Identification of potassium phase in catalysts supported on zeolite NaX and performance in transesterification of Jatropha seed oil

•Potassium acetate transforms to potassium carbonate and located in NaX cavities.•The basic sites and biodiesel yields increased with K loading.•The highest biodiesel yield was 95% from 16K/NaX, higher than our previous work.•The potassium content did not change after the catalytic testing.

Zeolite NaX was synthesized by using rice husk silica and used as a catalyst support. It was impregnated with potassium acetate buffer solution to produce xK/NaX where x was potassium loading of 4, 8, 12 and 16 wt.%. After calcination the zeolite characteristic in all catalysts were still observed. The surface area and micropore volume decreased with potassium loading indicating that the cavities were occupied. The potassium precursor was mainly converted to carbonate which had strong basicity. As the basicity increased with the potassium loading, the bettter catalytic performance in transesterification of Jatropha seed oil to biodiesel was observed. The best catalyst was 16K/NaX which gave 95.2 ± 0.96% biodiesel yield.

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