Copper–aluminum hydrotalcite type precursors for NOx abatement

• Cu oxides catalysts from Cu–Al hydrotalcite type precursors.
• Synthesis and drying temperatures are two relevant parameters in the synthesis.
• Hydrotalcite and malachite mixture phases.
• Catalysts heterogeneity promotes N2O production.

The reduction of NO by CO has been extensively studied for controlling the exhaust emissions. Most papers written on this subject have focused on supported noble metal catalysts and their drawbacks, which include their scarcity and high cost, and the tendency to form N2O as a byproduct during light-off over TWC (three-way catalyst). A copper–aluminum hydrotalcite-type precursor was successfully synthesized with metal ratio Al/(Al + Cu) = 0.17, using carbonate as compensation anion. Different synthesis parameters were varied aiming to find a pure phase with high synthesis yield. The catalysts were obtained after calcination to 600 °C and their performance was evaluated in NO reduction by CO. Another precursor containing hydrotalcite and malachite phases was used to compare properties and performance of the catalysts. The formation of the hydrotalcite phase in precursors and mixed oxides in the catalysts was evidenced by X-ray diffraction (XRD) and Raman spectroscopy. Redox properties were studied with TPR/TPO/TPR cycles, which show different reducible copper species for each material. The catalyst derived from pure copper–aluminum hydrotalcite-type precursor has attained an excellent performance promoting low N2O yield.

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