Coadsorption Of H2O Research Articles

Classification of adsorbates in scanning tunneling microscopy images of Fe3O4(111) surfaces exposed to water and carbon monoxide

Understanding the structure of catalyst surfaces with adsorbed molecules is key to improving catalyst design. Scanning tunneling microscopy (STM) allows the observation of adsorption states and sites and provides insights into diffusion and desorption processes; however, the presence of multiple types of molecules on the surface presents challenges such as the identification of species and verification of reaction progress, particularly at room temperature or higher. In this study, we develop a protocol for the height classification analysis of STM images using the Watershed algorithm. This method is applied to a system involving the co-adsorption of H2O and CO on the Fe3O4(111) surface, which represents the beginning of the water-gas shift reaction. Water molecules and dissociated OH species were identified in STM images of the Fe3O4(111) surface following the adsorption of water. Furthermore, gradual changes in the types of surface species were observed upon exposure of the surface to CO, indicating reaction progression. Our observations suggest that CO may react with molecular water rather than with dissociated OH on Fe sites. Despite its simplicity, the height classification analysis effectively identifies changes in the adsorbates on the catalyst surface. This method can be extended to other catalyst surfaces with adsorbed gasses.

Mechanistic insight into electrochemical CO2 reduction on Mo single-atom catalyst and its hydrate: A computational study

By using density functional theory calculation, we investigated the CO2 reduction to CH4 on molybdenum-doped graphene (Mo@Gra) and identified two major paths from the HCOO* and COOH* intermediates with different onset potential. Both HCOO* and COOH* would continent hydrogenating to CH4 by an eight proton-electron coupling transfer process via HCOO path and COOH path. By the HCOO path, the formation of HCOO* is exergonic and the potential determining step (PDS) is OH* to H2O* by an endergonic process of 0.70 eV. On the other hand, the formation of COOH* from CO2* is endergonic with the same PDS and a limiting potential (UL) of –0.70 V. In addition, nitrogen coordinated Mo-graphene (Mo@3N-Gra) also illustrated for CO2 reduction and the corresponding UL is found to be –1.88 V. In addition, we also explore the mechanisms of CO2 reduction on the water pre-adsorption surface for realistic experiments. The UL required to overcome was reduced to –0.25 V for 3H2O*Mo@Gra with three H2O co-adsorption environment, suggesting the catalytic performance can be enhanced by water promotion effect. Two structures of hydrated structures, 2H2O*OH*Mo@3N-Gra and 3H2O*Mo@3N-Gra, were selected for stimulate realistic experiments. Compared to the Mo@3N-Gra catalyst, the UL reduces to –0.48 and –0.70 V for 2H2O*OH*Mo@3N-Gra and 3H2O*Mo@3N-Gra, respectively. Although, Mo-N doped graphene has better CO2 capture ability and selectivity, it needs more onset potential to produce CH4. Our calculations demonstrated that the electrocatalytic performance can be enhanced by the hydration effect.

Effect of Co-Adsorbed Guest Adsorbates on the Separation of Ethylene/Ethane Mixtures on Metal-Organic Frameworks with Open Metal Sites.

Direct determination of the equilibrium adsorption and spectroscopic observation of adsorbent-adsorbate interaction is crucial to evaluate the olefin/paraffin separation performance of porous adsorbents. However, the experimental characterization of competitive adsorption of various adsorbates at atomic-molecular level in the purification of multicomponent gas mixtures is challenging and rarely conducted. Herein, solid-state NMR spectroscopy is employed to examine the effect of co-adsorbed guest adsorbates on the separation of ethylene/ethane mixtures on Mg-MOF-74, Zn-MOF-74 and UTSA-74. 1H MAS NMR facilitates the determination of equilibrium uptake and adsorption selectivity of ethylene/ethane in ternary mixtures. The co-adsorption of H2O and CO2 significantly leads to the degradation of ethylene uptake and ethylene/ethane selectivity. The detailed host-guest and guest-guest interactions are unraveled by 2D 1H-1H spin diffusion homo-nuclear correlation and static 25Mg NMR experiments. The experimental results verify H2O coordinated on open metal sites can supply a new adsorption site for ethylene and ethane. The effects of guest adsorbates on the adsorption capacity and adsorption selectivity of ethylene/ethane mixtures are in the following order: H2O>CO2>O2. This work provides a direct approach for exploring the equilibrium adsorption and detailed separation mechanism of multicomponent gas mixtures using MOFs adsorbents.

