Designed SO42-/Fe2O3-SiO2 solid acids for polyoxymethylene dimethyl ethers synthesis: The acid sites control and reaction pathways

The designed model SO42-/Fe2O3-SiO2 catalysts with varied acidic strength and Bronsted acid sites were successfully prepared. The properties of acid sites can be regulated by preparation method and silica incorporation. The S/Fe sample without silica had stronger acid strength, more Bronsted acid sites and higher acid density, which showed the best catalytic performance. NH3-TPD, pyridine-IR and methanol/dimethoxymethane adsorption-desorption techniques were employed to reveal the relationship between acid properties of the catalysts and catalytic activity for the reaction of trioxane with methanol. Further, this reaction is determined by the strength of acid sites on catalyst surface and does not affect by the inner pore diffusion. These findings suggest that the catalytic activity and selectivity can be monitored mainly by acid strength and Bronsted acid sites on the sulfated oxides, while trioxane decomposition process seems to be a vital step and polyoxymethylene hemiacetals are supposed to be the key intermediates. Meanwhile, a large number of acid sites and a higher surface area of the catalysts can also improve the catalytic performance. These results should provide some specific guidance for understanding of the reaction mechanism and the catalyst design. (C) 2014 Elsevier B.V. All rights reserved.