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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.

The use of non-noble nickel-based catalysts for low temperature CO methanation has been a challenge in recent years. Herein, MgAl layered double oxides sample with high dispersion synthesized by a facile N-(2-Hydroxyethyl) ethylenediaminetriacetic acid assisted wetness impregnation approach, demonstrates much superior catalytic activity and exceptional stability for CO methanation in comparison with the classical Ni/MgAl-LDO catalyst prepared by the ordinary wetness impregnation method. HRTEM results showed that N-(2-Hydroxyethyl)ethylenediaminetriacetic acid played a positive role in the dispersion of Ni, as well as Ni-support interaction. Well-dispersed Ni particles with a size of about 5 nm were formed in the presence of N-(2-Hydroxyethyl) ethylenediaminetriacetic acid. Compared to the Ni/MgAl-LDO prepared by conventional impregnation method, the NH-Ni/MgAl-LDO exhibited superior catalytic performance, especially excellent thermal stability. The NH-Ni30/MgAl-LDO catalyst was found to keep a 70 % CO conversion even at 160 °C which demonstrates its good low temperature performance. From the in situ FTIR observations, this good performance at low temperatures may be linked to the delocalization of electrons around CO caused by surface hydroxyl groups.

The dye wastewater produced in the printing and dyeing industry causes serious harm to the natural environment. TiO2 usually shows photocatalytic degradation of dye under the irradiation ultravilet light rather than visible light. In this work, a large number of oxygen vacancies and Ti3+ defects were generated on the surface of the TiO2 nanoparticles via Ar plasma. Compared with pristine TiO2 nanoparticles, the as-obtained Ar plasma-treated TiO2 (Ar-TiO2) nanoparticles make the energy band gap reduce from 3.21 eV to 3.17 eV and exhibit enhanced photocatalytic degradation of organic dyes. The Ar-TiO2 obtained exhibited excellent degradation properties of methyl orange (MO); the degradation rate under sunlight irradiation was 99.6% in 30 min, and the photocatalytic performance was about twice that of the original TiO2 nanoparticles (49%). The degradation rate under visible light (λ > 400 nm) irradiation was 89% in 150 min, and the photocatalytic performance of the Ar-TiO2 was approaching ~4 times higher than that of the original TiO2 nanoparticles (23%). Ar-TiO2 also showed good degradation performance in degrading rhodamine B (Rho B) and methylene blue (MB). We believe that this plasma strategy provides a new method for improving the photocatalytic activity of other metal oxides.

As a methanation tool, two-dimensional (2D) carrier-loaded Ni has attracted the attention of many researchers. We successfully prepared 2D MgAl layered double oxides (LDO) carriers via flash nanoprecipitation (FNP). Compared to the LDO samples prepared by conventional co-precipitation (CP), the 2D MgAl-LDO (FNP) has more oxygen vacancies and more exposed active sites. The Ni/MgAl-LDO (FNP) catalyst demonstrates a CO conversion of 97%, a CH4 selectivity of 79.8%, a turnover frequency of 0.141 s-1, and a CH4 yield of 77.4% at 350 °C. The weight hourly space velocity was 20,000 mL•g-1•h-1 with a synthesis gas flow rate of 65 mL•min•, and a pressure of 1 atm. A control experiment used the CP method to prepare Ni/MgAl-LDO. This material exhibits a CO conversion of 81.1%, a CH4 selectively of 75.1%, a TOF of 0.118 s-1, and a CH4 yield of 61% at 450 °C. We think that this FNP method can be used for the preparation of more 2D LDO catalysts. [ABSTRACT FROM AUTHOR]