Category Archives: ChemCatChem

Homogeneous Iron‐Catalysed Oxidation Of Non‐Activated Alkanes With Hydrogen Peroxide

Posted on 9 October 2023 by

A novel synthetic protocol for the direct oxidation of alkanes, including cyclic and linear ones, to give ketones and alcohols using hydrogen peroxide as terminal oxidant under ambient conditions is presented. The active catalyst for this challenging transformation is conveniently generated by combination of simple Fe salts with N-methyl bis(picolylamine).

Abstract

A novel synthetic protocol for the direct oxidation of alkanes, including cyclic and linear ones, to give ketones and alcohols using hydrogen peroxide as terminal oxidant under ambient conditions is presented. The active catalyst for this challenging transformation is conveniently generated by combination of simple Fe salts with N-methyl bis(picolylamine) (Me-bpa). Utilizing picolinic acid as additive leads to improved yields of ketones and alcohols (32-57 %). The reaction can be conveniently scaled up to multi-g scale.

The Role of Water in Carbon Dioxide Adsorption in Porphyrinic Metal‐Organic Frameworks

Posted on 9 October 2023 by

MOFs combined with photochemistry for CO₂ photoreduction have great potential for addressing the challenge of reducing CO₂ emissions. Herein, a combined visible-infrared spectroscopic approach is reported to study the initial step of CO₂ photoreduction: adsorption of CO₂ in the presence of water into porphyrinic Zr-MOFs. The findings will serve as guideline to tune adsorption site and photophysical properties of the photosensitizer.

Abstract

Capturing and converting CO₂ through artificial photosynthesis using photoactive, porous materials is a promising approach for addressing increasing CO₂ concentrations. Porphyrinic Zr-based metal-organic frameworks (MOFs) are of particular interest as they incorporate a photosensitizer in the porous structure. Herein, the initial step of the artificial photosynthesis is studied: CO₂ sorption and activation in the presence of water. A combined vibrational and visible spectroscopic approach was used to monitor the adsorption of CO₂ into PCN-222 and PCN-223 MOFs, and the photophysical changes of the porphyrinic linker as a function of water concentration. A shift in CO₂ sorption site and bending of the porphyrin macrocycle in response to humidity was observed, and CO₂/H₂O competition experiments revealed that the exchange of CO₂ with H₂O is pore-size dependent. Therefore, humidity and pore-size can be used to tune CO₂ sorption, CO₂ capacity, and light harvesting in porphyrinic MOFs, which are key factors for CO₂ photoreduction.

Ammonia Synthesis by Mechanochemistry

Posted on 9 October 2023 by nFederico Cuccu, nDuncan L. Browne, nAndrea Porcheddun

The manufacture of ammonia is a technologically well developed field. The application of mechanochemistry for the preparation of ammonia has been realized over the past few years and may offer new opportunities for consideration. Here we highlight and describe some of those examples.

Abstract

The design and use of organic, inorganic, and metal-based catalysts is critical to academic and industrial laboratories all around the world. In this framework, ammonia production embodies the most iconic use of catalysis. This review aims to describe the most recent and exciting developments in the mechanocatalytic preparation of ammonia.

Two‐Dimensional Amorphous Iridium Oxide for Acidic Oxygen Evolution Reaction

Posted on 9 October 2023 by

Amorphous iridium oxide (Am−IrO₂) nanosheets were successfully synthesized by the mixed molten salt method, which reaches the ultralow overpotential of 230 mV at 10 mA cm⁻². DFT theoretical calculations indicate that origin of oxygen defects promotes the oxygen evolution reaction (OER) activity of Am−IrO₂.

Abstract

The increasing popularity of proton exchange membrane electrolysis technology for hydrogen production has brought attention to the electrolytic water reaction. However, the slow kinetics of the oxygen evolution reaction (OER) at the anode have great influence on the overall efficiency of the reaction. While iridium oxide shows excellent stability under acidic conditions, its OER activity still needs to be improved. Here, we synthesized two-dimensional amorphous iridium oxide (Am−IrO₂) nanosheets with the thickness of only 6 nm by a mixed molten salt method. Such nanosheets show an ultralow overpotential of only 230 mV at 10 mA cm⁻² in 0.5 M H₂SO₄. The overpotential increases only 40 mV after 90 hours of the stability test at this current density. Am−IrO₂ can maintain the current density of ~400 mA cm⁻² after 120 hours of test at 1.8 V in the PEM device, demonstrating good industrial prospects. Density functional theoretical calculations show that the oxygen vacancies, together with the upshift of the O 2p band center, are responsible for the improvement of OER in Am−IrO₂.

