The effect of Cu loading on the selective catalytic reduction of NO _x in diesel exhaust over SAPO-34

Ammonia selective catalytic reduction (NH₃-SCR) is currently the most effective technical approach for NO _x removal from exhaust gases. In this study, Cu _x -SAPO-34 catalysts were prepared by a two-step ion-exchange method using H-SAPO-34 molecular sieves as the support, and the effect of copper loading on the NH₃-SCR performance of Cu _x -SAPO-34 catalysts was systematically investigated. The NH₃-SCR performance evaluation device was set up to explore the influence of different copper loadings on the catalyst performance. Multiple characterization techniques, including XRD, ICP, XPS, BET, H₂-TPR, and NH₃-TPD, were employed to study the impact of the physical structure and chemical properties of Cu _x -SAPO-34 catalysts on NH₃-SCR performance from a microscopic perspective. Additionally, first-principles calculation methods were used to systematically investigate the evolution laws of the SAPO-34 support structure, Cu species morphology, active site characteristics, and NH₃-SCR reaction pathways under the regulation of Cu loading. The results show that Cu₄-SAPO-34 demonstrates superior denitrification activity at lower temperature ranges compared to the Cu₂-SAPO-34 and Cu₆-SAPO-34 samples, and the conversion rate increases with the increase in temperature, reaching a maximum of 98.66% at 170 °C and gradually decreasing from 360 °C. The NH₄-SAPO-34 has a larger specific surface area, which shows a trend of first increasing and then decreasing with the increase in Cu content. The Cu loading does not destroy the framework structure of the molecular sieve, and the XRD diffraction peaks of all catalyst samples maintain the original chabazite (CHA) structure of the H-SAPO-34 molecular sieve. The Cu₄-SAPO-34 has the largest total number and highest strength of acidic sites, and excessive Cu loading will cover or neutralize some acidic sites, leading to a decrease in acidity. The adsorption of NH₃ is the first step of the entire reaction, and the calculation reveals that the Cu²⁺ site is the active site of the reaction.