Jeroen van den Reijen

PhD Candidate

Employed since: 2013
Phone: +31 6 22736364
E-mail: j.e.vandenreijen (at) uu.nl
Room: 4th floor study area

The stability of supported Ag nanoparticulate catalysts.

Epoxides form the base chemicals for bulk consumer products like antifreeze, polyesters and polyurethanes and therefore, indirectly for many plastic we use every day. In industry supported silver catalysts are used for the production of these epoxides by the selective oxidation of olefins (primarily ethylene and propylene). Catalysts are required because the unselective pathway leads to complete combustion, but only silver catalysts are able to obtain high yields for this reaction. [1]

By synthesizing model catalysts based on highly ordered support materials, the deposition of silver can be controlled and deactivation by particle growth can be monitored by using analysis techniques like electron microscopy and tomography. The produced catalysts still resemble industrial catalysts so they may still be used under realistic catalytic conditions.

Generally silica materials are used for ordered support materials, since these are easy to produce with high periodicity and tuneability. However, silica catalyzes the undesired reaction path in aqueous phase reaction and deactivation mechanisms may depend on support type. Therefore ordered mesoporous titania and alumina will be synthesized using various methods to obtain sufficient periodicity to be able to follow deactivation via sintering effects using tomography.

Mesoporous alumina can be obtained by grafting of Al2O3 crystals onto an existing mesoporous silica (MPS), combining the chemical properties of alumina with the structural properties of MPS. Obtaining a homogeneous layer of alumina is a challenge in this synthesis. [2]

Mesoporous titania can be produced using both hard and soft template methods. The first consists of crystallizing a titanium salt in mesoporous carbon to create a structure similar to the MPS. [3] Soft templating is done by forming titania around micelles creating the desired mesostructure. This is the same method as used for the production of MPS, but due to the high reactivity of the Ti precursors extreme conditions are required to control the crystal growth. [4]

The mesoporous support materials will be used to deposit silver particles onto the surface to create catalysts that can be tested under realistic operating conditions.

[1] Mavrikakis, M., Doren. D.J., Barteau, M.A., J. Phys. Chem. B, 102 (1998) 394-399

[2] Baca, M., de la Rochefoucauld, E., Ambroise, E., Krafft, J.-M., Hajjar, R., Man, P.P., Carrier, X., Blanchard, J., Microporous and Mesoporous Materials, 110 (2008) 232-241

[3] Lu, A.-H., Schmidt, W., Taguchi, A., Spliethoff, B., Tesche, B., Schüth, F., Angew. Chem., 114 (2002) 3639-3642

[4] Alberius, P.C.A., Frindell, K.L., Hayward, R.C., Kramer, E.J., Stucky, G.D., Chmelka, B.F., Chem. Matter., 14 (2002) 3284-3294