Time‐resolved DRIFT Spectroscopy Study of Carbonaceous Intermediates during the Water Gas Shift Reaction over Au/Ceria Catalyst

Posted on 9 October 2023 by

Modulated experiments (MES-PSD) by diffuse reflectance infrared (DRIFT) spectroscopy allowed identification of carboxyl species as a key intermediate during WGS reaction over Au/CeO₂ catalyst.

Abstract

ChemCatChem homepage for more articles in the collection. The mechanism of the low-temperature water gas shift reaction (LTWGS) on an Au/CeO₂ catalyst was investigated by means of in situ diffuse reflectance infrared (DRIFT) spectroscopy. Under steady-state LTWGS reaction (373–623 K), the catalyst is partially reduced, and signals from carbonate/formate dominates the infrared spectra. Time-resolved pulse of CO experiment under a constant partial pressure of water at 423 K indicates that Ce⁴⁺ can be reduced to Ce³⁺ and that formate (HCOO) species cannot be directly related to the CO₂ production. Further information was obtained by performing modulation excitation spectroscopy (MES) experiments coupled with a phase-sensitive detection (PSD) method. Under periodic modulation of the CO partial pressure while keeping the H₂O concentration constant, most of the intense bands of carbonate and formate remained constant, indicating that these species are only spectators. The same is observed for the concentration of Ce³⁺. Conversely, signals in-phase with the conversion of CO to CO₂ are observed and assigned to carboxyl [C(O)OH] and carboxylate (CO₂ ^δ−) species, while some monodentate formate (m-HCOO) also changes but at a lower rate. A plausible associative reaction mechanism where carboxyl/carboxylate are key intermediates is postulated.

Systematic Search for Thermal Decomposition Pathways of Formic Acid on Anatase TiO2 (101) Surface

Posted on 9 October 2023 by nHitoshi Nabata, nSatoshi Maedan

The mechanism governing the temperature dependence of the dissociation products in the thermal decomposition of formic acid on the anatase TiO₂(101) surface is identified by systematically and automatically exploring reaction path networks for clean, protonated, and oxygen-deficient surfaces.

Abstract

In this study, the reaction pathways for the thermal decomposition of formic acid on the anatase TiO₂ (101) surface were systematically investigated. The investigation was carried out using a single-component artificial force induced reaction method that combines density functional theory calculations. In order to uncover the overall mechanism at low surface coverage, we explored reaction path networks for three different conditions of the anatase TiO₂ (101) surfaces: clean, protonated, and oxygen-deficient surfaces. Previous temperature-programmed desorption (TPD) experiments had shown that H₂O desorption starts at a low temperature of about 300 K, while CO and formaldehyde desorption starts at high temperatures of about 500 K. The present reaction path networks are consistent with the overall trend observed in the TPD experiments. Using the reaction pathways extracted from these networks, the overall dissociation mechanism has been discussed.

Dehydration of Amides by Redox‐Active Phenalenyl Based Mn‐Catalyst

Posted on 9 October 2023 by nSoumi Chakraborty, nAmit Biswas, nSwadhin K. Mandaln

A Mn-complex bearing redox-active phenalenyl (PLY) ligand can undergo three successive reductions to generate an active catalyst consisting of ligand-centered radical, which plays the key role in activating inert PMHS for silylative dehydration of amide to nitrile under ambient conditions, following a radical pathway.

Abstract

A redox-active phenalenyl ligand coordinated Mn(III)-complex can be reduced chemically to generate an active catalyst containing a ligand-centered radical. This chemically reduced Mn-catalyst shows excellent catalytic reactivity for silylative dehydration of a wide range of primary amides (including late-stage diversification of various bio-active molecules) to synthesize nitriles using an inert and inexpensive silane, polymethylhydrosiloxane (PMHS), under mild conditions. Control experiments suggest a radical pathway for the present catalytic reaction, initiated by the ligand-centered radical.

Dynamic Change of Rh Oxidation State During Lean‐Rich Perturbation and Light‐Off of Three‐Way Catalysis Analysed using In Situ Diffuse Reflectance UV‐vis Spectroscopy

Posted on 9 October 2023 by

In Situ DRS Analysis of Rh in Three-Way Catalysts: The Rh redox in TWCs was studied using time-resolved in situ diffuse reflectance UV-vis spectroscopy in different modes with air-to-fuel ratio (A/F) step, A/F perturbation, and temperature ramping.

