Problems encountered in powder X-ray diffraction analysis of zeolites and molecular sieves

Powder diffraction patterns contain far poorer information than single crystal intensity data mainly due to equivalent and overlapping reflections. This report reviews the basic problems of powder X-ray diffraction studies of zeolites and molecular sieves, various techniques used for the refinement of the unit cell parameters encountered. Emphasis is given to the preparation of fully crystalline sample by carefully optimizing the conditions of crystallization and then collecting the data from the diffractometer. While indexing the powder patterns of known and unknown phases using computer programs, the problems encountered for indexing zeolite samples with large unit cells are discussed with examples. Scientists are still exploring new ideas and computer programs for the structural analysis of zeolites and molecular sieves from their powder x-ray diffraction profiles.