VOCs combustion catalysts based on composites of exfoliated organo-Laponite and multimetallic (Mn, Al, Zr, Ce) hydrotalcites prepared by inverse microemulsion

Abstract

Composites of exfoliated organo-Laponite and multimetallic (Mn, Al, Zr, Ce) hydrotalcite-like nanoparticles obtained by inverse microemulsion method were used as precursors of catalysts for total oxidation of toluene. The materials were characterized with XRF, XPS, XRD, HRSEM, TEM/HRTEM, H2 TPR, and N2 adsorption/desorption at −196 °C. Features of nanocrystalline hydrotalcite-like phase could be identified in all active phase precursors obtained by inverse micellar route, of poorer order in samples doped with Ce and/or Zr. Mn-Al active phase in calcined (600 °C) composites formed uniform particles of ca. 30–40 nm diameter, while upon addition of Zr and/or Ce the active phase disintegrated forming very fine oxide particles, rarely exceeding 10 nm. All composites were very active in the total oxidation of toluene, those promoted with Zr and/or Ce showing performance superior to the undoped counterpart. Beneficial role of Zr and Ce promoters was attributed to the improved dispersion and amorphization of the mixed oxide phase, accompanied by its enhanced reducibility and increase of the catalysts specific surface area and pore volume. Addition of Ce resulted in an increase of the surface contribution of Mn4+ ions, advantageous for combustion activity. Best catalytic performance was obtained for the composite of Laponite with Mn-Al active phase promoted with both Zr and Ce, which showed excellent activity and stability. Catalysts obtained by the novel design performed much better than the references prepared from conventionally synthesized hydrotalcites and sodium or cetyltrimethylammonium form of Laponite.