Low temperature propylene SCR of NO by copper alumina catalyst

Abstract

NO reduction to N 2 by C 3H 6 was investigated on various copper alumina catalysts prepared by a precipitation method with different copper (Cu) weight percentages to that of aluminium (Al). The catalysts were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis (TGA), Fourier transformed infrared (FT-IR) spectroscopy, Brunner Emmett Teller surface area (BET-SA), X-ray photoelectron spectroscopy (XPS), H 2-TPR (temperature programmed reduction) and scanning electron microscopy (SEM) techniques. It is found that the catalyst preparation method as well as the copper content exerts a significant influence on catalytic activity for NO to N 2 conversion. From the DTA analysis it is found that there is a loss of water and CO 2 at 114 to 390 °C and total weight loss by TGA at around 600 °C. A high conversion (70%) of NO to N 2 is obtained by the Cu–Al (3:7) catalyst at 300 °C in the presence of 600 ppm NO x + 600 ppm C 3H 6 + 8 vol.% O 2. The order of catalysts for higher NO to N 2 conversion is as follows: Cu–Al (3:7) > Cu–Al (2:8) > Cu–Al (4:6) > Cu–Al (1:9) > Cu–Al (7:3). The XPS results show that the Cu–Al (3:7) catalyst calcined at 600 °C possess highly dispersed surface copper (Cu 2+) species. The presence of high surface availability of copper (44.8%), in particular as CuAl 2O 4 phase, with a high percent intensity of 44 in the Cu–Al (3:7) catalyst is the key to obtaining high efficiency (70%) in a wide range of temperatures (250–400 °C). From in situ diffused reflectance infrared Fourier transformed (DRIFT) spectral analysis, evolution of different intermediate species like –NO 2, R–NO, –COO −, –CN, –NCO and –NH 2 were observed with varying intensities on different Cu–Al catalysts at different reaction temperatures.