Methanol oxidation catalysts

Figure 28. XANES for an unsupported PtRu black catalyst (a and c) as prepared and (b and d) following fuel cell testing as a methanol oxidation catalyst and reference compounds at (a and b) the Pt L3 edge and (c and d) the Ru K edged (Reproduced with permission from ref 102. Copyright 2001 American Chemical Society.)...

Iron molybdates, well known as selective methanol oxidation catalysts, are also active for the propene oxidation, but not particularly selective with respect to acrolein. Acetone is the chief product at low temperature (200°C), whereas carbon oxides, besides some acrolein, predominate at higher temperatures [182,257], Firsova et al. [112,113] report that adsorption of propene on iron molybdate (Fe/Me = 1/2) at 80—120°C causes cation reduction (Fe3+ -> Fe2+) as revealed by 7-resonance spectroscopy. Treatment with oxygen at 400°C could not effect reoxidation (in contrast to similarly reduced tin molybdate). The authors assume that this phenomenon is related to the low selectivity of iron molybdate. 

This chapter presents the design and application of a two-stage combinatorial and high-throughput screening electrochemical workflow for the development of new fuel cell electrocatalysts. First, a brief description of combinatorial methodologies in electrocatalysis is presented. Then, the primary and secondary electrochemical workflows are described in detail. Finally, a case study on ternary methanol oxidation catalysts for DMFC anodes illustrates the application of the workflow to fuel cell research. 

Since the formation of strongly bonded surface CO constitutes the major kinetic hurdle for the oxidation of methanol at low overpotentials, model calculations of the CO tolerance should also give guidance in the development of ternary methanol oxidation catalysts. In fact, model calculations of the CO tolerance of ternary Pt-Ru-X alloys have been performed (Fig. 11.14) [18] revealing activity trends similar to those observed in the experimental combinatorial methanol oxidation study (Fig. 11.13) Figs 11.13 and 11.14 identify Pt-Ru-Co ternary composi-... 

The diverse combinatorial screening described in the previous sections revealed active Pt-Ru-Co methanol oxidation catalysts, especially near Pt20Co6oRu2o. A second primary screening cycle (Fig. 11.8) focused on a more limited compositional space to isolate the active region in more detail. Figs. 11.15 and 11.16 show the design and the sampled compositional space of a Pt-Ru-Co ternary library. The design contains a pure Pt catalyst, Pt-Co binaries (row A), Pt-Ru binaries (column 1)... 

Methane oxidation catalyst 14.7.2.1. Methanol oxidation catalyst ... 

Develop non-noble metal methanol oxidation catalysts. 

In the case of the reaction conducted over a combined Ag-CsOH/Si02 and CsOH-Zr/Si02 catalyst system, the yield of MMA and the selectivity to MMA in the overall reaction are decided mainly by the performance of the catalyst for the aldol-type-condensation reaction by the performance of CsOH/Si02 catalyst, rather than by the performance for methanol oxidation catalyst (Ag-CsOH/Si02). 

Dickinson AJ, Carrette LPL, Collins JA, Friedrich KA, Stimming U. Performance of methanol oxidation catalysts with varying Pt Ru ratio as function of temperature. J Appl Electrochem 2004 34 975-80. 

Sen F, Gokagac G. Different sized platinum nanoparticles supported on carbon an XPS study on these methanol oxidation catalysts. J Phys Chem C 2007 111 5715-20. 

Rajesh B, Thampi RK, Bonard J-M, Mathieu HJ, Xanthopoulos N, Viswanathan B. Conducting polymeric nanotubes as high performance methanol oxidation catalyst support. Chem Comm 2003 16 2022-3. 

In addition, quaternary Pt-Ru-based alloys were also investigated as methanol oxidation catalysts for further improving the anode performanee in DMFCs. Some of the quaternary alloys, such as Pt-Ru-W-Sn [41], Pt-Ru-Os-Ir [42], Pt-Ru-W-Mo [43], Pt-Ru-Ni-Zr [44], and Pt-Ru-Ir-Sn [45], have been demonstrated to be more active than the state-of-the-art Pt-Ru catalyst towards the MOR. Due to a huge... 

Cobalt is used to promote CO oxidation in reformers [284, 285], suggesting PtCo alloys may be useful catalysts for H2 oxidation in the presence of CO. PtCo alloys have been proposed as improved methanol oxidation catalysts [286] because cobalt may assist with CO removal (CO is an intermediate in meflianol electrooxidation) through a mechanism analogous to the PtRu bifunctional mechanism. PtCo alloys have also been studied as improved ORR catalysts [200, 287, 288]. In addition to their improved ORR kinetics, these alloys have been shown to be more tolerant to methanol crossover in direct methanol fuel cells (DMFCs), again possibly through improved CO removal kinetics [289]. However, Stevens et al. [235] observed no impact on CO-stripping with the addition of eobalt to Pt, and explained this as due to surface cobalt dissolving away. 

Fachini ER, Diaz-Ayala R, Casado-Rivera E, File S, Cabrera CR. Surface coordination of ruthenium clusters on platinum nanoparticles for methanol oxidation catalysts. Langmuir 2003 19 8986-93. 

Briand, L. (2006). Investigation of the nature and number of surface active sites of supported and bulk methanol oxide catalysts, in J. Fierro (ed.). Metal Oxides Chemistry and Applications, CRC Rress, Boca Raton, FL, pp. 353-390. 

Figure 2 Microprobe Raman analysis of an iron-molybdate methanol oxidation catalyst (a) mixture of M0O3 and Fe2(Mo04)3 (b) Fe2(Mo04)3 (c) M0O3.

Morante-Catacora, T.Y., Ishikawa, Y. Cabrera, C.R. Sequential electrodeposition of Mo at Pt and PtRu methanol oxidation catalyst particles on HOPG surfaces. J. Electroanal. Chem. 621 (2008), pp. 103-112. 

This half-cell was used for evaluating methanol oxidation catalysts and catalyst layers [24], as described in the following section. It is expected that this cell could also be suitable to mimic fuel cell operating conditions for other liquid fuel oxidation because the WE structure is similar to the structure of the anode in a direct liquid fuel ceU. 

The concentration of Bronsted and Lewis acidic sites (Table 10.3) was calculated based on the intensity of the respective bands and their corresponding molar extinction coefficients (e) by applying Lambert-Beer law. The quantification of sites showed that the total number of acidic sites of the zeolite did not change after addition of Cu and that a modification in the nature of the acidic sites occurs, wherein Bronsted sites are transformed into Lewis sites. An evaluation of the methanol oxidation catalysts, used as a reaction model, showed that activity and selectivity are influenced by the distribution of acidic sites. 

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