13 Search Results

Recycling diverse waste plastics poses challenges due to complex sorting and processing, resulting in high costs and inefficiency. To tackle this, we present a metal-free catalytic sorting method for targeted deconstruction of polyester from post-consumer plastic waste, encompassing textiles, plastic mixtures, and multilayer packaging materials. This method employs N-methylpiperidine, a tertiary amine catalyst in methanol, to depolymerize polyethylene terephthalate (PET). Operating under these conditions (160°C, 1 h), we achieve 100% yields of dimethyl terephthalate and ethylene glycol. This technique also effectively breaks down other polyesters, including polylactic acid, polycarbonate, and polybutylene terephthalate, yielding high-yield monomers at relatively low temperatures. Throughmore » comprehensive nuclear magnetic resonance (NMR) analysis, we propose that N-methylpiperidine’s role is in enhancing methanol nucleophilicity and activating PET’s ester bond. Our insights advance the chemical recycling of post-consumer plastic waste, offering a potentially simple and efficient path to closing the polyester production loop.« less

The electrochemical carbon dioxide reduction reaction (CO₂RR) using renewable energy sources is a promising solution for mitigating CO₂ emissions. In particular, CO₂RR to formate represents a commercially profitable target. However, a comprehensive understanding of the catalytic mechanisms of Sn-based catalysts under reaction conditions, including the real-time structural evolution of catalysts and the role of all key reaction intermediates in influencing the CO₂RR selectivity, is still lacking. The current study reports a framework to study the selectivity preference of Sn-based bimetallic catalysts using a combination of electrochemical measurements, in situ characterization, and density functional theory (DFT) calculations. The addition of amore » second metal (Co, Ni, Ag, Zn, Ga, Bi) was found to play a vital role in affecting the CO₂RR performance. In situ X-ray absorption near edge structure (XANES) measurements revealed a dynamic evolution in the Sn valence state induced by different secondary metals. A multidimensional descriptor involving all the key reaction intermediates was developed to assess formate selectivity using a 2-dimensional volcano plot. Finally, this research offers an effective framework for understanding CO₂RR catalytic selectivity by considering both the real-time structural evolution of catalysts and all the key intermediates involved.« less

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO₂ (400 ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO₂ insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400 ppm) CO₂ from gas mixtures via O$$-$$C bondmore » formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using ¹³C-labeled CO₂ sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40 kJ mol^-1 between CO₂ and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO₂ release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO₂ insertion. In conclusion, the as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO₂ in crystalline scaffolds.« less

Abstract Developing atomically synergistic bifunctional catalysts relies on the creation of colocalized active atoms to facilitate distinct elementary steps in catalytic cycles. Herein, we show that the atomically-synergistic binuclear-site catalyst (ABC) consisting of $$$${{{{{\rm{Zn}}}}}}^{\delta+}$$$$ ${\mathrm{Zn}}^{\delta +}$ -O-Cr ⁶⁺ on zeolite SSZ-13 displays unique catalytic properties for iso-stoichiometric co-conversion of ethane and CO ₂ . Ethylene selectivity and utilization of converted CO ₂ can reach 100 % and 99.0% under 500  °C at ethane conversion of 9.6%, respectively. In-situ/ex-situ spectroscopic studies and DFT calculations reveal atomic synergies between acidic Zn and redoxmore » Cr sites. $$$${{{{{\rm{Zn}}}}}}^{\delta+}$$$$ ${\mathrm{Zn}}^{\delta +}$ ( $$$$0 \, < \, \delta \, < \, 2$$$$ $0<\delta <2$ ) sites facilitate β-C-H bond cleavage in ethane and the formation of Zn-H ^{δ -} hydride, thereby the enhanced basicity promotes CO ₂ adsorption/activation and prevents ethane C-C bond scission. The redox Cr site accelerates CO ₂ dissociation by replenishing lattice oxygen and facilitates H ₂ O formation/desorption. This study presents the advantages of the ABC concept, paving the way for the rational design of novel advanced catalysts.« less

Palladium (Pd)-based catalysts efficiently convert ammonium formate solution to hydrogen at low temperatures (<100 °C), but they tend to deactivate quickly during stability testing. This manuscript presents a systematic investigation into the catalytic properties of Pd–Ag bimetallic catalysts, focusing on their surface compositions and exploring the mechanisms behind the deactivation of Pd/Ag-based catalysts. Here this study reports a carbon-supported Pd–Ag bimetallic nanoparticle (NP) catalyst obtained through a galvanic replacement method, which showed enhanced formate dehydrogenation performance. The best catalyst, Pd₃Ag₁₀/ACA-G (Pd–Ag bimetallic NPs with a 3 : 10 mass ratio loaded on acid-washed activated carbon, prepared by the galvanic replacementmore » method), presents the highest activity with a TOF of 5202 h^-1 (~2.6-fold of commercial Pd/C). The enhanced electron density of Pd–Ag bimetallic nanoparticles, coupled with the advantages of a smaller nanoparticle size, and the modulation of hydrogen adsorption energy through the Ag/Pd surface alloy on the Ag/Pd(111) facet, collectively resulted in experimentally higher turnover rates of hydrogen production. The changes on the catalyst surface, including surface Ag fraction decrease, NP size growth, and O-containing species (carboxylate, etc.) adsorption, gradually resulted in catalyst deactivation.« less

