Atmospheric pressure conversion of carbon dioxide to cyclic carbonates using a metal-free Lewis acid-base bifunctional heterogeneous catalyst

Zn-MOF as a Single Catalyst with Dual Lewis Acidic and Basic Reaction Sites for CO2 Fixation

Continuous increase in carbon dioxide (CO2) emissions are causing imbalances in the environment, which impact biodiversity and human health. The conversion of CO2 to cyclic carbonates by means of metal-organic frameworks (MOFs) as a heterogeneous catalyst is a prominent strategy for rectifying this imbalance. Herein, we have developed nitrogen-rich Zn (II) based metal-organic framework, [Zn(CPMT)(bipy)]n (CPMT = 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole; bipy = 4,4'-bipyridine), synthesized via a mixed ligand strategy. This Zn-MOF showed high chemical stability in both acidic and basic conditions, and in organic solvents for a long time. On account of the concurrent presence of acid-base active sites and strong chemical stability under abrasive conditions, this Zn-MOF was employed as an effective catalyst for the coupling of CO2 and epoxides, under atmospheric pressure, mild temperature, and neat conditions. This Zn-MOF shows remarkable activity by producing high yields of epichlorohydrin carbonate (98%) and styrene carbonate (82%) at atmospheric CO2 pressure, 70 °C temperature, and 24 h reaction time, with turnover numbers (TON) of 217 and 181, respectively. The Zn-MOF could be reused for up to seven cycles with structural and framework integrity. Overall, this work demonstrates the synthesis of a novel and highly efficient MOF for CO2 conversion.

Harnessing the Synergy of Fe and Co with Carbon Nanofibers for Enhanced CO2 Hydrogenation Performance

Amid growing concerns about climate change and energy sustainability, the need to create potent catalysts for the sequestration and conversion of CO2 to value-added chemicals is more critical than ever. This work describes the successful synthesis and profound potential of high-performance nanofiber catalysts, integrating earth-abundant iron (Fe) and cobalt (Co) as well as their alloy counterpart, FeCo, achieved through electrospinning and judicious thermal treatments. Systematic characterization using an array of advanced techniques, including SEM, TGA-DSC, ICP-MS, XRF, EDS, FTIR-ATR, XRD, and Raman spectroscopy, confirmed the integration and homogeneous distribution of Fe/Co elements in nanofibers and provided insights into their catalytic nuance. Impressively, the bimetallic FeCo nanofiber catalyst, thermally treated at 1050 °C, set a benchmark with an unparalleled CO2 conversion rate of 46.47% at atmospheric pressure and a consistent performance over a 55 h testing period at 500 °C. Additionally, this catalyst exhibited prowess in producing high-value hydrocarbons, comprising 8.01% of total products and a significant 31.37% of C2+ species. Our work offers a comprehensive and layered understanding of nanofiber catalysts, delving into their transformations, compositions, and structures under different calcination temperatures. The central themes of metal-carbon interactions, the potential advantages of bimetallic synergies, and the importance of structural defects all converge to define the catalytic performance of these nanofibers. These revelations not only deepen our understanding but also set the stage for future endeavors in designing advanced nanofiber catalysts with bespoke properties tailored for specific applications.

Fluorescence and colorimetric dual-mode multienzyme cascade nanoplatform based on CuNCs/FeMn-ZIF-8/PCN for detection of sarcosine

It is critical to develop a highly efficient and sensitive method for detecting the biomarker sarcosine (SA) of prostate cancer due to its importance for men's health. In our work, a fluorescence (FL) and colorimetric dual-mode multienzyme cascade nanoplatform for SA detection was designed and constructed. CuNCs/FeMn-ZIF-8/PCN nanocomposites with high FL properties and peroxidase-like activity were successfully prepared by encapsulating copper nanoclusters (CuNCs) into FeMn-ZIF-8 and then loaded onto P-doped graphitic carbon nitride (PCN). Furthermore, the nanocomposites served as carriers for the immobilization of sarcosine oxidase (SOX) to construct a high-efficiency dual-mode multienzyme cascade nanoplatform CuNCs/SOX@FeMn-ZIF-8/PCN for the detection of SA. The intermediate H2O2 generated in the cascade caused the FL quenching of nanocomposites and the discoloration of 3,3',5,5'-tetramethylbenzidin. The linear ranges for SA detection in the dual-mode system were 1-100 μM (FL) and 1-200 μM (colorimetric), with detection limits of 0.34 and 0.59 μM, respectively. This nanoplatform exhibited notable repeatability, specificity, and stability, making it suitable for detecting sarcosine in real human urine samples. Therefore, this dual-mode multienzyme cascade nanoplatform would have a potential applicative prospect for detecting SA and other biomarkers in real clinical samples.

