Synthesis And Characterization Of New Porous Heteropoly Compound Catalytic Materials

Heteropoly compounds have great utilities in catalysis because of their acidity and oxidation-reduction quality, and porous materials have been studied extensively due to their utilities as high surface area catalysts and sorption medias. In this paper, a surfactant salt of the heteropoly acid with two-dimensional layered structure has been hydrothermally synthesized in a Teflon-lined autoclave with the template cetyltrimethylammonium bromide, phosphomolybdic acid or phosphotungstic acid as the initial material. On such basis, a new porous structured heteropoly acid catalyst is obtained by salt-gel reaction, using tetraethyl orthosilicate as the silicon source. Calcination to decompose the organic structure- directing agent will collapse the structure of the heteropoly anion and invariably lead to dense oxide phases, hence here we removed the template cetyltrimethylammonium bromide by extraction with the solvent HCl/EtOH. The materials have been characterized by IR, XRD, TEM, AFM, electron probe microanalysis, elementary analysis, and nitrogen BET surface measurements. The results show that the pore diameter is 30-40 nm, the surface area of the porous material is up to 106-140 m2/g and the Keggin structure remains intact after the extraction. Furthermore, in a sol-gel reaction the heteropoly acid supported on the silica has also been synthesized, which has the high surface areas 150~170 m2/g and the pore diameter about 60 nm after the same series of characterization. The porous heteropoly acid can give a good activity in acid catalysis and oxidation catalysis reaction.