Development of advanced mesostructured catalytic coatings on microstructured substrates for fine chemicals synthesis

Microreactors have a large potential in development of very selective and environmentally benign routes for the production of fine chemicals and pharmaceuticals, because full selectivity control can be achieved by total structure uniformity at multiple length scales. First of all, on the nanoscale by using appropriate mesoporous coatings and by obtaining (bi-)metallic clusters with a narrow particle size distribution. Then, on the microscale by synthesizing only a thin (500-1000 nanometer) coating support layer on the walls of reaction channels to avoid long diffusion pathways in the macropores. Finally, on the macroscale, by providing the same residence time and reaction conditions in every microchannel in a microfabricated reactor. The proposed research is aimed at the development of new types of stable catalytic mesoporous coatings for efficient fine chemicals synthesis under controlled conditions. The unique characteristics of mesostructured materials, namely high pore volume and surface area combined with narrow pore-size distribution, make them particularly suitable for various fine chemicals synthesis processes, in particular processes for which catalyst separation is unfeasible. Potentially most stable coatings are sol-gel derived crystalline (or amorphous) silicon and transition metal (preferrably titanium) oxides. Synthesis of the latter materials is complicated by moisture sensitivity of the required precursors. Moreover, at present there is insufficient knowledge concerning optimal synthesis conditions and optimal coating properties (such as morphology, pore size distribution, number of acid sites per unit of internal area, etc.) for incorporation of (bi-)metallic catalysts. New sol-gel chemistry strategies for coating synthesis, starting from newly developed precursors, will be developed in combination with the evaporation induced self-assembly (EISA) method. Various experimental techniques will be used and developed to obtain insight in physical and chemical phenomena that determine the catalytic performance as well as the stability of the coatings. Pore morphology and internal surface features of mesoporous coatings will be modified to achieve a good binding of active catalysts with the support. This will create a high surface area available for reactant adsorption. In turn, this will allow efficient operation of wall coated microstructured reactors in various catalytic reactions. In the second part of the project, we will focus on understanding the influence of catalyst crystallite size effects, type/stoichiometry of bimetallic (Pt-Sn, Ru-Pt and Rh-Sn) clusters on the kinetics of citral hydrogenation. The bimetallic nanoparticle catalysts are discrete anchored clusters, prepared by the gentle decarbonylation of the parent, mixed-metal precursor anions. They will be inserted along with their counterions into a mesoporous support. The mesoporo-encapsulated clusters will be activated by heating in vacuo. The diameter of the resulting, well-dispersed, isolated and anchored bimetallic nanoparticles is in the range of approximately 1-2 nanometers. The catalytic coatings will be tested in the heterogeneously catalyzed hydrogenation of citral to the corresponding unsaturated alcohols which represent a broad class of industrially relevant compounds useful in the specialty, pharmaceutical and other high-value sectors of the chemicals. Long term performance of catalytic coatings will be evaluated.