Enhanced catalytic benzene oxidation over a novel waste-derived Ag/eggshell catalyst

Abstract

Catalytic oxidation plays a key role in transforming gaseous benzene into harmless matter, in which it is essential to look for a low-cost, environmentally friendly and efficient green catalyst/support. Herein, Ag nanoparticle (Ag NP) loaded-eggshell catalysts were successfully synthesized by a simple impregnation method, in which waste eggshells were used as an efficient template and catalyst support. SEM, XRD and ICP-OES results show that a different number of Ag NPs are uniformly distributed on the surface of eggshells, which are defined as Ag₁/eggshell (10.8%), Ag₂/eggshell (19.9%) and Ag₃/eggshell (34.3%) catalysts according to the amounts of loaded Ag NPs. Then, the activity between the three catalysts and the pure Ag NPs was assessed based on the catalytic oxidation of benzene. Our results show that the Ag NP loaded-eggshell catalysts exhibit superior catalytic activity compared with the pure Ag NPs. Considering the balance between the cost and catalytic performance, the Ag₂/eggshell catalyst was selected as the optimum research object in the subsequent work. The Ag₂/eggshell catalyst calcined at 500 °C exhibited excellent catalytic activity, which is assigned to the unique channel structure of eggshell, good low-temperature reducibility, and high dispersion of particles (sizes effects) on the surface of eggshell as well as the synergetic interaction between the Ag NPs and eggshell. Furthermore, the Ag₂/eggshell catalyst exhibited predominant stability even after 200 h of on-stream reaction. The reaction mechanism is put forward based on the in situ FTIR experimental results, in which some carboxylate intermediate species are confirmed. Accordingly, the waste eggshell is considered as a promising supporting material for the large-scale synthesis of noble metal catalyst with high catalytic performance and stability for VOC oxidation.