Hydrodechlorination of tetrachloroethene over Pd/Al2O3:: influence of process conditions on catalyst performance and stability

The influence of process parameters (temperature, pressure, hydrogen flow rate, and nature of solvent) on both activity and stability of a 0.5% Pd on alumina catalyst used for tetrachloroethene (TTCE) hydrodechlorination in an organic matrix was studied. In the range of temperature studied (250-350degreesC), higher temperatures lead to higher initial activity but faster deactivation. Increasing hydrogen flow rates, up to 0.8 L/min (STP), produce higher activity and stability of the catalyst, whereas pressure in the range 0.5-2 MPa has no significant effect. In all the cases, both hydrodechlorination and hydrogenation of the double bond take place, yielding ethane as the main product. Concerning to the solvent, there is no difference in the initial catalytic activity for either toluene or n-decane, but n-decane leads to faster catalyst deactivation. The effect of temperature and space time in TTCE conversion at the period of constant catalytic activity can be modelled by a kinetic model assuming first order for TTCE and zero-order for H-2. Finally, the performance of the Pd alumina-supported catalyst is compared with that of a I'd carbon-supported catalyst with the same metal load, used in previous works. Although the carbon-supported catalyst yields higher initial conversion, the alumina-supported catalyst is more resistant to deactivation. (C) 2003 Elsevier Science B.V. All rights reserved.