Excitonic Effects of the Excited-State Photocatalytic Reaction at the Molecule/Metal Oxide Interface.

Excitonic effects caused by the Coulomb interaction between electrons and holes play a crucial role in photocatalysis at the molecule/metal oxide interface. As an ideal model for investigating the excitonic effect, coadsorption and photodissociation of water and methanol molecules on titanium dioxide involve complex ground-state thermalcatalytic and excited-state photocatalytic reaction processes. Herein, we systemically investigate the excited-state electronic structures of the coadsorption of H2O and CH3OH molecules on a rutile TiO2(110) surface by linear-response time-dependent density functional theory calculations and probe the reaction path for generating HCOOH or CO2, from ground-state and excited-state perspectives. The reaction barriers in excited-state calculations are significantly different from those in ground-state calculations during three processes, with the largest decrease being 0.94 eV for the Ti5c-O-CH2-O-Ti5c formation process.

Composition-dependent morphologies of CeO2 nanoparticles in the presence of Co-adsorbed H2O and CO2: a density functional theory study.

Catalytic activity is affected by surface morphology, and specific surfaces display greater activity than others. A key challenge is to define synthetic strategies to enhance the expression of more active surfaces and to maintain their stability during the lifespan of the catalyst. In this work, we outline an ab initio approach, based on density functional theory, to predict surface composition and particle morphology as a function of environmental conditions, and we apply this to CeO2 nanoparticles in the presence of co-adsorbed H2O and CO2 as an industrially relevant test case. We find that dissociative adsorption of both molecules is generally the most favourable, and that the presence of H2O can stabilise co-adsorbed CO2. We show that changes in adsorption strength with temperature and adsorbate partial pressure lead to significant changes in surface stability, and in particular that co-adsorption of H2O and CO2 stabilizes the {100} and {110} surfaces over the {111} surface. Based on the changes in surface free energy induced by the adsorbed species, we predict that cuboidal nanoparticles are favoured in the presence of co-adsorbed H2O and CO2, suggesting that cuboidal particles should experience a lower thermodynamic driving force to reconstruct and thus be more stable as catalysts for processes involving these species.

Direct air CO2 capture using coal fly ash derived SBA-15 supported polyethylenimine

Designing an amine modified silica derived from coal fly ash (CFA) towards direct air CO2 capture (DAC) provides an economic way to manage increasing atmospheric CO2 concentration utilizing solid wastes. In this work, rod-like SBA-15 (SBA-15-R) and wheat-like SBA-15 (SBA-15-W) with distinct pore lengths are synthesized from CFA by controlling the synthesis conditions and then modified by PEI via the wet impregnation method. Their CO2 adsorption behaviors under sub-ambient conditions are investigated to explore their feasibility under aggressive conditions. The adsorbents with various silica morphologies exhibit distinctive CO2 adsorption performance under ambient and sub-ambient conditions. At 35°C under dry conditions, the CO2 adsorption capacity increases with amine loading. The CO2 adsorption capacity (qe) of SBA-15-W-PEI with long channels reaches the highest qe of 1.92 mmol/g with 70 wt.% PEI loading due to a large amount of strong chemisorption sites. Under the sub-ambient conditions (-20°C, 400 ppm), SBA-15-R-PEI30 with short channels having weaker CO2 diffusion resistance exhibits promising CO2 uptake of 0.83 mmol/g. These findings indicate that the ultra-dilute CO2 adsorption at ambient temperature requires an adsorbent with large amounts of adsorption sites, whereas the adsorbents for cold temperature application should reconcile amine loading with CO2 diffusion resistance inside pores. The co-adsorption of H2O and CO2 significantly improves CO2 capacity from 0.83 mmol/g and 1.92 mmol/g to 1.81 mmol/g and 3.48 mmol/g for SBA-15-R-PEI30 (-20°C, 400 ppm) and SBA-15-W-PEI70 (35°C, 400 ppm), respectively. Furthermore, the CFA derived SBA-15-PEI shows good cyclic stability during five consecutive TSA cycles. Preparing the amine silica adsorbents from coal fly ash potentially reduces the adsorbent cost of DAC devices. Moreover, the systematic exploration of amine silica adsorbents at a wide range of temperatures guides the design of high-performance CO2 adsorbents employed under various climatic conditions.

