PtRu alloy catalyst

The apparent greater effectiveness of the small amount of Ru on the Pt surfaces in the PtRu Mix catalyst vs. the PtRu Alloy catalyst, as exhibited in Fig. 11, is consistent with the effect of Ru island size as noted above for methanol. Small Ru islands, such as those in the PtRuMix catalyts, cause the BF mechanism to be more effective at lower overpotentials. 

Y-M. Tsou, L. Cao, E. De Castro, Novel High Performance PtRu Alloy Catalysts for Methanol Oxidation and CO Tolerance Applications, Abs. 675,205th Meeting, 2004 The Electrochemical Society, Inc., 2004. 

Figure 4.15. Comparison between Pt decorated with Ru ( ) and a commercial Johnson Matthey PtRu alloy catalyst (o). Methanol oxidation current density measured after 20 h in 0.5 M CH3OH - 0.5 M H2SO4 293 K. Potential referred vs. SHE. [98]. (Reprinted from Journal of Catalysis, 203, Waszczuk P, Solla-Gullon J, Kim H-S, Tong YY, Montiel V, Aldaz A, et al.. Methanol electrooxidation on platinum/mthenium nanoparticle catalysts, 1-6, Cop3Tight2001, with permission from Elsevier.)...

Kim T, Takahashi M, Nagai M, Kobayashi K. Preparation and cbaracterization of carbon supported Pt and PtRu alloy catalysts reduced by alcobol for polymer electrolyte fuel cell. Electrochim Acta 2004 50 817-21. 

As the carbon-supported PtRu alloy catalyst seems the most practical for use in PEMFCs, many studies have investigated PtRu alloying with a third element, e.g., W, Mo, Sn, Mb, Au, Ag, Ir, Ni, in an attempt to further improve catalytic activity [21-25]. Some of the elements, such as W, Mo, Sn, Ir, andNi clearly show further improvement in activity due to flie co-catalytic effect, while other elements, such as Mb, Au, and Ag show no improvement but rather a negative effect CO/H2 electrooxidation activity. Furthermore, catalysts with different metal atomic ratios show unparallel activity toward CO/H2 electrooxidation. In summary, the... 

Equation (7.17) to equation (7.19) suggest that for a PtRu alloy catalyst there are two catalyst sites that can be occupied. Carbon monoxide adsorbs onto platinum, while the hydroxide ions adsorb onto ruthenium. Therefore, to understand the rates of reaction mathematically, the coverage of platinum and ruthenium by molecules should be considered. Enback and Lindbergh [64] developed a steady-state model to simulate the reaction kinetics of CO poisoning in the presence of a PtRu/C catalyst. The reaction kinetic parameters were obtained from fitting the model predictions to the experimental measurements and are listed in Table 7.2. The following equation set was used to describe their mathematical model ... 

PtRu alloy catalysts, which have been commercially used in the PEMFC industry, have been the most widely investigated and have been... 

However, the intermediate product during the oxidation of methanol makes the catalysis complicated, and the reaction rate for making CO out of methanol solution is slow. Moreover, a second metal such as Ruthenium (Ru) is required, which is explained by the bifunctional mechanism. In other words, activation of water or surface oxides at lower potentials makes the CO absorption bond weaker on the PtRu alloy catalyst. In the meantime, oxidative methanol dehydrogenation occurs on Pt by oxygen-like species on Ru, so that species on Pt-Ru pair sites enables the continuous oxidation of CO to CO. ... 

---