Study On Hydrogenation Of Cinnamaldehyde By Mesoporous Carbon Composite Supported Palladium Nano - Catalyst

Palladium catalysts have been widely used in hydrogenation reactions, such as the selective hydrogenation of cinnamaldehyde. However,aggregation and detachment of Pd nanoparticles, destruction of catalyst structure, as well as deactivation after absorbing sulfur usually occur during the catalysis. To provide solutions for these problems mesoporous carbon composite supported palladium catalysts（Pd/SH-MSC） were prepared by encapsulating the Pd nanoparticles inside the thiol functionalized ordered mesoporous polymer via a coordination-assisted pyrolysis procedure. The performance and poison tolerance of thiourea of the palladium catalysts in the selective hydrogenation of cinnamaldehyde in water were studied.The first chapter reviewed the category and the synthetic methods of mesoporous materials, and the developments of palladium catalysts.In chapter two, mesoporous carbon composite supported palladium catalysts（Pd/SH-MSC） were prepared. Firstly, thoil-functionalized mesoporous polymer materials are synthesized involving a multiple self-assembly approach. Then, Pd2+ were introduced into the polymer by the coordination between SH and PdCl2. Upon carbonization at a high temperature of 600°C, thoil were completely removed, and the palladium precursor were reduced to form monodispersed Pd nanoparticles of 2.5 nm. The finally obtained materials possess the ordered mesostructure with p6 mm space group, high surface area（600m2/g）, large pore volume（0.50cm3/g）, and uniform bimodal mesopore size（4.8nm）.In chapter three, the catalytic activities and the resistance of thiourea of the palladium catalyst in the selective hydrogenation of cinnamaldehyde in water were investigated. A completely conversion of cinnamaldehyde with a conversion rate（TOF） value 2.5 s-1in water can be achieved at 80°C and 1 MPa H₂ in 2 h for 3Pd/SH-MSC, which was much better than that of commercial Pd/C. The main product was 3-phenylpropyl aldehyde（HCAL）, and the selectivity was 80%. 3-phenyl-propanol was found as the by product, and no unsaturated alcohols from hydrogenation at the C=O bond was detected. The enhanced hydrogenation activity in 3Pd/SH-MSC is much related to the selective modification of low-coordinated surface sites such as the edges and corners on 2.5 nm Pd particles by carbon which facilitates subsurface hydrogen diffusion. Carbon deposition can also be responsible to the high poison tolerance of thiourea by blocking the low-coordinated surface sites with accessibility to sulfur. Trapping agent-poisoning test by solid SH-SBA-15 revealed the unobvious leaching of Pd into solution, and confirmed the active site of palladium in the pore. The catalyst can be reused at least 6 times.The fourth chapter is the the whole work.