Tuning products selectivity in the catalytic oxidation of glycerol employing Metal-ZSM-11 materials
Copper and chromium supported on ZSM-11 (MEL type structure) microporous zeolites were investigated as catalysts for glycerol oxidation towards dihydroxyacetone and lactic acid. ZSM-11 was synthesized by hydrothermal crystallization. Subsequently an alkaline treatment of desilication was carried out, in order to generate zeolites with micro-mesoporosity. An ionic exchange with ammonium chloride was done to recover acids sites, and then, Cr (III) and Cu (II) species were incorporated onto these materials. Finally, thermal treatment at 500 ºC was carried out. These materials were characterized by different techniques, and then, evaluated in glycerol oxidation reaction, employing H2O2 as an oxidizing agent. The maximum conversion of glycerol (≈70%) was reached over Cr-ZSM-11 catalyst, with a selectivity to dihydroxyacetone of ≈28%. Meanwhile Cu-ZSM-11 offered 50% of glycerol conversion with a selectivity to 68% towards lactic acid. In both cases, the optimal reaction conditions were studied to maximize the selectivity towards the products mentioned above.