Studies on metal alkoxides and carboxylates for use as catalyst precursors
This thesis describes research carried out to investigate the feasibility of preparing high activity heterogeneous catalysts from the thermal decomposition of mixed metal alkoxides, carboxylates and hydroxycarboxylates, focusing in particular on the Cu/ZnO/Al(_2)0(_3) methanol synthesis catalyst. The rationale behind the project is discussed in the opening chapter of the thesis which is followed by literature reviews of heterogeneous catalysis and the chemistry of metal alkoxides, carboxylates and hydroxycarboxylates. Series of co-precipltation/crystallisation reactions of copper and zinc formates, oxalates and adipates were carried out as potential routes to double salts, Some such compounds were formed but in most cases mixtures of the individual salts resulted (xrd).Thermal decompositions of alkoxides and carboxylates of copper and zinc were investigated both as separate compounds and as mixtures. The nature of volatile species evolved (gas-phase ir) and of the solid residues (microanalysis, xrd) was different for the mixed decompositions compared to the individual ones, The conditions employed in decompositions of copper (II) formate with zinc methoxide (e.g. under vacuum or a stream of or N(_2) or N(_2)/H(_2)) affected the physical nature of the copper metal/zinc oxide residues, smallest particles resulting when using a N(_2) stream (transmission electron microscopy). Some of these materials showed activity for methanol synthesis. The reaction of soluble copper alkoxides (e.g. Cu(_I)0Bu) with anhydrous zinc 2-hydroxybenzoate, Zn(OzCCeH*(OH))^, led to the formation of apparently mixed metal compounds, for example CuZn(0(_2)CC(_6)H(_4)0)(_2)Py. The preparation of a new soluble alkoxy derivative of zinc is also reported: Li(_2)ZnCl(_2)(0CH(_2)CH(_2)(X:H(_2)CH(_2)0CH(_3))(_2).A summary of the results of the experimental work is given in relation to the project as a whole.