area and pore structure parameters of different catalysts

Catalyst	BET specific surface area/ (m²·g^-1)	Micropore volume/ (cm³·g^-1)	Micropore area/ (m²·g^-1)	Average pore size/nm	Co content/% (in mass)
Co₂Mg	12.7434	0.002212	6.0318	14.6403	50
Co₂Mg/CNO	23.4634	0.002876	6.0278	19.4730	29
Co₂Mg/CNO’	23.4880	0.003788	8.6815	20.0063	29
Co₂Mg/K-CNO	28.5727	0.002307	4.8487	18.2552	29
Co₂Mg/K-CNO’	34.8266	0.002539	8.6815	17.6383	29

Fig. 2 XRD patterns of catalysts before (a) and after (b) reduction at 500 ℃

Fig. 3 XPS spectra of Co2Mg/CNO, Co2Mg/K-CNO and Co2Mg/K-CNO’ (a) Co2p; (b) Mg1s; (c) C1s

Fig. 4 SEM images of catalysts (a) CNOs; (b) Co2MgO4; (c) Co2Mg/CNO; (d) Co2Mg/CNO’; (e) Co2Mg/K-CNO; (f) Co2Mg/K-CNO’

Fig. 5 TEM (a) and HRTEM (b) images of Co2Mg/K-CNO’

Fig. 6 H2-TPR (a) and CO2-TPD (b) profiles of catalysts

Fig. 7 Comparison of catalytic activity for ammonia decomposition (a) Co-Mg synergy; (b) K-activated carriers; (c) Different ratios of Co-Mg

Fig. 8 Ammonia conversion (a), hydrogen generation rate (b) and activation energy (c) of catalysts

Table 2 Catalytic performance of Co-based catalysts for ammonia decomposition

Catalyst	Temperature/℃	GHSV/(mL·g_cat^-1·h^-1)	NH₃ conversion/%	Ref.
Co₂Mg/K-CNO’	550	12000	99.6	This work
20CoNaTi-NT	550	6000	41	[22]
35%Co/SiC-700	550	30000	78.3	[23]
CoO_x@C-700A	500	15000	55	[24]
90CoAl	500	30000	37.8	[25]
Co/CNTs	500	6000	61	[26]
Co-Mo/SiO₂-Cap	500	6000	20	[27]
Co/CeO₂	500	6000	62	[28]
26Co-CAT(A)	500	6000	58	[29]
Fe/CNTs	500	6000	15	[26]
Co/MWCNTs	500	6000	74.6	[30]

Fig. 9 Ammonia conversion (a) and long-term stability (b) of Co2Mg/K-CNO’

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