Thermogravimetric determination of coke deposits on alumina-supported noble metal catalysts used as hydrodechlorination catalysts

摘要

The deactivation of 0.5 wt.% Pd on alumina, 0.5 wt.% Rh on alumina and 0.5 wt.% Pt on alumina catalysts for the hydrodechlorination of tetrachloroethylene (TTCE) in organic matrix has been studied. Experiments were carried out in a continuous fixed-bed reactor at 250 degreesC, 5 bar, 1.3 g catalyst min/mmol TTCE and 0.8 nl/min of hydrogen. The Pd catalyst is the most stable at the studied conditions, followed by Rh and Pt. In order to study the causes of deactivation, fresh and used catalysts were characterised by nitrogen porosimetry, X-ray diffraction (XRD), thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO) and pulse hydrogen chemisorption. Characterisation results indicate that the deactivation is caused mainly by the formation of carbonaceous deposits, being negligible the effects of poisoning by HCL It was observed that in addition to the amount of coke, its combustion temperature is an important parameter, showing a higher capacity to deactivate the catalysts the cokes with lower combustion temperatures (obtained from differential thermogravimetry (DTG) profiles). (C) 2001 Elsevier Science B.V. All rights reserved. [References: 14]