Enhanced CO2 Adsorption Research Articles

Development of efficient CO2 adsorbents: Synthesis and performance evaluation of dopamine-modified halloysite nanotubes loaded with ZIF-8

Carbon capture, utilization, and storage (CCUS) is a crucial technology for achieving carbon reduction targets. The key to CCUS technology lies in developing and designing efficient and low-cost CO2 capture materials. Metal-organic frameworks (MOFs) have emerged as promising CO2 adsorbents in the field of carbon capture. However, high agglomeration of nanoparticles and high cost have severely hindered the application of MOF-based solid adsorbents. This study employs an in-situ growth method to prepare a novel “corncob-shaped” PHNT@ZIF-8 composite material. During the reaction process, surface modification of halloysite nanotubes (HNT) enhances the interaction between HNT and ZIF-8. The resulting PHNT@ZIF-8 exhibits an enhanced CO2 adsorption capacity of 1.48 mmol/g. Notably, the functionalized PHNT@ZIF-8 as CO2 adsorbents demonstrated significant adsorption properties: a high specific surface area of 409.74 m2/g, good selectivity in simulated flue gas composition of 15%/85% (CO2/N2) (39.1), excellent thermal stability, and superior regenerability. Moreover, PHNT@ZIF-8 adsorbs CO2 primarily through van der Waals forces, which involve low energy and are easily reversible. After eight adsorption–desorption cycles, CO2 capacity retention rate remains as high as 93% (1.37 mmol/g). This work enriches the repertoire of solid CO2 composite adsorbents, providing a novel pathway for enhancing CO2 adsorption performance.

Synergistic effect of carbon molecular sieve and alkali metal nitrate on promoting intermediate-temperature adsorption of CO2 over MgAl-layered double hydroxide

The development of intermediate-temperature adsorbents with high CO2 adsorption capacity is crucial for the tandem integration with CO2 hydrogenation catalyst, aimed at enhancing economy viability and minimizing energy consumption in Carbon capture, utilization and storage (CCUS). Although certain porous carbon materials (PCM) have been employed to enhance CO2 adsorption capability of layered double hydroxide (LDH), there remains an urgent necessity to identify more cost-effective and efficient PCM alternatives. Herein, alkali metal nitrates ((Li0.3Na0.18K0.52)NO3, hereafter referred to as LiNaK) modified layered double hydroxide (LDH)/carbon molecular sieve (CMS) composite (LiNaK-LDH/CMS) as promising adsorbents for CO2 capture was reported. The effects of CMS addition and nitrate loading, the calcination and adsorption temperature, as well as the cycling stability were investigated systematically. The results revealed that the CO2 capture capacity of the LiNaK-modified layered double oxide (LDO)/CMS composite (30 mol%LiNaK-LDO/CMS15%)-incorporating with 15 wt% CMS addition and 30 mol% nitrate loading-achieved a remarkable CO2 adsorption capacity of 1.32 mmol/g at 300 °C due to the synergetic interactions between CMS and nitrate; this represents nearly a sevenfold enhancement compared to initial LDO performance. Moreover, the 30 mol%LiNaK-LDO/CMS15% adsorbent also demonstrated commendable cyclic stability after ten adsorption cycles, retaining over 85 % of its initial adsorption capacity. Based on both obtained adsorption performance and characterization data from the adsorbents, a pre-adsorption enhancing CO2 intermediate-temperature adsorption mechanism over LiNaK-LDH/CMS composite through air calcination processes. This study significantly advances LDH-based adsorbent for future research into CO2 intermediate-temperature adsorption.

Post-crosslinking knitting strategy for triazine-functionalized ionic hypercrosslinked polymers: Enhanced CO2 adsorption and conversion

Pore engineering has gained significant recognition as a pivotal strategy to tailor the structure and functionality of porous materials. In this study, a post-crosslinking knitting strategy was employed to fabricate a series of triazine-functionalized ionic hypercrosslinked polymers (IHCPs) using low specific surface area ionic polymers as precursors and external crosslinkers α,α′-dichloro-p-xylene (DCX) and α,α′-dibromo-p-xylene (DBX) through the Friedel Crafts alkylation reaction. This post-crosslinking knitting methodology increases the specific surface area of the resulting IHCPs, leading to enhanced CO2 adsorption capabilities (reaching 1.92 mmol·g−1 at 1 bar and 273 K), enhanced a remarkable 5.6-fold increase in CO2 uptake compared to the original ionic polymers. Of particular interest, inclusion of –NH– groups in PTA-2-DBX exhibits a synergistic catalytic effect facilitated by hydrogen bonding interactions that enable efficient conversion of CO2 into various cyclic carbonates under solvent- and cocatalyst-free conditions with yields exceeding 99 %. Furthermore, PTA-2-DBX demonstrates excellent recyclability while maintaining its activity even after five consecutive cycles. This study offers an effective approach for modulating pores in ionic polymers while highlighting the promising applications of triazine-functionalized IHCPs as dual-functional materials for both CO2 capture and conversion.

