Size‐Dependent Catalytic Activity of Supported Palladium Nanoparticles for Aerobic Oxidation of Alcohols

Abstract

Silica-alumina (SiO 2 -Al 2 O 3 )-supported palladium catalysts prepared by adsorption of the tetrachloropalladate anion (PdCl 4 2À ) followed by calcination and reduction with either hexanol or hydrogen were studied for the aerobic oxidation of alcohols. The mean size of the Pd particles over the SiO 2 -Al 2 O 3 support was found to depend on the Si/Al ratio, and a decrease in the Si/Al ratio resulted in a decrease in the mean size of the Pd nanoparticles. By changing the Si/Al ratio, we obtained supported Pd nanoparticles with mean sizes ranging from 2.2 to 10 nm. The interaction between the Pd precursor and the support was proposed to play a key role in tuning the mean size of the Pd nanoparticles. The Pd/SiO 2 -Al 2 O 3 catalyst with an appropriate mean size of Pd particles could catalyze the aerobic oxidation of various alcohols to the corresponding carbonyl compounds, and this catalyst was particularly efficient for the solvent-free conversion of benzyl alcohol. The intrinsic turnover frequency per surface Pd atom depended significantly on the mean size of Pd particles and showed a maximum at a medium mean size (3.6-4.3 nm), revealing that the aerobic oxidation of benzyl alcohol catalyzed by the supported Pd nanoparticles was structure-sensitive.

Hydrotalcite‐Supported Gold Catalyst for the Oxidant‐Free Dehydrogenation of Benzyl Alcohol: Studies on Support and Gold Size Effects

“…It can be expected that the dehydrogenation of benzyl alcohol involves the cleavage of the b-CÀH bond. This CÀH bond activation, or b-H elimination, has been proposed as the rate-determining step in the oxidative dehydrogenation of alcohols by O 2 over several catalysts such as Ru/Al 2 O 3 , [46] Pd/hydroxyapatite, [47] Pd/Al 2 O 3 , [48] Pd/SiO 2 -Al 2 O 3 , [49] and the hydrogen-transfer dehydrogenation of alcohols catalyzed by Cu/Al 2 O 3.…”

Selective oxidation of allylic alcohols over highly ordered Pd/meso-Al2O3 catalysts

“…Amino-functionalised silica supports offer one route to help stabilise highly dispersed Pd nanoparticles [22], [23] and [24], but require additional preparative steps, generating associated waste, and narrow the pore dimensions hindering intra-pore mass transport. An alternative approach to stabilising highly dispersed palladium is to select a support material with a greater affinity for the element, such as alumina [25] or silica-alumina [26], wherein Al-rich supports favour sub-2 nm (or even atomically-dispersed) palladium.…”

Catalysing Sustainable Fuel and Chemical Synthesis

“…character. Particle size dependency was also reported for the catalytic transformation of benzyl alcohol over Pd nanoparticles dispersed on alumina, SiO 2 and NaX zeolite supports [131,132]. For Pd/NaX and Pd/SiO 2 -Al 2 O 3 , benzyl alcohol selox was fastest over particles between 3 and 5 nm, whereas geraniol and 2-octanol were structure-insensitive.…”