Optimization of Tailoring of CuO_x Species of Silica Alumina Supported Catalysts for the Selective Catalytic Reduction of NO_x

Abstract

A series of CuO x catalysts dispersed on SiO2−Al2O3 support with a copper content from 0.2 to 12 wt % corresponding to 0.04−3.7 atomCu nm-2 was prepared by chemisorption-hydrolysis method from copper solutions. The catalysts were characterized in their bulk (XRD, redox cycles with H2 and O2) and surface (N2 adsorption, SEM, XPS, and DRS) properties. Copper species were found to be uniformly spread on the SiO2−Al2O3 support as small aggregates both in the low and high copper loaded samples. Spectroscopic evidence agrees with Cu2+ presence in an axially distorted octahedral environment of O-containing ligands. At high copper loading, the existence of copper centers in closer interaction occurred forming structures of oxocations-like type. Temperature programmed reduction (TPR) experiments confirmed the presence of dispersed copper species which underwent complete reduction. Comparing the position and shape of two successive TPR profiles, carried out interposing an oxidation run (temperature programmed oxidation), it was found that the smallest CuO x centers (<1 atomCu nm-2) are characterized by low stability and high mobility. Increasing the copper content diminished the mobility of the CuO x species, as larger CuO x aggregates were formed. The selective catalytic reduction of NO x with ethene in the presence of excess oxygen was studied in a flow apparatus at fixed reactant concentration (1500 ppm of NO x and C2H4 and 15000 ppm of O2) and contact time (8 g s mmol-1), with an online FT-IR analytical device. Catalysts containing up to about 1 atomCu nm-2 displayed very little activity, while catalysts with higher copper content were active and selective. Maximum activity was associated with samples containing 1.5−2 atomCu nm-2, while samples with higher copper concentration were less active. Results point to the need to individuate relationships between structure and catalyst properties and activity to optimize the preparation of suitable tailored copper-containing catalysts.

The Potential of Activated Carbon Made of Agro-Industrial Residues in NOx Immissions Abatement

“…Even though only NO2 is supplied to the system, other nitrogen oxides-containing species (as NO) are formed due to reduction of NO2 in the presence of activated carbon [11][12][13][14][15][16][17]. The reduction of NO2 to NO is highly undesirable because the separation capacities of activated carbons for NO are negligible.…”

“…Despite the emission reduction measures implemented for automotive and industrial exhaust gases [13][14][15][16], vehicle occupants and urban population are particularly affected by high or even increasing nitrogen oxides immissions. As a result, the interest in adsorptive cabin air filters and HVAC (Heating, Ventilation and Air Conditioning) filters is rising.…”

Adsorption-catalytic Purification of Gas Mixtures from Sulphur Dioxide by Sorbent of Phosphoric Production Wastes

“…The model gas mixture is prepared by mixing of gaseous sulfur dioxide, supplied from balloon 1 through a gasholder with layer of oil, by preventing dissolution of sulfur dioxide in water 2 . A constant level of water in the gasholder is kept up by controlling water layer in the water tank 3 . The gas is mixed with air, supplied by a compressor 4 .…”

“…The initial sorbent, that has a light gray color, with a specific gravity of 2,86 g/cm 3 , hygroscopic moisture of 0,37%, a bulk density of 1,74 g/cm 3 and grain size of 0,074-2,5 mm, is subjected to the pre-grinding for obtaining the homogeneous mass and more reactive surface. Chemical composition of termophosphorus slag is shown in Table 1 and an electronic image is presented in Figure 2.…”

“…The most promising, for the purification of waste gases from sulfur dioxide is the use of metals, especially alkaline earth or amphoteric metals oxides or carbonates as an adsorbent (Bennici et al, 2003;Smirnov et al, 2005;Bretschneider and Kurfurst, 1989;Li et al, 2004;Chmielarz et al, 2006). However, a special preparation of individual metal oxides significantly complicates and makes the process more expensive.…”