Hybrid-phase catalysts heterogeneous

In the sixties of past century, a few patents issued to Bergbau Chemie [5,48,49] and to Mobil Oil [50-52], respectively described the use of CFPs as supports for catalytically active metal nanoclusters and as carriers for heterogenized metal complexes of catalytic relevance. For the latter catalysts the term hybrid phase catalysts later came into use [53,54], At that time coordination chemistry and organo-transition metal chemistry were in full development. Homogeneous transition metal catalysis was expected to grow in industrial relevance [54], but catalyst separation was generally a major problem for continuous processing. That is why the concept of hybrid catalysis became very popular in a short time [55]. 

An important research area of catalysis is the heterogenization of metal complexes showing excellent activity and selectivity in the homogeneous phase (hybrid catalysts) [1]. The main advantage of supported metal complexes over unsupported ones is the ease of separation from the reaction media, which makes them economically convenient [2]. On the other hand, the main problems related with the heterogenization on solid supports are metal complex leaching and decrease in catalytic activity. 

Toshiba, in collaboration with Tokyo Electric Power Company, has developed a hybrid catalytic combustion. Here only a part of the fuel is converted heterogeneously on the catalyst. The system consists of a pre-combustion mixing zone, a low-temperature catalyst zone, and a gas-phase combustion zone. The fuel-air mixture is controlled to maintain the temperature of the catalyst below 800 C, because the catalyst is not stable above the temperature. More fuel is added downstream to attain the final combustion temperature. The function of the catalyst is to be a source of additional "pre-heat" to support the lean, homogeneous down-stream combustion. 

In catalysis, the immobilization and heterogenization of catalytic nano-compounds on a solid support facilitates the access of reactants to the catalytic sites, prevents aggregation and allows recovery and reuse, as well as prolonging the life of the catalyst. Depending on the specific type of process, the reaction can occur in gas or in liquid phase. Table 5.2 summarizes the various interesting types of applications that use hybrid catalytic nanocomposite membranes for conversion and separation of chemical compounds in a single stage (Ozdemir et al, 2006 Biswas et al, 2011 Domenech et al, 2011). 

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