The direct synthesis of H2O2 from H2 and O2 is a strongly desired reaction for green processes and a promising alternative to the commercialized anthraquinone process. The design of efficient catalysts with high activity and H2O2 selectivity is highly desirable and yet challenging. Metal dopants enhance the performance of the active phase by increasing reaction rates, stability, and/or selectivity. The identification of efficient dopants relies mostly on catalysts prepared with a random and non‐uniform deposition of active and promoter phases. To study the promotional effects of metal doping on Pd catalysts, we employ colloidal, bimetallic nanocrystals (NCs) to produce catalysts in which the active and doping metals are colocalized to a fine extent. In the absence of any acid and halide promotors, PdSn and PdGa NCs supported on acid‐pretreated TiO2 (PdSn/s‐TiO2, PdGa/s‐TiO2) were highly efficient and outperformed the monometallic Pd catalyst (Pd/s‐TiO2), whereas in the presence of an acid promotor, the overall H2O2 productivity was also further enhanced for the Ni‐, Ga‐, In‐, and Sn‐doped catalysts with respect to Pd/s‐TiO2.

Fe 3 O 4 /CoFe 2 O 4 nanorods were obtained via a simple seed-mediated synthesis. Nanorods were used as seeds to grow CoFe 2 O 4 by thermal codecomposition of the cobalt(II) and iron(III) acetylacetonate precursors. The growth process was monitored by electron microscopy (SEM, TEM), and the resulting nanorods were characterized by powder X-ray diffraction analysis and IR and Raman spectroscopy. Magnetometry and AC susceptometry studies revealed a distribution of Neél relaxation times with an average blocking temperature of 140 K and a highfield magnetization of 42 Am 2 /kg. Complementarily recorded 57 Fe−Mossbauer spectra were consistent with the Fe 3 O 4 /CoFe 2 O 4 spinel structure and exhibited considerable signs of spin frustration, which was correlated to the internal and surface structure of the nanorods.

Hydrogen peroxide production by direct synthesis (H 2 + O 2 → H 2 O 2 ) is a promising alternative to the commercialized indirect process involving sequential hydrogenation and oxidation of anthraquinones. Metal dopants are known to enhance the performance of Pd-based catalysts in this reaction by increasing H 2 O 2 rates and selectivity. Recently, binary and ternary Pd-based alloys with Pb have been proposed as catalysts by theoretical studies, but these compositions lack experimental proof. Herein, shape-selective Pd 3 Pb nanocrystals were created to produce catalysts where the active and doping metal are colocalized to a fine extent. This strategy enables us to study the effects of both Pb doping and nanocrystal shape on the catalytic performance in direct H 2 O 2 synthesis. In order to achieve these goals, we developed a procedure for the shape-controlled synthesis of Pb-doped nanocrystals with phase-pure, intermetallic Pd 3 Pb composition. By a change of the ligands, uniform Pd 3 Pb nanocrystals with cubic, cuboctahedral, and spherical shapes as well as flowerlike aggregates were obtained, which were supported on acid-treated TiO 2 . We show that the catalytic efficiency in direct H 2 O 2 synthesis not only is influenced by the nanocrystal composition but also depends on the particle shape. Pd 3 Pb cubes, predominately terminated by their (200) facets, outperformed not only the monometallic Pd reference catalyst but also Pd 3 Pb nanocrystals with other shapes. Further DFT calculations and surface studies indicated not only the electronic modification of Pd surface atoms with a higher barrier for O 2 dissociation on Pd 3 Pb but also a lack of larger Pd ensembles in Pd 3 Pb cubes which are known to cleave O−O bonds and form water.