Showing papers by "Sounak Roy published in 2022"

Photo- and Electrocatalytic Reduction of CO2 over Metal-Organic Frameworks and Their Derived Oxides: A Correlation of the Reaction Mechanism with the Electronic Structure.

Abstract: A Ce/Ti-based bimetallic 2-aminoterephthalate metal-organic framework (MOF) was synthesized and evaluated for photocatalytic reduction of CO2 in comparison with an isoreticular pristine monometallic Ce-terephthalate MOF. Owing to highly selective CO2 adsorption capability, optimized band gaps, higher flux of photogenerated electron-hole pairs, and a lower rate of recombination, this material exhibited better photocatalytic reduction of CO2 and lower hydrogen evolution compared to Ce-terephthalate. Thorough probing of the surface and electronic structure inferred that the reducibility of Ce4+ to Ce3+ was due to the introduction of an amine functional group into the linker, and low-lying Ti(3d) orbitals in Ce/Ti-2-aminoterephthalate facilitated the photoreduction reaction. Both the MOFs were calcined to their respective oxides of Ce1-xTixO2 and CeO2, and the electrocatalytic reduction of CO2 was performed over the oxidic materials. In contrast to the photocatalytic reaction mechanism, the lattice substitution of Ti in the CeO2 fluorite cubic structure showed a better hydrogen evolution reaction and consequently, poorer electroreduction of CO2 compared to pristine CeO2. Density functional theory calculations of the competitive hydrogen evolution reaction on the MOF and the oxide surfaces corroborated the experimental findings.

Electro-Oxidation Reaction of Methanol over La2–xSrxNiO4+δ Ruddlesden–Popper Oxides

Abstract: How materials’ crystalline structure influences the underlying electronic configuration, along with redox properties, and plays a pivotal role in electrocatalysis is an intriguing question. Here, solution combustion-synthesized La2–xSrxNiO4+δ (x = 0–0.8) Ruddlesden–Popper (RP) oxides were explored for an electrocatalytic methanol oxidation reaction. Optimal doping of bivalent Sr2+ in the A site enabled the tetragonal distortion and oxidation of Ni2+ to Ni3+ that resulted ultimately in enhanced covalent hybridization of Ni 3d–O 2p with a closer proximity of the O 2p band to the Fermi level. The RP oxide La1.4Sr0.6NiO4+δ exhibited the highest methanol oxidation reactivity vis-à-vis the formation of HCO2H. The proposed mechanism over La1.4Sr0.6NiO4+δ considers a lattice oxygen-mediated methanol oxidation reaction, owing to Fermi-level “pinning” at the top of the O 2p band, which facilitated lattice oxygen atoms prone to oxidation. A high surface concentration of the key active species of Ni–OOH was observed to form during the methanol oxidation reaction with the help of lattice oxygen atoms and oxygen vacancies in La1.4Sr0.6NiO4+δ. The present study offers a uniquely comprehensive exploration of structural and surface properties of RP oxides toward methanol oxidation reactions.

Controlling C-C coupling in electrocatalytic reduction of CO2 over Cu1-xZnx/C.

Abstract: From the perspective of sustainable environment and economic value, the electroreduction of CO2 to higher order multicarbon products is more coveted than that of C1 products, owing to their higher energy densities and a wider applicability. However, the reduction process remains extremely challenging due to the bottleneck of C-C coupling over the catalyst surfaces, and therefore designing a suitable catalyst for efficient and selective electrocatalytic reduction of CO2 is a need of the hour. With the target of producing C3+ products with higher selectivity, in this study we explored the nano-alloys of Cu1-xZnx as electrocatalysts for CO2 reduction. The nano-alloy Cu1-xZnx synthesized from the corresponding bimetallic metal organic framework materials demonstrated a gradual enhancement in the selectivity of acetone upon CO2 electroreduction with higher doping of Zn. The Cu1-xZnx alloy opened up a wide possibility of fine-tuning the electronic structure by shifting the position of the d-band centre and modulating the interaction with intermediate CO and thus enhanced the selectivity of desirable products, which might not have been accessible otherwise. The postulated molecular mechanism of CO2 electroreduction involving the desorption of the poorly adsorbed intermediate CO due to the presence of Zn and spilling over of free CO to Cu sites in the nano-alloy Cu1-xZnx for further C-C coupling to yield acetone was corroborated by the first principles studies.

The role of synthesis vis-à-vis oxygen vacancies of Co3O4 in oxygen evolution reaction

Abstract: Oxygen evolution reaction over oxide vacancy induced spinel Co3O4 is a topic of tremendous scientific attention owing to the favourable adsorption of water, as also shown here through DFT calculations....

Chemically stable metal oxide nanocomposite based external filters for gas purification from petrol automobile exhaust

Abstract: Current exhaust gas catalytic converters are expensive as it makes use of precious metals such as Platinum (Pt), Palladium (Pd) and Rhodium (Rh) as active components in conversion catalysts. However, these converters do not convert all toxic gases (e.g.: CO, NOX, HC) into less harmful pollutants, before emitting them to atmosphere, particularly for automobiles with old petrol engines and fuel types (standard unleaded petrol) causing more air pollution. In this work, equimolar Copper – Aluminium oxide-based nanocomposites were synthesised using wet chemical synthesis method and its effectiveness as a catalyst for removal of NOx gas was explored. An external filter with the proposed catalyst was fitted to the tailpipe of a 350-cc petrol engine and the impact on exhaust gas emissions was assessed. Chemical growth, composition of the nanocomposites prepared and the relevant functional properties were characterized using X-Ray Diffraction, Adsorption studies and Gas Chromatography. Nanocomposite was deposited on ceramic substrate, which was then mounted inside housing and connected to the tailpipe for testing. Emission tests were carried out with and without the exhaust filter. A reduction in NOx along with CO and HC components of the exhaust gas by about 45, 33 and 12% respectively was obtained when the proposed nanocomposite was used to treat the tailpipe emissions.