Most of the literature I read says to calcine heterogeneous catalysts when preparing them. When synthesizing heterogeneous catalysts, what is the reason for calcining them?
For heterogeneous catalysis calcining of the catalyst allows for the following:
- mechanically and thermodynamically stable macrostructure (matrix) with defined geometry, surface and pore size;
- predictable activity based on calcining regime (generally, there is a temperature peak for maximum activity, and further extreme temperature treatment often lowers catalyst's activity);
- pure composition without traces of organics and majority of other undesired impurities;
- production convenience and scalability (for example, metal oxide catalyst manufacturing process can be easily implemented within mining and processing plants);
- when distributed over support, more uniform distribution of metal oxide is achieved, and upon slow treatment crystallinity of the catalyst can also be tweaked.
One of the most important reasons to calcine a catalyst preparation is to decompose the impregnated metal salts. This includes decomposition of nitrates, chlorides, carbonates and organic chelates, leaving a metal or metal oxide on the support surface.