Gas-phase dehydration of glycerol to acrolein catalysed by caesium heteropoly salt

Caesium 12-tungstophosphate, Cs2.5H0.5PW12O40 (CsPW), possessing strong Bronsted acid sites is an active catalyst for the dehydration of glycerol to acrolein in the gas-phase process at 275 C and 1 bar pressure. The initial glycerol conversion amounts to 100% at 98% acrolein selectivity, however, decreases significantly with the time on stream (similar to 40% after 6 h) due to catalyst coking, without impairing acrolein selectivity. Doping CsPW with platinum group metals (PGM) (0.3-0.5%) together with co-feeding hydrogen improve catalyst stability to deactivation, while maintaining high selectivity to acrolein. The enhancing effect of PGM was found to increase in the order: Ru similar to Pt < Pd. The catalyst 0.5%Pd/CsPW gives 96% acrolein selectivity at 79% glycerol conversion, with a specific rate of acrolein production of 23 mmol h(-1) g(cat)(-1) at 275 C and 5 h time on stream, exceeding that reported previously for supported heteropoly acids (5-11 mmol h(-1) g(cat)(-1) per total catalyst mass). Evidence is presented regarding the nature of acid sites required for the dehydration of glycerol to acrolein, supporting the importance of strong Bronsted sites for this reaction. (C) 2010 Elsevier B.V. All rights reserved.