Temperature programmed reduction of copper-silica catalysts prepared by ion exchange method.

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Temperature programmed reduction (TPR) has been used to study copper–silica catalysts which were prepared by ion exchange method and the effects of preparation of catalysts upon their reducibilities were elucidated. Three peaks appeared with maxima at 265–300 °C (α), 400 °C (β), and 650–800 °C (γ) over the catalysts calcined at 500 °C. Highly dispersed cupric oxide clusters were reduced to metallic copper, giving α peak. Isolated copper(II) ions which were strongly interacted with silica surface were reduced stepwise to metallic copper through copper(I) ion species, giving α and γ peaks. However, isolated copper(II) ions which were weakly interacted with the support gave α and β peaks. When the catalysts were precalcined above 800 °C, the fourth peak (α′) appeared at 330–350 °C and α, β, and γ peaks diminished. This was assigned to the reduction of bulk CuO which was crystallized from species described above. The reducibility of copper–silica catalyst was found to depend strongly upon the conditions of preparation.
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