*2.2. Catalytic Filter Preparation*

The preparation procedure of the CDPF began with the preliminary dipping for 30 min of one of the assembled bare DPFs in a 1:1 HF:HNO3 acid mixture maintained at 45 ◦C, aiming at increasing the initial average pore diameter [23]. This procedure allowed the enhancement of the catalyst loading capacity, ensuring similar pressure drops. The selected active species was copper ferrite (CuFe2O4), owing to its high activity and very good stability demonstrated in the catalytic oxidation of soot, shown in our previous works [10,22,23].

The catalyst precursor solution was prepared by mixing iron nitrate and copper nitrate (2:1 molar ratio) in distilled water, with continuous stirring at 80 ◦C. The CDPF was prepared following the previously optimized preparation procedure [44] by repeating the phases of impregnation in the prepared solution, with drying at 80 ◦C and calcination at 1000 ◦C after each impregnation, until the desired load of active species of 30 %wt was reached.
