Shape-Selective Synthesis of Intermetallic Pd₃Pb Nanocrystals and Enhanced Catalytic Properties in the Direct Synthesis of Hydrogen Peroxide

Abstract

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.

Triethyl-Borates as Surfactants to Stabilize Semiconductor Nanoplatelets in Polar Solvents and to Tune Their Optical Properties

“…It is well known that the properties of NCs in polar phases are important as this may affect the effectiveness of energy storage and conversion. ( Naina et al, 2021 ), biomedicine ( Gao et al, 2021 ), etc. However, research on the fluorescence properties of NPLs in polar solvents is extremely limited, because they are not stable in polar solvents due to aggregation, etching, and digestion ( Sun and Buhro, 2020 ).…”

Catalytic CO Oxidation and H2O2 Direct Synthesis over Pd and Pt-Impregnated Titania Nanotubes

“…H2, O2 and N2 leaving the reactor were periodically analyzed using a micro-GC. The H2O2 concentration was analyzed ex situ by UV-Vis spectroscopy (Figure 7a) [40]. As a result, the as-prepared Pd/TNT catalysts show a H2 conversion of 42% and 49% as well as a H2O2 selectivity of 32% and 13% in the case of long Pd/TNTs and short Pd/TNTs, respectively (Figure 7b).…”

“…Similar to the aforementioned CO oxidation, the long Pd/TNTs again outperform the short Pd/TNTs in terms of H 2 O 2 selectivity and productivity. Under these reaction conditions, the long Pd/TNTs show a high H 2 O 2 productivity with respect to a Pd nanoparticlederived reference catalyst on acid-pretreated, commercial TiO 2 (P25) [40]. Compared to Pd catalysts supported on conventional TiO 2 , the long Pd/TNTs revealed an especially high H 2 O 2 productivity, particularly in the case of a non-electrochemical catalytic process of direct H 2 O 2 synthesis [32,33].…”

“…H 2 O 2 direct synthesis was performed in a semi-continuous 300 mL batch reactor (30 • C, 40 bar). The semi-continuous batch reactor was operated as a batch reactor with respect to the liquid phase containing the suspended catalyst, whereas the gas phase (H 2 /O 2 /N 2 4/20/76) was continuously supplied during the reaction (total flow of 250 mL NTP /min) [40]. The Pd/TNTs (1.3 mg Pd per experiment) were suspended in ethanol as the reaction medium (200 mL).…”

Bimetallic Pd/Sn‐based Nanoparticles and their Catalytic Properties in the Semihydrogenation of Diphenylacetylene

“…[3] Recently, the solution-mediated synthesis of shape-selected, intermetallic Pd 3 Pb nanocubes with enhanced catalytic properties in direct hydrogen peroxide synthesis was achieved. [4] We have also reported on the synthesis of Pt/Sn-based NPs with solidsolution and intermetallic structures which reveal high selectivity in the hydrogenation of α,β-unsaturated aldehydes. [5] Like Pt/Sn systems, Pd/Sn alloys are also of great interest.…”