In-operando spectroscopic observation of the intermediates formed during various electrocatalytic oxidation and reduction reactions is crucial to propose the mechanism of the corresponding reaction. Surface enhanced resonance Raman spectroscopy coupled to rotating disc electrochemistry (SERRS-RDE), developed about a decade ago, proved to be an excellent spectroscopic tool to investigate the mechanism of heterogeneous oxygen reduction reaction (ORR) catalysed by synthetic iron porphyrin complexes under steady state conditions in water. The mechanistic information helped develop better ORR catalysts with 2nd sphere residues in the porphyrin rings. To date, the application of this SERRS-RDE setup is limited to ORR only because the thiol self-assembled monolayer (SAM) modified Ag electrode, used as the working electrode in these experiments, suffers from stability issues at more cathodic and anodic potential where H2O oxidation, CO2 reduction, H+ reduction reaction occurs. The current investigation shows the development of 2nd generation SERRS-RDE setup consisting of Ag-nanostructure (AgNS) modified graphite electrode as the working electrode. These electrodes show higher stability (compare to the conventional thiol SAM modified Ag electrode) upon exposure to very high cathodic and anodic potential with a good signal to noise (S/N) ratio in the Raman spectra. The behaviour of this modified electrode towards ORR is found to be the same as SAM modified Ag electrode and same ORR intermediates are observed during electrochemical ORR. At higher cathodic potential the signatures of Fe(0) porphyrin, an important intermediate in H+ and CO2 reduction reactions, was observed at the electrode-water interface in-operando.
The reduction of SO2 to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO2 to H2S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO2 to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO2 by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that FeIITPP reduces SO2 by 2e−/2H+ to form an intermediate [FeIII−SO]+ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO2 could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.
Reduction of SO2 to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and environment as well as enable its valorization into valuable chemicals. While the coordination of SO2 to transition metals are documented, its reduction using molecular catalysts has remained elusive. Alternatively, the naturally occurring heme enzyme sulfite reductase is known to reduce SO2 to H2S and is an integral part of the global sulfur cycle. However, its action is not yet mimicked in artificial systems outside of the protein matrix even after several decades of its structural elucidation. Here reduction of SO2 by iron (II) porphyrin, a synthetic analogue of heme, is demonstrated. A combination of spectroscopic and analytical methods indicates that SO2 is reduced by 2e -/2H + by Fe II TPP to form an intermediate [Fe III -SO] + species which releases SO. The SO obtained from the chemical reduction of SO2 could be valorized in the form of a Diels-Alder adduct of butadiene resulting in an organic sulfoxide.
Reduction of SO¬2 to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and environment as well as enable its valorization into valuable chemicals. While the coordination of SO2 to transition metals are documented, its reduction using molecular catalysts has remained elusive. Alternatively, the naturally occurring heme en-zyme sulfite reductase is known to reduce SO2 to H2S and is an integral part of the global sulfur cycle. However, its action is not yet mimicked in artificial systems outside of the protein matrix even after several decades of its structural elucidation. Here reduction of SO2 by iron (II) porphyrin, a synthetic analogue of heme, is demonstrated. A combination of spectroscop-ic and analytical methods indicates that SO2 is reduced by 2e-/2H+ by FeIITPP to form an intermediate [FeIII-SO]+ species which releases SO. The SO obtained from the chemical reduction of SO2 could be valorized in the form of a Diels-Alder ad-duct of butadiene resulting in an organic sulfoxide.
The reduction of SO2 to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO2 to H2S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO2 to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO2 by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that FeIITPP reduces SO2 by 2e−/2H+ to form an intermediate [FeIII−SO]+ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO2 could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.
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