Toward rational design of a novel hierarchical porous Cu-SSZ-13 catalyst with boosted low-temperature NOx reduction performance

Abstract Nitrogen oxide (NOx), one of the main air pollutants exhausted from diesel vehicles, is harmful to the environment and human health and has been selectively catalytically reduced to N2 by Cu-exchanged zeolites with chabazite structures (CHA, Cu-SSZ-13). Unfortunately, the conventional Cu-SSZ-13 catalyst still has disadvantages in real applications, such as diffusion limits and micropore blocking due to formation of ammonium sulfates, especially at low reaction temperatures. Here, a highly crystalline hierarchical porous Cu-SSZ-13 zeolite (termed Cu-SSZ-13-HP) with enriched mesopores was rationally designed and prepared via a dual-template method for the first time. The novel Cu-SSZ-13-HP catalyst displayed boosted low-temperature activity (temperature of 70% conversion below 150 °C) and broadened active temperature window (between 175 and 500 °C, NOx conversion above 90%) compared with conventional Cu-SSZ-13 with only micropores. Importantly, Cu-SSZ-13-HP also exhibited superior hydrothermal stability and enhanced sulfur dioxide (SO 2) tolerance, even when exposed to 100 ppm of SO2 for 4 h. The in situ diffuse reflectance infrared Fourier transform spectroscopy revealed that the NH3 selective catalytic reduction reaction might conform to the Langmuir–Hinshelwood mechanism in which ammonia (NH3) and NOx were activated by the acid and redox sites, respectively. The Cu-SSZ-13-HP catalyst developed by the dual-template strategy might be a good candidate for low-temperature reduction of NOx exhaust from diesel vehicles.