Weibin Li

Selective catalytic reduction of nitric oxide by ethylene in the presence of oxygen over Cu2+ ion-exchanged pillared clays

Abstract Cu 2+ ion-exchanged pillared clays are substantially more active than Cu 2+ -ZSM-5 for selective catalytic reduction (SCR) of NO by hydrocarbons. More importantly, H 2 O (or SO 2 ) has only mild effects on their activities. First results on Cu 2+ -exchanged TiO 2 -pillared montmorillonite were reported by this laboratory (Yang and Li, Ref. [1]), that showed overall activities two to four times higher than Cu 2+ -ZSM-5. A delaminated pillared clay was subjected to Cu 2+ ion-exchange and studied for SCR by C 2 H 4 in this work. The Cu 2+ ion-exchanged delaminated Al 2 O 3 -pillared clay yielded substantially higher SCR rates than both Cu 2+ -exchanged TiO 2 -pillared clay and Cu 2+ -ZSM-5 at temperatures above 400°C. The peak NO conversion was 90% at 550°C and at a space velocity of 15,000 h −1 (with O 2 = 2%). The peak temperature decreased as the concentration of O 2 was increased. The macroporosity in the delaminated pillared clay was partially responsible for its higher peak temperatures (than that for laminated pillared clays). At 1000 ppm each for NO and C 2 H 4 , the NO conversion peaked at 2% O 2 for all temperatures. H 2 O and SO 2 caused only mild deactivation, likely due to competitive adsorption (of SO 2 on Cu 2+ sites and H 2 O on acid sites). The high activity of Cu 2+ -exchanged Al 2 O 3 -pillared clay was due to a unique combination of the redox property of the Cu 2+ sites and the strong Lewis acidity of the pillared clay. The suggested mechanism involved NO chemisorption (in the presence of O 2 ) on Cu 2+ O Al 3+ -on the pillars, and C 2 H 4 activation on the Lewis acid sites to form an oxygenated species.

Low temperature vapor-phase preparation of TiO2 nanopowders

The preparation of TiO2 nanopowders by vapor-phase hydrolysis of TiCl4 below 600°C is studied in this paper. Influences of preparation variables, such as preparative temperature, residence time, reactant concentration, and H2O/TiCl4 mole ratio, on TiO2 particle size, morphology and chlorine contamination are investigated, followed by discussion. It shows that the hydrolysis temperature exerts greatest influences, while the residence time hardly have impact on product particles below 400°C, among the hydrolysis variables investigated. The chlorine contamination on nanopowders occurs during the preparation which can be greatly reduced by proper control on preparation variables. Unlike the high temperature gas-phase processes such as oxidation route and flame synthesis, low-temperature route shows the ready control on product powders, and thus obtains titania powders with small size, narrow size distribution and very weak agglomeration. In addition, the decreased energy consumption, retarded corrosion on the reactor and the reduced operation problems would be expected for the low temperature processes.

Improvement of thermal stability of Ti-Zr mesoporous oxides using CTAB surfactant templates mixed with auxiliary organic additives

Abstract Several auxiliary organic additives such as dodecylamine, Triton-X 100, triethanolamine and hexamethylenetetramine (HMTA) were all found to be able to improve thermal stability of the 1:1 molar ratio Zr/Ti mesoporous oxides prepared from inorganic salt precursors using cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions. Particularly, a high surface area, i. e., 386 m2/g was available on the Ti-Zr mesoporous oxides prepared from CTAB and HMTA after calcinations at 450 °CC, meanwhile the mesoporous structures still retained on the calcined sample.