High Catalytic Activity of Pd₁/ZnO(101̅0) toward Methanol Partial Oxidation: A DFT+KMC Study

Abstract

We perform density functional theory (DFT) calculations of the energetics for several pathways associated with methanol partial oxidation (MPO) reaction on singly distributed Pd on ZnO (Pd1/ZnO) and use them in kinetic Monte Carlo (KMC) simulations for elucidating reaction mechanism. We compare these results for Pd1/ZnO with those obtained for the same set of reactions on a 32-atom Pd16Zn16 nanocluster. Our KMC simulations show that Pd1/ZnO offers high, temperature-dependent selectivity (∼93%) for H2 production and a moderate one (∼76%) for CO2, in good agreement with experiment (which reports 90 and 85%, respectively). On the other hand, Pd16Zn16 yields no selectivity for H2 but almost perfect, temperature-independent selectivity (∼100%) for CO2 and H2O, leading to full oxidation of methanol. The high activity of Pd1/ZnO for MPO can be credited to the singly distributed Pd sites and to the Pd-modified geometric and electronic structures of the neighboring Zn sites, and its high H2 selectivity may be related to the abundant supply of H atoms resulting from methanol decomposition on the surface. Pd loading has a decisive impact on adsorption and dissociation of methanol and oxygen. With higher Pd loadings, the activity of the Zn site alters in such a way that it provides weaker binding to methanol and stronger binding to O2, thereby resulting in facile O2 dissociation. Singly distributed Pd atoms not only serve as a more stable binding site for methanol than does Pd in Pd16Zn16 but also induce spontaneous CO2 formation and nearly spontaneous dissociation of H2O. In an alternate but slower pathway for production of CO2 involving HCOO* intermediate on Pd1/ZnO, the rate-limiting step is dissociation of H2COO*, followed by decomposition of HCOO* into CO2* and H*.

Computational Screening of Efficient Single‐Atom Catalysts Based on Graphitic Carbon Nitride (g‐C3N4) for Nitrogen Electroreduction

“…In addition, we compared the NN bond lengths of the adsorbed N 2 molecule on the NRR catalysts with relatively good activities toward NRR, namely single Ti, Pt, W, Co, and Mo atoms supported by g‐C 3 N 4 . Interestingly, the NN bond lengths of the adsorbed N 2 molecule also shows a volcano shape (Figure b), which well resembles that of the limiting potential (Figure ) and suggests that the adsorbed N 2 molecule can be more sufficiently “activated” on W@C 3 N 4 than other catalysts.…”

“…Such catalysts not only maximize the efficiency of metal usage to 100% and significantly reduce the metal cost, especially for noble metal catalysts, such as Au, Pt, Ir, and Pd, but also provide great potentials to achieve high activity and selectivity due to the high ratio of the low‐coordinated metal atoms . These advantages distinguish SACs from their corresponding bulk materials and nanoparticles, and SACs have already emerged as a new class of catalyst for a variety of important reactions, such as CO oxidation, methanol partial oxidation, water‐gas shift, selective hydrogenation of 1,3‐butadiene, some important organic reactions, such as oxidation, hydrogenation, CC coupling and reforming, electrocatalytic, or photocatalytic reactions …”

Atomic-Scale Structure and Catalysis on Positively Charged Bimetallic Sites for Generation of H2

“…On the basis of computational studies, 26 methanol dehydrogenation is the rate-determining step for efficient production of H 2 through MPO over Pd−Zn/ZnO and pure ZnO. Their overall reaction barriers are 1.33 and 2.78 eV, respectively.…”

Rational screening of single-atom-doped ZnO catalysts for propane dehydrogenation from microkinetic analysis

“…ZnO has been extensively studied in a great many of catalytic reactions, such as methanol synthesis, 25 methanol partial oxidation, 26 methanol steam reforming, 27,28 the water-gas shift reaction, 29 and the dehydrogenation of light alkanes. 17,30 To inhibit deactivation and improve the catalytic performance for a specific reaction, synthesis of composite oxides and modification of ZnO have been proposed.…”

“…27 Rawal et al also found that, in the methanol partial oxidation reaction, Pd1-ZnO showed remarkable and excellent catalytic performance compared to Pd16Zn16 and pristine ZnO( 1010 ), where they attributed the increased activity to the great influence of the singly dispersed Pd atom on the local environment of the active Zn sites. 26 Despite a great deal of research, it is still not clear how the doped single atoms would modify the electronic structure of the ZnO surface and how the two components actually function in the chemical reactions. More importantly, there are no rules based on simple physical properties that can be used to guide us in predicting the trend in the activity of the single-atom-doped ZnO catalysts.…”