title: High-temperature hydrodechlorination of ozone-depleting chlorodifluoromethane (HCFC-22) on supported Pd and Ni catalysts.
abstract: The hydrodechlorination of chlorodifluoromethane (HCFC-22) was performed by a catalytic reaction and noncatalytic thermal decomposition at high temperatures of 400-800 °C. After 47 h of time-on-stream on a supported palladium (Pd) catalyst, the gas phase composition of difluoromethane (HFC-32) is 41.0%, with 4.9% of the HCFC-22 remaining, indicating the conversion of up to 95.1% of HCFC-22. The supported nickel catalyst's deactivation is significant as it exhibits the low conversion of HCFC-22 under the same reaction conditions. The deactivation of the catalyst is caused by the polymerization of adsorbed methyl radicals, which competes with the formation of HFC-32. With concentrated reactants at high reaction temperatures, there was an increase in the catalytic activity; however, unwanted tar, methane, and trifluoromethane (HFC-23) by-products are also produced. The use of catalyst suppresses the formation of these by-products. Considering the compositions of the products of the catalytic and noncatalytic reactions, we demonstrate that the use of the supported-metal catalysts and hydrogen flow suppresses tar formation and lowers the required reaction temperature.
authors.affiliation: Clean Energy Research Center, National Agenda Research Division, Korea Institute of Science and Technology, Seoul, Republic of Korea.
authors.forename: Jeong-Myeong
authors.initials: JM
authors.lastname: Ha
authors.forename: Daewoo
authors.initials: D
authors.lastname: Kim
authors.forename: Jaehoon
authors.initials: J
authors.lastname: Kim
authors.forename: Byoung Sung
authors.initials: BS
authors.lastname: Ahn
authors.forename: Yunje
authors.initials: Y
authors.lastname: Kim
authors.forename: Jeong Won
authors.initials: JW
authors.lastname: Kang
mesh_terms: D000327:Adsorption; D002384:Catalysis; D005617:Chlorofluorocarbons, Methane / Q000737:chemistry*; D006358:Hot Temperature; D008697:Methane / Q000031:analogs & derivatives / Q000737:chemistry; D009532:Nickel / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*
chemical_list: D005617:Chlorofluorocarbons, Methane; C051224:methyl radical; D010165:Palladium; D010126:Ozone; C009755:fluorocarbon 22; D009532:Nickel; C007782:dichlorodifluoromethane; D008697:Methane