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Ni-Al mixed metal oxides have been successfully prepared by high shear mixer (HSM) and coprecipitation (CP) methods for low temperature CO methanation. In this work, Ni-Al (HSM-CP) catalyst presented small Ni crystallite size and high surface area, which all contribute to the methanation reaction at low temperature conditions. The obtained Ni-Al (HSM-CP) sample exhibited a mass of defective oxygen, thereby accelerating the dissociation of CO and ultimately increasing the activity of the catalyst. Ni-Al (HSM-CP) catalyst offered the best activity with CO conversion=100 % and CH4 selectivity=93 % at 300 ℃, and the CH4 selectivity can reach 81.8 % at 200 °C. In situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) show that CHO and COH intermediates with lower activation energy barriers are produced during the reaction, and hydrogen-assisted carbon-oxygen bond scission is more favorable.

In this work, the solution plasma-assisted method was used to prepare NiMnAl-LDO (layered double oxides) catalysts with different treatment times, which were used for the CO2 methanation reaction. Solution plasma treatment can enhance the dispersibility of the catalyst, create oxygen defects and improve the chemical adsorption capacity of the catalyst. The results show that the low-temperature activity of the catalyst has been improved after the solution plasma treatment. We demonstrate that the NiMnAl-LDO-P(20) catalyst with high dispersion has the highest catalytic activity in CO2 methanation (81.3% CO2 conversion and 96.7% CH4 selectivity at 200 °C). Even though working for 70 h, the catalyst is still highly stable. This work provides a great promise for improving the low-temperature activity of Ni-based catalysts.

CO methanation has attracted much attention because it transforms CO in syngas and coke oven gas into CH4. Here, porous Al2O3 microspheres were successfully used as catalyst supports meanwhile the Mn was used as a promoter of Ni/Al2O3 catalysts. The as-obtained Ni/Al2O3 and Mn–Ni/Al2O3 samples display a micro-spherical morphology with a center diameter near 10 μm. Versus the Ni/Al2O3 catalyst, the 10Mn–Ni/Al2O3 catalyst exhibits a high specific surface area of 92.5 m2/g with an average pore size of 7.0 nm. The 10Mn–Ni/Al2O3 catalyst has the best performance along with can achieve a CO conversion of 100% and a CH4 selectivity of 90.7% at 300 °C. Even at 130 °C, the 10Mn–Ni/Al2O3 catalyst shows a CO conversion of 44.0% and a CH4 selectivity of 84.1%. The higher low-temperature catalytic activity may be since the catalyst surface contains more CO adsorption sites and thus has a stronger adsorption performance for CO. Density functional theory (DFT) calculations confirm that the Mn additive enhances the adsorption of CO, especially for the 10Mn–Ni/Al2O3 catalyst with the strongest adsorption energy.

Hollow-structured SiO2, which comprises a void space inside a distinct shell with its intriguing physicochemical properties and huge potential, has been widely applied in many methanation catalysts. However, the common methods for preparing SiO2 hollow microspheres are cumbersome and time consuming. Highly uniform hollow nanoflowers, silica (SiO2) nanospheres with different sizes, were synthesised through a rapid, time-saving method known as flash nanoprecipitation. An assembling particle mechanism of the hollow structure of Mo–polydopamine complex was established and tetraethyl orthosilicate underwent uniform hydrolysis on the surface of the hierarchical structure. Spherical SiO2 samples with different morphologies were prepared as catalyst carriers, and Ni-based methanation catalysts were prepared using an impregnation method. Ni particles with size of 3 nm were successfully attached to the surface of MoDo–H–SiO2, while the particle sizes of Ni on CTS–MoDo–H–SiO2 was 7 nm. The small particles (3 nm) were found to significantly increase in size (20–50 nm), decrease by 90% in stability test with a weight hourly space velocity (WHSV) of 26,000 mL.g−1.h−1, which is detrimental to catalyst stability. However, the medium sized particles (7 nm) remained confined via a suitable interaction involving the support, thus displaying enhanced stability, with 100% CO conversion at 250 °C and no obviously decrease in stability test Although more active sites can be provided with smaller active metals, catalysts with small sized particles deactivate faster and to a larger extent than catalysts with medium sized particles. Thus, the smaller the particle size of the active component, the worse the stability.

Low-temperature performance of non-noble metal Ni-based catalysts in CO2 methanation still faces great challenges. A series of NiMnAl-LDO (layered double oxides) catalysts with different processing conditions were prepared using the high-shear mixer-assisted method. The FH-C (80 °C) catalyst exhibited high activity in low-temperature CO2 methanation, and CO2 conversion and CH4 selectivity reached 85% and 97% at 200 °C. Characterization results show that the strong shear force of the high-shear mixer can improve the dispersion of the catalyst and reduce the particle size of the catalyst. The high-shear mixer treatment increases the CO2 chemisorption and the number of strongly basic sites on the catalyst. The main reason for the low-temperature activity of the catalyst is that the high-shear mixer increases the number of oxygen vacancies in the catalyst. In situ infrared probes into the surface species and intermediate products of the catalyst, confirming that formate is an intermediate product of the CO2 methanation reaction. Density functional theory calculations demonstrated that increasing the content of oxygen vacancies is beneficial for increasing the CO2 adsorption capacity of the catalyst and reducing the reaction energy barrier of CO2 → COOH*.

Ni/Al2O3 spherical catalysts were prepared by high shear mixer (HSM)-assisted coprecipitation (CP) and spray drying (SD) method for carbon monoxide (CO) and carbon dioxide (CO2) methanation. The effect of HSM technology on low-temperature methanation performance was studied. Ni/Al2O3 (HSM-CP-SD) catalysts provide excellent performance such as CO conversion of 100% and CH4 selectivity of 90% at 300 °C; the CO2 conversion was 86.2% and CH4 selectivity was 95.3% at 350 °C. Even at 200 °C, the catalyst prepared by HSM still offers a CO conversion of 90% and CH4 selectivity of 82%, whereas the Ni/Al2O3 (CP-SD) has no activity. The high performance was attributed to the small Ni nanoparticles and high dispersion. The Ni/Al2O3 (HSM-CP-SD) catalysts exhibit micro-spherical morphology with a big pore size of 3.46 nm, stronger metal-support interactions, and CO adsorption capacity. The catalyst prepared by HSM shows potential application for CO/CO2 methanation, and HSM technology can optimize other heterogeneous catalytic reactions.