The invention comprises a process for manufacturing a catalyst substrate which is a shaped porous structure, said process comprising the steps of providing non-woven fibers with an average length in the range of 4-50 mm, an average diameter in the range of 5-300 microns, and a length over diameter ratio in the range of 50 to 500 into a mould to form a fibrous aggregate with volume (V), and compressing the fibrous aggregate to form a porous structure. The compression is carried out in such a manner that the volume of the fibrous aggregate in compressed state (Vcompressed) is at most 90% of the volume (V) of the fibrous aggregate before compression. The invention further relates to the catalyst substrate prepared and to a catalyst comprising the catalyst substrate.