Efforts have been devoted to exploring the effective composite catalysts for low-temperature selective catalytic reduction of NOx by CO (CO-SCR) using Fe-Cu bimetal oxide (Fe2Cu1) as the active component and rice husk ash (RHA), amorphous SiO2, and activated carbon (AC) as supports. The results showed that the beneficial role of RHA as a catalyst support for CO-SCR was primarily reliant on amorphous SiO2 in RHA and not on AC. Both Fe2Cu1/RHA and Fe2Cu1/amorphous SiO2 catalysts exhibited the best catalytic performance of CO-SCR, which had good stability, wide active temperature range, high conversion ratio, 100% N2 selectivity, and superior resistance to O2, SO2, and H2O (g). The CO and NOx conversion ratios of Fe2Cu1/amorphous SiO2 could reach up to approximately 100% from 100 to 500 °C. The excellent SCR performance was associated with the large specific surface area and good structural stability of amorphous SiO2, the uniform distribution of active sites, dual redox cycle of Fe2O3 and CuO species, and many surface-adsorbed oxygen species, which made amorphous SiO2-based catalysts highly competitive for application in the SCR process. This research provides the underlying insights for the improvement of industrial application to realize ″non-ammonia SCR″ technology with near-zero NOx/CO emissions synergistically at low temperatures.

Piperazine (PZ) blends containing PZ and monoethanolamine (MEA)/N-methyldiethanolamine (MDEA)/2-amino-2-methyl-propanol (AMP) were experimentally and computationally investigated to analyze their potential capabilities for CO2 capture, and the shuttle mechanism of PZ for enhanced CO2 absorption were verified. In experiments, the concentration of both PZ and MEA/MDEA/AMP were varied to show the effect of concentration ratio and the influence of amine components on the CO2 absorption rate and capacity. Experimental results showed that all the PZ blends possessed high absorption rates and large absorption capacities. To further understand the interaction behavior of amines/products and possible reaction pathways, both qualitative and quantitative 13C NMR analyses were conducted. The results indicated the conversion between absorption products, which can release free PZ to capture CO2 and consequently improve the absorption performance. Moreover, the static quantum mechanical calculations and ab initio molecular dynamics (AIMD) simulations combined with metadynamics sampling were conducted to evaluate the thermodynamic stability of absorption products and kinetically favorable key elementary reactions in PZ blends. This study highlights an accurate description of the shuttle effect of PZ for the enhanced CO2 capture by PZ blends.