CO Chemisorption Research Articles

Unified mechanistic understanding on CO2 sorption by Na-doped Li4SiO4: Experimental and DFT study

The addition of molten Na2CO3 can drastically accelerated the extremely slow sorption kinetics of Li4SiO4-based CO2 sorbents in the sorption enhanced reforming process. However, the lack of a unified consensus about the effect of doped Na2CO3 on the CO2 capture process, now delays the development of more-effective Li4SiO4 sorbents. Here, sorption tests, sturactural characterzations and periodic density functional theory calculations were combined to develop a better mechanistic understanding CO2 sorption on Na-doped Li4SiO4. The Na-doped Li4SiO4 exhibited a better CO2 capture performance than pure Li4SiO4 even below the melting point of any eutectic mixtures. Structural characterizations revealed that rather than generating physical favorable characteristics, the Na doping substituted at the Li site and created lithium–sodium orthosilicates (Li4-xNaxSiO4). Theoretical calculations agreeing with experimental results further demonstrated that Li4-xNaxSiO4 presented a weaker Na-O bond and generated more active phases (quasi Li2O groups) for larger sorption energies, more charge transfers and stronger CO32– bond formation, in turn providing more reactive sites for enhanced CO2 chemisorption as comparing with pure Li4SiO4. Finally, we propose a new and unified sorption mechanism independent of the traditional “melting layer” explanation.

Photocatalytic CO2 reduction of CuO-Zn1-xCuxO (ZCO)/Ti3C2Tx MXene heterojunctions with enhanced interfacial charge transfer

Photocatalytic CO2 reduction reaction (CO2RR) synthesis of recycled fuel is a promising pathway to assist the mitigating fossil fuel depletion. Finding efficient and inexpensive high performance CO2RR semiconductor photocatalysts is a giant challenge in the field of photocatalytic reduction. This work constructs the novel-designed interfacial Schottky junction of CuO-Zn1-xCuxO (ZCO)/Ti3C2Tx via electrostatic spinning and electrostatic self-assembly techniques. The catalysts exhibit tight contact heterogeneous interface companies with enhanced CO2 chemisorption capability and proved by various characterizations for efficient carrier separation and migration capacity. The optimized ZCO/Ti3C2Tx nanosheet composites significantly improved their photocatalytic performance. The best samples yielded 5.855 and 2.518 μmol g−1 h−1 of CO and CH4, which are 6 and 1.73 times higher than the conversion of ZCO, respectively, and maintain stability after four cycles without the use of sacrificial agents. In addition, the mechanism and reaction pathways of the photocatalytic process are proposed through In-situ diffuse reflectance Infrared Fourier Transform Spectroscopy (In-situ DRIFTS) and X-ray absorption near edge structure (XANES) analysis. This work provides a new semiconductor/co-catalyst system for the photocatalytic reduction of CO2 and demonstrates that Ti3C2Tx MXene is a hopeful and inexpensive co-catalyst.

Simulating CO2 diffusivity in rigid and flexible Mg-MOF-74 with machine-learning force fields

The flexibility of metal–organic frameworks (MOFs) affects their gas adsorption and diffusion properties. However, reliable force fields for simulating flexible MOFs are lacking. As a result, most atomistic simulations so far have been carried out assuming rigid MOFs, which inevitably overestimates the gas adsorption energy. Here, we show that this issue can be addressed by applying a machine-learning potential, trained on quantum chemistry data, to atomistic simulations. We find that inclusion of flexibility is particularly important for simulating CO2 chemisorption in MOFs with coordinatively unsaturated metal sites. Specifically, we demonstrate that the diffusion of CO2 in a flexible Mg-MOF-74 structure is about one order of magnitude faster than in a rigid one, challenging the rigid-MOF assumption in previous simulations.

