Catalyst alloys

Fig. 10. Coefficient of H atom recombination on Ni-Cu alloy catalysts as a function of the alloy composition, at 20°C. A, on Ni-Cu foils (59), O, on Ni-Cu evaporated films af ter their previous homogenization at 400°C (65,65a) d, on Ni-Cu foils after a multiple hydrogen absorption-desorption treatment (64a).

The temperature behavior of the alloy catalysts in the heterogeneous recombination of hydrogen atoms was different for rich in nickel alloys from one side and for rich in copper from the other. For the three alloy catalyst films, i.e. Ni97Cu3, Ni77Cu23, and Ni57Cu43 (numbers represent... 

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

Cold-Nickel Alloy Catalysts for Steam Reforming... 

Figure 8.7. Steam reforming of n-butane as a function of time for a conventional Ni catalyst and a novel Ni-Au alloy catalyst, showing the superior stability ofthe latter. [Adapted from...

We review our work on techniques and methods for examining the diffraction patterns from supported Pt,Pd and alloy catalysts, as well as the results that have been obtained in the last decade with these procedures in our group. 

Advancing from carbon-supported Pt to carbon-supported Pt alloy catalysts, to enhance the performance per milligram Pt by three- to four-fold [Mukeijee and Srinivasan, 1993 Mukeijee et al., 1995]. 

Interpretation of this observed correlation between a lowered affinity of the metal surface to oxygen and a higher rate of ORR measured at a Pt shell over a Pt-alloy core has also been at the center of recent theoretical work, based primarily on DFT calculations of electronic properties and surface bond strengths for a variety of expected ORR intermediates at metal and metal alloy catalysts. The second part of this chapter contains a discussion of these valuable contributions and of outstanding issues in tying together this recent theoretical work and ORR experimental data. 

Besenbacher F, Chorkendorff I, Clausen BS, Hammer B, Molenbroek AM, Nprskov JK, Stensgaard I. 1998. Design of a surface alloy catalyst for steam reforming. Science 279 1913-1915. 

Greeley J, Mavrikakis M. 2004. Alloy catalysts designed from first-principles. Nature Mater 3 810-815. 

Paulus UA, Wokaun A, Scherer GG, Schmidt TJ, Stamenkovic V, Radmilovic V, Markovic NM, Ross PN. 2002. Oxygen reduction on carbon-supported Pt-Ni and Pt-Co alloy catalysts. J Phys Chem B 106 4181-4191. 

Savadogo O, Lee K, Oishi K, Mitsushimas S, Kamiya N, Ota K-I. 2004. New palladium alloys catalyst for the oxygen reduction reaction in an acid medium. Electrochem Commun 6 105 109. 

We have found new CO-tolerant catalysts by alloying Pt with a second, nonprecious, metal (Pt-Fe, Pt-Co, Pt-Ni, etc.) [Fujino, 1996 Watanabe et al., 1999 Igarashi et al., 2001]. In this section, we demonstrate the properties of these new alloy catalysts together with Pt-Ru alloy, based on voltammetric measurements, electrochemical quartz crystal microbalance (EQCM), electrochemical scanning tunneling microscopy (EC-STM), in situ Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). 

We have also clarified for Pt/CB that ORR activity is not affected by differences in the particle size. It is very important for highly dispersed alloy catalysts to examine the... 

Min M, Cho J, Cho K, Kim H. 2000. Particle size and alloying effects of Pt-based alloy catalysts for fuel cell applications. Electrochim Acta 45 4211-4217. 

Yano H, Song JM, Uchida H, Watanabe M. 2008. Temperature dependence of oxygen reduction activity at carbon-supported PtxCo (X = 1, 2, and 3) alloy catalysts prepared by the nanocapsule method. J Phys Chem C 112 8372-8380. 

Figure 11.11 Linear cyclic voltammograms of carbon-supported nanosized Pt and Pt-Cr alloy catalysts with different atomic ratios (prepared using the carbonyl route [Yang et al., 2004]) recorded in 0.5 M HCIO4 saturated with pure oxygen at a scan rate of 5 mV s and a rotation speed of 2000 rev min Current densities are normalized to the geometric surface...

Colmenares L, Wang H, Jusys Z, Jiang L, Yan S, Sun GQ, Behm RJ. 2006. Ethanol oxidation on novel, carbon supported Pt alloy catalysts— Model studies under defined diffusion conditions. Electrochim Acta 52 221-233. 

Fig. 6. Activities of copper-nickel alloy catalysts for the hydrogenolysis of ethane to methane and the dehydrogenation of cyclohexane to benzene. The activities refer to reaction rates at 316° C. Ethane hydrogenolysis activities were obtained at ethane and hydrogen pressures of 0.030 and 0.20 atm., respectively. Cyclohexane dehydrogenation activities were obtained at cyclohexane and hydrogen pressures of 0.17 and 0.83 atm, respectively (74).

It is reasonable to ask two questions in relation to studies using evaporated alloy films, viz, why work with alloys and why prepare alloy catalysts in this particular form ... 

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