Advances in membrane materials and their fabrication technology are, among many potential solutions, one of the most direct, effective and feasible approaches technologies for solving key issues in both energy and environmental emerging systems. Complex membrane architectures are being developed in our Institute with oxides, non-oxides, hybrid or composite materials, and new reaction pathways are also investigated to orient the formation of stable material designs. An important part of the research activity in our group is currently focussed on zeolite membrane due to their specific properties coupling attractive functionalities such as adsorption/separation & catalytic activity which could be advantageously applied in the treatment, separation and/or filtration of gases and vapors. The principal bottleneck of zeolite membrane bears on an unavoidable formation of intercrystalline defects during the synthesis and poor molecular sieving effect limiting their industrial applications. Number of strategies have been already reported in the literature for producing zeolite membranes with a reduced number of irregularities, with tailored inter-/intra-crystalline pathways and/or with specific adsorption or catalytic activity. In this work we report on both in-situand ex-situmodifications of MFI zeolites, for preparing membranes with enhanced efficiency for gas separation or catalytic reactor applications. A special attention will be paid to an original post-synthesis modification strategy in supercritical CO2(scCO2). This novel modification method is based on a controlled transport/infiltration of specific alkoxides into a zeolite membrane followed by their catalytic cracking leading to a blocking of the MFI intercrystalline pathways and/or a reduction of zeolite channel size for increasing membrane selectivity while maintaining high permeance. The application of this method open the way to a large range of (green) strategies for the controlled modification of zeolite membranes by using on-stream methods.