Dear Daniel,

The type of acidity will be based on the metal you are going to impregnate.

Hi Daniel. The silica-alumina support has an acidity itself. Simplified, alumina materials have Brönsted acidity (protons in the terminal Al-OH) and Lewis (on the Al surface). Equivalently, in the silica, although its acidic nature is weaker than that of alumina.

By incorporating metal support you must take into account the nature of the incorporated metal, and according to it, the kind of acidity generated.

I hope I've been helpful.

Regards

Thank you very much for your answers. I'm working on tin-impregnated silicas and according to the analyses the principal tin species provide Lewis acidity to the material.

Best regards.

Hi dear Daniel,

The kind of acidity in your supports (because are MCM-41 and SBA-15 which don't contain Al in the framework) is Lewis. The explanation of this is because Si and O are bonded covalently and of course they don't have hydroxyl groups availables that allow to increase Brönsted acidity. Other explanation of this fact is because electronegativity, bond angle and d-orbital available provides a change of the electronic density that result in Lewis acidity.

Definition of Lewis acidity is related with the capability of an atom or molecule to receive electronic density, in your case, both Si and Sn are atoms which can receive electrons for their atomic orbitals.

With kind regards,

Julián E. Sánchez-Velandia.