Abstract
Here we report an economical synthesis method for high-silica (Si/Al∼17) LTA zeolites using colloidal silica and ammonium fluoride as Si and F sources, respectively. When both 1,2-dimethyl-3-(4-methylbenzyl)imidazolium and tetramethylammonium ions are used as organic structure-directing agents, the LTA crystallization was found to strongly depend on the particle size of the colloidal silica employed. However, the type of Al and F sources had little effect on the formation of this small-pore zeolite. The catalytic properties of three high-silica Cu-LTA catalysts synthesized using the same Si source (Ludox HS-40 colloidal silica) but different Al sources (aluminum hydroxide, aluminum metal, and pseudoboehmite) for the selective catalytic reduction of NOx with NH3 (NH3-SCR) are also presented. Despite the presence of a large amount of extraframework Al, all of the catalysts exhibited considerably higher activity maintenance than the current commercial Cu-SSZ-13 catalyst even after hydrothermal aging at 900 °C.
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