Nanostructured Carbon Nitride for Continuous-Flow Trifluoromethylation of (Hetero)arenes

Efficient catalytic methods for the trifluoromethylation of (hetero)arenes are of particular importance in organic and pharmaceutical manufacturing. However, many existing protocols rely on toxic reagents and expensive or sterically hindered homogeneous catalysts. One promising alternative to conduct this transformation involves the use of carbon nitride, a non-toxic photocatalyst prepared from inexpensive precursors. Nonetheless, there is still little understanding regarding the interplay between physicochemical features of this photocatalyst and the corresponding effects on the reaction rate. In this work, we elucidate the role of carbon nitride nanostructuring on the catalytic performance, understanding the effect of surface area and band gap tuning via metal insertion. Our findings provide new insights into the structure-function relationships of the catalyst, which we exploit to design a continuous-flow process that maximizes catalyst-light interaction, facilitates catalyst reusability, and enables intensified reaction scale-up. This is particularly significant given that photocatalyzed batch protocols often face challenges during industrial exploitation. Finally, we extrapolate the rapid and simplified continuous-flow method to the synthesis of a variety of functionalized heteroaromatics, which have numerous applications in the pharmaceutical and fine chemical industries.

Role of fiber density of amine functionalized dendritic fibrous nanosilica on CO2 capture capacity and kinetics

Textural properties of the solid sorbents are critical to tuning their CO2 capture performance. In this work, we studied the effect of fiber density (in turn, pore size, distribution, and accessibility) on CO2 capture capacity and kinetics. CO2 solid sorbents were prepared by physisorption of tetraethylenepentamine (TEPA) molecules on dendritic fibrous nanosilica (DFNS) with varying fiber density. Among the various DFNS, the DFNS with moderate fiber density [DFNS-3] showed the best CO2 capture capacity under the flue gas condition. The maximum CO2 capture capacity achieved was 24.3 wt % (5.53 mmol/g) at 75 °C for DFNS-3 under humid gas conditions. Fiber density also played a role in the kinetics of CO2 capture. DFNS-1 with dense fiber density needed ∼10.4 min to reach 90 % capture capacity, while DFNS-3 (moderate fiber density) needed only 6.4 min, which further decreased to 5.9 min for DFNS-5 with lightly dense fibers. The DFNS-impregnated TEPA also showed good recyclability during 21 adsorption and desorption cycles under humid and dry conditions. The total CO2 capture capacity of DFNS-3 (14.7) in 21 cycles was 108.9 and 105.0 mmol/g under humid and dry conditions, respectively. Adsorption lifetime calculation and recyclability confirmed the fiber density-dependent CO2 capture performance.

Transition Metal Phosphide Nanoarchitectonics for Versatile Organic Catalysis

Transition metal phosphides (TMP) posses unique physiochemical, geometrical, and electronic properties, which can be exploited for different catalytic applications, such as photocatalysis, electrocatalysis, organic catalysis, etc. Among others, the use of TMP for organic catalysis is less explored and still facing many complex challenges, which necessitate the development of sustainable catalytic reaction protocols demonstrating high selectivity and yield of the desired molecules of high significance. In this regard, the controlled synthesis of TMP-based catalysts and thorough investigations of underlying reaction mechanisms can provide deeper insights toward practical achievement of desired applications. This review aims at providing a comprehensive analysis on the recent advancements in the synthetic strategies for the tailored and tunable engineering of structural, geometrical, and electronic properties of TMP. In addition, their unprecedented catalytic potential toward different organic transformation reactions is succinctly summarized and critically analyzed. Finally, a rational perspective on future opportunities and challenges in the emerging field of organic catalysis is provided. On the account of the recent achievements accomplished in organic synthesis using TMP, it is highly anticipated that the use of TMP combined with advanced innovative technologies and methodologies can pave the way toward large scale realization of organic catalysis.

A butterfly-like lead-doped titanium-oxide compound with high performance in photocatalytic cycloaddition of CO2 to epoxide

The cycloaddition reaction of CO₂ to epoxides is quite promising for CO₂ capture and storage as well as the production of value-added fine chemicals. Herein, a novel atomically precise lead-doped titanium-oxide cluster with the formula Ti₁₀Pb₂O₁₆(phen)₄(Ac)₁₂(DMF)₂ (denoted as Ti10Pb2; phen = 1,10-phenanthroline; Ac = acetate; DMF = dimethylformamide) was synthesized through a facile solvothermal process, and is a molecular photocatalyst with surface-anchored main-group metal active sites. Its structure was characterized by single-crystal X-ray diffraction and other complementary techniques. Ti10Pb2 showed high photo-response and charge-separation efficiency under simulated sunlight irradiation. Ti10Pb2 was successfully used in the cycloaddition reaction of CO₂ with epoxides under solvent-free conditions. While its catalytic activity due to the Lewis acidity was moderate, simulated solar light irradiation further enhanced the reaction rate, demonstrating the synergistic effect of photocatalysis and Lewis-acid thermocatalysis.

