Microkinetic Modeling with Size-Dependent and Adsorbate–Adsorbate Interactions for the Direct Synthesis of H₂O₂ over Pd Nanoparticles

Abstract

As a bottleneck in the direct synthesis of hydrogen peroxide, the development of an efficient palladium-based catalyst has garnered great attention. However, elusive active centers and reaction mechanism issues inhibit further optimization of its performance. In this work, advanced microkinetic modeling with the adsorbate–adsorbate interaction and nanoparticle size effect based on first-principles calculations is developed. A full mechanism uncovering the significance of adsorbate–adsorbate interaction is determined on Pd nanoparticles. We demonstrate unambiguously that Pd(100) with main coverage species of O2 and H is beneficial to H2O2 production, being consistent with experimental operando observation, while H2O forms on Pd(111) covered by O species and Pd(211) covered by O and OH species. Kinetic analyses further enable quantitative estimation of the influence of temperature, pressure, and particle size. Large-size Pd nanoparticles are found to achieve a high H2O2 reaction rate when the operating conditions are moderate temperature and higher oxygen partial pressure. We reveal that specific facets of the Pd nanoparticles are crucial factors for their selectivity and activity. Consistent with the experiment, the production of H2O2 is discovered to be more favorable on Pd nanoparticles containing Pd(100) facets. The ratio of H2/O2 induces substantial variations in the coverage of intermediates of O2 and H on Pd(100), resulting in a change in product selectivity.

Reversed Charge Transfer to Modulate the d-Band Center of Pd for Efficient Direct H2O2 Synthesis

“…17−20 Unfortunately, the OOH* intermediates adsorption is often too strong and thus impacts their subsequent protonation and the desorption of the generated H 2 O 2. 21,22 One promising approach to overcome the issue is to incorporate a secondary metal such as Ag, 23 Au, 24,25 Sn, 26,27 Pb, 28,29 and Zn 30 to form an alloy structure. These additional metals effectively modify the electronic configuration of Pd and thus weaken the intermediates adsorption and prevent undesired side reactions.…”

“…However, it is also active toward H 2 O 2 decomposition/hydrogenation, which greatly reduces the efficiency of Pd-based catalysts. − Specifically, Pd-based catalysts easily undergo severe leaching and loss of their catalytic activity. , O 2 adsorption and OOH* intermediate protonation are two important steps during the hydrogenation of oxygen and depend on the surface properties of the catalysts. − Unfortunately, the OOH* intermediates adsorption is often too strong and thus impacts their subsequent protonation and the desorption of the generated H 2 O 2. , One promising approach to overcome the issue is to incorporate a secondary metal such as Ag, Au, , Sn, , Pb, , and Zn to form an alloy structure. These additional metals effectively modify the electronic configuration of Pd and thus weaken the intermediates adsorption and prevent undesired side reactions. , …”

Palladium–Tin Alloy Nanoparticles in Different Crystalline Phases for Direct Hydrogen Peroxide Synthesis

“…Hydrogen peroxide (H 2 O 2 ), as a crucial green chemical, has been widely utilized in energy, medical treatment, and the military. − It has conventionally been produced through the anthraquinone process in industry, which has many disadvantages, including high energy input and complex synthesis procedures . In contrast, directly synthesizing H 2 O 2 from hydrogen and oxygen is economical and sustainable. , Palladium (Pd)-based materials are effective catalysts for the direct H 2 O 2 synthesis (DHS) reaction. , However, there is prominent H 2 O 2 degradation and hydrogenation in individual Pd-based materials . To address the issue, various strategies have been developed to tailor the coordination and electron distribution of Pd to enhance the DHS performance, such as synthesizing palladium oxide, Pd-based bimetal catalysts, , ligand modification of Pd, and Pd with the controlled strain effect .…”

Revealing the Size and Potential Dependent D2O Microkinetics on Pt Nanoparticles Using Grand Canonical Ensemble Modeling

“…In this assumption, the terrace, step, and corner atom sites from the cuboctahedral nanoparticle are represented by Pt (111), Pt (211), and Pt 55 , respectively. Within this method, reactions on these sites were considered separately, and the microkinetic reaction rate was calculated by summing up the overall reaction rate for each surface. , …”

“…To better assess the activity of Pt nanoparticles under electrochemical conditions, polyhedral models with multiple sizes of diameters were constructed. We combine the energy parameters calculated from the FCP method and size dependent site distribution rule assumption − to determine the reaction rate of D 2 O and H 2 O on Pt nanoparticle quantitatively. Pt nanoparticles were assumed as the cuboctahedral shape of various sizes, , where the active sites could be classified into the terrace, the step, and the corner site.…”