Moon Jo Chung

Deactivation of Pd catalysts in the hydrodechlorination of chloropentafluoroethane

Abstract The deactivation behavior of Pd catalysts on different supports in the hydrodechlorination of chloropentafluoroethane (CF 3 CF 2 Cl) was investigated. Changes of the BET surface area and the metal percentage exposed, measured by a multipurpose in situ catalyst characterization system during the reaction, gave some information about the deactivation mechanism of the Pd catalysts. The deactivation of the Pd catalysts was mainly caused by sintering of Pd particles rather than by coking. The sintering of Pd particles on the catalyst surface was promoted by the reaction of hydrogen fluoride with the support of the catalysts.

Preparation and characterization of magnesia-supported chromium catalysts for the fluorination of 1,1,1-trifluoro-2-chloroethane (HCFC-133a)

Abstract Chromium oxides dispersed on various supports by precipitation method were tested for the catalytic fluorination of HCFC-133a to HFC-134a. Catalytic activity decreased in the order of MgO>Al 2 O 3 >MgF 2 >TiO 2 >ZrO 2 . The most active Cr/MgO, when properly activated and pre-fluorinated before the reaction, shows superior activity to other catalysts that have been reported so far. Isolated (monomeric) Cr(VI) species that was formed during an optimized thermal activation were changed into fluoride (Cr x F y ) and oxyfluoride (Cr x O y F z ) form of monomeric and oligomeric Cr species during the pre-fluorination with HF, the latter of which are believed to be active sites for the reaction. High pre-fluorination temperature accelerates the formation of crystalline Cr 2 O 3 due to the formation of crystalline MgF 2 from MgO which anchors the isolated Cr(VI).

Adsorption equilibria of chloropentafluoroethane on activated carbon powder

An equilibrium study was conducted on the adsorption of chloropentafluoroethane (CFC-115, CF3CF2Cl) on activated carbon powder between 298.15 K and 373.15 K. Experimental data were fitted with several isotherm equations. Among the twoparameter equations, the BET equation showed the best results over the entire relative pressure range studied. When the pressure range was divided into two regions, a better result was obtained by applying the Langmuir equation in the lower pressure range and the BET equation in the higher relative pressure region. Among the threeparameter equations, the Langmuir-Freundlich equation gave better results than the RedrichPeterson equation. The isosteric heat of adsorption of CFC-115 on the activated carbon powder was estimated. It was found to have the same order of magnitude with the heat of condensation, which indicates that the adsorption was primarily due to physical forces.