Lead-Decorated Titanium Oxide Compound with a High Performance in Catalytic CO2 Insertion to Epoxides

The CO₂ cycloaddition to epoxides is an efficient method for CO₂ capture and storage, important not only for reducing greenhouse gas emission but also for producing cyclic carbonates, which are valuable industrial materials. In this study, we report a novel high-nuclearity titanium oxide cluster (TOC) inlayed with main-group element Pb²⁺, H₂Ti₁₆Pb₉O₂₄(SA)₁₈(DMF)₁₀(OH₂)₂ (denoted as 1; SA = salicylate; DMF = N,N-dimethylformamide), which has the property of visible-light absorption and has shown high catalytic activities for cycloadditions of CO₂ under visible-light irradiation. The cluster was synthesized in a high yield in a facial solvothermal process. Its structure and electronic structure were characterized by single-crystal X-ray diffraction, density functional theory calculations, and complementary techniques. The cycloaddition reactions were performed under solvent-free conditions. While the catalytic activity due to the Lewis acidity was moderate, visible-light irradiation further folded the reaction rates. The turnover number reached 3400 with a turnover frequency of 120 h^-1. Mechanism studies indicated a synergistic effect of the Lewis acidity and photogenerated charge carriers. The performance of 1 in reversible I₂ uptake was also investigated. This study demonstrates the high potential of heterometal-decorated TOCs in the cost-effective and efficient CO₂ cycloaddition reaction under mild conditions.

Environmentally sustainable synthesis of cyclic carbonates from epoxides and CO2 promoted by MCM-41 supported dual imidazolium ionic liquids catalysts

A type of MCM-41 supported dual imidazolium ionic liquids have been synthesized and efficiently used as catalysts in the sustainable chemical conversion of CO2 and epoxides into cyclic carbonates. It was shown that the highest efficiency was achieved in the cycloaddition of a variety of epoxides and CO2 in the presence of the MCM-41@DILSCN solid catalyst under mild conditions. More interestingly, the catalyst was stable, very active, robust, and displayed good recyclability without significant loss of catalytic activity after six consecutive cycles during the process. Overall, the present protocol of synthesizing cyclic carbonates under solvent free conditions using MCM-41@DILSCN is promising for industrial applications.

Cr-Ti Mixed Oxide Molecular Cages: Synthesis, Structure, Photoresponse, and Photocatalytic Properties

The solvothermal reaction of titanium isopropoxide and chromate in the presence of benzoate produced two novel host-guest clusters encapsulating Cs⁺ or H₃O⁺, (H₃O)@Ti₇Cr₁₄ and Cs@Ti₇Cr₁₄. The most remarkable feature is that the Ti₇O₇ ring is concentrically embraced by a Cr₁₄O₁₄ ring to form a rigid Ti₇Cr₁₄ host. ESI-MS and ¹³³Cs NMR revealed that the overall framework structures are preserved, whereas the benzoate ligands on the two clusters may be labile in solutions. Both (H₃O)@Ti₇Cr₁₄ and Cs@Ti₇Cr₁₄ exhibit good UV-vis light-responsive properties and photocatalytic activities, with absorption edges extending up to 780 nm. Cs@Ti₇Cr₁₄ is an effective visible-light-responsive photocatalyst in both the heterogeneous methylene dye degradation and homogeneous CO₂ cycloaddition reaction under mild conditions like room temperature and 1 bar of CO₂. According to the mechanism studies, Cs⁺, as a rigid guest, can significantly improve the photogenerated charge separation efficiency of the Ti₇Cr₁₄ host, thereby improving its interface charge separation properties, photocurrent, and photocatalytic activities. Our findings not only provide new members of heterometallic titanium oxide clusters to enrich the metal oxide cluster family but also open up new possibilities for their photoresponses, which may play an important role in solar energy harvesting for sustainable chemistry.

