Synergistic effect of binary Co and Ni cations in hydrotalcite-derived Co2-xNixAlO catalysts for promoting soot combustion

Surface coordination unsaturation cation in hydrotalcite-derived CoAl oxides is crucial to improve catalytic performance during soot combustion. Herein, the hydrotalcites-derived Co2-xNixAlO catalysts were prepared by the co-precipitation method. The characteristic nanosheet structure of hydrotalcite-derived CoAl oxides can promote mass transfer efficiency of the reactants. The cobalt elements partially replaced by nickel elements in hydrotalcite-derived CoAl oxides can induce the formation of coordination unsaturated cations and surface anion defects (oxygen vacancies) for increasing surface area and active site. The synergistic effect of binary Co and Ni ions in hydrotalcites-derived Co2-xNixAlO catalysts can boost adsorption-activation properties for O2 and NO. Hydrotalcites-derived Co2-xNixAlO catalysts exhibit excellent catalytic performances for soot combustion, and their catalytic activity strongly depends on the synergistic effect of binary Co and Ni cations. Among the catalysts, Co1.5Ni0.5AlO catalyst has the highest catalytic activity (T50 = 333 °C, TOF = 1.01 × 10−2 s−1). Based on the characterization results, the catalytic mechanism for soot combustion is proposed: the synergistic effect of binary Co and Ni cations in Co2-xNixAlO catalysts can boost the key step of NO oxidation to NO2. The in-depth understanding on the synergistic effect of Co and Ni cations is meaningful for the development of the ternary hydrotalcite-derived catalysts for soot combustion.