Metal-containing heterogeneous catalysts often need to be calcined before reduction, so what are some examples of catalysts that perform better without calcination? What is the reason and how many categories can the principle be divided into?
Gangli Zhu
Catalysis can be heterogeneous and homogeneous. If you do not calcine the catalyst, it will usually be in a hydrated state and should be classified as a homogeneous catalyst. Calcined heterogeneous catalysts have a strict crystal lattice, on the plane of which the molecules of the reacting substances are activated. As an example, we can cite Ti (OH)4 and TiO2.
Have a good day! Heterogeneous catalysts in the process reduction also losing water. (Like in zeolite dehydration) But you must do it gradually increasing the temperature so as not to destroy the crystal lattice. (1)(Dehydration (100C+ -depends on pore distribution). At the same time activation of metal particles occurs (transformation of particles from oxide form to metallic form).
Brønsted active sites(BAS) in zeolite during high-temperature treatment, transform to Lewis acid sites (when water losess). The framework dealumination often occurs, thus generating octahedral aluminium species. BAS more active in any reaction than LAS, may be this is the reason of losses of activity in some type reaction during the calcination. (2)
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