Formation of a strong, high-porosity spinodal silica and its impregnation with a perfluoro ionomer to obtain a high performance solid acid catalyst composite

Abstract

Spinodal silicas, with similar properties to phase-separated glasses but showing high mechanical strength, with large pore sizes and porosities (total pore volume to total particle volume) of 0.7 or more have been produced by adding monobasic sodium phosphate and ammonium molybdate to a silica sol, drying to obtain particles, baking at about 700°C, and washing in hot water. The porosity was governed mainly by the monobasic sodium phosphate and ammonium molybdate addition, and the microstructure and pore size by the baking temperature and time, with short low-temperature baking yielding a spheroidal silica similar in properties to silica gels and high-temperature baking resulting in the spinodal microstructure. Spinodal silica particles of 1.1 µm average pore size and 0.74 porosity were filled with perfluoro ionomer solution and heat treated at 250°C after solvent removal, to obtain composite particles of 0.7 µm average pore size and 0.51 meq g−1 exchange capacity. The composite particles exhibited high mechanical strength and resistance to chemical desorption of the perfluoro ionomer, and strong catalytic activity as shown by the reaction rate constant of 0.98 L mol−1 min−1 eq(H+)−1 for the synthesis of ethyl acetate at 60°C and ambient pressure, which was 1.4 to several times the rate obtained under the same conditions with commercially available catalysts.