Abstract: Chemical combination (C) between an active solid phase which is covalently bound to the surface of an inert solid phase, characterized in that said solid active phase essentially consists in a solid solution of a mixture of at least a magnesium oxide type phase compound and at least a magnesium silicate type phase compound in which Al, and Rh and/or Ni cations are soluted and characterized in that said inert solid phase is either a compound represented by the general formula (I): AlaNibRhcMgdSieOf??(I) wherein a, b, c, d, and e are integers which are greater than or equal to 0, f is an integer greater than 0, the sum a+b+c+d?0, and wherein (3a+2b+3c+2d+4e)/2=f, or a mixture of compounds represented by the said general formula (I), provided that at least one of the Si, Al, Mg, Rh or Ni elements, which is present in the solid active phase, is also present in the solid inert phase. Use of a catalyst in chemical reactions involving the conversion of hydrocarbonaceous feedstocks.