Collective Synergistic Catalysis of Electrochemical CO2 Reduction on Nonstoichiometric Double Perovskites

AbstractPerovskite oxides show great promise as an alternative catalyst to the conventional nickel cermets for CO2 reduction reactions (CO2RR) in solid oxide electrolysis cells (SOECs) owing to their advantages of redox stability and coking resistance. Nevertheless, practical applications of these oxides are prevented largely by their poor CO2RR activities. Herein, a novel donor and acceptor co‐doped nonstoichiometric double perovskite, La0.3Sr1.55Fe1.5Ni0.1Mo0.4O6−δ (LSFNM), is developed with in situ exsolved FeNi3 nanoparticles to efficiently catalyze CO2RR in SOECs. Pure CO2 electrolysis over the impregnated FeNi3@LSFNM catalysts is evaluated on two types of SOECs—one with thin (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 (SSZ) electrolytes supported on 430L alloys and the other with thin La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolytes supported on impregnated SmBa0.5Sr0.5Co2O5+δ (SBSCO)@LSGM anodes, producing unprecedently high current densities of 2.84 A cm−2 for the former and 3.07 A cm−2 for the latter at 1.5 V and 800 °C. Experimental analysis and density‐functional theory (DFT) calculations reveal collective synergistic catalysis of oxygen vacancies (), the doping Ni2+ ions and FeNi3 nanoparticles via the cooperative ‐O(CO2), and Ni(II)–C(sp) and Ni(0)–O(CO2) interactions in LSFNM, not only facilitating CO2 chemisorption on oxygen vacancies but also destabilizing and dissociating surface carbonates in the vicinity of FeNi3 spontaneously into CO.

The role of reverse Boudouard reaction during integrated CO2 capture and utilisation via dry reforming of methane

Integrated carbon capture and utilisation (ICCU) is an emerging technology for simultaneous CO2 adsorption and conversion into value-added products. This provides a more sustainable approach compared to carbon capture and storage. Dual-functional materials (DFMs) that couple CO2 sorbents (e.g. CaO) and catalysts (e.g. Ni) enable direct utilisation of sorbed CO2 for reactions like dry reforming of methane (DRM). However, the potential interactions between sorbent and catalyst components within DFMs may induce distinct mechanisms compared to individual materials. Elucidating these synergies and interfacial phenomena is vital for guiding the rational design of DFMs. This article investigates the respective roles of Ni/SiO2 catalyst and sol–gel synthesised CaO sorbent in integrated CO2 capture and utilisation via dry reforming of methane (ICCU-DRM) using a decoupling approach. Through decoupled reactor experiments, it is found that Ni/SiO2 activates CO2 to react with carbon deposits from CH4 decomposition, achieving maximal CO and H2 yields of 43.41 mmol g−1 and 46.78 mmol g−1 as well as 87.2 % CO2 conversion at 650 °C. Characterisation shows that coke would encapsulate Ni nanoparticles and be active for CO2 conversion via Boudouard reaction, indicating sufficient catalyst-sorbent contact is necessary for CO2 spillover. In-situ DRIFTS reveals that no obvious CH4-CaCO3 reaction occurs, CO2 chemisorption on Ni/SiO2 enables the reverse Boudouard reaction, which is further verified by DFT calculations. The findings elucidate the dependent and synergistic roles of Ni/SiO2 and CaO/CaCO3 in ICCU-DRM, and highlight the importance of catalyst-adsorbent interactions in optimising dual-functional materials.

Post‐combustion carbon dioxide adsorption of concurrent activated and surface modified palm kernel shell‐derived activated carbon

