Advantages of bimetallic nitric oxide reduction catalysts consisting of heavy metals rich in hazardous wastes

Abstract

Abstract High-value-added recycling of hazardous waste is a key problem in environmental science and engineering. In previous reports, a hazardous-waste-derived catalyst showed better activity than a catalyst synthesised from pure reagents for the reduction of nitric oxide. The multimetallic nature of hazardous waste was speculated to increase the catalytic activity. In this work, a further investigation was conducted to confirm this speculation. It was found that bimetallic catalysts showed better activity than monometallic ones at 50–200 °C. A bimetallic catalyst removed 75.05% of nitric oxide (990 ppm) at 150 °C, whereas monometallic ones removed only 19.50%. Moreover, the bimetallic catalyst removed 11.46 mmol/g of nitric oxide after 1200 min at 300 °C, which was a much higher concentration than that removed by the monometallic catalyst (2.72 mmol/g). Experimental and simulated Raman spectroscopy revealed that enhanced activity was accompanied by a larger blue shift of the metal band (indicating catalytic centre activity) and a smaller blue shift of the carbon band (indicating reductant stability). In a theoretical calculation, a second metal changed the electron density difference of the catalytic centre and activated the distant reductant, increasing both the low-temperature activity and activity stability. The main result of this study explained the reason bimetallic catalysts outperformed the monometallic ones. Because hazardous waste usually contains bimetallic species, it can be used as a suitable resource for producing effective catalysts.