Up-scaled synthesis of flower-like SiO2 microspheres via continuous flash nanoprecipitation and their application as a catalyst support

Abstract

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.

Keywords

• SiO2 hollow materials
• Flash-nanoprecipitation
• CO methanation
• Ni-based catalysts