The biogenic silica-derived Ni-phyllosilicate catalyst with Ru modification: effect of the hydroxylation enhancement and reduction procedure

Abstract

Ni-phyllosilicate is difficultly formed on the surface of biogenic silica (E) extracted from equisetum fluviatile after calcination, resulting in poor catalytic activity at low temperature (<400 °C). In this work, the hydroxylation treatment of E was carried out to address the problem of lack of the surface silanol group and difficult formation of Ni-phyllosilicate, and the second metal Ru was added using a special procedure to further improve the activity of the catalyst. The surface silanol group concentration of silica (HE) was increased from 0.5 to 0.7 mmol/g after hydroxylation treatment, resulting in formation of more Ni-phyllosilicate with Ni content increase from 11.3 to 17.0 wt%. Considering the great gap of reduction difficulty of Ni-phyllosilicate (>800 °C) and RuO2 species (190 °C), RuO2 species was doped onto the 750 °C-pre-reduced Ni-phyllosilicate via impregnation, and metallic Ru together with Ni could be obtained simultaneously after reduction at a low temperature of 400 °C. The obtained Ru-modified Ni-phyllosilicate catalyst showed high CO2 conversion of 77.3% and CH4 selectivity of 96.4% with high turnover frequency (1.22 s−1, 180 °C) and low activation energy (71.25 kJ/mol). In situ Diffused Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) results revealed that more active formate intermediates (m-HCOO- and m-CO32−) result in high catalytic activity of the Ru-modified Ni-phyllosilicate catalyst. In addition, this catalyst exhibited high anti-sintering property, long-term stability, and hydrothermal stability under severe conditions owing to the Ni-phyllosilicate–based structure.