High Catalytic Activity Of Pd1/Zno(1010) Toward Methanol Partial Oxidation: A Dft+Kmc Study

Keywords

DFT+KMC; methanol partial oxidation; Pd-Zn nanoalloy; Pd/ZnO catalyst; reaction pathways; reaction rates; single-site catalyst

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.

Publication Date

6-1-2018

Publication Title

ACS Catalysis

Volume

8

Issue

6

Number of Pages

5553-5569

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1021/acscatal.7b04504

Socpus ID

85046772975 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/85046772975

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