Impacts of externally added Brønsted and Lewis acid on conversion of furfural to cyclopentanone over Ni/SiC catalyst

The conversion of furfural to cyclopentanone (CPO) involves not only hydrogenation but also acid-catalysis reactions. The step of the acid-catalysis might be catalyzed by Lewis acid or Brønsted acid or both, which was investigated in this study by employing Ni/SiC, a catalyst with “clean” surface containing negligible amounts of acidic sites. Lewis acid (nitrate salts and chloride salts) or Brønsted acid (D008, a solid acid resin catalyst) with externally added to the reaction medium. The results showed that both Lewis acid and Brønsted acid could catalyze the conversion of furfural to CPO. The further hydrogenation of furfuryl alcohol (FA) to tetrahydrofurfuryl alcohol was main side reaction, which could be suppressed more effectively with the Lewis acid like CrCl₃. The yield of CPO could be up to ca. 88.1 % with the Ni/SiC-CrCl₃ catalytic system. The chelation of CrCl₃ with FA stabilized the C[dbnd]C bond in the furan ring and the hydroxyl group, preventing the side reactions while facilitating CPO formation. The synergistic effects between the cation and anion was essential for the conversion of FA to CPO as the varied nitrate salts or chloride salts chelated with furfural, FA or other reaction intermediates in distinct ways, determining distribution of the products.