A metal which react inversely with metal is IRON
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Metal particles play a key role in chemical transformations that require activation of H2 or hydrogenation/dehydrogenation of substrates. In many cases, the metal particles provide only one step in the catalytic cycle. For instance, metals have low activity in CO2 reduction because of weak CO2 adsorption, whereas the polar surface of oxides readily adsorbs CO2 but suffers from low activity for H2 activation1,2,3. Thus, metal–oxide interfaces are much more effective because both the redox sites required to activate CO2 and the metals providing active H2 are in proximity. Challenges for maximizing such interfaces are stabilizing small metal particles on oxide supports4,5,6,7 or forcing migration of oxides onto metal particles while avoiding harsh synthesis conditions8,9,10,11,12.
Inverse catalysts—oxides supported on metals—offer an attractive alternative to overcome the constraints of typical supported metal catalysts because reactants can bind to sites in the oxide overlayer, onto the metal domains, or at their interface. Typically, surface science research selects only well-defined inverse catalysts to provide a basic understanding of their adsorption and catalytic properties; however, advancing from this approach into the more complex conditions relevant to technical applications is essential13,14,15,16. In this regard, a major obstacle is encountered because typical surface science approaches for preparing inverse catalysts, such as reduction at high temperature12, deposition in ultrahigh vacuum1,13, and deposition at atomic layers17, are challenging to scale beyond certain models.
We report here a simple galvanic replacement approach for generating inverse FeOx/metal nanostructures. During galvanic replacement, one metal dissolves as a sacrificial template while a different metal ion in solution is reductively deposited onto the template. This process is driven by the differences of reduction potentials of the redox pairs, allowing a single, simple, and low-temperature step for synthesis of nanostructures18,19,20,21,22,23. Following this, research has focused on preparing metals18, metal alloys19,24, oxides21, and metal–oxides25,26 with controllable shapes. In our case, the solid support undergoing oxidation—hyperstoichiometric and sometimes referred to as cation-excess or partially reduced magnetite (Fe3O3.7)27—supplies electron equivalents in the form of Fe2+ enriched at the oxide surface, which reduce Rh3+ or Pt4+, thereby depositing metal nanostructures (Eqs. (1)–(3)).