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook

Light olefins are important feedstocks and platform molecules for the chemical industry. Their synthesis has been a research priority in both academia and industry. There are many different approaches to the synthesis of these compounds, which differ by the choice of raw materials, catalysts and reaction conditions. The goals of this review are to highlight the most recent trends in light olefin synthesis and to perform a comparative analysis of different synthetic routes using several quantitative characteristics: selectivity, productivity, severity of operating conditions, stability, technological maturity and sustainability. Traditionally, on an industrial scale, the cracking of oil fractions has been used to produce light olefins. Methanol-to-olefins, alkane direct or oxidative dehydrogenation technologies have great potential in the short term and have already reached scientific and technological maturities. Major progress should be made in the field of methanol-mediated CO and CO₂ direct hydrogenation to light olefins. The electrocatalytic reduction of CO₂ to light olefins is a very attractive process in the long run due to the low reaction temperature and possible use of sustainable electricity. The application of modern concepts such as electricity-driven process intensification, looping, CO₂ management and nanoscale catalyst design should lead in the near future to more environmentally friendly, energy efficient and selective large-scale technologies for light olefin synthesis.

Guanidyl-implanted UiO-66 as an efficient catalyst for the enhanced conversion of carbon dioxide into cyclic carbonates

The development of heterogeneous catalysts for promoting epoxide cycloaddition with carbon dioxide is highly desirable for recycling CO₂ and achieving the goal of carbon neutrality. Herein, we designed and synthesized Zr-based metal organic frameworks (MOFs) by implanting functional guanidyl into the framework via mixing different molar ratios of 4-guanidinobenzoic acid (Gua) with 1,4-benzenedicarboxylic acid (BDC). Consequently, a small sized Zr-MOF (∼350 nm) can be prepared by implanting Gua with 20% molar ligands, denoted as UiO-66-Gua_0.2(s). Compared to large sized and different guanidyl Zr-MOFs, UiO-66-Gua_0.2(s) exhibited an optimal activity on catalyzing epoxide cycloaddition with CO₂ in the presence of the Bu₄NBr cocatalyst. A yield of 97% for the product of chloropropene carbonate was achieved at 90 °C under 1 atm CO₂. The great performance of UiO-66-Gua_0.2(s) might be attributed to the synergistic effect of guanidyl groups as hydrogen-bond donors and Zr centers acting as Lewis-acidic sites. In addition, the heterogeneous catalyst of UiO-66-Gua_0.2(s) exhibited a great versatility towards converting other epoxides and a satisfactory recyclability for five consecutive runs. Moreover, a plausible reaction mechanism has been proposed for UiO-66-Gua_0.2(s) in promoting CO₂ epoxide cycloaddition reactions.

A Study on the Stability of Carbon Nanoforms-Polyimidazolium Network Hybrids in the Conversion of CO2 into Cyclic Carbonates: Increase in Catalytic Activity after Reuse

Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO2 into cyclic carbonate under high temperature and CO2 pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved catalytic activity. Beside the low catalytic loading (0.05-0.09 mol%) and the absence of Lewis acid co-catalysts, all the materials showed high TON values (up to 1154 for epichlorohydrin with SW-1:2). Interestingly, despite the loss of part of the polymeric coating for crumbling or peeling, the activity increases upon recycling of the materials, and this behaviour was ascribed to their change in morphology, which led to materials with higher surface areas and with more accessible catalytic sites. Transmission electron microscopy analysis, along with different experiments, have been carried out in order to elucidate these findings.

Pyrene-based ammonium bromides combined with g-C3N4 for the synergistically enhanced fixation reaction of CO2 and epoxides

A new type of pyrene-based ammonium bromides (PABs) was synthesized via the reaction of bromomethyl pyrene and tertiary amines with different alkyl chains combined with graphitic carbon nitride (g-C₃N₄) through π–π stacking interactions. The new pyrene-based ammonium bromides were investigated both in homogenous phase and heterogeneous phase combining with g-C₃N₄ for the CO₂ fixation reaction of epoxides under mild conditions. Obviously, the combination was proved to be an efficient system for the conversion of epoxides. The interaction between g-C₃N₄ and PABs was confirmed by quantum chemical calculations. g-C₃N₄/Py-C₁₂ exhibited an excellent yield of cyclic carbonates (above 93%) at 80 °C, atmospheric pressure and solvent-free conditions. A preliminary kinetic study was performed using g-C₃N₄/Py-C₁₂ and the activation energy was calculated to be 61.5 kJ mol⁻¹.

The synergistic interaction of g-C₃N₄ and PABs plays an important role in the CO₂ fixation reaction with epoxides.

TiO2/g-C3N4 heterojunction hollow porous nanofibers as superior visible-light photocatalysts for H2 evolution and dye degradation

Hollow porous TiO2/g-C3N4 exhibited high photocatalytic performance ascribed to multiple light reflections and fast photoelectron transport in heterojunctions.

Synthesis of a BiPO4/Bi4O5I2 heterostructure for efficient degradation of oil field pollutants

In this research, composite photocatalysts were found to have a superior photocatalytic performance.