Solvent-Free Synthesis of Nickel Nanoparticles as Catalysts for CO2 Hydrogenation to Methane

Abstract

The solid-state combustion method was used to prepare nickel-based catalysts for CO2 hydrogenation from [Ni(C3H4N2)6](NO3)2 and [Ni(C3H4N2)6](ClO4)2. These complexes were synthesized by adding nickel nitrate and perchlorate to melted imidazole. The composition and structure of the obtained complexes was confirmed by ATR FTIR, powder XRD, and elemental analysis. The stages of thermal decomposition of the complexes and their kinetic parameters were established. It was found that incomplete gasification of more thermostable Ni(C3H4N2)6](ClO4)2 led to the formation of carbon, nitrogen, and chlorine impurities. According to powder XRD and XPS, the solid products of gasification of both complexes consist of NiO and Ni0 covered with nickel hydroxide and/or a carbonate layer. In the case of the sample prepared from [Ni(C3H4N2)6](ClO4)2, this layer was pronounced. Therefore, it limits the nickel reduction in the reaction medium of CO2 hydrogenation, even at 450 °C. The surface of the sample prepared from [Ni(C3H4N2)6](NO3)2 contains nickel oxide, which is easily reduced. So, the catalyst active phase is already formed at 250 °C in the presence of CO2 and efficiently catalyzes CO2 hydrogenation as the temperature increases. Therefore, [Ni(C3H4N2)6](NO3)2 is a promising precursor for the CO2 hydrogenation catalyst, and its solvent-free synthesis follows Green Chemistry principles.

CO2 Methanation: Solvent-Free Synthesis of Nickel-Containing Catalysts from Complexes with Ethylenediamine

“…At an even higher temperature (400 °C), an active phase is formed in the sample obtained from the nickel perchlorate complex. The comparison of previously obtained experimental data [ 12 , 13 ] with the results of this work shows that the Ni-2En-NO 3 sample with a high content of nickel oxide showed the highest activity in CO 2 methanation ( Figure S7 ). Thus, the [Ni(C 2 H 8 N 2 ) 2 ](NO 3 ) 2 complex is a promising precursor for the CO 2 methanation catalyst, especially since less ethylenediamine is required for its solvent-free synthesis.…”

“…The formation of [Ni(C 3 H 4 N 2 ) 6 ](NO 3 ) 2 and [Ni(C 3 H 4 N 2 ) 6 ](ClO 4 ) 2 complexes was confirmed by IR spectroscopy and powder XRD. Using these compounds, the bulk [ 12 ] and supported [ 13 ] nickel catalysts were prepared by SSC. The resulting solid combustion products consisted of both oxidized and reduced nickel phases.…”

Cobalt–Imidazole Complexes: Effect of Anion Nature on Thermochemical Properties

“…The (2) high-temperature stage is characterized by intense heat release and a large amount of complete gasification products of the complex, mainly H 2 O, N 2 , CO, N 2 O, and CO 2 . In addition, in the case of the [Co(C 3 H 4 N 2 ) 6 ](NO 3 ) 2 complex, NO and NH 3 are formed, but there is no oxygen, which is typical for the decomposition of a nickel complex of similar composition [ 9 ]. For the [Co(C 3 H 4 N 2 ) 6 ](ClO 4 ) 2 complex, the release of oxygen was observed at 450 °C, and HCl was a minor product of its thermal decomposition.…”

“…In this case, the organic ligand in the [Co(C 3 H 4 N 2 ) 6 ](NO 3 ) 2 complex undergoes almost complete gasification, probably due to the oxygen formed during the thermal decomposition of the nitrate anion. That is why oxygen was not identified with the dynamic mass spectrometry in the gaseous products of the complex thermal decomposition, as is typical for nickel complexes of a similar composition [ 9 ]. As a result, Co 3 O 4 with a slight admixture of CoO is formed.…”

“…However, it is difficult to achieve phase homogeneity, which reduces the yield of metal–organic compounds and requires further purification of the target product from the impurities of the reagents. To obtain metal–organic complexes from thermally stable compounds, it was proposed to melt their precursors in a stoichiometric ratio [ 7 ], which was developed in our research works [ 8 , 9 ]. This approach is especially interesting for complex compounds, which should be synthesized in well-dried solvents to prevent the complete or partial hydrolysis of the reagents or products of their interaction.…”