Influence of the nitrogen content on butan-1-ol and butan-2-ol dehydration properties of nitrided phosphates

摘要

Conversions and selectivities of butan-2-ol and butan-1-ol dehydration were studied over a series of 3 AlPO(N) samples with increasing nitrogen contents (0, 11 and 20 wt.%) in a conventional continuous flow micro reactor system at 200 and 275℃ for butan-2-ol and butan-1-ol dehydration respectively. Those reactions were chosen as test reactions of the changes induced by nitridation on the acid, basic and bifunctional acid-base properties of AlPON under catalytic conditions. Cis- and trans-2-butene are the main reaction products from butan-2-ol dehydration, indicating an E2 elimination mechanism, with a strong El character. The number of active sites for butan-2-ol dehydration decreases with nitrogen enrichment, in parallel with the number of acid sites evaluated by ammonia chemisorption experiments. Dibutylether is the main reaction product from 1-butanol dehydration, indicating that two alcohol molecules can be activated simultaneously on adjacent acid and basic sites. The number of acid-base conjugated sites catalysing the intermolecular dehydration of butan-1-ol is increased at the beginning of nitridation, but an optimum density of sites is attained for intermediate nitrogen contents. The activity of AlPON for those two reactions is compared to the activities of AlGaPON, ZrPON and VAlON oxynitrides. Product distribution over VAlON differs considerably from that observed over the nitrided phosphates. Butyraldehyde is the main product obtained from reaction of butan-1- ol; it reveals the presence of redox sites over VAlON.