Abstract
The catalytic conversion of glycerol to acrolein by liquid-phase
dehydration over molecular sieves catalysts was studied. In order to
understand the role of the acidity, structure and porosity, five
structures were synthesized and evaluated. The lower the Si/Al ratio,
the higher the activity; large pore molecular sieves, as HY showed high performance (conversion =89.0%; selectivity to acrolein =99.5%), while
siliceous molecular sieves such as SBA-15 possessing weak acidity,
exhibited low conversion (40.6%) and decreased selectivity to acrolein
(84.0%). The structure and the acidity govern the selectivity to
acrolein and hydroxyacetone, the latter being a by-product mainly
dependent on the amount of weak and medium strengths acidic sites, as in
the case of H beta. The activity has almost the same order of the
acidity: HY > H beta > Mor > SBA-15 > ZSM-23. Modifications of the most
acidic and active catalysts by silanation (CVD) or Pt incorporation did
not result in an enhanced conversion. The studies of reusability and the
nature of the coke deposits indicated that heavy polycondensed and
cyclic C-6 compounds resulting from the reaction between glycerol and
acrolein block the pores and the acidic sites. The blockage was the main
cause of deactivation, whereas acidic site poisoning led to a less
extensive deactivation of the surface active sites. From these results,
it was possible to establish acidity-activity-deactivation relationships
that allow to explain the behaviour of the catalysts. (C) 2010 Elsevier
B.V. All rights reserved.
Users
Please
log in to take part in the discussion (add own reviews or comments).