| http://www.w3.org/ns/prov#value | - The particulate inorganic compounds mentioned above are preferably porous oxides including concretely SiO2, Al2 O3, MgO, ZrO2, TiO2, B2 O3, CaO, ZnO, BaO, ThO2, etc., or mixtures of porous oxides, for example, SiO2 --MgO, SiO2 --Al2 O3, SiO2 --TiO2, SiO2 --V2 O5, SiO2 --Cr2 O3 and SiO2 --TiO2 --MgO. Of these particulate inorganic compounds, preferred are those consisting essentially of at least on
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