BACKGROUND: Acrylic acid commercially produced by the successively catalytic oxidation of propylene has a high cost. The synthesis of acrylic acid by aldol condensation between coal derivatives, acetic acid and formaldehyde, is an economic alternative to the propylene oxidation process. However, the development of an environmentally friendly and effective catalyst has remained a challenge. RESULTS: Diboron trioxide [B 2 O 3 (6-20%)]/silica (SiO 2 ) nanocomposites with B 2 O 3 particle sizes of 1-2 nm prepared by the wetness impregnation of boric acid into silica aerogel and subsequent calcination at 500 °C effectively catalyzed the gas-phase aldol condensation reaction between acetic acid and formaldehyde (trioxymethylene) to acrylic acid with a selectivity of ≈87% at 340-400 °C. Bismuth (Bi-), tungsten (W-) and caesium (Cs)-doped B 2 O 3 /SiO 2 nanocomposites had higher catalytic activities in the gas-phase aldol condensation reaction to acrylic acid than the undoped B 2 O 3 /SiO 2 nanocomposite. CONCLUSION: Weak-strength Lewis acid and alkali sites of the B 2 O 3 (6-20%)/SiO 2 nanocomposites co-catalyzed the aldol condensation reaction to form acrylic acid. The doping of B 2 O 3 /SiO 2 nanocomposites with Bi, W and Cs components results in the formation of BiBO 3 , WO 3 and CsBO 2 phases, which lead to an increase in acidity and basicity resulting in higher catalytic activity in the formation of acrylic acid.

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