A ready-to use, highly sustainable solution for large scale exhausts catalytic abatement was developed: the active bricks. An environmentally-friendly composite was synthesized by depositing La0.6Sr0.4Ga0.3Fe0.7O3, by combustion synthesis, on a fly ash-based geopolymer improved to bear the high temperatures (> 900 degrees C) required for synthesis. The geopolymer was obtained using by-products and was synthesized at RT: its production is sustainable and cost efficient. Prepared composites have been tested for methane oxidation and show good, durable activity above 400 degrees C. Thermal stability was also proved. Composites are a good solution for oxidation of fuel residues in industrial processes. [GRAPHICS] .