In situ synthesis of CuSAPO-34/cordierite and its selective catalytic reduction of nitrogen oxides invehicle exhaust: The effect of HF

CuSAPO-34/cordierite catalysts were prepared via in situ hydrothermal synthesis technique with and without HF. The morphology and structure of the synthesized samples were characterized in the present work. The NOx selective catalytic reduction (SCR) activities of the catalysts were evaluated with a fixed-bed reactor in simulated diesel vehicle exhaust. The results indicate that the addition of HF into the initial gel during the preparation of CuSAPO-34/cordierite can accelerate the crystallization and improve the relative crystallinity of CuSAPO-34, which lead to the compact morphology of the products. Furthermore, the existence of HF can increase the specific pore volume, BET surface area and CuSAPO-34 loading of the catalyst. For the crystallization time of 24 h, the loading amounts of CuSAPO-34 are 20.3 wt% and 13.6 wt% for the samples prepared with and without HF, respectively. The obvious improvement of the catalytic activities for NOx removal has been obtained over the catalysts prepared with HF. The active temperature window (NOx conversion rate > 95%) of the samples prepared with HF is wider(340-600 degrees C) than the samples prepared without HF(440-540 degrees C). The catalysts with HF present great endurance ability for the aging treatment at 650 degrees C with 15 vol.% H2O. The low temperature activity for NOx removal of the catalyst prepared with HF is not affected by the aging treatment and the maximum NOx conversion rate of the aging catalyst at the crystallization time of 12 h is about 96%, but only 80% for the catalyst without HF. The roles of HF and the different performances of the samples prepared with and without HF were discussed with the aid of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques. (C) 2012 Elsevier Ltd. All rights reserved.