title: Catalytic hydrodechlorination of chloroaromatic gas streams promoted by Pd and Ni: the role of hydrogen spillover.
abstract: Catalytic hydrodechlorination (HDC) is an effective means of detoxifying chlorinated waste. Involvement of spillover hydrogen is examined in gas phase dechlorination of chlorobenzene (CB) and 1,3-dichlorobenzene (1,3-DCB) over Pd and Ni. The catalytic action of single component Pd and Ni, Pd/Al(2)O(3), Ni/Al(2)O(3) and physical mixtures with Al(2)O(3) has been considered. Catalyst activation is characterized in terms of temperature programmed reduction, the supported nano-scale metal phase by transmission electron microscopy and hydrogen/surface interactions by chemisorption/temperature programmed desorption. Pd/Al(2)O(3) generated significantly greater amounts of spillover hydrogen (by a factor of over 40) compared with Ni/Al(2)O(3). Hydrogen spillover on Pd/Al(2)O(3) far exceeded the chemisorbed component, whereas chemisorbed and spillover content was equivalent for Ni/Al(2)O(3). Inclusion of Al(2)O(3) with Ni and Ni/Al(2)O(3) increased spillover with an associated increase in specific HDC rate (up to a factor of 10) and enhanced selectivity to benzene from 1,3-DCB. HDC rate delivered by Pd and Pd/Al(2)O(3) was largely unaffected by the addition of Al(2)O(3). This can be attributed to the higher intrinsic HDC performance of Pd that results in appreciable HDC activity under conditions where Ni/Al(2)O(3) was inactive. Spillover was partially recovered (post TPD) for the Ni samples but the loss was irreversible in the case of Pd.
authors.affiliation: Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Amorim
authors.forename: Mark A
authors.initials: MA
authors.lastname: Keane
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D002384:Catalysis; D002713:Chlorine / Q000737:chemistry; D002722:Chlorobenzenes / Q000737:chemistry*; D005740:Gases; D006859:Hydrogen / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D014865:Waste Disposal, Fluid / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D002722:Chlorobenzenes; D005740:Gases; D014874:Water Pollutants, Chemical; D002713:Chlorine; D010165:Palladium; C042146:1,3-dichlorobenzene; D009532:Nickel; D006859:Hydrogen; D000537:Aluminum Oxide