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

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 tetrachloroethy lene (TTCE) in organic matrix has been studied. Experiments were carried ou t 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 stabl e 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), thermograv imetry (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 carbon aceous deposits, being negligible the effects of poisoning by HCL It was ob served that in addition to the amount of coke, its combustion temperature i s an important parameter, showing a higher capacity to deactivate the catal ysts the cokes with lower combustion temperatures (obtained from differenti al thermogravimetry (DTG) profiles). (C) 2001 Elsevier Science B.V. All rig hts reserved.