AbstractThis research applied a concurrent activation and surface modification (CAM) process to synthesize palm kernel shell‐derived activated carbon (PKSdAC) to obtain CO2 affinity surface functionalization. The CAM process is a simplified activated carbon activation process that is cost‐effective. The CAM process used in this study integrates sulphuric acid activation and barium chloride functionalization. The formation of barium sulphate is targeted to incorporate barium through a reduction process with carbon‐containing material at elevated temperatures into PKSdAC to obtain basic metal surfaces functional group for chemical adsorption. The optimal temperature for CAM‐PKSdAC CO2 adsorption performance was at 40–60 °C, established through temperature‐programmed desorption of CO2 (TPD‐CO2) analysis. The CAM‐PKSdAC adsorption performance was tested using a lab‐scale adsorption system. The bed CO2 content was determined using gas chromatography coupled with a thermal conductivity detector (GC‐TCD) by manual syringe injection. CAM‐PKSdAC exhibited a high CO2 adsorption capacity of 0.89 mmol g−1 from TPD‐CO2, and 1.91 mmol g−1 from GC‐TCD at 40 °C and 1 bar. It showed comparable CO2 adsorption capacity to conventional surface modified‐activated PKSdAC (1.96 mmol g−1) while higher than commercial and modified ACs (1.14–1.60 mmol g−1), but lower than potassium hydroxide modified ACs (1.81–2.10 mmol g−1) at 40 °C and 1 bar. Barium promoted chemisorption of CO2 as supplementary reaction, which increases adsorption capacity. The non‐linear Dubinin Radushkevich model strongly correlates with the experimental adsorption data for CAM‐PKSdAC adsorption, indicating the physisorption process via micropore filling on CAM‐PKSdAC. CAM‐PKSdAC showed moderate reusability with negligible variation in adsorption capacity after 10 adsorption–desorption cycles. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Effective Prevention of Palladium Metal Particles Sintering by Histidine Stabilization on Silica Catalyst Support

AbstractA robust method for enhancing the dispersion and stabilization of small metal nanoparticles in heterogeneous catalysts is developed. It involves in situ complexation of palladium(II) by histidine, in water, prior to impregnation in fumed silica. TEM images show that the histidine facilitates dispersion of the Pd(II) into finer nanoscale particles (≈2 nm) uniformly distributed on the support, rather than the large clusters (≈5 nm) seen in the absence of histidine. After hydrogen reduction, assessments using CO chemisorption and propylene hydrogenation indicate that the coordinated histidine might obscure the active sites on the Pd particles. However, as histidine decomposes between 220 and 300 °C in air, these materials are treated at 225 °C in air for 48 h. Afterwards the Pd(II) particles remain the same size, but after hydrogen reduction, there is a 2.4‐fold increase in CO gas adsorption, indicative of an expanded Pd surface area. Furthermore, superior catalyst stability (activity >200 h) is observed during propylene hydrogenation at 250 °C. This is consistent with histidine use having generated widely spaced, uniformly small, Pd nanoparticles on the silica support which is expected to help prevent agglomeration (sintering) during catalysis. This is a convenient low‐cost strategy for reducing metal content, preventing sintering and optimizing catalyst performance.

Valorization of Crab Shells as Potential Sorbent Materials for CO2 Capture.

This study delves into the potential advantage of utilizing crab shells as sustainable solid adsorbents for CO2 capture, offering an environmentally friendly alternative to conventional porous adsorbents, such as zeolites, silicas, metal-organic frameworks (MOFs), and porous carbons. The investigation focuses on crab shell waste, which exhibits inherent natural porosity and N-bearing groups, making them promising candidates for CO2 physisorption and chemisorption applications. Selective deproteinization and demineralization treatments were used to enhance textural properties while preserving the natural porous structure of the crab shells. The impact of deproteinization and demineralization treatments on CO2 adsorption and speciation at the atomic scale, via solid-state NMR, and correlated findings with textural properties and biomass composition were investigated. The best-performing sample exhibits a surface area of 36 m2/g and a CO2 adsorption capacity of 0.31 mmol/g at 1 bar and 298 K, representing gains of ∼3.5 and 2, respectively, compared to the pristine crab shell. These results underline the potential of fishing industry wastes as a cost-effective, renewable, and eco-friendly source to produce functional porous adsorbents.

