Chemical and morphologic interactions of oxide particles on the aluminosilicate matrix prepared by Sol-Gel method

Several ceramic materials have been studied for heterogeneous catalysis applications. In spite of some ceramic oxides to be active for transesterification reactions, the surface area can be a disadvantageous aspect for high yield conversion. By the other hand, many porous ceramics are inactive as catalyst for transesterification, but can be used as matrix support. In this work, it was synthesized porous ceramic of aluminosilicate in order to obtain a matrix composite for heterogeneous catalysis applications. TEOS and aluminium nitrate were used as raw materials to obtain porous matrix with composition Si_0.75Al_0.25O_1.88 by Sol Gel method. The powder samples were grinded and calcinated at 500 and 600 deg C for 4 hours in order to investigate the chemical and morphologic interactions occurring on the aluminosilicate matrix with 10wt% of zinc aluminate and bismuth oxide. As result, the silicon-aluminum oxy-hydrates of the gel precursor decomposes under 350 deg C, but the complete organic matter elimination occurs only above 550 deg C, as showed by TG/DTG analysis. That powder samples were characterized by XRD and BET techniques and the results are discussed under the chemical and morphologic interactions viewpoints. Zinc aluminate particles act as wall coalescence barrier and preserve the surface of composite samples much more than non-modified matrix or the isolated ceramic powders when the temperature was 600 deg C. The matrix thermal treated at 500 deg C does not present chemical reaction among the ceramic constituents, but at 600 deg C, the bismuth oxide forms solid solution with the aluminosilicate matrix and the XRD peak disappear on the XRD pattern. Keywords: biodiesel, heterogeneous catalysis, transesterification. (author)