Slurry phase methanation of carbon monoxide over nanosized Ni–Al2O3 catalysts prepared by microwave-assisted solution combustion

• The nano Ni–Al2O3 catalyst is prepared by microwave-assisted solution combustion.
• The reactants decompose simultaneously is conducive to form a stable combustion.
• A moderate and sustained combustion is crucial for the prepared catalyst.
• The optimized catalyst has small Ni particles and large specific surface area.
• The catalyst prepared by urea has more dispersive Ni species after reduction.

The clean transformation of coal into natural gas is an interesting topic in green chemistry, as well as a promising process for the production of natural gas. In the present work, the methanation of CO was performed in a slurry-bed reactor with a series of nanosized Ni–Al2O3 catalysts prepared by microwave-assisted solution combustion with different fuels (urea, glycine, ethylene glycol and citric acid). As compared with other fuels, a majority of urea and nitrates simultaneously decompose and occur in extensive overlapped temperature ranges during heating, which is conducive to the formation of a moderate and sustained combustion reaction. In addition, the thermodynamic calculation and thermogravimetric analysis indicate that the amount of heat generated during combustion is the minimum when urea was used as fuel. By the formation of a stable combustion and a relative low combustion temperature, the NiAl-U catalyst exhibits the largest BET area and metal surface area, the smallest Ni particle size and more dispersive Ni species, as evidenced by XRD, TEM, N2 adsorption–desorption, H2-TPR and H2 pulse chemisorption characterizations. In the slurry methanation of CO, the conversion of CO and selectivity for CH4 over NiAl-U catalyst reach up to 95.7% and 96.2% at 300 °C, 1.0 MPa and 3000 mL/gcat h, respectively, which are superior to those of other combustion-synthesized catalysts and commercial catalyst. In addition, The NiAl-U catalyst exhibits significant improvement in anti-sintering during 200 h lifetime test, mainly because of smaller Ni particle size, high dispersity of Ni active species on support and high stability of support. The findings presented here are expected to provide new approaches for rational design of nanosized Ni–Al2O3 catalysts for CO methanation reactions in slurry phase.

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