Abstract Designing cost‐efffective electrocatalysts for the oxygen evolution reaction (OER) holds significant importance in the progression of clean energy generation and efficient energy storage technologies, such as water splitting and rechargeable metal–air batteries. In this work, an OER electrocatalyst is developed using Ni and Fe precursors in combination with different proportions of graphene oxide. The catalyst synthesis involved a rapid reduction process, facilitated by adding sodium borohydride, which successfully formed NiFe nanoparticle nests on graphene support (NiFe NNG). The incorporation of graphene support enhances the catalytic activity, electron transferability, and electrical conductivity of the NiFe‐based catalyst. The NiFe NNG catalystmore » exhibits outstanding performance, characterized by a low overpotential of 292.3 mV and a Tafel slope of 48 mV dec ⁻¹ , achieved at a current density of 10 mA cm ^{− 2} . Moreover, the catalyst exhibits remarkable stability over extended durations. The OER performance of NiFe NNG is on par with that of commercial IrO ₂ in alkaline media. Such superb OER catalytic performance can be attributed to the synergistic effect between the NiFe nanoparticle nests and graphene, which arises from their large surface area and outstanding intrinsic catalytic activity. The excellent electrochemical properties of NiFe NNG hold great promise for further applications in energy storage and conversion devices.« less

Metal–organic framework (MOF)-derived nanoscale porous materials are widely deployed in carbon capture, but the CO₂ capacity is varied by different post-treatments, and its mechanism is still unclear. In this work, we prepared UiO-66 and treated it with methanol solvent and thermal activation approaches, which showed ~3 times enhanced CO₂ capacities from 15.1 to 45.0 mg/g and excellent recyclability of 10 cycles. The methanol treatment efficiently removes the residual guest molecules, including N,N-dimethylformamide, dangling organic linkers, and their derivatives, in the micropores (~0.8 nm) of UiO-66 and improves the surface area, pore volume, and void fraction to enhance the CO₂ capacitymore » close to the ideal UiO-66 materials. The molecular dynamics simulation also proved a good linear relationship between the surface areas, void fraction, and CO₂ capacity. This work provides a deep understanding of the MOF’s activation mechanism and its applications in CO₂ capture.« less

Direct air capture (DAC) of CO₂ by solid porous materials represents an attractive “negative emission” technology. However, state-of-the-art sorbents based on supported amines still suffer from unsolved high energy consumption and stability issues. For this work, taking clues from the CO₂ interaction with superbase-derived ionic liquids (SILs), high-performance and tunable sorbents in DAC of CO₂ was developed by harnessing the power of CaO- and SIL-engineered sorbents. Deploying mesoporous silica as the substrate, a thin CaO layer was first introduced to consume the surface-OH groups, and then active sites with different basicities (e. g., triazolate and imidazolate) were introduced as amore » uniformly distributed thin layer. The as-obtained sorbents displayed high CO₂ uptake capacity via volumetric (at 0.4 mbar) and breakthrough test (400 ppm CO₂ source), rapid interaction kinetics, facile CO₂ releasing, and stable sorption/desorption cycles. Operando diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) analysis under simulated air atmosphere and solid-state NMR under ¹³CO₂ atmosphere demonstrated the critical roles of the SIL species in low-concentration CO₂ capture. The fundamental insights obtained in this work provide guidance on the development of high-performance sorbents in DAC of CO₂ by leveraging the combined advantages of porous solid scaffolds and the unique features of CO₂-philic ionic liquids.« less

Direct air capture (DAC) of CO₂ has emerged as the most promising “negative carbon emission” technologies. Despite being state-of-the-art, sorbents deploying alkali hydroxides/amine solutions or amine-modified materials still suffer from unsolved high energy consumption and stability issues. Here, in this work, composite sorbents are crafted by hybridizing a robust metal-organic framework (Ni-MOF) with superbase-derived ionic liquid (SIL), possessing well maintained crystallinity and chemical structures. The low-pressure (0.4 mbar) volumetric CO₂ capture assessment and a fixed-bed breakthrough examination with 400 ppm CO₂ gas flow reveal high-performance DAC of CO₂ (CO₂ uptake capacity of up to 0.58 mmol g^-1 at 298 K)more » and exceptional cycling stability. Operando spectroscopy analysis reveals the rapid (400 ppm) CO₂ capture kinetics and energy-efficient/fast CO₂ releasing behaviors. The theoretical calculation and small-angle X-ray scattering demonstrate that the confinement effect of the MOF cavity enhances the interaction strength of reactive sites in SIL with CO₂, indicating great efficacy of the hybridization. The achievements in this study showcase the exceptional capabilities of SIL-derived sorbents in carbon capture from ambient air in terms of rapid carbon capture kinetics, facile CO₂ releasing, and good cycling performance.« less