Framework compositions, modified

Equation (IS) provides the zeolite chemist with a powerful quantitative method for the determination of framework composition of zeolites. By comparing (Si/A1)NMR values with the results of chemical analysis, which gives bulk composition, the amount of nonframework (six-coordinated) aluminum can be calculated. This is of particular value in the study of chemically modified zeolites (see Sections III,J-III,M). 

Highly ordered mesoporous mono- and bi-metallic incorporated catalysts with high porosity and surfece area are very active and selective in oxidation reaction of aromatic hydrocarbons such as styrene and benzene. Their framework composition can be modified by incorporation of various transition metals in the single or associated forms. The ordered hexagonal arrangement, the morphology, the surface area, and the catalytic activity and selectivity can be modified by method of the synthesis, nature and content of the metal and the molar ratio of the metals. Very active catalysts were obtained by incorporation of chromium and nickel in the hexagonal ordered structure. 

The acid properties of SAPO-5 samples can be modified either by the con x>sition of framework, or by ion-exchange or impregnation. These changes in the acid properties can have certain implications on the catalytic performances. This assertion is proved by the results shown in Figure 3, where it can be observed that the decrease of the phosphorus cont t and partially of the aluninium determines an increase of the activity, but the selectivity is kept constant. The difference between the framework compositions deter-... 

The Payne effect of carbon black reinforced rubbers has also been investigated intensively by a number of different researchers [36-39]. In most cases, standard diene rubbers widely used in the tire industry, bke SBR, NR, and BR, have been appbed, but also carbon black filled bromobutyl rubbers [40-42] or functional rubbers containing tin end-modified polymers [43] were used. The Payne effect was described in the framework of various experimental procedures, including pre-conditioning-, recovery- and dynamic stress-softening studies [44]. The typically almost reversible, non-linear response found for carbon black composites has also been observed for silica filled rubbers [44-46]. 

The synthetic conditions, compositions and properties of the starting and dealuminated zeolite samples are presented in Table 1. The method of dealumination of the NH4 -form of Y zeolite with a solution of (NH4)2Sip6 is based on isomorphous substitution of aluminium in the zeolite structure by silicon. As the eoncentration of (NH4)2Sip6 increases, the overall Si/Al ratio in zeolite (determined by chemical analysis) increases. The IR spectra of the modified samples on various steps of synthesis were used to determine the Si/Al ratio in the zeolite framework. 

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