Structure and properties of compounds formed during the preparation of nickel‐on‐silica catalysts

So far various metal hydrosilicates have been described in literature, but a detailed study of the components in the system metal oxide‐silica‐water occurring during the preparation of hydrogenation catalysts with added silica, has not been published. The results of a study of the system NiO‐SiO2‐H2O are given in this article, which also describes influence of the silica on the reducibility of the compounds. The formation of nickel hydrosilicates under various conditions was studied by means of X‐ray diffraction and thermal analysis. At relatively low temperatures (under 100° C) badly crystallized compounds are formed; thermal analysis indicated the presence of incomplete hydrosilicates, viz. nickel antigorite and/or nickel montmorillonite. The degree of crystallization of these hydrosilicate gels can be much improved by hydrothermal treatment. The stable end products resulting from this treatment are Ni(OH)2, Ni3(OH)4Si2O5 (nickel antigorite), Ni3(OH)2(Si2O5)2 (nickel montmorillonite) and SiO2 (quartz). The reducibility with hydrogen was measured as a function of the temperature. It varies greatly both with the silica content and with the degree of perfection of the hydrosilicate structure, the hydrothermally treated nickel montmorillonite being of all the most difficult to reduce. Generally the reduction leads to formation of nickel in a cubic form; however in the case of the hydrothermally treated nickel montmorillonite and nickel antigorite gels there are indications that part of the reduced nickel atoms remain in the places they occupied as ions in the hydrosilicate structure.