Proton zeolite matrix

Conversion plots in Fig. 2 give a hint for a correlation between Pd content and the period of time until deactivation sets in. Under the adjusted standard reaction conditions PdY-2.0 deactivates already after 60 min time on stream (TOS). Increasing the Pd concentration in the zeolite matrix up to 7.6 wt.%, we found the active interval being prolonged to about 260 min. For a PdY-14.6 sample at least no deactivation occurred within a space of 360 min. It seems noteworthy that, obviously, protonation protects it from poisoning. HPdY-2.0 (Fig. 2b) shows a similar behaviour towards deactivation like a proton-free Y zeolite with a much higher Pd content (PdY-7.6 in Fig. 2c). 

In the presence of carbon monoxide, CO, metals such as Mo, Re or Ru frequently form carbonyls, which subsequently may be encaged in zeolites and, after decomposition, transformed into small metal aggregates. However, in several cases, the encapsulated carbonyls are transferred into cationic species and anchored as such in the zeolite matrix. For example, Co2(CO)g was oxidized by the protons of H-Y to Co + and held at sites in the supercages, as suggested by IR investigations [251]. Formation of the cations may be due to a reaction as described by Eq. (23). 

Highly acidic natural clays, montmorillonite are complex layers of S1O4 and AIO4 tetrahedra. They also contain small amounts of MgO and Fe20j. These impurities are leached with sulfuric aid, which also adds protons to increase maximum pK values from -3.0 to -8.2. These clays were the first cracking catalysts used with fixed and moving beds. However, they were quickly replaced by the superior synthetic silica-aluminas that were ideal for fluidized beds. Today, they are used as the matrix in zeolite-based cracking catalyst. 

The surfaces of zeolites ean thus display Brpnsted or Lewis acid sites or a combination of the two, depending on how the zeolite is prepared. Brpnsted acid sites are converted into Lewis acid sites as the temperature is increased above approximately 500°C and water is driven off The overall catalytic activity of zeolites as solid acids depends on the number and the properties of the acid site. The strength of the acid sites is directly related to the framework composition of the zeolite. Zeolites with low Si/Al ratios can have higher concentrations of catalytic sites, and zeolites with high Si/Al ratios show strong acidity. Their classifications are shown in Table 2. An H-Y or H-ZSM-5 zeolite with a low density of acid groups is like an ideal solution of dispersed noninteracting protons in a solid matrix. 

Another example of inorganic phase incorporation with the sPEEK polymeric matrix is constituted by the use of zeolite. Intaraprasit and Kongkachuichay [151] studied the incorporation of Analcime natural zeolite (10 wt%) in sPEEK, achieving a high proton conductivity of —4.0 X10 S/cm at 90 °C and 100% RH (Table 3.8). 

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