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.