Hollow-SiO2@Cu x Zn y Mg z Al-LDHs as catalyst precursors for CO2 hydrogenation to methanol

Abstract

We report a new synthetic strategy for preparing well-organised, spherical and mesoporous, mixed-metal, hollow-core@layered double hydroxides. Hollow-SiO₂@Cu _x Zn _y Mg _z Al-LDHs (x + y + z = 2.32 ± 0.06) were prepared by exploiting a unique "memory effect" feature of LDH materials. The reconstruction with simultaneous incorporation of Cu²⁺ and Zn²⁺ into the LDH shell was achieved by exposing hollow-SiO₂@Mg₂Al-LDO to an aqueous solution containing Cu²⁺ and Zn²⁺ cations. The effect of a single reconstruction step with various concentrations of Cu²⁺ and Zn²⁺ solutions (20-80 mM), as well as the implementation of five successive cycles of calcination-reconstruction on the chemical composition, morphology, texture and structure of the resulting materials are described. Hollow-SiO₂@Cu _x Zn _y Mg _z Al-LDHs are precursors to active catalysts for CO₂ hydrogenation to methanol. The most active catalyst exhibits a space-time yield for methanol of 1.68 g_MeOH g_Cu ^-1 h^-1 at 270 °C (3 : 1 CO₂ : H₂, 30 bar) which represents a 1.7-fold increase in space-time yield compared to commercial Cu/ZnO/Al₂O₃ catalyst under the same conditions.