Thermally Induced Structure and Functionality Evolution of a Pt‐based Lean NOx Trap Catalyst

Applying a NOx trap catalyst to effectively remove NOx contaminants from the oxygen‐rich exhaust is still very challenging, due to the lack of use guidance based on deactivation mechanisms. The temperature‐dependent Pt sintering rate constant was described using Pt dispersion determined by pulse CO chemisorption. It was found that 700‐850 ºC was the determining temperature regions for the significant Pt sintering, according to the sintering kinetics and the evolution of active Ptδ+ sites. The weak basicity plays a critical role in trapping NOx at low‐temperature (≤ 300 ºC), and the NOx trap efficiency decreases because of the loss of catalytic activity and medium basicity caused by forming BaAl2O4 phase. The reduction of NOx towards N2 on the Pt crystallites smaller than 18 nm is structure sensitive and decreases with losing the reducibility of catalysts. The security for long‐time use of a NOx trap catalyst should be exposed to the exhaust gas within 750 ºC, and effectively removing NOx contaminants requires it to be worked in the 350‐500 ºC regions. These findings can guide engineers and applied chemists how to efficiently use a NOx trap catalyst in the automotive exhaust purification system.

Photocatalytic conversion of CH4 and CO2 to acetic acid over Cu/ZnO catalysts under mild conditions

The conversion of methane (CH4) and carbon dioxide (CO2) into high-value products under mild conditions is crucial for addressing the greenhouse effect and advancing C1 chemistry. In this study, Cu/ZnO catalysts were prepared through a one-step wet reduction process, and the catalytic conversion of CH4 and CO2 into acetic acid molecules (CH3COOH) was achieved via photon activation at ambient temperature. The yield of acetic acid was 411.6 μmol/Lgcat−1h−1 with a selectivity of 89.5 % under optimal conditions (100 mWcm−2 light intensity, 25 ± 2 °C, 2 MPa pressure, and a 1:1 CH4:CO2 volume ratio). Enhanced solubility of CH4 in aqueous under increased pressure and temperature was observed to improve acetic acid production. Additionally, the catalytic mechanism involved surface chemisorption of CH4 and CO2, facilitated by ZnO and Cu in the catalyst, leading to C-C coupling and subsequent acetic acid formation, driven by photogenerated electron-hole migration. This study provides a foundational understanding for the synthesis of value-added chemicals through CH4 and CO2 conversion via C-C coupling in mild environments.

Co-ZIF-derived dual Co and Co3S4 nanoparticles encapsulated in N-doped carbon matrix for efficient photocatalytic CO2 reduction

In this study, a novel N-doped carbon-coated dual Co and Co3S4 nanoparticles composite (Co-Co3S4@NC) has been developed by pyrolysis of an ideal flower-like Co-ZIF precursor followed via subsequent hydrothermal sulfidation. Under visible-light irradiation, the Co-Co3S4@NC exhibits outstanding performances for CO2 reduction with H2O vapor into CO (23.14 μmol g−1 h−1) and CH4 (0.62 μmol g−1 h−1) in a continuous flow system, significantly outperforming the single Co@NC photocatalyst. The experimental results demonstrate that the energy band structure in Co-Co3S4@NC can provide a more favorable reduction potential for the effective reduction of CO2. Moreover, the presence of Co3S4 is beneficial for the rapid separation and transfer of charges, thereby enhancing the utilization of photogenerated charge carriers. Thanks to its unique composition, Co-Co3S4@NC possesses abundant active sites for chemisorption and activation of CO2, which facilitates CO2 photoreduction. The reaction mechanism is revealed in detail by analyzing the key intermediate species obtained through in situ DRIFTS. The current work offers a facile route for the construction of MOF-derived composites for promising photocatalytic reactions.

