An inorganic material constituted by at least two elementary spherical particles, each of said spherical particles comprising metallic particles in the form of a polyoxometallate with formula (XxMmOyHh)q−, where H is a hydrogen atom, O is an oxygen atom, X is an element selected from phosphorus, silicon, boron, nickel and cobalt and M is one or more elements selected from vanadium, niobium, tantalum, molybdenum, tungsten, iron, copper, zinc, cobalt and nickel, x being equal to 0, 1, 2, or 4, m being equal to 5, 6, 7, 8, 9, 10, 11, 12 or 18, y being in the range 17 to 72, h being in the range 0 to 12 and q being in the range 1 to 20 (y, h and q being whole numbers), said metallic particles being present within a mesostructured matrix based on an oxide of at least one element Y selected from the group constituted by silicon, aluminium, titanium, tungsten, zirconium, gallium, germanium, tin, antimony, lead, vanadium, iron, manganese, hafnium, niobium, tantalum, yttrium, cerium, gadolinium, europium and neodymium and a mixture of at least two of these elements, said matrix having pores with a diameter in the range 1.5 to 50 nm and having amorphous walls with a thickness in the range 1 to 30 nm, said elementary spherical particles having a maximum diameter of 200 microns.