Transformation of reduced graphene aerogel-supported atomically dispersed iridium into stable clusters approximated as Ir6 during ethylene hydrogenation catalysis

Ionic Liquid Sheath Stabilizes Atomically Dispersed Reduced Graphene Aerogel‐Supported Iridium Complexes during Ethylene Hydrogenation Catalysis

“…[9] The scanning transmission electron microscopy (STEM) images that complemented these results confirmed the atomic dispersion of the iridium on the rGA surface. [9] In addition to these earlier results, infrared (IR) spectra now provide additional evidence of atomic dispersion of the iridium. Thus, IR spectra characterizing the metal precursor and the supported complex, Ir(C 2 H 4 ) 2 /rGA, show that acac ligands were dissociated from the iridium during chemisorption of the precursor and that π-bonded ethylene ligands remained on the iridium (Figure S1 in Supporting Information (SI)).…”

“…rGA-supported Ir(C 2 H 4 ) 2 with an Ir loading of 9.9 wt % was synthesized by the reaction of Ir(C 2 H 4 ) 2 (acac) (acac is acetylacetonato) with rGA, prepared by reducing GA at 700 °C in Ar, [8] as reported earlier. [8,9] The synthesis was analogous to that used for iridium complexes on MgO [10] and on zeolite Y. [11] The reported extended X-ray absorption fine structure (EXAFS) data characterizing the same batch of the Ir(C 2 H 4 ) 2 /rGA catalyst before coating it with the IL sheath indicated that each Ir atom was bonded to approximately six low-Z-scatterers, inferred to be two O atoms of the rGA support and four C atoms of the two π-bonded ethylene ligands.…”

“…[9] During TGA, the sample was treated in an air : N 2 (40 : 60) mixture at temperatures up to 800 °C, which led to the complete decomposition of the rGA. [9] The remaining mass in the TGA pan was characterized as IrO 2 , determining an Ir loading of 9.9 wt % on the Ir(C 2 H 4 ) 2 /rGA. [8,9,12] To further confirm the bonding and site-isolation of Ir complexes on rGA, we prepared an analogous iridium complex on rGA at 10 wt % Ir loading, using Ir(CO) 2 (acac) as the precursor.…”

“…[9] The remaining mass in the TGA pan was characterized as IrO 2 , determining an Ir loading of 9.9 wt % on the Ir(C 2 H 4 ) 2 /rGA. [8,9,12] To further confirm the bonding and site-isolation of Ir complexes on rGA, we prepared an analogous iridium complex on rGA at 10 wt % Ir loading, using Ir(CO) 2 (acac) as the precursor. IR spectra included bands at 2064 and 1984 cm À 1 assigned to iridium gem-dicarbonyl ligands (Figure S3).…”

“…Replacing these ligands with reactive ethylene ligands -as in rGAsupported Ir(C 2 H 4 ) 2 complexes -led to the formation of clusters (approximated as Ir 6 ) under conditions of ethylene hydrogenation catalysis at 100 °C, even at a relatively high iridium loading of 9.9 wt %. [9] Here we illustrate how coating of rGA-supported Ir(C 2 H 4 ) 2 complexes with an ionic-liquid (IL) sheath hinders the metal aggregation under ethylene hydrogenation conditions -and even in pure H 2 -at an Ir loading of 9.9 wt %. We chose 1-ethyl-3-methyl-imidazolium acetate ([EMIM][OAc]) as the IL, as it has been shown to provide a substantial increase in the electron density on metal centers supported on SiO 2 .…”