Homework 01

Zeolite Rho has a unit cell composition of (Na,Cs)₁₂[Al₁₂Si₃₆O₉₆].46H2O with structure as shown in Figure 1 The unit cell is composed of 48-T atom polyhedra having 26-hedron cage, so called the a-cage as shown in Figure 2. The window size is approximately 0.45 nm. The structure is built by connecting a-cage with D8R secondary building units in body centre cubic type. Zeolite Rho structure is quite flexible. It can be distorted upon heating or experience strong molecular interaction. This is because the structure is made of large cage with the same size. The flexibility of zeolite Rho can also be modified by ion exchange. It was found that when dehydrate, the Na-Rho is more flexibible than Cs-Rho. This is because Cs⁺ is a large cation and it can inhibit movement of tetrahedral (TO₄) unit in the a-cage.

Figure 1 Zeolite Rho Structure Figure 2 a-cage (26-hedron cage)

1. What is the SiO2/Al2O3 ratio of zeolite Rho?

2. What is the type of zeolite Rho structure, cage or channel?

3. What are 3 main secondary building units of zeolite Rho?

4. If there is no exchangeable cations in double-8-ring, how many cation in a-cage per 1 cage of zeolite Rho on average? Show by calculation

5. Suggest the flexibilty of Ca-Rho as compared to Na-Rho