Vapor phase nitration of benzene over solid acid catalysts: III. Nitration with nitric acid (2); mixed metal oxide treated with sulfuric acid and heteropolyacid partially neutralized Original Research Article

Vapor phase nitration of benzene over solid acid catalysts is expected to be a clean process without sulfuric acid waste. In this research we investigated the vapor phase nitration of benzene by dilute nitric acid. We found that the catalytic activity of mixed metal oxides containing TiO2 or ZrO2 was improved greatly by the treatment with sulfuric acid at 500°C and that the catalytic activity of heteropolyacid can be increased greatly by partial neutralization with Cs or Tl. The reasons for these enhancements were identified as the increase of acid strength and the active surface area, respectively. The catalytic activity is very stable, especially for the mixed oxide treated with sulfuric acid. The TiO2(4)–MoO2(1) after treatment with sulfuric acid at 500°C showed a high activity: 87% yield of nitrobenzene (STY=0.72 kg/kg cat h) for more than 528 h on stream.