Confinement of molecular complexes for catalytic N2 reduction

Selected Conference on AbstractNational audienc

Confinement of molecular complexes for catalytic N2 reduction

Selected Conference on AbstractNational audienc

Confinement of molecular complexes for catalytic N2 reduction

International audienc

Confinement of molecular complexes for catalytic N2 reduction

International audienc

Probing ultrafast photochemical mechanisms of molecular and heterogenized rhodium bipyridine photocatalyst

Molecular and heterogenized rhodium bipyridine (Bpy) complexes are highly active and selective for the carbon dioxide photoreduction into formic acid using visible light as sole energy source. The excited state of the molecular 5,5’-di(pyren-1-yl)-2,2’-bipyridine Pyr2Bpy and of the corresponding conjugated microporous polymer PyrBpy-CMP, envisioned as macroligand, as well as of their organometallic complexes with pentamethylcyclopentadienyl (Cp*) rhodium [Pyr2Bpy]Cp*RhCl2 and Cp*Rh@PyrBpy-CMP have been investigated by femtosecond UV-vis transient absorption spectroscopy. In both polymers PyrBpy-CMP and Cp*Rh@PyrBpy-CMP the fs measurements reveal the formation of a broad excited state absorptions bands decaying in the sub-ns time scale. For Cp*Rh@PyrBpy-CMP , the ultrafast energy transfer from the framework to the catalytic centres is demonstrated. Pyr2Bpy and [Pyr2Bpy]Cp*RhCl2 have been studied as model molecular building blocks of the CMP. The results show the participation of a mesomeric intramolecular charge transfer (MICT) state and of a twisted intramolecular charge transfer state (TICT) stabilized by the torsion of the pyrene and bipyridine moiety, that are then converted into ligand to metal charge transfer states (LMCT) in [Pyr2Bpy]Cp*RhCl2. The photophysical parameters determined for the molecular compounds were applied to calculate the Förster Resonance Energy Transfer rate from the light-harvesting organic units to the heterogenized Rh metal centres. Finally, the role of the triethanolamine, a common sacrificial electron donor (SED) employed for the CO2 reduction, as an efficient quencher of the excited states of the Pyr2Bpy is demonstrated. This quenching reaction is expected to occur for a wide range of organic and organo-metallic photocatalysts, and its consequences on the reduction of the photoconversion yield are certainly underestimated for most of the applications

Molecular rhodium complex within N-rich porous polymer macroligand as heterogeneous catalyst for the visible-light driven CO2 photoreduction

The heterogenization of molecular catalysts within a porous solid acting as macroligand can advantageously open access to enhanced stability and productivity, and thus to more sustainable catalytic process. We report here porous organic polymer (POP) made through metal-free polymerization using bipyridine repeating units. This N-rich POP is an efficient macroligand for the heterogenization of molecular rhodium complexes. The intrinsic catalytic activity of the heterogenized catalyst is slightly higher than that of its homogeneous molecular counterpart for formic acid production as unique carbon containing product. The heterogenization of the rhodium catalysts enables recycling for a total productivity up to 8.3 grams of formic acid per gram of catalyst after 7 cycles of reaction using visible light as sole energy source

Spin crossover and cooperativity in nanocrystalline [Fe(pyrazine)Pt(CN)4] thin films deposited by matrix-assisted laser evaporation

Thin film structures with controlled functionalities are critical to exploit the exceptional application capacity of spin crossover complexes. Here, we report spin crossover (SCO) in thin films of [Fe(pyrazine)Pt(CN)4] nanocrystalline particles (NPs) deposited on monocrystalline Si by laser-mediated evaporation of a cryogenically frozen suspension of the title compound. Both X-ray diffraction and microscopic imaging of the films (thickness ~ 120 nm) confirm resembled structure of pristine nanocrystals. However, their spin crossover behavior is dramatically altered going from the cooperative and sharp transition within temperature hysteresis (16 K) around the room temperature region for reference NPs to a gradual transition type shifted downwards to 170 K for the thin films. The decrease in cooperativity within the film is due to side effect of laser-induced desorption that results in rearrangement of the pyrazine-pillared 3D framework into stacked 2D Fe[Pt(CN)4] sheets in the laser affected NP regions. The observed effects have significant implications for future study on the cooperative spin transition in laser-engineered nanocrystalline films

Electrochemical CO2 Reduction with a Heterogenized Iridium-Pincer Catalyst in Water

International audienceImmobilization of well-defined homogenous (electro)catalysts onto conductive supports offers an attractive strategy for designing advanced functional materials for energy conversion. In this context, this study reports (i) the introduction of a pyrene anchoring group on a PNP-pincer Ir-I complex previously described as a selective catalyst for the electrodriven CO2 reduction (CO2RR) into CO in DMF/water mixtures, (ii) the comparison of its CO2RR activity in DMF/water mixtures with the ones of two pyrene-free reference complexes, and (iii) its activity in pure water after immobilization onto carbon nanotubes (CNTs). Surprisingly, in homogeneous conditions we find HCOO-, instead of CO, as the main CO2 reduction product for the three catalysts. After immobilization on CNTs, even if non-negligible competitive proton reduction reaction is observed in fully aqueous media, the complex is still able to drive CO2RR and produce HCOO- with a significantly lower overpotential with respect to solution studies

Molecular Rhodium Complex within N‐Rich Porous Polymer Macroligand as Heterogeneous Catalyst for the Visible‐Light Driven CO2 Photoreduction

The heterogenization of molecular catalysts within a porous solid acting as macroligand can advantageously open access to enhanced stability and productivity, and thus to more sustainable catalytic process. Herein, a porous organic polymer (POP) made through metal‐free polymerization using bipyridine repeating units is reported. This N‐rich POP is an efficient macroligand for the heterogenization of molecular rhodium complexes. The intrinsic catalytic activity of the heterogenized catalyst is slightly higher than that of its homogeneous molecular counterpart for formic acid production as a unique carbon‐containing product. The heterogenization of the rhodium catalysts enables recycling for a total productivity of up to 8.3 g of formic acid per gram of catalyst after 7 reuses using visible light as the sole energy source