MOF-Derived Robust and Synergetic Acid Sites Inducing C-N Bond Disruption for Energy-Efficient CO2 Desorption

Functionalized Dual/Multiligand Metal-Organic Frameworks for Efficient CO2 Capture under Flue Gas Conditions

Reducing carbon dioxide (CO2) emissions has become increasingly urgent for China, particularly in the industrial sector. Striking a balance between a high CO2 adsorption capacity and long-term stability under practical conditions is crucial for effectively capturing CO2 from flue gas. In this study, a series of functionalized MFM-136 adsorbents were synthesized in which -NO2 and -NH2 groups were grafted onto the kagome lattice of MFM-136. Modifications with -NH2 groups were found to be highly effective for CO2 adsorption, specifically, the CO2 adsorption capacity peaked at 4.35 mmol/g for NH2(0.6)-MFM-136, representing a 55% enhancement more than MFM-136. Concurrently, the CO2/N2 selectivity for NH2(0.6)-MFM-136 was increased 1.57 times. Verification of novel adsorption sites introduced by NH2-H2L4 was conducted by using in situ DRIFT analysis and DFT calculations. It turns out that NH2-H2L4 modification can effectively mitigate the chemical deposition from the impurity gases and significantly improve the adsorbent's hydrophobicity and its tolerance to impurity gases. Remarkably, the reduction in the CO2 absorption capacity for NH2(0.6)-MFM-136 was 34% less than that for MFM-136 after 24 h of exposure to simulated flue gas, making NH2(0.6)-MFM-136 a promising candidate for the potential application of stable and selective CO2 capture under industrial flue gas conditions.

Cerium-MOF-Derived Composite Hierarchical Catalyst Enables Energy-Efficient and Green Amine Regeneration for CO2 Capture

The excessive energy consumed restricts the application of traditional postcombustion CO2 capture technology and limits the achievement of carbon-neutrality goals. Catalytic-rich CO2 amine regeneration has the potential to accelerate proton transfer and increase the energy efficiency in the CO2 separation process. Herein, we reported a Ce-metal-organic framework (MOF)-derived composite catalyst named HZ-Ni@UiO-66 with a hierarchical structure, which can increase the CO2 desorbed amount by 57.7% and decrease the relative heat duty by 36.5% in comparison with the noncatalytic monoethanolamine (MEA) regeneration process. The composite catalyst of the CeO2 coating from the UiO-66 precursor on the HZ-Ni carrier shows excellent stability with a long lifespan. The HZ-Ni@UiO-66 catalyst also shows a universal catalytic effect in typical blended amine systems with a large cyclic capacity. The HZ-Ni@UiO-66 catalyst effectively decreases the energy barrier of the CO2 desorption reaction to reduce the time required to reach thermodynamics, consequently saving the energy consumption generated by water evaporation. This research provides a new avenue for advancing amine regeneration with less heat duty at low temperatures.

Enhancing CO2 capture of an aminoethylethanolamine-based non-aqueous absorbent by using tertiary amine as a proton-transfer mediator: From performance to mechanism

Non-aqueous absorbents (NAAs) have attracted increasing attention for CO2 capture because of their great energy-saving potential. Primary diamines which can provide high CO2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N-diethylaminoethanol (DEEA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N-dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO2 absorption performance. Specifically, the CO2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%-22.7%, respectively. The TA-enhanced CO2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO-) to store CO2, thus enhancing CO2 absorption. For CO2 desorption, the TA first provided protons directly to AEEACOO- as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO-. Consequently, the presence of TA made it easier for AEEACOO- to obtain protons to decompose, resulting in enhanced CO2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO2 absorption performance and the regenerability, which was an efficient way to "kill two birds with one stone".

Sulfur Migration Enhanced Proton-Coupled Electron Transfer for Efficient CO2 Desorption with Core-Shelled C@Mn3O4

Transforming hazardous species into active sites by ingenious material design was a promising and positive strategy to improve catalytic reactions in industrial applications. To synergistically address the issue of sluggish CO2 desorption kinetics and SO2-poisoning solvent of amine scrubbing, we propose a novel method for preparing a high-performance core-shell C@Mn3O4 catalyst for heterogeneous sulfur migration and in situ reconstruction to active -SO3H groups, and thus inducing an enhanced proton-coupled electron transfer (PCET) effect for CO2 desorption. As anticipated, the rate of CO2 desorption increases significantly, by 255%, when SO2 is introduced. On a bench scale, dynamic CO2 capture experiments reveal that the catalytic regeneration heat duty of SO2-poisoned solvent experiences a 32% reduction compared to the blank case, while the durability of the catalyst is confirmed. Thus, the enhanced PCET of C@Mn3O4, facilitated by sulfur migration and simultaneous transformation, effectively improves the SO2 resistance and regeneration efficiency of amine solvents, providing a novel route for pursuing cost-effective CO2 capture with an amine solvent.

