Selective hydrogenation of CO2 to CH4 over two-dimensional nickel silicate molecular sieves

Abstract

Two-dimensional (2D) Ni-containing delaminated MWW layers (Ni-DML) were synthesized by hydrothermal treatment of a borosilicate MWW precursor with a nickel nitrate solution, and their catalytic properties were investigated for the selective hydrogenation of CO₂. Increasing the hydrothermal temperature promoted the structural transformation of 3D tectosilicate into 2D phyllosilicate. The isomorphic substitution of the framework boron by nickel was facilitated by increasing the hydrothermal temperature, and the content of Ni on Ni-DML was increased up to 38 wt% at 180 °C with high dispersion. The framework Ni in Ni-DML formed metallic Ni clusters in situ, which were active for the selective hydrogenation of CO₂ to CH₄. However, a significant reduction in the number of micropores was observed at hydrothermal temperatures above 160 °C because of the transformation of the delaminated MWW layers to 2D nickel phyllosilicates. A volcano-shaped distribution in the CH₄ yield was observed with respect to the hydrothermal temperature.