(574f) Kinetic Analysis of CO Methanation on Sn Promoted Pt/?-Al2O3 Catalysts

The promotion of platinum supported catalysts with tin has been shown to significantly improve the yields towards aldehydes and alcohols in the hydrodeoxygenation reaction of carboxylic acids. Literature suggests that tin could affect the system causing electronic and/or geometric effects, though it remains unclear which effect is the dominant in this system. The use of CO and H₂ static chemisorption as a standard catalyst characterization technique to define site density may lead to underestimated values for turnover frequencies. To overcome such limitation, a series of Pt-Sn/γ-Al₂O₃ catalysts, with Sn/Pt atomic ratio of 0 – 2, was synthesized by means of the strong electrostatic absorption technique and tested for carbon monoxide methanation with both the traditional steady state differential reactor and the transient kinetic isotopic technique (SSITKA). The catalyst activities were compared under the reference temperature of 593K, atmospheric pressure, CO partial pressure of 7.6 torr, H₂ partial pressure of 380 torr (CO/H₂ ratio of 50/1), and a drop in mass normalized rate of reaction of two orders of magnitude was observed between the monometallic platinum and the bimetallic Sn/Pt 2:1. Though, in the hydrogen partial pressure range of 95 – 380 torr, carbon monoxide partial pressure range of 11.3 – 37.8 torr, and temperatures from 593K – 648K, no significant differences were found in apparent barriers and reactant orders throughout the formulations, with 95%CI values of 71-73 kJ/mol for apparent barrier, 0.73 – 0.78 for hydrogen order, and 0.05-0.09 for carbon monoxide. The results were compared to SSITKA using H₂/D₂ and ¹³CO/¹²CO exchanges, and insights were used to resolve electronic and geometric effects.