Design of Amine-Containing Nanoporous Materials for Postcombustion CO2 Capture from Engineering Perspectives.

ConspectusCarbon dioxide (CO2) capture and storage (CCS) is a means to enable the continued use of fossil fuels in the short term. In particular, postcombustion CO2 capture has attracted considerable attention because it can be retrofitted into existing power plants and industrial plants. Among various CO2 capture technologies, the absorption of CO2 using aqueous amines has been industrially employed for decades. However, such amine scrubbing technologies have inherent limitations of environmental and health concerns due to volatile amine loss, corrosion, and high energy demands for regeneration. To overcome these limitations, CO2 adsorption using solid adsorbents has emerged as a promising alternative due to its noncorrosiveness and low energy demand. Various amine-containing adsorbents have been synthesized and investigated for postcombustion CO2 capture. These materials are prepared by physically impregnating low-vapor-pressure amine polymers or by chemically grafting amines onto nanoporous materials. A wide variety of amine guests and nanoporous hosts (e.g., SiO2, Al2O3, zeolites, MOFs, and polymers) have been combined to develop advanced CO2 adsorbents.The design of CO2 adsorbents is a multifaceted puzzle that must ultimately consider integration with large-scale CO2 capture processes. Various engineering aspects need to be carefully considered. Unfortunately, a significant proportion of previous studies has primarily focused on the use of novel materials for improving the CO2 adsorption capacity. In this Account, we describe key challenges and solutions to develop energy-efficient and stable amine-containing adsorbents for postcombustion CO2 capture via temperature swing adsorption (TSA). We found that a high CO2 working capacity, often overemphasized in the literature, does not necessarily guarantee a low energy demand for CO2 capture. Suppressing coadsorption of H2O during the CO2 adsorption in humid flue gas is also a significant factor. Amine-containing adsorbents can be degraded through various pathways, including hydrothermal degradation of nanoporous hosts and chemical degradation of amine guests via urea formation and oxidation. To inhibit such degradation pathways, it is extremely important to properly design the nanoporous structures of the hosts and the molecular structures of the amine guests. By combining macroporous silica hosts, poly(ethylenimine) (PEI) functionalized with various alkyl epoxides, and phosphate-based oxidative stabilizers, we could synthesize adsorbents exhibiting low energy demands for CO2 capture and unprecedentedly high thermochemical stability under TSA conditions. The macroporous silica host synthesized by assembling fumed silica particles via spray-drying exhibited high hydrothermal stability and enabled uniform distribution of bulky amine polymers within its pores. The functionalization of PEI with alkyl epoxides converted its primary amines into hindered secondary amines, leading to a significant reduction in energy demand for TSA cycles and a remarkable improvement in long-term stabilities. The oxidative stability of amines could be drastically improved by adding phosphate metal-binding reagents, which can poison ppm-level metal impurities that catalyze amine oxidation. The present discussions will provide important insights into designing practical adsorbents for CO2 capture from engineering perspectives.

