Gas phase dehydration of glycerol over, lanthanum-modified beta-zeolite

• Beta zeolite partially exchanged with lanthanum is active for glycerol dehydration.
• Medium-strength acidity is needed in order to obtain good activity and stability.
• Coke deposits leads to a fast pore blockage.
• After few minutes on stream, only the external surface is active.
• The preparation procedure decreased the crystallinity only 2%.

Glycerol dehydration to acrolein was studied using beta zeolites. Three catalysts were used, the parent catalyst in the protonic form (H-B), and this catalyst after two ion exchanges, both with lanthanum nitrate (LCL-B) and one with lanthanum nitrate and the second with ammonium nitrate (LCH-B). The catalysts were characterized by XRD, XPS, FTIR with pyridine adsorption, pyridine TPD, BET, SEM, ICP, and pulses of 1-butene. Coke was characterized by TPO. Activity tests were carried out in gas phase. It was found that LCH-B and H-B catalysts had similar density of acid sites, but the strength distribution was different, having the former a higher proportion of medium-strength acid sites. Because of this, a better performance in glycerol dehydration was displayed by this catalyst. The changes in acidity were due to the generation of new acid sites that occurred during the preparation, forming acid silanols attached to silica-reach and alumina-reach species. Coke was rapidly formed on the three catalysts, completely blocking the pores. Therefore, after a short time on oil, only the external surface is available for the reaction. Nevertheless, reasonable conversion and stability was obtained with LCH-B catalyst.

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