Experimental and DFT studies on the characteristics of PbO/PbCl2 adsorption by Si/Al- based sorbents in the simulated flue gas

ABSTRACT Mineral oxides are effective in-furnace sorbents used to control lead (Pb) emissions in flue gas at high temperatures. In this paper, the PbO/PbCl2 adsorption characteristics of sorbents were investigated via experimental and density functional theory (DFT) methods. The results show that Si/Al-based compounds can chemically adsorb Pb, and the adsorption is related to the Si-O and Al-O bonds in the sorbents. Exposed Si and O atoms on SiO2 surfaces and exposed Al and O atoms on Al2O3 surfaces are the active sites for Pb adsorption, and PbO is easier to remove than PbCl2. Pb adsorption is promoted in a mixture of SiO2 and Al2O3. Doping Si atoms into Al2O3(100) promotes PbO adsorption, and doped three-coordinate Si atoms have a more obvious promotion effect than doped two-coordinate Si atoms. Doping Al atoms into SiO2(001) has no obvious effect on PbO adsorption. The effect of temperature on Pb adsorption was studied by thermodynamic analysis. The Gibbs free energy difference for PbO adsorption on SiO2(001) increases from -373.04 to 32.42 kJ/mol as the temperature increases from 300 to 1800 K. High-temperature calcination changes the bond length and bond angle of the system, affecting the stabilities of atomic configurations and decreasing the Pb adsorption capacity.