Use of La-Co@NPC for Sulfite Oxidation and Arsenic Detoxification Removal for High-Quality Sulfur Resources Recovery in Desulfurization Process

Ammonia desulfurization is a typical resource-recovery-type wet desulfurization process that is widely used in coal-fired industrial boilers. However, the sulfur recovery is limited by the low oxidation rate of byproduct (ammonium sulfite), leading to secondary SO2 pollution due to its easy decomposability. In addition, the high toxic arsenic trace substances coexisting in desulfurization liquids also reduce the quality of the final sulfate product, facing with high environmental toxicity. In this study, nitrogen-doped porous carbon coembedded with lanthanum and cobalt (La-Co@NPC) was fabricated with heterologous catalytic active sites (Co0) and adsorption sites (LaOCl) to achieve sulfite oxidation and the efficient removal of high toxic trace arsenic for the recovery of high-value ammonium sulfate from the desulfurization liquid. The La-Co@NPC/S(IV) catalytic system can generate numerous strongly oxidizing free radicals (·SO5- and ·O2-) for the sulfite oxidation on the Co0 site, as well as oxidative detoxification of As(III) into As(V). Subsequently, arsenic can be removed through chemical adsorption on LaOCl adsorption sites. By using the dual-functional La-Co@NPC at a concentration of 0.25 g/L, the rate of ammonium sulfite oxidation reached 0.107 mmol/L·s-1, the arsenic (1 mg/L) removal efficiency reached 92%, and the maximum adsorption capacity of As reached up to 123 mg/g. This study can give certain guiding significance to the functional material design and the coordinated control of multiple coal-fired pollutants in desulfurization for high-value recovery of sulfur resources.

Embedded Mo/Mn Atomic Regulation for Durable Acidity-Reinforced HZSM-5 Catalyst toward Energy-Efficient Amine Regeneration

Metal-molecular sieve composites with high acidity are promising solid acid catalysts (SACs) for accelerating sluggish CO2 desorption processes and reducing the energy consumption of CO2 chemisorption systems. However, the production of such SACs through conventional approaches such as loading or ion-exchange methods often leads to uncontrolled and unstable metal distribution on the catalysts, which limits their pore structure regulation and catalytic performance. In this study, we demonstrated a feasible strategy for improving the durability, surface chemical activity, and pore structure of metal-doped HZSM-5 through bimetallic Mo/Mn modification. This strategy involves the immobilization of Mo-O-Mn species confined in an MFI structure by regulating MoO42- anions and Mn2+ cations. The embedded Mn/Mo species of low valence can strongly induce electron transfer and increase the density of compensatory H+ on the MoMn@H catalyst, thereby reducing the CO2 desorption temperature by 8.27 °C and energy consumption by 37% in comparison to a blank. The durability enhancement and activity regulation method used in this study is expected to advance the rational synthesis of metal-molecular sieve composites for energy-efficient CO2 capture using amine regeneration technology.

Laser-Assisted Design of MOF-Derivative Platforms from Nano- to Centimeter Scales for Photonic and Catalytic Applications

Laser conversion of metal-organic frameworks (MOFs) has recently emerged as a fast and low-energy consumptive approach to create scalable MOF derivatives for catalysis, energy, and optics. However, due to the virtually unlimited MOF structures and tunable laser parameters, the results of their interaction are unpredictable and poorly controlled. Here, we experimentally base a general approach to create nano- to centimeter-scale MOF derivatives with the desired nonlinear optical and catalytic properties. Five three- and two-dimensional MOFs, differing in chemical composition, topology, and thermal resistance, have been selected as precursors. Tuning the laser parameters (i.e., pulse duration from fs to ns and repetition rate from kHz to MHz), we switch between ultrafast nonthermal destruction and thermal decomposition of MOFs. We have established that regardless of the chemical composition and MOF topology, the tuning of the laser parameters allows obtaining a series of structurally different derivatives, and the transition from femtosecond to nanosecond laser regimes ensures the scaling of the derivatives from nano- to centimeter scales. Herein, the thermal resistance of MOFs affects the structure and chemical composition of the resulting derivatives. Finally, we outline the "laser parameters versus MOF structure" space, in which one can create the desired and scalable platforms with nonlinear optical properties from photoluminescence to light control and enhanced catalytic activity.

Nonacid Carbon Materials as Catalysts for Monoethanolamine Energy-Efficient Regeneration

In the CO₂ capture process, solid acid catalysts have been widely adopted to decrease energy consumption in the amine regeneration process owing to abundant acid sites. However, acid sites unavoidably degenerate in the basic amine solution. To address the challenge, nonacid carbon materials including carbon molecular sieves, porous carbon, carbon nanotubes, and graphene are first proposed to catalyze amine regeneration. It is found that carbon materials can significantly increase the CO₂ desorption amount by 47.1-72.3% and reduce energy consumption by 32-42%. In 20 stability experiments, CO₂ loading was stable with the max difference value of 0.01 mol CO₂/mol monoethanolamine (MEA), and no obvious increase in the relative heat duty (the maximum difference is 4%) occurred. The stability of carbon materials is superior to excellent solid acid catalysts, and the desorption performance is comparable. According to the results of theoretical calculation and experimental characterization, the electron-transfer mechanism of nonacid carbon materials is proposed, which is not only beneficial for MEA regeneration but also the probable reason for the stable catalytic activity. Owing to the excellent catalytic performance of carbon nanotube (CNT) in the HCO₃^- decomposition, nonacid carbon materials are quite promising to enhance the desorption performance of novel blend amines, which will further reduce the cost of carbon capture in the industry. This study provides a new strategy to develop stable catalysts used for amine energy-efficient regeneration.