To develop and enhance cost-effective technologies for capturing, utilizing, storing, and conversion into valuable chemicals of two significant greenhouse gases, carbon dioxide (CO₂) and methane (CH₄), a deep understanding and control of the chemical interactions are essential. Bulk magnesium oxide (MgO) is commonly employed for capturing and storing CO₂ through the formation of magnesium carbonates. Additionally, there is considerable research interest in copper (Cu)-based catalysts due to their unique ability to selectively catalyze the partial oxidation of methane to methanol at lower temperatures. This study delves into the growth and reactivity of MgO nanostructures on a Cu₂O/Cu(111) substrate, employing scanning tunneling microscopy (STM) and synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Nanostructures of MgO, spanning from 0.01 to 0.35 monolayers (ML), exhibited diverse morphologies. A structured copper oxide film with embedded MgO clusters was observed, with smaller clusters (0.2-0.5 nm in width, 0.4-0.6 Å in height) evident at lower MgO coverages. Conversely, at higher coverages, randomly dispersed MgO nanoparticles (0.4-2.5 nm in width, 1.5-2.0 Å in height) formed on the copper oxide surface. These oxide nanostructures displayed notable reactivity towards CO₂, CH₄, and H₂. On MgO nanostructures smaller than 1 nm in width, CO₂ dissociated into CO and C species through partial or complete decomposition instead of forming plain carbonates. Additionally, Mg nano clusters with a coverage of 0.05-0.2 ML activated CH₄ at room temperature, leading to its dissociation into CH_x species and surface H. Furthermore, dissociation of H₂ occurred at low temperatures (≤ 400 K), reacting with CuO_x and C-containing groups. The size and morphology of MgO nanostructures influenced their reactivity, allowing for direct conversion of CO₂ or CH₄ into methanol [CO₂ → CH₃OH or CH₄ → CH₃OH] and dry reforming of methane by CO₂ [CO₂ + CH₄ → 2CO + 2H₂]. This investigation underscores the size- and morphology-dependent reactivity of MgO nanostructures, showcasing behavior distinct from bulk MgO.

Arephin Islam

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