Understanding the catalytic performance and deactivation behaviour of second-promoter doped Pt/WOx/γ-Al2O3 catalysts in the glycerol hydrogenolysis for selective and cleaner production of 1,3-propanediol

The selective aqueous-phase glycerol hydrogenolysis is a promising reaction to produce commercially useful 1,3-propanediol (1,3-PDO). The Pt-WOx bifunctional catalyst can catalyse the glycerol hydrogenolysis but the catalyst deactivation via sintering, metal leaching, and coking can predominantly occur in the aqueous phase reaction. In this work, the effect of reaction temperature, pressure and second promoter (Cu, Fe, Rh, Mn, Re, Ru, Ir, Sn, B, and P) on catalytic performance and deactivation behaviour of Pt/WOx/γ-Al2O3 was investigated. When doped with Rh, Mn, Re, Ru, Ir, B, and P, the second promoter boosts catalytic activity by promoting great dispersion of Pt on support and increasing Pt surface area. The increased Brønsted acid sites lead to selective synthesis of 1,3-PDO than 1,2-propanediol (1,2-PDO). The characterization studies of fresh and spent catalysts reveal that the main cause of catalyst deactivation is the Pt sintering, as interpreted based on XRD, CO chemisorption, and TEM analyses. The Pt sintering is affected depending on the second promoter that can either or reduce the interaction between Pt, WOx, and Al2O3. As an electron acceptor of Pt in Pt/WOx/γ-Al2O3, Re and Mn as second promoters resulted in increased Pt2+ on the catalytic surface, which strengthens the contact between Pt and γ-Al2O3 and WOx, resulting in a decrease in Pt sintering. The metal leaching and coking are not affected by the presence of second promoter. The catalyst modified with a second promoter possesses improved catalytic activity and 1,3-PDO production, however the stability continues to remain a challenge. The present work unravelled the determining parameters of catalytic activity and deactivation, thus providing a promising protocol toward effective catalysts for glycerol hydrogenolysis.

Vacancy pair induced surface chemistry reconstruction of Cs2AgBiBr6/Bi2WO6 heterojunction to enhance photocatalytic CO2 reduction

Cs2AgBiBr6/Bi-O vacancy pair Bi2WO6 (Cs2AgBiBr6/VBi-OBi2WO6) heterojunction was synthesised for photocatalytic CO2 reduction under visible light irradiation. The characterisation results show that the Bi-O vacancy pairs can reconstruct the surface electronic states of the heterojunction. The optimal 10%Cs2AgBiBr6/VBi-OBi2WO6 heterojunction exhibited a substantial CO yield of 48.5 μmol/g, approximately 22 times higher than that of Bi2WO6, exceeding the performance of most of the Bi-based photocatalysts reported to date. The enhanced activity of 10%Cs2AgBiBr6/VBi-OBi2WO6 was due to exposed Bi sites that facilitate the chemisorption and activation of CO2 and the lower reaction energy barrier for the protonation of CO2 to CO via the formation of COOH* intermediates with the cooperation of surface four-coordinated H2O molecules. Furthermore, charge migration from Cs2AgBiBr6 to VBi-OBi2WO6 and space-charge distribution in the heterojunction under visible light irradiation were demonstrated. This work reveals defective heterojunction catalysts that facilitate the transformation of reactive molecules in surface/interfacial reactions.

Tuning the electronic structure of GaN monolayer by the single-atom promotor for hydrogenation of CO2

The efficient and cost-effective conversion of captured CO2 into valuable chemicals has garnered significant attention, driving the exploration of catalysts for CO2 capture and conversion. Here, we investigated a series of GaN monolayers with single metal atoms (M@GaN, M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, and In) using first-principles calculations and ab initio molecular dynamics (AIMD) simulations. We propose a novel approach to enhance CO2 activation performance by tuning the single atom promotor (SAP). Compared to pristine GaN sheet, Ni@GaN, Cu@GaN, and Zn@GaN are predicted to have higher activity for CO2 adsorption and activation, in which the CO2 chemisorption process is predicted to be exothermic (−0.36 to −0.46 eV) with the low barrier (0.21–0.28 eV). This improvement can be attributed to occupied electronic states near the Fermi level in the N atom connected to SAP in the M@GaN (M = Ni, Cu, and Zn), enabling a better match with the LUMO level of CO2. In addition, compared with the AlN monolayer with better CO2 capture capability, Ni@GaN, and Zn@GaN exhibit considerable promise as catalysts for the hydrogenation of CO2 to HCOOH.

