Highly efficient hydrogen peroxide direct synthesis over a hierarchical TS-1 encapsulated subnano Pd/PdO hybrid

Improving Catalytic Activity towards the Direct Synthesis of H2O2 through Cu Incorporation into AuPd Catalysts

With a focus on catalysts prepared by an excess-chloride wet impregnation procedure and supported on the zeolite ZSM-5(30), the introduction of low concentrations of tertiary base metals, in particular Cu, into supported AuPd nanoparticles can be observed to enhance catalytic activity towards the direct synthesis of H2O2. Indeed the optimal catalyst formulation (1%AuPd(0.975)Cu(0.025)/ZSM-5) is able to achieve rates of H2O2 synthesis (115 molH2O2kgcat−1h−1) approximately 1.7 times that of the bi-metallic analogue (69 molH2O2kgcat−1h−1) and rival that previously reported over comparable materials which use Pt as a dopant. Notably, the introduction of Cu at higher loadings results in an inhibition of performance. Detailed analysis by CO-DRFITS and XPS reveals that the improved performance observed over the optimal catalyst can be attributed to the electronic modification of the Pd species and the formation of domains of a mixed Pd2+/Pd0 oxidation state as well as structural changed within the nanoalloy.

In Situ Hydrogen Peroxide Production for Selective Oxidation of Benzyl Alcohol over a Pd@Hierarchical Titanium Silicalite Catalyst

Using in situ generated H2O2 is potentially an effective approach for benzyl alcohol selective oxidation. While the microporous titanium silicate (TS-1) supported with Pd is promising for selective oxidation, the Pd particles are preferentially anchored on the external surface, which leads to the problems such as non-uniform dispersion and low thermal stability. Here, we prepared a Pd@HTS-1 catalyst in which the Pd subnanoparticles were encapsulated in the channels of the hierarchical TS-1 (HTS-1), for benzyl alcohol selective oxidation with in situ produced H2O2. We find that the oxidation rate of benzyl alcohol by in situ H2O2 over the Pd@HTS-1 is up to 4268.8 mmol h-1 kgcat -1, and the selectivity of benzaldehyde approaches 100%. In contrast to the conventional Pd/HTS-1, the present Pd@HTS-1 benefits the benzyl alcohol selective oxidation due to the increased dispersion of Pd particles (forming uniformly dispersed subnano-sized particles), as well as the confinement effect and hierarchical porosity of the HTS-1 host. We further suggested that hydrogen peroxide produced in situ from the molecular hydrogen and oxygen over the Pd sites can be spilled over to the framework Ti4+ sites, forming the Ti-OOH active species, which selectively oxidizes the chemisorbed benzyl alcohol to benzaldehyde on the Pd sites.