Catalyst based on solid microporous crystalline material and method of improving diesel fraction quality using said catalyst

Process for improving the quality of diesel fractions, which process comprises carrying out a step selected from among hydrogenation of aromatics, opening of the naphthene rings, and a hydrogenation/opening step which is a combination of both, wherein said process is carried out with the use of a catalyst comprising at least:

• one matrix comprising at least one oxide selected from an amorphous oxide, an oxide with low crystallinity, and a mixture of both,
• at least one microporous crystalline solid material which, in the calcined and anhydrous state, has the molar composition X2O3:nYO2:mZO2 in which X is a trivalent element, Y is at least one tetravalent element other than Ge, and Z is Ge, the value (n+m) is at least 5, and may be between 5 and ∞, and the value of n/m is at least 1, and which has, in its calcined and anhydrous state, an X-ray diffractogram containing at least diffraction lines with values of d=13.64, 7.87, 4.82, 4.55, 4.11 and 3.41 Å, and
• at least one hydrogenating component.