A study on microwave synthesis of unique Zn1-3xCuxCexCrxO nanoparticles with efficient photocatalytic reactivity under visible sunlight irradiation

The study investigates the synthesis and characterization of Cu, Ce, and Cr co-doped ZnO nanoparticles (Zn1-3xCuxCexCrxO with x = 0.00, 0.03, and 0.05) using a microwave-assisted sol–gel technique. Powder X-ray diffraction confirmed the monoclinic structure of the nanocrystalline ZnO with an average crystallite size ranging from 41 nm to 47 nm. Fourier-transform infrared analysis revealed chemisorption of H2O and CO2 onto the ZnO surface upon exposure to the atmosphere. Energy-dispersive X-ray spectroscopy confirmed the presence of Zn, Cu, Ce, Cr, and O in the samples. Scanning electron microscopy images depicted agglomerated crystals with both agglomeration and non-agglomeration of smaller crystallites. Notably, a red shift in the UV–Vis spectrum was observed at a 3 % doping concentration, with an increase in photocatalytic efficiency from 56 % to 67 % compared to pure ZnO. Furthermore, an overall enhancement in photocatalytic performance was noted with increasing doping concentration, indicating potential applications in organic pollutant degradation. The study also highlighted a decrease in the band gap between pure and doped ZnO with escalating doping content, suggesting promising prospects for photocatalytic applications by suppressing carrier recombination.

Integrated experimental and theoretical studies for unravelling CO2 capture of dual function CeO2-CaO bio-based sorbents

Solid CaO-based sorbents for CO2 capture represent a promising alternative technology compared to traditional amine scrubbing methods. However, CaO-based sorbents are rapidly sinter and easily decrease CO2 uptake capacity with regenerated carbonation–calcination cycle. Thus, in this study, doping CaO with CeO2 make it an excellent candidate for improving stability and facilitating CO2 capture efficiency. The dual function of CaO bio-based sorbents with varying ratios of cerium (Ce) were derived from naturally occurring blood clam using the gel-combustion method. Their nanostructures and physicochemical properties were characterized through the specific methods, including in situ XAS, CO2 chemisorption and physisorption, XPS, XRD, and SEM. An in-depth understanding of CO2 adsorption mechanism was further emphasized using a density functional theory (DFT) simulation. The results demonstrate that nanosized CeO2-CaO, with a mole ratio of 1:9, exhibited the highest performance for CO2 capture (6.44 mmol CO2/g sorbent). It is postulated that Ce serves as a physical barrier, effectively partitioning adjacent CaO grains and thereby diminishing the sintering rate. CaO is identified as the primary adsorption site, in contrast to CeO2. Mixing the Ce-Ca dual oxide initiates the electron-rich O at the O’ site. The electron localization at the O’ active site improves the activity of O’, making the performance CeCa(200) for capturing CO2 capture dominant. This discovery suggests that CeO2-CaO holds promise as a sustainable alternative sorbent for future CO2 capture applications.

Post-combustion CO2 capturing by KOH solution: An experimental and statistical optimization modeling study

A pilot-scale bubble column contactor has been utilized for carbon dioxide chemisorption from simulated flue gas in the temperature range 30°C to 50°C. The influence of the most important operating parameters has been investigated. A total of 25 experiments were designed using the response surface methodology (RSM) and were then carried out in the bubble contact column. The results revealed that the liquid volume in the column, the alkaline concentration, and the temperature had a positive effect, while the gas hold-up had a negative effect on the CO2 removal efficiency. A statistical model has been developed using the RSM D-optimal experimental design method. To achieve the highest CO2 chemisorption, several operating conditions have been optimized. The model predicted that the maximum percentage of carbon dioxide removal would be 86.64%, and under the same operating conditions the experimental removal efficiency was 87.12%.

