Study of the state of rhodium in the potassium rhodiumundecatungstosilicate/alumina system by diffuse-reflectance IR spectroscopy

Abstract

Adsorption of CO on the catalytic system Ks[SiWI jRhO391/AI~O3 was studied by diffusereflectance IR spectroscopy. The electronic state of rhodium and thermal stability of the system in the redox cycles were studied. The oxidized heteropotycompound (HPC) contains the charged forms Rh +. Rh 2+, and Rh 3~. Their ratio strongly depends on the pre-treatment temperature of the sample. In the reduced HPC two main forms of rhodium exist: the ionic Rh + and metallic Rh ~ The supported HPC structure is stable in an oxidative medium at temperatures below -900 K. The properties of the K dSiW~ )RhO39]/AI203 system are retained in the redox cycles up to --670 K. and the highly dispersed state of rhodium is observed up to 9O0 K.

Noble Metals in Polyoxometalates

“…[26c] Absorption of carbon monoxide by a material described as "K 5 [SiW 11 RhO 39 ]/Al 2 O 3 " (possibly containing the aqua deriv-ative, but otherwise uncharacterized) has been investigated by diffuse reflection infrared spectroscopy at temperatures up to 900 K. [55] High-yield syntheses of [PW 11 O 39 Rh III X] 5À (X = Cl, Br) have been achieved by hydrothermal reactions of the lacunary polytungstate with RhCl 3 in the presence of excess halide anion. [56] Salts of these complexes were characterized by elemental analysis, 31 confirmed by analytical ultracentrifugation and X-ray structure analysis of the potassium salt (Figure 6 d) 5À and dibenzyl under prolonged (5 h) photolysis at ambient temperature.…”

Edelmetalle in Polyoxometallaten

“…Trotz dieser Zweifel erwies sich das Zonnevijlle‐Anion “[SiW 11 O 39 Rh(H 2 O)] 5− ” als katalytisch aktiv in der Oxidation von Alkanen durch tert ‐Butylhydroperoxid, wenn es in eine Lösung von n ‐Hexylammoniumbromid in Benzol überführt wurde 26c. Die Absorption von Kohlenmonoxid durch ein als “K 5 [SiW 11 RhO 39 ]/Al 2 O 3 ” beschriebenes Material (enthält wahrscheinlich das Aqua‐Derivat, wurde aber nicht weiter charakterisiert) wurde durch Infrarot‐Spektroskopie bei diffuser Reflexion bei Temperaturen bis 900 K verfolgt 55…”

Co‐Dissolved Isostructural Polyoxovanadates to Construct Single‐Atom‐Site Catalysts for Efficient CO2Photoreduction

“…To date, a large amount of mono-metal-substituted POMs have been reported, such as [H 3 Pt IV W 6 O 24 ] 5À , [Pt IV Mo 6 O 24 ] 8À , [PtV 9 O 28 ] 7À (PtV 9 ) and [CoW 12 O 40 ] 3À . [33][34][35][36][37] In theory, it should be much more easier to disperse nano-sized clusters compared to disperse an ultra-small atom. [38][39][40] As a result, the uniform dispersion of mono-metal-substituted POMs should represent an ideal strategy to anchor single-atom centers on the functional supports.…”