Theoretical evaluation of the microporosity of pillared layered double hydroxides

Over the last ten years, the concept of pillaring has frequently been appli ed on layered double hydroxides (LDHs). Due to the variety of possible anio nic pillaring species and the adjustable layer charge density, LDHs offer g ood perspectives with regard to the creation of porous adsorbents and catal ysts. But despite these possibilities, their porosity properties can still not compete with those of industrially applicable materials like zeolites. In this study, theoretical calculations based on geometrical models and per formed on both Fe(CN)(6)-MgAl-LDHs (A) and [PV2W10O40]-ZnAl-LDHs (B) were r eported. Properties such as the micropore volume and the interpillar distan ce were calculated, and compared to experimental data. For a M(II)/M(III) r atio in the layers of 3, the theoretical maximum micropore volumes were 0.3 843 cm(3)/g (A) and 0.1497 cm(3)/g (B), respectively. By implementing param eters like the stack size, pillars on the outside of the stacks and the pos sibility of collapse, the model was adjusted in order to create a realistic picture of the microstructure of pillared LDHs. This led to a better under standing of the limiting factors, and gave an explanation for the relativel y low micropore volumes of pillared LDHs. For the Fe(CN)(6)-MgAl-LDHs, smal l interpillar distances were responsible for the partial inaccessibility of the interlayer regions by N-2. This effect was the most pronounced for hig h charge density LDHs. The situation for the [PV2W10O40]-ZnAl-LDHs is more complex. Probably due to an incomplete pillaring process, the theoretical m aximum values are not reached.