Development of Ce-doped NH2-UiO-66(Zr) photocatalysts for efficient CO2 reduction in an aqueous system

A series of bimetallic NH2-UiO-66(Zr/Ce) catalysts with varying Zr/Ce molar ratios were synthesized using a straightforward solvothermal method. Among the tested samples, NH2-UiO-66(Zr/Ce1:1) demonstrated superior performance, attributed to its optimized electronic structure, enhanced CO2 adsorption capacity, and efficient separation of photogenerated electron-hole pairs, outperforming the NH2-UiO-66(Zr) variant. The NH2-UiO-66(Zr/Ce1:1) exhibited a bandgap of 2.67 eV, CO2 adsorption capacity of 65.85 cm3/g, and a photocurrent density of 0.43 μA·cm−2. This catalyst achieved achieving a CO production rate of 30.04 μmol·g−1·h−1, representing a 1.66-fold improvement over NH2-UiO-66(Zr), with CO selectivity increasing from 95.2 % to 97.2 %. The results underscore the efficacy of Zr/Ce bimetallic NH2-UiO-66 for CO2 reduction, highlighting the potential of structural modifications in NH2-UiO-66 to enhance photocatalytic performance. This study provides valuable insights into the design and development of advanced catalysts for efficient and sustainable CO2 reduction.

Multi-species defect engineering synergistic localized surface plasmon resonance boosting photocatalytic CO2 reduction

Inadequate charge carrier kinetics and a scarcity of active sites still challenge photocatalytic CO2 reduction reaction (CO2RR). We exploit the synergy between multi-species defect engineering and the localized surface plasmon resonance (LSPR) effect in Bi/BiV1-mO4-m to address these limitations. Theoretical calculations show that V and O defects collectively modulate the work function of BiVO4, which induces hot electrons to transfer from Bi nanoparticles to BiV1-mO4-m. These electrons are then captured by O defects, confirmed by femtosecond transient absorption spectroscopy. Electron density is significantly increased at the O defects, enhancing CO2 adsorption and establishing it as a new reaction site. Bi/BiV1-mO4-m achieves photocatalytic CO2RR in pure water; Bi/BiV1-mO4-m achieves direct solar-driven photocatalytic CO2RR with a CO yield of 501 μmol/g/h under concentrated sunlight.

Transition-Metal-Doped CeO2 for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO2 Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO2) catalysts (M = Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO2 reduction. Temperature-programmed desorption (TPD) was conducted to study the CO2 binding strength on doped CeO2 surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO2 dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO2 adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i.e., CO2 conversion higher than 56% at 600 °C and 100% selectivity to CO. Cu exhibits 100% selectivity to CO but low CO2 conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO2 based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO2 adsorption energies for strong interaction with the surface to promote C-O bond scission.

Reversed Mg-Based Smectites: A New Approach for CO2 Adsorption

Addressing climate change requires transitioning to cleaner energy sources and adopting advanced CO2 capture techniques. Clay minerals are effective in CO2 adsorption due to their regenerative properties. Recent advancements in nanotechnology further improve their efficiency and potential for use in carbon capture and storage. This study examines the CO2 adsorption properties of montmorillonite and saponite, which are subjected to a novel microwave-assisted acid treatment to enhance their adsorption capacity. While montmorillonite shows minimal changes, saponite undergoes significant alterations. Furthermore, the addition of silica pillars to smectites results in a new nanomaterial with a higher surface area (653 m2 g−1), denoted as reversed smectite, with enhanced CO2 adsorption capabilities, potentially useful for electrochemical devices for converting captured CO2 into value-added products.

