Other Binary Catalytic Systems

4 Other Binary Catalytic Systems In 2012, Terada and Toda demonstrated a Rhj(OAc)yphosphoric acid relay catalysis for the formation of carbonyl 

SCHEME 2.99 Rapid synthesis of chiral julolidines by employing gold(I)/chiral Brpnsted acid relay catalysis. 

SCHEME 2.100 Relay catalytic cascade intramolecular hydrosUoxylation/asymmetric Diels-Alder reaction. 

Another interesting approach to enantioemiched heterocycles through a cascade catalysis procedure has recently been reported by Gong s research group [136]. In 

SCHEME 2.101 Relay catalysis for a carbonyl yUde fonnation/enantioselective reduction sequence. 

---

Recent years there have been a considerable interest in studying of binary catalytic systems based on stabilized nanocomposites and amorphous alloys of copper with other metals. The reason is that the catalytic activity of such systems in many cases is sufficiently higher than that of individual metals. The most convenient model for theoretical description of binary systems characterized by the absence of far order is a cluster model. However, quantum-chemical study of binary clusters comprises the significantly more c omplicated problem than that o f individual metals, b ecause a correct theoretical description of metal-another metal cluster systems requires that the used method should be in a position to provide good results of calculations of geometrical, electron stmctures and energetic characteristics of both of individual metals. 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

A general problem existing with all multicomponent catalysts is the fact that their catalytic activity depends not on the component ratio in the bulk of the electrode but on that in the surface layer, which owing to the preferential dissolution of certain components, may vary in time or as a result of certain electrode pretreatments. The same holds for the phase composition of the surface layer, which may well be different from that in the bulk alloy. It is for this reason that numerous attempts at correlating the catalytic activities of alloys and other binary systems with their bulk properties proved futile. 

The most important catalyst systems involving rare earth elements are the oxides and intermetallics. Catalytic properties of rare earth oxides are described in section 4 and those of intermetallic compounds in section 6. Reports on surface reactivities of other binary rare earth compounds are only sparse, and this is mentioned in section 5. A very interesting class of catalyst systems comprises the mixed oxides of the perovskite structure type. As catalysis on these oxides is mainly determined by the d transition metal component and the rare earth cations can be regarded essentially as spectator cations from the catalytic viewpoint, these materials have not been included in this chapter. Instead, we refer the interested reader to a review by Voorhoeve (1977). Catalytic properties of rare earth containing zeolites are, in our opinion, more adequately treated in the general context of zeolite catalysis (see e.g. Rabo, 1976 Katzer, 1977 Haynes, 1978) and have therefore been omitted here. 

A remarkable example for the chemo- and regioselectivity observed during a [2 -F 2 -b 2] reaction represents tbe intermolecular cyclottimerization between TMSA on one hand, another terminal alkyne on the other hand, and an enone mediated by a binary Ni/Al catalytic system (eq 42). 

There are several types of Ziegler-Natta and ROMP catalysts employed for cycloolefin polymerization, the majority of them being derived from transition metal salts and organometallic compounds [4-7]. These types are grouped into unicomponent, binary, ternary, and multicomponent catalytic systems as a function of the presence or absence of the organometallic cocatalyst or other additives, each of them being differentiated on the catalyst composition and selectivity toward vinylic or ring-opened polymerization. 

Electrodes The porous electrodes consist of carbon cloths loaded with a mixture of platinum and Nafion. In order to achieve a good contact between the electrode, the catalyst, and the electrolyte, the electrodes are pressed on the electrolyte membrane, which acts as the supporting component. Other catalysts such as binary Pt-Ru mixtures and ternary systems such as Pt- Ru- Sn have been studied for better CO tolerance [8]. The current density voltage curves of Fig. 7 show the effect of CO on the performance of a cell with platinum as catalyst. Fig. 8 shows the higher catalytic... 

The binary alloy of platinum and rhodium is especially known for the catalytic properties of its surfaces [123-126]. Therefore, various publications have already attended to this system for example. Refs [125-130] discuss the relevancy of Pt-Rh in three-way catalysts, and some empirical models about the catalytic process are developed in Refs [131-133]. Here, we take two steps back first, because the whole alloy Pt-Rh will be brought down to its atomic constituents, and second, because not the dynamics of the catalytic process itself wiU be under investigation but, more fundamentally, the equilibrium properties of a Pt-Rh surface. This approach joins other atomistic works on Pt-Rh surfaces, experimental papers such as Refs [1, 134], as well as numerous theoretical surveys such as Refs [2,106, 135-137]. 

---