abstracts - Институт катализа им. Г.К. Борескова

OP-III-13changes to the formation of stable intermediates INT1 and INT2. The first step is thedissociation of the first C-Cl bond. It results in the formation of adsorbed β-chloroethylspecies (INT1) in trans-position of the second C-Cl bond to Pt atom. The second step iscompleted with rearrangement of the trans-β-chloroethyl into a cis-conformation (INT2). Thethird step is the dissociation of the second C-Cl bond to form a C 2 H 4 molecule π-bonded tothe Pt-center on a chlorinated active center [Cl-AS-Cl]-C 2 H 4 (see Figure 2).Figure 2. The energy profiles of dechlorination reactions of 1,2-DCE to ethylene on Cu8Pt2nanocluster according to direct and step-by-step mechanisms.Although both channels for Pt-Cu system are thermodynamically possible, kineticrestrictions may exclude the direct mechanism and hence the reaction will proceed mainlythrough the consecutive mechanism. Thus, the essentially different rate of the CH 2 Cl-CH 2 Cl + H 2 reaction over Cu and Pt-Cu catalysts is not because of different rate of the C-Clbond dissociation. Most likely, the low rate of the reaction on Cu catalyst is caused by low Hequilibrium surface coverage due to the low heat of hydrogen adsorption. This results in ahigh equilibrium surface coverage of Cl and a low concentration of the free of Cl sitesavailable for 1,2-dichloroethane dissociation.References:1 V. Ponec and G.C. Bond, Catalysis by Metals and Alloys (Elsevier, Amsterdam, 1995).2 V.I. Kovalchuk and J.L. d'Itri, Appl. Catal. A 171 (2004) 13.3 L.S. Vadlamannati, V.I. Kovalchuk, and J.L. d'Itri, Catal. Lett. 58 (1999) 173.4.4 V.I. Avdeev, V.I. Kovalchuk, G.M. Zhidomirov, and J.L. d'Itri, Surf. Sci. 583 (2005) 46.340