Enhanced post-combustion CO2 capture and direct air capture by plasma surface functionalization of graphene adsorbent

Graphene has enormous potential to capture CO2 due to its unique properties and cost-effectiveness. However, graphene-based adsorbents have drawbacks of lower CO2 adsorption capacity and poor selectivity. This work demonstrates a one-step rapid and sustainable N2/H2 plasma treatment process to prepare graphene-based sorbent material with enhanced CO2 adsorption performance. Plasma treatment directly enriches amine species, increases surface area, and improves textural properties. The CO2 adsorption capacity increases from 1.6 to 3.3 mmol/g for capturing flue gas, and from 0.14 to 1.3 mmol/g for direct air capture (DAC). Importantly, the electrothermal property of the plasma-modified aerogels has been significantly improved, resulting in faster heating rates and significantly reducing energy consumption compared to conventional external heating for regeneration of sorbents. Modified aerogels display improved selectivity of 42 and 87 after plasma modification for 5 and 10 min, respectively. The plasma-treated aerogels display minimal loss between 17% and 19% in capacity after 40 adsorption/desorption cycles, rendering excellent stability. The N2/H2 plasma treatment of adsorbent materials would lower energy expenses and prevent negative effects on the global economy caused by climate change.

Sulfur-doped Bi2O2CO3 nanosheet for enhanced visible-light-driven photocatalytic CO2 reduction to CO with ultra-high selectivity.

The photocatalytic reduction of carbon dioxide (CO2) has emerged as a compelling strategy for the conversion of renewable energy. However, the expeditious recombination of photogenerated charge carriers and the inadequate light absorption capabilities are currently predominant challenges. Herein, we developed a facile hydrothermal approach to synthesize a sulfur doped Bi2O2CO3 nanosheet with a tunable energy band structure designed to enhance visible light absorption. Our findings indicate that the incorporation of sulfur into the catalytic sites induces an electron sink effect, significantly improving the separation efficiency of photogenerated charge carriers. Consequently, this sulfur-doped Bi2O2CO3 catalyst exhibits a remarkable carbon monoxide (CO) yield of 16.64 μmol gcat-1 h-1 with nearly 100 % selectivity under illumination ranging from 420 to 780 nm. Through in-situ characterization techniques and theoretical calculations, it was revealed that sulfur-coordinated bismuth sites greatly enhance CO2 adsorption and decrease the energy barrier for critical intermediates formation (*COOH), thus selectively driving the reaction towards CO production. This work not only advances our understanding of mechanisms underlying photocatalytic reduction of CO2 on sulfur-doped bismuth-based catalysts but also sets a precedent for developing sophisticated photocatalytic systems for enhanced photoreduction reactions.

Enhancing CO2 adsorption performance of cold oxygen plasma-treated almond shell-derived activated carbons through ionic liquid incorporation

To enhance the CO2 adsorption of almond shell-derived activated carbon (AC) samples treated with cold oxygen plasma, the samples were impregnated with cholinium-amino acid ionic liquids ([Cho][AA] ILs) using the vacuum-assisted impregnation method. The physicochemical and textural properties of the resulting composites (ILs@AC) were characterized using various techniques, including Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) spectroscopy, and Brunauer-Emmett-Teller (BET) surface area measurement. The CO2 adsorption performance of the samples was evaluated using a quartz crystal microbalance (QCM) over a temperature range of 288.15–308.15 K and gas pressures up to 1 bar. The IL@AC composite materials exhibited notably improved CO2 adsorption capacities compared to pristine AC. The CO2 adsorption isotherms onto the IL@AC composite samples closely conformed to the Langmuir isotherm model, indicating the dominant involvement of strong intermolecular interactions, particularly driven by amine functionalities. Meanwhile, the results revealed that [Cho][His]@AC showed lowered CO2 adsorption capacity compared to [Cho][Pro]@AC and [Cho][Gln]@AC. Among the studied ionic liquids, [Cho][Pro]@AC showed the highest absorption capacity (2.332 mmol·g−1 at 288 K and 1 bar). This was due to the obstruction of internal pores within the AC structure caused by excessive amine incorporation into its porous framework. In the meantime, for a deeper insight into the impregnation process of ILs onto the AC surfaces and their potential interactions with CO2 molecules, we conducted density-functional theory (DFT) calculations using the ωB97XD/6-31 + G(d,p) method. The calculated interaction energies, ranging from − 1.19 to − 1.44 eV, along with calculated quantum chemical descriptors, indicated a notable stabilization of IL species on the AC surfaces, with high affinity toward CO2 molecules.