Adsorption, sensing and catalytic properties of the pristine C24N24 nanocage to small gas molecules: A DFT-D3 investigation

Adsorption of small gases (H2, N2, O2, CO, NO, CO2, N2O, NO2, H2S, H2O, SO2, NH3, CH4, C2H4, and C2H2) on the C24N24 (noted by CNNC) was studied using the B3LYP-D3/6-31G(d,p) method. Adsorption energies and thermodynamics of all the studied gases adsorbed onto the CNNC and NBO charge analysis of their adsorption structures were obtained. Adsorption ability of the CNNC on gases was in order: H2O (ΔEads = −25.06 kcal/mol) > SO2 (ΔEads = −11.84 kcal/mol) > NH3 > C2H2 > H2S > N2O > CO2 > NO2 > O2 > NO > C2H4 > CH4 > SO2 > CO > H2 > N2. The high adsorption strength The CNNC was suggested to be a storage material for all studied gases and a potential to be a sensing material for NO. On the CNNC surface, co-adsorption of H2O and SO2 conversion to H2CO3 assumed as Langmuir-Hinshelwood mechanism and co-adsorption of H2O and CO2 co-adsorbed on the CNNC surface was assumed as Langmuir-Rideal mechanism were found. The H2O physisorption over C–N bond of the CNNC to form dissociative chemisorption on C–N bond via transition-state barrier was found.

Structure and Stability of (CeO2)n0,±1 (n=1-3) Clusters towards the Adsorption and Co-adsorption of CO and H2O from DFT Study

Stability of (CeO2)n0,±1(n=1-3) clusters and adsorption of CO and H2O as well as co-adsorption of CO/H2O species on the same clusters are studied using M06L/def2TZVPP level of theory. We have considered this study as this fundamental investigation may be a stepping stone for future investigation of water gas shift reaction (WGSR). Global/local reactivity descriptors and natural bonding orbital (NBO) analysis are also reported for all the clusters for understanding the nature of adsorption of CO and H2O molecules. From theoretical analysis, we have explored all the possible outcomes for CO/H2O adsorption and co-adsorption on (CeO2)n0,±1 (n=1-3) clusters.

(Digital Presentation) H2o and CO2 Surface Contamination of the Lithium Garnet Li7La3Zr2O12 Solid Electrolyte

Garnet-type Li7La3Zr2O12 is a promising solid-state electrolyte for lithium (Li)-ion batteries, and it readily reacts with H2O and CO2 when exposed to ambient air. Such reactions form a contamination layer on Li7La3Zr2O12, which is detrimental to the battery operation. Here, using first-principles calculations, we investigate the adsorption and reactions of H2O and CO2 on a Li7La3Zr2O12 surface. We show that H2O reacts through the exchange of protons and Li+ and produces metal hydroxide species. At high H2O coverage, half of the H2O molecules dissociate, while the other half remain intact. CO2 reacts with the Li7La3Zr2O12 surface directly to produce carbonate species. We clarify that the individual reactions of H2O and CO2 with Li7La3Zr2O12 are thermodynamically more favorable than the co-adsorption of H2O and CO2. Finally, we demonstrate that low temperature and high partial pressure promote the reactions of H2O and CO2 with Li7La3Zr2O12. Our study provides guidance on processing conditions for the garnet Li7La3Zr2O12 solid electrolyte to minimize its surface contamination.