Development of an Ir/TiO2 catalytic coating for plasma assisted hydrogenation of CO2 to CH4

The hydrogenation of CO2 to methane over a 20 wt% Ir/TiO2 catalytic coating has been investigated in a tubular dielectric barrier discharge (DBD) reactor. The 1.2 µm Ir/TiO2 coating was deposited onto the inner wall of a quartz tube by a combustion-evaporation method from a mixture containing a Ti precursor and a colloidal suspension of Ir nanoparticles (2 nm). The catalyst was characterised by XRD, SEM, TEM/EDS and CO chemisorption. The Ir(0) state in the as-synthesised film was confirmed by XPS. The CH4 conversion increased by 1.5 times, as compared to an empty tube. A maximum CO2 conversion rate of 2.1 μmol s−1 was achieved at a fuel production efficiency of 3.5%. Surface reactions onto the catalyst surface are responsible for enhancement of reaction rate. The results presented in this work open up new possibilities in plasma-catalysis, whereby efficient reactions can be carried out over small volumes of catalyst.

High-Capacity, Cooperative CO2 Capture in a Diamine-Appended Metal-Organic Framework through a Combined Chemisorptive and Physisorptive Mechanism.

Diamine-appended Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks are promising candidates for carbon capture that exhibit exceptional selectivities and high capacities for CO2. To date, CO2 uptake in these materials has been shown to occur predominantly via a chemisorption mechanism involving CO2 insertion at the amine-appended metal sites, a mechanism that limits the capacity of the material to ∼1 equiv of CO2 per diamine. Herein, we report a new framework, pip2-Mg2(dobpdc) (pip2 = 1-(2-aminoethyl)piperidine), that exhibits two-step CO2 uptake and achieves an unusually high CO2 capacity approaching 1.5 CO2 per diamine at saturation. Analysis of variable-pressure CO2 uptake in the material using solid-state nuclear magnetic resonance (NMR) spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) reveals that pip2-Mg2(dobpdc) captures CO2 via an unprecedented mechanism involving the initial insertion of CO2 to form ammonium carbamate chains at half of the sites in the material, followed by tandem cooperative chemisorption and physisorption. Powder X-ray diffraction analysis, supported by van der Waals-corrected density functional theory, reveals that physisorbed CO2 occupies a pocket formed by adjacent ammonium carbamate chains and the linker. Based on breakthrough and extended cycling experiments, pip2-Mg2(dobpdc) exhibits exceptional performance for CO2 capture under conditions relevant to the separation of CO2 from landfill gas. More broadly, these results highlight new opportunities for the fundamental design of diamine-Mg2(dobpdc) materials with even higher capacities than those predicted based on CO2 chemisorption alone.

Adapted CO chemisorption technique to measure metal particle dispersion on ceria-containing catalysts

Characterizing ceria-containing catalysts via common characterization techniques can be challenging. CO chemisorption is usually used to measure catalyst dispersion. However, the reaction between CO and ceria lattice oxygen leads to significant carbonate formation, resulting in an overestimation of the CO uptake and metal dispersion. Here, we propose a modified method to characterize ceria-containing catalysts which involves exposing the catalyst to CO2 prior CO adsorption to prevent further carbonate formation during CO chemisorption. We tested this method on Pd/CeO2 catalysts characterized by different ceria particle sizes and validated it via DRIFTS and CO oxidation kinetics. Validation conducted using CO oxidation kinetics showed that the TOFs derived by normalizing the reaction rates by the interfacial sites, which are the active sites, are similar for all the catalysts under investigation. Our results show that CO2-CO chemisorption can be a reliable technique for estimating metal dispersion of ceria-supported catalysts.