Abstract
Three of the widest pore aluminophosphate molecular sieves were synthesized, H1, VPI-5 and AIPO[4]-8, and three more layer compounds were observed. These are the most important compounds in the search for new porous materials. By controlling the gel chemistry, the interaction with the organic template, and reaction conditions the interesting compounds are separated from at least 3-5 other undesirable phases (dense phases or compound with small pore size). AIPO4-8 observed as a secondary phase in the different synthesis procedures to prepare H1, was obtained from a more viscous gel than the one used in the DPA system with all the other conditions similar to prepare HI. VPI-5 and H1 were found to be structurally similar but with some different physical properties, for example H1 was found thermally unstable with a phase transformation to AIPO[4]-8 at 100-300°C while VPI-5 was found stable at temperatures even higher than 650°C. The differences between these two compounds appear to be related to a structural aluminum excess in HI which represents weak structural sites where hydrolysis and or bond failure can occur with a ready transformation to AIPO[4]-8 . The solid state NMR on samples with different water contents demonstrated that bond breaking in dehydrated samples occurs as part of a strain mechanism relaxation. In both samples, H1 and VPI-5, the same phenomena is observed with some differences in the healing process when water is readsorbed, for example a more hydrophilic character is observed in HI. The strain relaxation is supported by an expansion in the c-axis and contraction of the a-axis as determined by the unit cell parameters of hydrated and dehydrated samples. Isomorphous elemental substitution in H1 and or VPI-5 is indicated to be promising for Si and Fe where about 10% of intended substitution is accepted into the framework by the reaction synthesis. Other metals such as Co, Mg, and Mn are supported to a lesser extent or direct the synthesis to other aluminophosphate phases.
Perez Oliveros, Jaime Olmedo (1991). Synthesis of wide pore crystalline aluminophosphates. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -1277000.