Shell fuel preparation

FIGURE 6.27 In this preparation of rocket fuel for the space shuttle, powdered aluminum is mixed with an oxidizing agent in a liquid polymer base that hardens inside the booster rocket shell. 

The catalytic applications of Moiseev s giant cationic palladium clusters have extensively been reviewed by Finke et al. [167], In a recent review chapter we have outlined the potential of surfactant-stabilized nanocolloids in the different fields of catalysis [53]. Our three-step precursor concept for the manufacture of heterogeneous egg-shell - nanocatalysts catalysts based on surfactant-stabilized organosols or hydrosols was developed in the 1990s [173-177] and has been fully elaborated in recent time as a standard procedure for the manufacture of egg-shell - nanometal catalysts, namely for the preparation of high-performance fuel cell catalysts. For details consult the following Refs. [53,181,387]. 

From the above experimental results, it can be seen that the both PtSn catalysts have a similar particle size leading to the same physical surface area. However, the ESAs of these catalysts are significantly different, as indicated by the CV curves. The large difference between ESA values for the two catalysts could only be explained by differences in detailed nanostructure as a consequence of differences in the preparation of the respective catalyst. On the basis of the preparation process and the CV measurement results, a model has been developed for the structures of these PtSn catalysts as shown in Fig. 15.10. The PtSn-1 catalyst is believed to have a Sn core/Pt shell nanostructure while PtSn-2 is believed to have a Pt core/Sn shell structure. Both electrochemical results and fuel cell performance indicate that PtSn-1 catalyst significantly enhances ethanol electrooxidation. Our previous research found that an important difference between PtRu and PtSn catalysts is that the addition of Ru reduces the lattice parameter of Pt, while Sn dilates the lattice parameter. The reduced Pt lattice parameter resulting from Ru addition seems to be unfavorable for ethanol adsorption and degrades the DEFC performance. In this new work on PtSn catalysts with more... 

The PtRu bimetallic system has been the catalyst of choice for MeOH oxidation in acid elecfrolyfes since its discovery by workers at Shell in the early 1960s2 In practice, PtRu lowers the overpotential for MeOH oxidation by >200 mV compared to pure Pt. The MeOH oxidation reaction on Pt and PtRu is probably the most studied reaction in fuel cell electrocatalysis due to its ease of sfudy in liquid electrolytes and the many possible mechanistic pathways. In recent years, the deposition of PtRu particles onto novel carbon supports and the novel PtRu particle preparation routes have proved popular as a means to demonstrate superiority over conventional PtRu catalysts. 

A preparation and characterization of new PtRu alloy colloids that are suitable as precursors for fuel-cell catalysts have been reported [43cj. This new method uses an organometallic compound both for reduction and as colloid stabilizer leading to a Pt/Ru colloid with lipophilic surfactant stabilizers that can easily be modified to demonstrate hydrophilic properties. The surfactant shell is removed prior to electrochemical measurements by reactive annealing in O2 and H2. This colloid was found to have nearly identical electrocatalytic activity to several other recently developed Pt/Ru colloids as well as commercially available Pt/Ru catalysts. This demonstrates the potential for the development of colloid precursors for bimetallic catalysts especially when considering the ease of manipulating the alloy composition when using these methods. 

A big amount of experimental studies of stability of many component systems Pt Me (where Me - transition metals Cr, Fe, Co, Ni, Ru) indicates about the formation of nanoclusters with core-shell structures [11-13], where mechanisms of the processes (including corrosive) with the formation of such structures are described. Firstly this is a surface segregation during the process of multicomponent nanocluster preparation [14], Due to such segregation nanocluster surface becomes enriched by one of the components, especially by platinum with the reduction of surface energy in segregated binary nanocluster [75]. In the process of corrosive influence (in model conditions or in tests of fuel cells) a prevailing dissolution of one component from basic metal Me and surface enrichment by platinum with the formation of a core-shell system. 

The modified ASTM2007M method was verified against ASTM2549 and other separation techniques such as SFC, HPLC and FIA. The comparison of results obtained by different laboratories and different methods for various diesel fuels is shown in Table 1. The results are shown for five commercial diesel fuels, two synthetic cmde blends and two conventional diesel blends prepared by Shell Canada Ltd. with approximately 20wt% and 30wt% aromatics. Results are also shown for a certified low aromatic fuel supplied by Chevron Research and Technology Company (Chevron low aromatic), and a commercial low sulfur diesel (Refl). 

Gao, H., Liao, S., Zeng, J., Xie, Y. Dang, D. Preparation and characterization of core-shell structured catalysts using PtxPdj, as active shell and nano-sized Ru as core for potential direct formic acid fuel-cell application. ElectrocMm. Acta 56 (2011), pp. 2024 2030. 

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