Hollow @CuMgAl double layered hydrotalcites and mixed oxides with tunable textural and structural properties, and thus enhanced NH3-NOx-SCR activity

Abstract

Well-organized, spherical, mesoporous hollow @CuMgAl-LDHs (layered double hydroxides) are prepared by the controlled removal of the SiO₂ from SiO₂@CuMgAl-LDH core–shell hybrids that in turn are synthesized via a bottom-up strategy. The materials are prepared with various Cu/Mg molar ratios (Cu/Mg = 0.05–0.50) while keeping the ratio of Cu and Mg constant, (Cu + Mg)/Al = 2. The effect of Cu doping and the silica core removal process (conducted for 4 h at 30 °C using 1 M NaOH) on the chemical composition, morphology, structure, texture and reducibility of the resulting materials are described. @CuMgAl-MOs (mixed oxides) obtained by thermal treatment of the @CuMgAl-LDHs are active and selective catalysts for the selective catalytic reduction of NO_x using ammonia, and effectively operate at low temperatures. The N₂ yield increases with increased Cu content in the CuMgAl shell, which is associated with the easier reducibility of the Cu species incorporated into the MgAl matrix. @CuMgAl-MOs show better catalytic performance than bulk CuMgAl MOs.