Hydrogen-assisted 1,2,3-trichloropropane dechlorination on supported Pt-Sn catalysts

The chemical kinetics behavior of Pt-Sn/C catalysts for hydrogen-assisted 1,2,3-trichloropropane dechlorination is understood in terms of a modification of Pt by both Sn and Cl. Catalysts with Pt:Sn atomic ratios ranging from 9:1 to 1:6 exhibit a 10-20 h time-on-stream (TOS) transient period characterized by a 2-3 fold decrease in activity. This transient behavior is followed by a 'steady state' period during which the activity remains essentially constant (5-7% change in conversion during 30-60 h TOS); however, the relative rates of hydrogenation and hydrodechlorination decrease. For catalysts with a Pt:Sn atomic ratio greater than or equal to 3, the decrease in relative rates manifests itself as an increase in propene selectivity at the expense of propane. In contrast, allyl chloride selectivity increases at the expense of propene for the catalysts with Pt:Sn ratio less than or equal to 1. Steady state turnover frequencies (TOFs) decrease with decreasing Pt:Sn atomic ratio to a minimum for the catalyst with the Pt:Sn=1. Further decreasing the Pt:Sn ratio results in a TOF increase, with the Pt1Sn6 catalyst TOF exceeding that of monometallic Pt/C. (C) 2000 Elsevier Science B.V. All rights reserved.