Thermogravimetric determination of coke deposits on alumina-supported noble metal catalysts used as hydrodechlorination catalysts S. Ordo Ân Äez * , H. Sastre, F.V. Dõ Âez Department of Chemical and Environmental Engineering, University of Oviedo, Julia Ân Claverõ Âa s/n, 33006 Oviedo, Spain Abstract 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 ®xed-bed reactor at 2508C, 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 thecokeswithlowercombustiontemperaturesobtainedfromdifferentialthermogravimetryDTG)pro®les). # 2001Elsevier Science B.V. All rights reserved. Keywords: Tetrachloroethylene; Hydrodechlorination; Pd catalyst; Pt catalyst; Rh catalysts; Catalyst deactivation; Coke determination 1. Introduction Chlorinated organic solvents, specially tetrachlor- oethyleneTTCE),arewidelyusedinmanyindustries, beingthemainapplicationsdry-cleaningandprepara- tion of textile ®bres, degreasing of metals, extraction of organic compounds and cleaning of electronic devices. So in these uses, organic wastes with high content in TTCE are produced, being the disposal of thesewastesamajorenvironmentalandsocialproblem because of the TTCE toxicity and its capability for accumulating in the environment for long time. The incineration of these wastes is feasible, but it canleadtothereleaseofevenmoretoxiccompounds, suchasdioxinsandfurans[1].Hence,catalytichydro- dechlorination treatment with hydrogen, yielding hydrocarbons and hydrogen chloride) might be an interesting alternative [2]. Although,thecatalystsmostextensivelystudiedfor the hydrodechlorination of organochlorinated com- poundsinorganicmatrixarethehydrotreatmentones [3], in previous works of our research group it was observedthatpreciousmetalcatalystsaremoreactive [4]. In addition, these catalysts are active at moderate pressures and temperatures 1±5 bar, 2508C), while Thermochimica Acta 379 2001) 25±34 * Corresponding author. Tel.: 34-985-10-3437; fax: 34-985-10-3434. E-mail address: cromat@sauron.quimica.uniovi.es S. Ordo Ân Äez). 0040-6031/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0040-603101)00598-6