Enhanced NOx adsorption using calcined Zn/Mg/Ni/Al hydrotalcite-like compounds

We report an improved absorbent material for NOx, a major component of acid rain and other environmentally hazardous chemicals. This new material is based on the hydrotalcite-like compounds and incorporating Mg and Zn markedly enhances the capacity of adsorbing NOx. Ni/Al, Mg/Ni/Al, and Zn/Mg/Ni/Al hydrotalcite-like compounds were synthesized by coprecipitation, characterized by X-ray diffraction (XRD), ICP, infrared (IR), and scanning electron microscopy (SEM) and tested for the performance in adsorption of NOx on derived mixed oxides. The prepared adsorbents give better performance than the conventional activated carbons. The adsorption capacity for NOx is highly dependent on the composition of adsorbent materials. The capacity is highest for Zn1Mg1Ni1Al1 at 2300 mg/g, with 73% efficiency. The physical and structural properties of the materials before and after NOx adsorption were investigated to gain a better understanding of the underlying mechanism. IR d-spacing and SEM measurements indicate that physisorption and chemisorption have occurred cooperatively. Adsorption of NOx has led to the reformation of layered double structure by the resultant nitrates and nitrites around the oxide sites between the positively charged layers of the hydrotalcite. As a consequence, it catalyses more and more NOx to be absorbed. Other possible mechanisms are also discussed.