Ultrafast Laser Manufacture of Stable, Efficient Ultrafine Noble Metal Catalysts Mediated with MOF Derived High Density Defective Metal Oxides

Abstract

subdivision reduces cost, but nano-and atomic-scale PGM catalysts can suffer from severe aggregation and degradation under practical use conditions. [1][2][3][4][5] This is due to coalescence and Ostwald ripening of metal nanoparticles (MNPs) driven by high surface energy. Catalysts constructed by dispersion of nanosized precious metals on metal oxide supporting particles are widely explored to deal the aggregation issue. [6][7][8][9][10][11][12] However, because of the limited contact between them and the lack of surface bonding to stabilize the MNPs, the deterioration of catalytic efficiency still occurs due to noble metal coalescence, especially under high operating temperature (>500 °C). [13][14][15][16][17] Surface defect engineering of the metal oxide supporting particles has been developed and refined to enhance support coupling with noble MNPs. [18][19][20] However, sophisticated pretreatment of the metal oxide supports and complicated synthetic procedures of noble MNPs still hinder their wide applications. It is challenging to establish a straightforward method to synthesize uniform catalysts in which preformed PGM nanoparticles are homogeneously mixed with metal oxide supports via strong surface coupling to retard the aggregation issue. In addition, metal oxides and PGM nanoparticles with smaller particle size are highly desired because they expose much more surface area and create the enriched active sites for the reaction. [21][22][23] Unfortunately, the established methods, either rely on high temperature calcination or low temperature wet-impregnation, suffer from aggregation of MNPs or weak bonding of the MNPs on the metal oxide supports.Herein, by virtue of metal-organic framework (MOF) incorporation of noble metal ions and advanced ultrafast laser processing, we report the synthesis of uniformly mixed noble metal nanoclusters with sub-2 nm size conjoined on surfacedefective CeO 2 nanoparticles with sub-5 nm size (M@CeO 2 , M = Pt, Au, Rh, Ru). This is achieved by direct laser conversion of cerous MOF (Ce-MOF) incorporated with corresponding noble metal ions under ambient conditions. MOFs, with precisely and atomically arranged metal oxide units jointed by organic linkers, exposed extremely high surface area where Supported metal nanoparticles (MNPs) undergo severe aggregation, especially when the interaction between MNPs and their supports are limited and weak where their performance deteriorates dramatically. This becomes more severe when catalysts are operated under high temperature. Here, it is reported that MNPs including Pt, Au, Rh, and Ru, with sub-2 nm size can be stabilized on densely packed defective CeO 2 nanoparticles with sub-5 nm size via strong coupling by direct laser conversion of corresponding metal ions encapsulated cerous metal-organic frameworks (Ce-MOFs). Ce-MOF serves as an ideal dispersion precursor to uniformly encapsulate noble metal ions in their orderly arranged pores. Ultrafast laser vaporization and cooling forms uniform, ultrasmall, well-mixed, and exceptionally dens...

Destruction of Metal–Organic Frameworks: Positive and Negative Aspects of Stability and Lability

“…The laser-induced product exhibited high stability and activity for CO oxidation even under long reaction period. 275…”

“…Through ultrafast laser vaporization and cooling, Ce-MOFs transformed rapidly, within tens of nanoseconds, into defective CeO 2 nanoparticles that showed strong coupling with well-dispersed ultrasmall noble metal nanoparticles. The laser-induced product exhibited high stability and activity for CO oxidation even under long reaction period …”

PtNi Bimetallic Nanoparticles on MgAlO Microflower Supports as Adsorbents for Desulfurization of Benzene

“…The spectrum and curve obtained by deconvolution simulation are shown in Figure S2. After careful deconvolution from the overlapped peaks of Pt 4f and Al 2p, peaks located at binding energies of 71.2 and 74.5 eV were assigned to Pt 4f 7/2 and Pt 4f 5/2 of Pt 0 on the Pt/MgAlO adsorbent, respectively. , When the Ni was introduced into the Pt/MgAlO adsorbent, the binding energies of Pt 4f 7/2 and Pt 4f 5/2 shifted to 71.4 and 74.7 eV (Figure B). This result revealed that the electron binding energy of Pt moves to higher binding energy.…”

Controlled growth of ultrafine metal nanoparticles mediated by solid supports

“…There are three common ways to introduce nucleation and anchoring sites in supports: installing organic functional groups, heteroatom doping and creating defect sites. [30][31][32][33][34][35] Organic functional groups can bind the metal ions in the precursor solution. It is a common method to capture the metal ions and anchor the resulting UMNPs in organic or hybrid supports, such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs).…”

“…Jiang et al used Pt ion-doped Ce-MOFs to create Pt UMNPs (< 2 nm) supported on CeO 2 particles (s-Pt/CeO 2 ) through an ultrafast laser induced reduction. 34 In this process, the MOF crystals absorb laser photons and generate high pressure and high temperature, causing the pyrolysis of organic liners and reduction of metal ions. Nanocrystalline CeO 2 particles with abundant defects on their surface were in situ precipitated, which serve as anchoring sites for Pt UMNPs.…”