Promotional effects of Er incorporation in CeO₂(ZrO₂)/TiO₂ for selective catalytic reduction of NO by NH₃

A series CeO₂(ZrO₂)/TiO₂ catalysts were modified with Er using a sol-gel method. The catalytic activity of the obtained catalysts in the selective catalytic reduction (SCR) of NO with NH₃ was investigated to determine the appropriate Er dosage. The catalysts were characterized using X-ray diffraction, N₂ adsorption, NH₃ temperature-programmed desorption, H₂ temperature-programmed reduction, photoluminescence spectroscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The results showed that the optimum Er/Ce molar ratio was 0.10; this catalyst had excellent resistance to catalyst poisoning caused by vapor and sulfur and gave more than 90% NO conversion at 220-395℃ and a gas hourly space velocity of 71400 h^-1. Er incorporation increased the Ti³⁺ concentrations, oxygen storage capacities, and oxygen vacancy concentrations of the catalysts, resulting in excellent catalytic performance. Er incorporation also decreased the acid strength and inhibited growth of TiO₂ and CeO₂ crystal particles, which increased the catalytic activity. The results show that high oxygen vacancy concentrations and oxygen storage capacities, large amounts of Ti³⁺, and low acid strengths give excellent SCR activity.