Study on CO2 capture in humid flue gas using amine-modified ZIF-8

The CO2 adsorption performance of most adsorbents were inhibited by water vapor which is a ubiquitous component of flue gas. It is critical to find an adsorbent with long-term stability in the presence of water vapor. In this study, both theoretical and experimental study were carried out to investigate the CO2 capture capacity in humid flue gas of PEI impregnated ZIF-8. Grand canonical Monte Carlo (GCMC) simulation was performed to calculate the co-adsorption of CO2 and H2O on ZIF-8-PEI. The simulation result indicates that water vapor has no negative impact on CO2 adsorption of ZIF-8-PEI. Then, ZIF-8 with different PEI weight was synthesized and characterized. It is found that ZIF-8 with 30 wt.% PEI not only shows the highest CO2 uptake of 1.4 mmol/g in dry condition but also exhibits excellent CO2/N2 separation performance. More important is that the adsorption capacity of ZIF-8-PEI30% was improved to 1.7 mmol/g when the adsorbents were imposed to humid flue gas with 50% relative humidity (RH). Moreover, it only shows a slight decrease after 50 adsorption/desorption cycles. Hence, water plays an excellent promoter role in CO2 capture of ZIF-8-PEI30%, and it is a promising adsorbent to be used in humid flue gas.

Structure, Stability and Reactivity of (Ceo2)N0,±1 (N=1, 2) Clusters Towards the Adsorption and Co-Adsorption of Co and H2o from Dft Study

Structure, Stability and Reactivity of (Ceo2)N0,±1 (N=1, 2) Clusters Towards the Adsorption and Co-Adsorption of Co and H2o from Dft Study

Enhanced adsorption of CO2 on cellulose and chitosan surface by H2O Co-adsorption

Adsorption of CO2 on biopolymers such as cellulose (CELL) and chitosan (CS) attracts researchers’ interest, in particular, the aerogel formation with high surface area and unique physical properties. In this work, we studiedthe molecular adsorption of CO2 molecule on the CELL and CS surfaces by performing density functional theory (DFT) calculations, using dimeric and trimeric structures as model compounds. The structure of the individual CELL and CS along with the molecular adsorbed CO2 systems CELLCO2 and CSCO2 were investigated using B3LYP/6-311++G(d,p) level of theory. The interaction energy of CELLCO2 indicated a weak physical adsorption process, where CSCO2 showed higher binding energies. The co-adsorption of CO2 and H2O on CELL and CS surfaces was also investigated. The results showed that H2O stabilized the adsorption of the CO2 on CELL and CS surface through hydrogen bond (HB), where the adsorption energies increased in the presence of the H2O molecule. The stability of CELLCO2 and CSCO2 was supported by an increase in the charge transfer process. This result highlighted the role of the humidity for the stabilization of CO2 on biopolymers surface.

Tensile strain induced surface reactions for co-adsorption of H2O and OH− on vacancy Al (111) surface

The strain and stress are important factors for influencing the performances of transition metal surface. The co-adsorption H2O and OH− on vacancy Al (111) surface under tensile strain conditions was investigated based on the density functional theory. We found that OH− can induce dissociation of H2O molecules, the dissociation phenomenon only occurs on three special configurations. The lattice distortion of vacancy Al surface is more sensitive to strain than the perfect surface, and the description of vacancy formation energy and surface energy is limited by the strain of each time. Although the strain cannot change the reaction path of H2O on the dissociated surfaces, it can reduce the energy barrier of the dissociation reaction and induce more stable adsorption of the reactants on the vacancy Al surface, promoting erosion of Al surface.

H2O and O2 co-adsorption on 3C-SiC (111) by first-principle calculations: The role of water in initial oxidation

First-principle calculations were employed to investigate the initial oxidation behaviors of CVD-SiC in wet oxygen. The H2O/O2 co-adsorption behaviors with different H2O/O2 molecular ratios and coverages on (3 × 3) 3C-SiC (111) surface were studied by geometry optimization and property calculation. The results showed that the OO bond in SiOO structure had higher bond energy than that in Si-O-O-H structure, indicating the weaker bond energy of OO bond in the formed hydroperoxyl. First-principle molecular dynamic (FPMD) simulations confirmed that the formation of hydroperoxyl as an intermediate was feasible during the dissociation of molecular oxygen, which played an important role in O2 activation. The static calculation results indicated that the formation of hydroperoxyl needed to experience a lower activation energy barrier (0.35 eV), which demonstrated more likely occurrence than the direct dissociation of molecular oxygen. In brief, the introduction of molecular water could enhance the oxidation rate of 3C-SiC in initial stage by the formation of hydroperoxyl. This work revealed the initial oxidation mechanism of 3C-SiC (111) in wet oxygen and the role of water in initial oxidation, which could also provide a new view to explain the accelerated oxidation rate of SiC in wet oxygen.