Impact of aminopropyl units on physisorption in mesostructured silica is larger for CH4 than CO2 and depends on pore curvature

Mesoporous silica-based materials attract great interest for diverse applications, including capture, storage, and catalysis due to their large surface area, uniform pore size distribution, and customizable surface. The regular 2D hexagonal pore symmetry of MCM-41 makes it an ideal model. Amine groups are introduced to enhance CO2 adsorption, but the interplay of factors influencing overall performance, including pore size, remains unclear. This computational study explores the physisorption of CO2 and CH4, shedding light on the microscopic details underlying adsorption capacity and selectivity. Three aminopropyl-functionalized MCM-41 models with different pore size are compared through Grand Canonical Monte Carlo and Molecular Dynamics simulations. Aminopropyl chains affect CO2 adsorption, but its affinity for the preserved silanol groups is larger. In addition, the competitive interaction between amine and silanol groups emerged, and it is pore curvature dependent. Surprisingly, CH4 physisorption is influenced even more by surface functionalization. Results show a non-monotonic trend as a function of pore size. Local density of the alkyl chains plays the major role. Overall, the intermediate pore size demonstrates the best performance, thanks to the balance among the various effects. The study emphasizes the importance of understanding the interplay between material texture and gas interactions to optimize adsorption performance.

Combined experimental and grand canonical Monte Carlo simulation study of CO2 capture in nitrogen and sulfur co-doped biochar derived from biowaste: Cost analysis, kinetics, and equilibrium

Nitrogen (N) and sulfur (S) co-doped biochar was produced from an agricultural waste. Heat treatment was combined with the use of dopants including thiourea, CO2, and air. The results show that the modified N and S co-doped biochar with the use of CO2 gas agent at 1123 K for 2 hr in the modification process, had the highest CO2 adsorption capacity of 4.36 and 3.05 mmol/g at 273 and 298 K at 1 bar among others in literature even it had lower surface area or pore volume. This is due to the containing of N and S on the solid surface and superior pore size of 1.0 nm. Moreover, the modified biochar had superior kinetics and CO2/N2 selectivity and was more economical than its unmodified biochar. To support experimental observation and better understand individual characteristics of functionalized carbons, a grand canonical Monte Carlo simulation was carried out to systematically illustrate the effect of N and S functional groups, pore size and pore volume on CO2 adsorption. The surface chemistry was the minor factor and played the key role in CO2 adsorption capacity at low pressures until it became saturated by adsorbate molecules at 0.3 bar. S was stronger than N for enhanced CO2 adsorption capacity. Whereas the pore size was the major factor in both low and moderate pressures (< 23 bar). The optimum pore size was found in a range of 0.66⎼4.0 nm which was pressure-dependent. The pore volume became the main factor at higher pressures (> 23 bar).

Eutectic molten salt assisted fabrication of microporous biochar for greenhouse gases adsorption

The utilization of eutectic molten salt technology has emerged as a prominent area of investigation aimed at fabricating a novel carbon material sorbent based on biomass wastes. The adsorption mechanism on CO2 adsorption remains inadequately elucidated as well. Herein, the biochar fabrication process involving eutectic molten salt method at intermediate-low temperature of 550 °C was successfully achieved and investigated in detail. The impacts of molten salt composition, monomer salt’s anion and cation, and pyrolysis parameters were firstly studied on the resulting microporous biochar of 1.8 nm pore diameter and 975 m2/g surface area. The optimized conditions are 550 °C, 15 °C min−1 ramp rate, 120 min holding time, Na+ cation, NO3– anion, and ternary salt KCl/NaNO3/Na2SO4 of 32.5/30.4/37.1. The efficient adsorbent exhibited abundant micropores and a substantial specific surface area, leading to enhanced CO2 adsorption quantity of 3.75 mmol/g (the calculated capacity is up to 4.54 mmol/g) at pressure state of 1.6 MPa. Investigation into key factors, adsorption kinetics, and adsorption isotherm revealed that CO2 capture by optimal adsorbent predominantly stemmed from micropore filling, van der Waals forces, hydrogen bonds, and Lewis acid-base interactions. This research contributes novel insights into the utilization of biochar adsorbents for CO2 capture in the realm of industry.

