In-situ hydrothermal synthesis of Cu-SSZ-13/cordierite for the catalytic removal of NOx from diesel vehicles by NH3

Abstract

Cu-SSZ-13/cordierite monolithic catalyst was prepared by in situ hydrothermal synthesis method. The physicochemical properties of the as-prepared Cu-SSZ-13/cordierite were investigated by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, N2-adsorption, inductively coupled plasma, X-ray photoelectron spectroscopy, and solid-state NMR techniques. The removal of nitrogen oxides (NOx) from simulated diesel vehicle exhaust gas was performed using fixed-bed reactor. The effects of crystallization time and addition of HF during hydrothermal synthesis, reaction space velocity, and aging treatment of catalyst on the catalytic performances of NOx reduction reactions were investigated. The results indicate that the optimum crystallization time was 72h. Highly crystalline structure of zeolite Cu-SSZ-13 was formed, in a close combination with a carrier, via one step hydrothermal process. Cu-SSZ-13/cordierite showed excellent DeNOx performance for selective catalytic reduction (SCR) and anti-aging properties in a simulated diesel exhaust gas under a high space velocity. At a high space velocity of 72,000h−1, the highest conversion and N2 selectivity of 94% and 90%, respectively, were achieved. After the aging for 50h at 720°C, NOx reduction rate was still >80% in the temperature range of 350–550°C. The larger height to diameter ratio of the same catalysts enhanced the NH3-SCR catalytic activity and broadened the active temperature window. The addition of HF increased the catalytic activity and anti-aging performance of the sample.