Robust metal-organic frameworks for dry and wet biogas upgrading

Biofuels are considered as viable, sustainable and renewable alternatives to fossil fuels. One amongst them is biomethane which has emerged as one of the valuable contributors in facilitating the essential transition towards green energy sources. Industrially, anaerobic digestion of biomass results in the production of crude biogas that comprises mainly of methane (CH4) and other components like carbon dioxide (CO2) and water (H2O). Biogas is saturated in water vapour which must be removed to ensure the operational stability and safety of the technology systems that handles wet biogas and employs the end-product biomethane. Through a series of separation processes, the biogas is cleaned (drying) and upgraded (CO2/CH4 separation) to biomethane. The adsorptive separation technology with nanoporous materials for biogas upgrading has become progressively competitive due to their meritorious features. In particular, metal-organic frameworks (MOFs) have shown a tremendous potential in upgrading biogas under dry conditions. However, their affinity for water promotes competitive co-adsorption, and this, coupled with their relatively low hydrolytic stability affects their upgrading performance negatively. This fact requires the complete removal of moisture before the adsorptive based gas separation upgrading process can be carried out. A similar situation applies for highly hydrophilic zeolite adsorptive systems. In this work, we present two permanently porous MOFs made of aluminium metal ions (Al(III)) and tetra-carboxylate ligands with strong CO2 binding pockets comprising of two aromatic rings which are 7 Å apart. Both MOFs are robust, and adsorption isotherms revealed that they are porous to CO2 and CH4 at 303 K with isosteric heat of adsorption of −25 to −40 and −13 to −16 kJ/mol, respectively. Interestingly, these materials are found to be non-porous to water at low relative humidity as shown by water vapour isotherms. Inspired by their single component sorption behaviours, we demonstrate that their biogas upgrading performance is not affected regardless of the high water vapour content (4 vol% and 85% RH) in the feed gas of the multicomponent fixed bed breakthrough experiments. This is due to the lack of competitive co-adsorption of CO2 and H2O within the hydrophobic CO2 binding pockets. This makes both MOFs presented in this work as industrially relevant candidates for biogas upgrading application which can withstand residual moisture of dried biogas as well as the momentary breakthroughs of wet biogas.

Investigating H2O and CO2 co-adsorption on amine-functionalised solid sorbents for direct air capture

Direct air capture can be an invaluable technology to limit the devastating global temperature increase caused by anthropogenic emissions. Amine-functionalised porous adsorbents combined with temperature-vacuum swing regeneration can remove carbon dioxide from the air in high purities and hence is a promising technology for direct air capture. An example, of a commercially available amine-functionalised adsorbent, Lewatit VP OC 1065®, is selected for study in this work. These materials selectively adsorb high quantities of carbon dioxide. However, they also adsorb significant amounts of water. Mechanistic mathematical descriptions of this multi-component adsorption do not currently exist, leading to inaccurate performance estimates from process modelling. In this study, we will present mathematical descriptions based on equilibrium and dynamic co-adsorption data. This expands the co-adsorption isotherm modelling on the previous empirical approaches detailed in literature. [1], [2] Meanwhile, we will present the effect of water on carbon dioxide adsorption kinetics for the first time. These results will lead to better modelling and improved optimisation of direct air capture processes. We also believe that water and carbon dioxide’s adsorption on Lewatit VP OC 1065® is now fully characterised, allowing for accurate process assessment as a benchmark direct air capture sorbent. Performance of new novel adsorbents, such as amine-functionalised metal-organic frameworks, can be compared to Lewatit VP OC 1065® to decide whether the adsorbent deserves further investigation.