Abstract

This study investigated the redox behaviour of Rh in three-way catalysts (TWC) using time-resolved in situ diffuse reflectance UV-vis spectroscopy in different modes with air-to-fuel ratio (A/F) step, A/F perturbation, and temperature ramping. When Rh/ZrO₂−CeO₂ (Rh/ZC) and Rh/ZrO₂ (Rh/Z) containing fully oxidised Rh were treated at 400 °C under simulated TWC conditions with A/F stepping from 15.0 (fuel-lean) to 14.1 (fuel-rich), a steep increase in the metallic fraction (Rh⁰/Rh) and a simultaneous increase in Kubelka–Munk function (ΔKM) at λ=450 nm occurred near the stoichiometric point (A/F=14.6). Metallic Rh became abundant until A/F=14.1, where the largest ΔKM was attained. In the A/F perturbation mode, the Rh oxidation state fluctuated with repetitious switching of rich and lean gas feeds, but the ΔKM oscillation amplitude was lessened for Rh/ZC compared to Rh/Z because of the oxygen-scavenging function of ZC. Furthermore, the changes in Rh oxidation state during TWC light-off were analysed in the temperature-ramping mode. Under rich conditions, Rh⁰/Rh and ΔKM increased after 200 °C, where the formation of Rh metal led to efficient conversions of CO and NO. However, metallic Rh did not appear during light-off under the lean condition, where NO conversion was negligible.

Enhancing the Hydrodeoxygenation and Isomerization using Re Nanoparticles Decorated on Ni/SAPO‐11 Catalysts for Direct Production of Low‐Cold Flow Diesel from Triglycerides

Posted on 9 October 2023 by

Direct production of low-cold flow diesel: The bifunctional Re nanoparticles decorated on Ni/SAPO-11 catalyst was designed for an economically combined process of direct triglycerides hydro-deoxygenation and isomerization into low-cold flow diesel. The diesel production comprising iso-alkanes components with proper catalyst lifetime and low carbon deposition is attributed to the fabricated active metal species on bimodal SAPO-11 features with large distribution of Lewis acidic sites.

Abstract

The novel bifunctional Ni−Re supported on bimodal SAPO-11 catalyst was designed for an economically combined process of direct triglycerides hydro-deoxygenation and isomerization into low-cold flow diesel. The catalyst with a Ni to Re molar ratio of 1 : 0.12 exhibited superior performance for diesel production containing large fraction of iso-alkanes in comparison to Ni and Re benchmarks. Comprehensive characterizations revealed that the detection of Ni and Re co-existed with NiO and ReO_x on SAPO-11 after the reduction confirmed by XRD, XANES, and XPS analysis gave a large distribution of Lewis acid sites (>80 %) noticed by Pyridine-DRIFTS measurement. Under investigations of WHSV, reaction temperature, and H₂ pressure, the NiRe_0.12 catalyst contributed a nearly theoretical 77.1 % liquid yield, accompanied by a 18.2 % jet-range and 52.1 % diesel-range yields with a classification for 46.8 % iso-alkanes and 23.5 % normal alkanes yields; whereas, the cold-flow properties of liquid product were in the ranges of winter diesel standard. It was remarkably noticed that the combination effects of Ni and nanosized Re species substantially improved the diesel production comprising iso-alkanes components with proper catalyst lifetime and low carbon deposition attributing to the fabricated active metal species on bimodal SAPO-11 features with large distribution of Lewis acidic sites.

Al‐Ce Intermetallic Phase for Ambient High‐Performance Electrocatalytic Reduction of Nitrate to Ammonia

Posted on 9 October 2023 by

Here, nanoporous Al₁₁Ce₃ intermetallic phase has been designed for efficiently catalyzing nitrate reduction and Zn−NO₃ ⁻ battery, which realizes notable high NH₃ yield rate and electricity output.

Abstract

The conversion of NO₃ ⁻-to-NH₃ by electrolysis is an appealing approach for wastewater treatment; however, such a process is hindered by the lack of efficient catalysts. Herein, taking the nanoporous Al₁₁Ce₃ intermetallic phase as an example, its electrocatalytic NO₃ ⁻ reduction reaction capability is first demonstrated. Benefiting from the unique structural feature, optimized intermediates adsorption and formation behavior, and restrained hydrogen evolution, the catalyst shows a remarkable electrochemical performance with a peak faradaic efficiency of 91 % and yield rate of 4.35 mg h⁻¹ mg_cat ⁻¹, along with robust activity over 30 h. Further, a Zn−NO₃ ⁻ battery by using Al₁₁Ce₃ as the cathode was designed, which gives a maximal power density of 8.5 mW cm⁻² and a corresponding NH₃ yield rate of 1.97 mg h⁻¹ mg_cat ⁻¹.