Flaming combustion and smoldering of active impregnated cigarette butts: A novel method for synthesis of nanostructured MnOx catalysts for NOx reduction

In the present study, a novel combustion method was proposed to synthesize nanomaterials, and nano-sized MnOx was prepared by this method as example. Being different from the traditional solution combustion synthesis method, a cigarette butt (CB, a typical municipal solid waste), rather than the pure soluble organics (e.g., glycine, urea, citric acid, etc.), was used as the fuel. In this process, the cellulose acetate-based cigarette butt also acted as the support or template, because the manganese nitrate in the solution will be adsorbed and dispersed uniformly on the surface of the cellulose acetate fillers. After burning the impregnated cigarette butts, the nano-sized MnOx was obtained. Both smoldering and flaming combustion with different ignition temperatures were considered in the combustion synthesis process. Thermogravimetric (TG) analysis was conducted to study the combustion behavior of the pure and manganese nitrate-loaded cigarette butts. XRD, FE-SEM, TEM, XPS, H-2-TPR and N-2 adsorption-desorption were conducted to detect the physical and chemical characteristics. The product obtained via this combustion method was main in the Mn3O4 phase. The prepared nanoparticles with different ignition temperatures have a uniform particle size distribution (40-50 nm). The MnOx synthesized by smoldering showed better porosity than the flaming-combustion-synthesized MnOx. The H-2-TPR and XPS characterization showed that both of the catalysts synthesized by either the smoldering or flaming combustion process, possessed similar redox properties. The nano-MnOx catalyst was applied for the selective catalytic reduction of NO, and the results suggested that MnOx synthesized by smoldering had more stable activity.