Evaluation of the physiochemical properties and catalytic performance of CuCoMnAl mixed oxides derived from layered double hydroxides precursors with different mole ratios of Cu/Co on the oxidation of toluene

Abstract

CuCoMnAl mixed oxides with different mole ratios of Cu/Co were synthesized by thermal decomposition of layered double hydroxides (LDHs) precursors. They were characterized using X-ray diffraction, scanning electron microscopy, N2 adsorption/desorption isotherm analysis, H2-temperature program reduction and X-ray photoelectron spectroscopy, and their catalytic properties were evaluated in the total oxidation of toluene. The precursors of LDHs consisted in hydrotalcite phase with gerhardtite, malachite and rhodochrosite phase for Cu-containing systems. The mixed metal oxide derived from LDHs contains tenorite phases and different spinel (Co3O4, CoAl2O4 and Co2AlO4) phases. XPS analysis confirmed the existence of copper, cobalt and manganese with different valence states in the Cu, Co, Mn-containing mixed oxides. H2-TPR analysis indicated that the reduction peaks of cobalt and manganese were significantly shifted to lower temperatures for Cu–Co–Mn–Al samples by doping a small amount of Cu. BET analysis showed the increase of large mesopores and macropores of the samples with the increase of Cu contents. Cu2Co2MnAl-MMO present the best catalytic activity at all temperature range. The synergetic interactions among Co, Cu and Mn species, Mn3+ and lattice oxygen were beneficial for the best catalytic activity of Cu2Co2MnAl-MMO.