FTIR and Reaction Kinetics Studies of the Hydrodehalogenation of CF2Br2, CH2Br2, and CD2Br2over a Pd/γ-Al2O3Catalyst
V. Yu. Borovkov, Parag P. Kulkarni, Vladimir I. Kovalchuk, Julie L. d’Itri · The Journal of Physical Chemistry B · 2004
A combination of FTIR and chemical reaction kinetics studies was employed to investigate the hydrodehalogenation of CF 2 Br 2, CH 2 Br 2, and CD 2 Br 2 catalyzed by Pd/γ-Al 2 O 3 . The products of the CF 2 Br 2 +H 2 reaction (CF 2 H 2, CF 3 H, C 1 −C 3 hydrocarbons) are typical for a reaction mechanism with the participation of:CF 2 and:CH 2 carbenes as the reaction intermediates. It was not possible to detect:CF 2 carbenes by FTIR during the adsorption studies. It is proposed that the carbenes are unstable on the Pd surface in the absence of H 2 and readily decompose to form carbonaceous deposits and adsorbed halogen atoms. Thus, room-temperature hydrogenation of the surface species formed during adsorption of CF 2 Br 2 on Pd/γ-Al 2 O 3 at room temperature yields only CH 4, HBr, and HF. The:CD 2 and:CH 2 carbenes formed from dissociation of CD 2 Br 2 and CH 2 Br 2 adsorbed on the Pd surface are stable at room temperature, as indicated by the formation of CD 2 H 2 upon hydrogenation of adsorbed species by H 2 and D 2, respectively.