Examination of the use of binderless zeolite blend as backfill materials to enhance CO2 adsorption in coal mine working face

The release and accumulation of CO2 in the working face of the coal mine is a major safety concern and requires an effective means to avoid the incidence of the mine. This present study therefore sought to develop a self-CO2 adsorbing backfill (SCAB) material to remove CO2 from the working environment, and simultaneously mitigate the movements of the surrounding rock layers. SCAB was formulated using coal mine solid waste activated with an alkali activator, and binderless 4 A zeolite was embedded in the backfill body. The total CO2 adsorption capacity was investigated using a CO2 flow-through method under ambient pressure and temperature conditions. The adsorption plateau was found in stages II and III respecting the predetermined curing time and zeolite contents. The maximum adsorption capacity was 143.8 mg-CO2/g-SCAB, resulting in an increase of up to 82 % in UCS compared to reference samples. The underlying mechanism was discovered in morphological analyses.1) The well distribution of zeolite in the SCAB body provided as diffusive pathways and adsorption sites for CO2 after standard curing. 2) The adsorbed CO2 underwent a desorption stage when the CO2 concentration decreased and reacted to the cementitious matrix of the SCAB body. 3) More CaCO3 crystals were generated and filled in the micro spaces of the SCAB body, which contributed to an increase in compressive strength. This study developed an effective approach to remove CO2 gas from the working face of the coal mine during backfilling. Adsorbed CO2 improved the strength of the material, provided as a novel multi-function backfill mining for sustainable green coal mining technology.

Understanding the influences and mechanism of water vapor on CO2 capture by high-temperature Li4SiO4 sorbents

Li4SiO4 sorbent attracts wide attention due to its high and stable CO2 adsorption. However, the process of CO2 capture is significantly affected by various impurities under the circumstance of industrial applications, and water vapor is one such impurity that needs to be well studied. Herein, we aim to evaluate the effect of water vapor on physicochemical characteristics of Li4SiO4-based sorbents during cyclic CO2 adsorption and desorption and to understand the action mechanism of H2O molecules on CO2 adsorption by Li4SiO4. Reaction tests show that water vapor can significantly enhance CO2 adsorption performance of sorbents, but the promotion effect varies with the different presence of water vapor during reactions. Material characterization and DFT calculation reveal that although the presence of water vapor leads to deterioration of internal pore structure of the sorbent, H2O molecule will form OH– on the surface of Li4SiO4 and further react with CO2 to generate HCO3–, thus the adsorption energy with water vapor presenting is increased with an observation of promoted CO2 adsorption.

Unveiling the role of silicon in boosting electrochemical carbon dioxide reduction via carbon nanotubes@bismuth silicates

Electrochemical CO2 reduction reaction (CO2RR) is one of the most attractive measures to achieve the carbon neutral goal by converting CO2 into high-value chemicals such as formate. Si in Bi silicates is promising to enhance CO2 adsorption and activation due to its strong oxygenophilicity. Whereas, its role in boosting CO2RR via the cheap Bi-based catalysts is still not clear. Herein, we design CNT@Bi silicates catalyst, demonstrating the highest FEHCOOH of 96.3 % at −0.9 V vs. reversible hydrogen electrode with good stability. Through X-ray photoelectron spectroscopy (XPS), in-situ Attenuated Total Reflectance-Fourier Transform Infrared (In-situ ATR-SEIRAS) experiments, and Density Functional Theory (DFT) calculations, the role of Si in Bi silicates was unveiled: tuning the electronic structure of Bi, weakening the Bi-O bond, and strengthening electron transfer from Bi to CO2, thereby promoting the generation of CO2*− and *OCHO intermediates. Additionally, carbon nanotubes (CNTs) promote not only the conductivity but also the generation of abundant oxygen vacancies in CNT@Bi silicates evidenced by the electron transfer from CNT to Bi silicates from XPS results. Further, the CNT@Bi silicates endows it with the highest electrochemical activation area. These findings suggest the effectiveness of Si in Bi silicates and structure tuning to design highly selective CO2RR catalyst for HCOOH production.

Negative Reaction Order for CO during CO2 Electroreduction on Au.

The potential-dependent negative fractional reaction orders with respect to the CO partial pressures were measured for CO2 electroreduction (CO2R) on Au under mass-transfer-controlled conditions using a rotating ring-disk electrode setup. At high overpotentials, the CO reaction order approaches -1 due to enhanced CO adsorption on Au, which is supported by kinetic analysis and density functional theory (DFT) simulations. This work illustrates that the CO site-blocking effect cannot be ignored, even on a weak CO-binding metal such as Au in the electrochemical environment. The CO site-blocking effect can greatly hamper the activity and the selectivity of the CO2R to CO. This observation enriches the current mechanistic understanding of the CO2R and could have significant implications not only in the theoretical modeling of the CO2R but also in the evaluation of intrinsic CO2R activity at practical current density and high conversion conditions.

