Microporous materials based on cations of medium acidic strength. such as, the alumino-silicate zeolites, represent one of the most widely used heterogeneous catalysts. Synthesising novel materials that could combine the molecular-sieve characteristics of Si-zeolites. with the much higher acidic strength and redox properties of early transition metal cations, would be a major breakthrough in catalysis. In this paper we examine this topic employing computer modelling in advance of experiment: we design suitable microporous structures of MoO3 and WO3, compare their relative energy with those of the known dense polymorphs of the materials. and finally explore the possibility of their synthesis via a template/host approach previously developed for zeolitic materials.