Synthesis Of Pd Nanoparticles Confined Within Mesoporous Channels Of SBA-15 And The Catalytic Properties For Aerobic Selective Oxidation Of Alcohols

Nano-sized metal particles have shown promising applications in heterogeneous catalysis due to their unique catalytic performance. However, size controlled synthesis of nanoparticles remains a challenge since they are thermodynamically susceptible to agglomeration. Mesoporous silica has high surface area and regular pore structure, such as SBA-15. Confining metal particles within the nanospace of mesoporous silica is an effective synthetic method for nanosized functional materials.The dissertation was aimed at the synthesis of Pd nanoparticles confined within the channels of SBA-15 and exploring its application as the catalyst in the aerobic oxidation of alcohols. The dissertation consists of the following two parts.The first part is the synthesis and characterization of Pd/SBA-15-ads catalyst. The catalyst preparation empolyed the SBA-15 with its organic template (P123) removed by ethanol extraction for the adsorption of cationic Pd precursor in alkaline solution followed by calcination and H2 reduction. Pd loadings were largely influenced by the pH of adsorption solution. HRTEM observations confirmed that most Pd particles prepared by this method were located inside the mesoporous channels of SBA-15 and were quite uniform in size (4-5 nm). XRD, N₂ adsorption-desorption and CO chemisorption were also used in the catalyst characterization.The second part is the studies of the catalytic performance of Pd/SBA-15-ads for the aerobic oxidation of alcohols. Pd/SBA-15-ads catalysts with Pd particles in ⁴ nm showed good catalytic performance for the aerobic oxidation of benzyl alcohol. Compared to Pd nanoparticles supported on NaX and Al₂O₃ support, the Pd/SBA-15-ads catalyst gave higher catalytic activity. However, the selectivity of benzaldehyde was only 80% and the by-product was toluene. Benzyl alcohol was found undergoing redox disproportion over Pd/SBA-15-ads catalyst under anaerobic conditions, producing equal amount of benzaldehyde and toluene. That is there were two parallel reactions occurred over Pd/SBA-15-ads catalyst during the aerobic conversion of benzyl alcohol: oxidation of benzyl alcohol to benzaldehyde and the redox disproportion of benzyl alcohol to benzaldehyde and toluene. Besides, the Pd/SBA-15-ads can also efficiently catalyze the solvent-free oxidation of some aromatic alcohols, secondary aliphatic alcohols and cyclic alcohols to corresponding carbonyl compounds.