Fundamental Understanding of Spinel Stabilized Metal Catalysts
Lei Nie, Yingwen Chen, Qiuxia Cai, Donghai Mei, Jun Liu, Yong Wang*
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington, 99354, United states
The stability of supported metal catalysts is a challenge for many industrially catalytic processes. Especially under harsh reaction conditions, such as biomass conversion and emission abatement (hydrothermal or high temperature), the loss of catalytic activity is either due to metal particle growth (“sintering”) or reaction of metal with the support materials to form solid solution. We have developed a novel synthesis approach to prepare a pure MgAl2O4 spinel material via controlled hydrolysis of alkoxide precursors in a non-aqueous solution (ethanol). We reported high thermal stability of Pt supported on this well-defined MgAl2O4 during highly severe thermal aging in oxidizing atmospheres. The strong interactions between spinel surface oxygens and Pt facets helped stabilize the Pt nanoparticles over the support surface. Conventional aqueous phase synthesized MgAl2O4 in house and commercial MgAl2O4 spinels were also investigated to compare. The bulk properties were similar according to XRD and TEM while the surface properties such as zeta potentials, acidity/basicity and degree of aluminum disorder (NMR) were very different between samples. The surface properties of spinel, dramatically affected by synthesis methods, would sequentially affect the initial dispersion and stability of the metal nanoparticles. Pt supported on MgAl2O4 from novel non-aqueous phase synthesis had the highest Pt dispersion and thermal stability. Accordingly, its catalytic activity of methanol oxidation and low temperature CO oxidation were the highest among the three. Meanwhile, the DFT calculation confirmed the oxygen terminated (100) surface (100_O) of spinel MgAl2O4 is the most stable surface under low oxygen pressure conditions. In sum, the metal can be highly dispersed over the novel synthesized spinel support and the metal nanoparticles could be stabilized via lattice matching between the spinel surface oxygens and epitaxial metals\metal oxides. Other metals, such as Pd, Ru, Ag and Au were also investigated and discussed.
 Li et al. Nature Communications 4 (2013) 2481
 Li et al. Chemistry of Materials 26 (2014) 5475
See more of this Group/Topical: Environmental Division