Some membrane separation processes are gradually taking over conventional processes such as distillation, evaporation or
crystallization as the technology progresses from bench-scale tests to large-scale prototypes. However, membranes for H2 and CO2 separation
constitute a daring technology still under development. This overview focuses on mixed matrix membranes (MMMs), a special
type of membranes in which a filler is dispersed in a polymer matrix, as a successful strategy to improve their permeability-selectivity
performance while keeping the polymer processability. In particular, among all the possible fillers for MMMs, layered materials (porous
zeolites and titanosilicates and graphite derivatives) are discussed in detail due to the several advantages they offer regarding selective
microporosity, crystallinity and, what is most important, high specific surface area and aspect ratio. In fact, a selective and as thin as possible,
i.e. with high aspect ratio, filler would help to develop high performance MMMs.