Catalysis of Organic..

308 Catalyst Library DesignBasic Principle of HRSThe Holographic Research Strategy (HRS) developed for catalyst library design andoptimization can be considered as a deterministic approach, i.e. the route ofoptimization is unequivocally determined by the applied setting parameters [23,24]. InHRS similarly to other methods, such as the genetic algorithm (GA) [11]], the testresults of the (n-1) th generation is used to design the n th generation. During theoptimisation, the Holographic Research Strategy uses the rank between catalyststested. This rank is usually called as an “elite list” which is used to design the nextcatalyst generation.In HRS the key setting parameters are as follows [23,24]: (i) the total number ofexperimental variables, (ii) the selected levels of experimental variables, (iii) initialarrangement of variables along the axes (see Fig. 1) and the way of variable positionchanges, (iv) the number of the best hits around which the new catalyst generation iscreated, and (v) the size and the form of the experimental regions used to design thenext catalyst generation.Undoubtedly all of these parameters can influence both the rate and the certaintyof optimum search. In this respect the importance of the size of the experimentalregion has already been discussed in our previous studies [23,24].When all compositional variables have been selected the next task is the definitionof the levels of these variables. The levels can be given either in absoluteconcentration or as a relative ratio. The necessary number of levels for a variable is thearbitrary decision of the experimenter. It depends on the range that has to be explored.Special attention has to be devoted to possible non-smooth areas. In a reasonablynarrow range the effect of a variable are usually investigated using 4 – 5 levels, whichaccording to our results proved to be sufficient. In an eight-dimensional experimentalspace containing 78,000 – 125,000 possible compositions less than 150-200measurements were sufficient to find or approach the optimum [23,24].The levels of the compositional variables strongly depend on the role of the givencomponent in the catalyst composition. For key components steps in 0.5 w % is verycommon. For compositional modifiers of the active metal small steps has to be used in0.05 or 0.1 w % interval. For the determination of the required amount of processmodifiers (quinoline, amides, sulfur) the dispersion (D) of the key metal has to bedetermined or estimated. The amount of this type of modifiers (M) is usually in therange of 0.05-0.2 M mod /A metal where M mod = amount of the modifier in moles and Ametal is the total amount metal in gram atoms. The amount of modifiers for the supportcan be one order higher than the metal content of the catalyst.According to the above considerations if the optimization is performed underfixed process parameters the initial step in library design is finished, i.e. the catalystsof the initial library can be introduced into the experimental hologram. However, it isstrongly recommended to include one or two process parameters into the librarydesign procedure. Reaction temperature and hydrogen pressure is the two mostimportant process parameters influencing both the activity and the reactivity.