1-Butanol dehydration on AlPO 4 and modified AlPO 4: catalytic behaviour and deactivation

Abstract

Synthesis and physico-chemical characterization of a pure A1PO 4 and A1PO 4 modified by introduction of SO 4 2− ions (2 wt.-%) or Na + ions (0.5 wt.-%) have been carried out. The influence of these ions on A1PO 4 activity and selectivity in the 1-butanol dehydration has been investigated. The acid-base properties of these catalysts were determined by ammonia and carbon dioxide TPD and FT-IR spectroscopy of absorbed pyridine. Ion incorporation leads to a modification in the A1PO 4 acid-base properties, especially on the acid sites strength, with only very minor modification of its textural properties. Thus, Na + ions decreased the number of strong acid sites whereas SO 4 2− ions increased it. A linear relationship between those acid sites and selectivity values was found. Butenes (1-butene and 2-butenes) selectivities increased when the concentration of stronger acid sites was increased while the opposite trend was observed for dibutyl ether selectivity. The resistance to deactivation of the catalysts was examined not only in function of time on-stream in the 1-butanol dehydration but also after treatment with water or methylcyclopentane in the feed (for generating coke). Both factors negatively affected the A1PO 4 activity and the reaction temperature determined which factor was of prevailing influence. Besides, acid sites strength had an important role in the A1PO 4 deactivation.