CO2 adsorption on a K-promoted MgO surface: A DFT theoretical study

The primary cause of global warming is the emission of greenhouse gases such as CO2. So reducing CO2 emissions is vital. This paper investigates the impact of the atom K as a promoter of MgO on the CO2 adsorption properties using the DFT theoretical computational method. By analyzing the adsorption energy, bader charge as well as the density of states and COHP, it was found that K-promoting the MgO (100) surface resulted in a redistribution of charge on the MgO surface and enhanced CO2 adsorption compared to the pure MgO surface. The presence of K atoms causes orbital hybridization among O (CO2) and Mg atoms, O (CO2) atoms and K atoms, and the surface O atoms and K atoms. These interactions lead to the formation of (MgO)Mg-O(CO2) and (CO2)O−K−O(MgO) chemical bonds. The adsorption energy of CO2 on the K-promoted MgO surface increased from -0.32 eV to -1.01 eV compared to the pure surface, enhancing the adsorption of CO2.

Vacancy-Engineered 1D Nanorods with Spatially Segregated Dual Redox Sites for Visible-Light-Driven Cooperative CO2 Reduction.

Cooperative CO2 photoreduction with tailored organic synthesis offers a potent avenue for harnessing concurrently generated electrons and holes, facilitating the creation of both solar fuels and specialized chemical compounds. However, controlling the crystallization and morphologies of metal-free molecular nanostructures with exceptional photocatalytic activities toward CO2 reduction remains a significant challenge. These hurdles encompass insufficient CO2 activation potential, sluggish multielectron processes, delayed charge-separation kinetics, inadequate storage of long-lived photoexcitons, unfavorable thermodynamic conditions, and the precise control of product selectivity. Here, melem oligomer 2D nanosheets (MNSs) synthesized through pyrolysis are transformed into 1D nanorods (MNRs) at room temperature with the simultaneous engineering of vacancies and morphology. Transient absorption spectral analysis reveals that vacancies in MNRs trap charges, extending charge carrier lifetimes. Additionally, carbon vacancies enhance CO2 adsorption by increasing amine functional centers. The photocatalytic performance of MNRs for CO2 reduction coupled with benzyl alcohol oxidation is approximately ten times higher (CH3OH and aromatic aldehyde production rate 27 ± 0.5 and 93 ± 0.5 mmol g-1 h-1, respectively) than for the MNSs (CH3OH and aromatic aldehyde production rate 2.9 ± 0.5 and 9 ± 0.5 mmol g-1 h-1, respectively). The CO2 reduction pathway involved the carbon-coordinated formyl pathway through the formation of *COOH and *CHO intermediates, as mapped by in situ Fourier-transform infrared spectroscopy. The superior performance of MNRs is attributed to favorable energy-level alignment, enriched amine surfaces, and unique morphology, enhancing solar-to-chemical conversion.

Micro-Structure Engineering in Pd-InOx Catalysts and Mechanism Studies for CO2 Hydrogenation to Methanol.

Significant interest has emerged for the application of Pd-In2O3 catalysts as high-performance catalysts for CO2 hydrogenation to CH3OH. However, precise active site control in these catalysts and understanding their reaction mechanisms remain major challenges. In this investigation, a series of Pd-InOx catalysts were synthesized, revealing three distinct types of active sites: In-O, Pd-O(H)-In, and Pd2In3. Lower Pd loadings exhibited Pd-O(H)-In sites, while higher loadings resulted in Pd2In3 intermetallic compounds. These variations impacted catalytic performance, with Pd-O(H)-In catalysts showing heightened activity at lower temperatures due to the enhanced CO2 adsorption and H2 activation, and Pd2In3 catalysts performing better at elevated temperatures due to the further enhanced H2 activation. In situ DRIFTS studies revealed an alteration in key intermediates from *HCOO over In-O bonds to *COOH over Pd-O(H)-In and Pd2In3 sites, leading to a shift in the main reaction pathway transition and product distribution. Our findings underscore the importance of active site engineering for optimizing catalytic performance and offer valuable insights for the rational design of efficient CO2 conversion catalysts.