CO-ADSORPTION CALCULATIONS OF CO AND H2O MOLECULES ON ATOMIC CU CLUSTER DEPOSITED ZNO SURFACE: A DENSITY FUNCTIONAL THEORY STUDY

Calculations of adsorption and reaction mechanism on ZnO surface have been investigated. In this work, the deposition of six atomic copper clusters (6Cu) on ZnO surface (called 6Cu/ZnO model), using density functional theory was employed to calculate for CO and H2O co-adsorption. In performance, on ZnO surface, 6Cu were adsorbed to obtain four stable sites of 6Cu/ZnO model, called as 6Cu-I, 6Cu-II, 6Cu-III, and 6Cu-IV. The calculated results found that the 6Cu-IV was the most stable surface model, thus, used to examine the co-adsorption of CO and H2O molecules. Further, CO and H2O co-adsorption on ZnO surface were calculated also to compare with 6Cu/ZnO surface. Based on co-adsorption energy calculations indicated that CO and H2O co-adsorption on 6Cu/ZnO surface were more favorable than on ZnO surface. The studied results will provide an insight into the effective adsorption of cluster on ZnO-based surface by deposition.

Embedded Cluster Study of the Co-Adsorption of HCl and H2O on PuO2 Surfaces

The simultaneous adsorption of HCl and H2O on the {111} and {110} surfaces of PuO2 has been studied using hybrid density functional theory within the periodic electrostatic embedded cluster method. A synergistic effect between co-adsorbed molecules is identified, such that HCl binding energies are enhanced by the presence of water. Higher levels of water also increase the HCl binding energy, forming very stable configurations on both surfaces for first-layer HCl interactions. Second-layer interactions are also explored, in which the HCl molecule is placed above a full monolayer of water on the surfaces. In such circumstances, the HCl reacts with a hydroxyl from the water monolayer to produce molecular water, with the chloride held to the surface via numerous chlorine-acceptor hydrogen bonds.

CO2 and H2O Coadsorption and Reaction on the Low-Index Surfaces of Tantalum Nitride: A First-Principles DFT-D3 Investigation

A comprehensive mechanistic insight into the photocatalytic reduction of CO2 by H2O is indispensable for the development of highly efficient and robust photocatalysts for artificial photosynthesis. This work presents first-principles mechanistic insights into the adsorption and activation of CO2 in the absence and presence of H2O on the (001), (010), and (110) surfaces of tantalum nitride (Ta3N5), a photocatalysts of significant technological interest. The stability of the different Ta3N surfaces is shown to dictate the strength of adsorption and the extent of activation of CO2 and H2O species, which bind strongest to the least stable Ta3N5(001) surface and weakest to the most stable Ta3N5(110) surface. The adsorption of the CO2 on the Ta3N5(001), (010), and (110) surfaces is demonstrated to be characterized by charge transfer from surface species to the CO2 molecule, resulting in its activation (i.e., forming negatively charged bent CO2−δ species, with elongated C–O bonds confirmed via vibrational frequency analyses). Compared to direct CO2 dissociation, H2O dissociates spontaneously on the Ta3N5 surfaces, providing the necessary hydrogen source for CO2 reduction reactions. The coadsorption reactions of CO2 and H2O are demonstrated to exhibit the strongest attractive interactions on the (010) surface, giving rise to proton transfer to the CO2 molecule, which causes its spontaneous dissociation to form CO and 2OH− species. These results demonstrate that Ta3N5, a narrow bandgap photocatalyst able to absorb visible light, can efficiently activate the CO2 molecule and photocatalytically reduce it with water to produce value-added fuels.