Catalysts quaternary

With regard to the electro-catalyst the main research issue is to identify a platinum-based catalyst, i.e. a binary, ternary or quaternary catalyst composed of platinum and one or more transition metals that will be more active (and thereby further reducing the applied potential), exhibit an improved lifespan, and have reduced platinum loadings to reduce the cost. The NWU, located in the North-West province of South Africa where the majority of the world s platinum is mined and produced, is currently setting itself up for the synthesis, characterisation and testing of platinum-based electro-catalysts specifically for normal water electrolysis as well as for S02 electrolysis. 

Standard Nd-based catalysts comprise binary and ternary systems. Binary systems consist of Nd chloride and an aluminum alkyl or a magnesium alkyl compound. In ternary catalyst systems a halide free Nd-precursor such as a Nd-carboxylate is combined with an Al- or Mg-alkyl plus a halide donor. By the addition of halide donors to halide-free catalyst systems catalyst activities and cis- 1,4-contents are significantly increased. In quaternary catalyst systems a solubilizing agent for either the Nd-salt or for the halide donor is used in addition to the components used in ternary systems. There are even more complex catalyst systems which are described in the patent literature. These systems comprise up to eight different catalyst components. 

The activity results for the quaternary catalysts, Ni-Cu-Zn-Al and Ni-Co-Zn-Al, (Fig. 3b) show an activity level similar (13-15%) to that obtained with the Ni-Zn-Al catalyst and this level remains constant over the reaction time. Regarding the selectivity towards methane (Fig. 4a), it can be observed that for these samples, independently of the initial value, a fast diminution is obtained until a residual value close to zero is reached. 

The temperature-programmed reduction profiles (Fig. 2) for the quaternary catalysts indicate that Ni and Cu reduction take place at different temperatures. However, the reduction of Ni in the Ni-Cu-Zn-Al catalyst occurs at a lower temperature than in the rest of the solids, so that the Cu reduction seems to catalyze the Ni reduction. These facts indicate that the results of catalytic activity obtained in this work can not be due to the formation, at least to any great extent, of an alloy between both metals (Ni and Cu). However, a clear interaction between both metals does exist since the Ni reducibility is clearly modified. 

Quaternary catalysts seem to be more effective than the other three catalysts. The optimum ratio of the four components of the quaternary catalyst are R A1 H P0 H20 C H NCCH ) = 1 0.15 0.15 0.10, as shown in Figure 4... 

Figure 5. Dependence of grafting efficiency and total conversion on the amount of quaternary catalyst used.

It is found that benzoin condensation of aldehydes are strongly catalysed by a PTC (quaternary ammonium cyanide in a two phase system). In a similar way, acyloin condensations are easily effected by stirring aliphatic or aromatic aldehydes with a quaternary catalyst (PTC), N-laurylthiazolium bromide in aqueous phosphate buffer at room temperature. The aromatic aldehydes reacted in a short time (about 5 min). However, aliphatic aldehydes require longer time (5-10 hr) for completion. Mixtures of aliphatic and aryl aromatic aldehydes give mixed a-hydroxy ketones. ... 

Ternary and Quaternary Catalyst Formulations PtRuMj/C and PtRuMiMFC... 

Figure 4.22 eompares the mass-normalized current as a function of anode potential and methanol eoneentration for selected quaternary catalyst formulations and a binary PtRu (1 1). The novel formulation with an atomic ratio of Pt Ru Os Ir = 2.35 1.45 1 0.2 increased more than 10 times the catalyst mass-normalized current compared to the industry standard Pt Ru (1 1). In spite of promising results, to the knowledge of the present author there has been no industrial follow up on the PtRuIrOs quaternary eatalyst formulation. 

Figure 4.22. Mass-normahzed anode current vs. methanol concentration and anode potential for selected quaternary catalyst compositions. 333 K [122]. Anode conditions methanol solution flow rate 12.5 mL min , 0 psig, 60 °C. Cathode conditions are the following 400 seem dry air, 0 psig. The electrol5de is Nafion 117. Potential V vs. RHE. (Reproduced with permission from J Phys Chem B 1998 102 9997-10003. Copyright 1998 American Chemical Society.)...

An interesting quaternary catalyst, namely PtRuRhNi was proposed by Park et al. [125]. Rh has been considered early on for CH3OH oxidation as a co-catalyst with Pt in binary PtRh formulations, with maximum acitivity (compared to pure Pt) observed at low Rh loadings of —10 at% [126]. In the quaternary composition prepared by the borohydride reduction method, low Rh and Ni content was employed eorresponding to Pt Ru Rh Ni = 10 8 1 1 atomic ratios [125]. In DMFC experiments using 5 mg cm" anode eatalyst load a maximum power output at 343 K of 180 mW em was achieved with PtRuRhNi eompared to 160 mW cm" obtained with PtRu. Moreover, the quaternary eatalyst showed very good stability over an extended operation time of 20 h [126],... 

Neburchilov V, Wang H, Zhang J. Low Pt content Pt-Ru-lr-Sn quaternary catalysts for anodic methanol oxidation in DMFC. Electrochem Commun 2007 9 1788-92. 

In this section we will focus on the preparation of Pt/Ru catalysts and Pt catalysts made with the iron group. Ternary and quaternary catalysts are not discussed specifically. However, similar principles apply to their synthesis. 

One final note regarding the use of crown ethers as phase transfer catalysts there is little literature which directly compares quaternary ammonium catalysts with crown ethers in liquid-liquid processes (see Sect. 1.10) [48]. There are examples where both have been tried and are effective. In general, however, it appears that for solid-liquid phase transfer processes, the crowns are far better catalysts than are the quaternary ammonium ions. In order for a solid-liquid phase transfer process to succeed, the catalyst must remove an ion pair from a solid matrix. The quaternary catalysts have no chelating heteroatoms with available lone pairs which would favor such a process. The combination of a quaternary catalyst and some simple coordinating amine or ether would probably succeed [28, 32, 34]. It seems likely, as mentioned above, that it is the combination of diamine and quaternary catalyst generated in situ which accounts for the success of Normanf s catalysts [28]. It is interesting to speculate on the possibility of using a quaternary ammonium compound and a drop of water as a catalytic system. 

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