Weaker CO Adsorption Research Articles

Hydroxylated TiO2-induced high-density Ni clusters for breaking the activity-selectivity trade-off of CO2 hydrogenation

The reverse water gas shift reaction can be considered as a promising route to mitigate global warming by converting CO2 into syngas in a large scale, while it is still challenging for non-Cu-based catalysts to break the trade-off between activity and selectivity. Here, the relatively high loading of Ni species is highly dispersed on hydroxylated TiO2 through the strong Ni and −OH interactions, thereby inducing the formation of rich and stable Ni clusters (~1 nm) on anatase TiO2 during the reverse water gas shift reaction. This Ni cluster/TiO2 catalyst shows a simultaneous high CO2 conversion and high CO selectivity. Comprehensive characterizations and theoretical calculations demonstrate Ni cluster/TiO2 interfacial sites with strong CO2 activation capacity and weak CO adsorption are responsible for its unique catalytic performances. This work disentangles the activity-selectivity trade-off of the reverse water gas shift reaction, and emphasizes the importance of metal−OH interactions on surface.

Electronegativity- induced cobalt-doped platinum hollow nanospheres with high CO tolerance for efficient methanol oxidation reaction

Although Platinum (Pt)-based alloys have garnered significant interest within the realm of direct methanol fuel cells (DMFCs), there still exists a notable dearth in the exploration of the catalytic behavior of the liquid fuels on well-defined active sites and unavoidable Pt poisoning because of the adsorbed CO species (COads). Here, we propose an electronegativity-induced electronic redistribution strategy to optimize the adsorption of crucial intermediates for the methanol oxidation reaction (MOR) by introducing the Co element to form the PtCo alloys. The optimal PtCo hollow nanospheres (HNSs) exhibit excellent high-quality activity of 3.27 A mgPt−1, which is 11.6 times and 13.1 times higher than that of Pt/C and pure Pt, respectively. The in-situ Fourier transform infrared reflection spectroscopy validates that electron redistribution could weak CO adsorption, and subsequently decrease the CO poisoning adjacent the Pt active sites. Theoretical simulations result show that the introduction of Co optimize surface electronic structure and reduce the d-band center of Pt, thus optimized the adsorption behavior of COads. This study not only employs a straightforward method for the preparation of Pt-based alloys but also delineates a pathway toward designing advanced active sites for MOR via electronegativity-induced electronic redistribution.

Atomically L12 ordered (PtHf)x(NiTi)100-x/CNT as bifunctional catalysts for hydrogen evolution reaction and methanol oxidation reaction with high activity and durability

Instead of a sluggish oxygen evolution reaction (OER), a methanol oxidation reaction (MOR) is combined with a hydrogen evolution reaction (HER) for efficient hydrogen production. Here, by data-driven and density functional theory (DFT) calculation, we establish a combined theoretical–and experimental strategy for designing L12 ordered structures. Based on L12-PtNiTi, Hf element is added. Hf atoms occupy the α-site (face-centered site of FCC) with Pt. Ni atoms occupy the β-site (corner site of FCC) with Ti. The (PtHf)x(NiTi)100-x nano-alloy maintains L12 structure, enhancing intrinsic anti-poisonous performance and reducing Pt content. L12 (PtHf)50(NiTi)50/CNT exhibits an overpotential of 19 mV for HER and a mass activity of 4.725 A/mgPt for MOR in acidic electrolyte. For coupling HER with MOR, the working voltage is merely 0.55 V at 10 mA cm−2. It is demonstrated by DFT calculations that ordered (PtHf)50(NiTi)50/CNT has superior electrocatalytic performance attributed to smaller H adsorption energy, stronger OH binding energy and weaker CO adsorption energy.

Revealing Real Active Sites in Intricate Grain Boundaries Assemblies on Electroreduction of CO2 to C2+ Products

AbstractAlthough intricate structural assemblies contribute to enhancing the activity of electrocatalytic CO2 reduction (ECR) to C2+ products, blindly coupling multiple design strategies may not yield the expected results, and even inhibit the activity of intrinsic catalytic sites. Therefore, elucidating the promoting or inhibitory effects of each design strategy on the CO2‐to‐C2+ conversion to clarify the real active sites and dynamic oxidation processes is of paramount importance. Here, commonly used grain boundaries (GBs), oxidation states, and alloying strategies are focused on, constructing four different types of catalysts structures: original Cu GBs, oxygen‐enriched grain boundary oxidation (GBO), Ag‐enriched GBO, and Cu/Ag GBs. Multiple operando characterizations reveal that GBs and GBO strengthen the resistance of the oxidative Cu species to the electrochemical reduction. The in situ generated strongly oxidative hydroxyl radicals alter the local reaction environment on the catalyst surface, inducing and stabilizing oxidative Cuδ+ species. Catalytic activity comparisons indicate that the oxidation state of Cu plays a decisive role in the CO2‐to‐C2+ conversion, and the nanoalloy effect tends to favor the CH4 production in intricate GBs assemblies. Theoretical calculations suggest that weak CO adsorption on GBO structures facilitates hydrogenation, promoting C–C coupling toward C2+ products.

Regulation research on weak co-adsorption and nonsteady-state capture for C6H6/CO2 over carbon materials

With the intention of capturing both benzene (C6H6) and carbon dioxide (CO2) from indoor air, it is assuring of getting both C6H6 and CO2 simultaneously adsorbed over activated carbon materials. Thus, in this study, how adsorption of C6H6 and CO2 performs over single-wall carbon materials is minutely investigated via density function theory (DFT). Specifically speaking, direct electronic interaction between C6H6 and CO2, co-adsorption features and nonsteady-state capture processes of C6H6/CO2 over single-wall carbon nanotube (CNT) as well as regulation of CNTs towards more stable adsorption are main contents in this study. According to results, C6H6 and CO2 are weakly mutually attracted because of limited electrostatic attraction forces and hydrogen-bond effects, which are also the major reason for consequent weak co-adsorption state over pure CNT. In the meantime, owing to repulsive forces of π-orbital electrons from pure CNT to C6H6, both of C6H6 and CO2 could be only captured by pure CNT in nonsteady state. However, with phosphorus (P) and aluminum (Al) embedded as dopants, surficial electron distribution is altered to a large degree and local electron-enriched centers of modified CNTs are formed to enhance connection with C6H6/CO2, especially stronger electrostatic positron–electron attraction and faster capture speeds from free-state to adsorption-state at relatively high temperatures. Overall, this study provides plentiful information of utilizing single-wall carbon materials for fast indoor air purification in a passive way.

Mechanistic exploration in controlling the product selectivity via metals in TiO2 for photocatalytic carbon dioxide reduction

Harnessing the power of the sun, the photocatalytic CO2 reduction process emerges as a pivotal sustainable solution, utilizing solar energy a premier, clean energy source known for its efficiency and economic viability in the current energy paradigm. This study investigates the impact of metals (Cu, Ag, Au) on enhancing the photocatalytic CO2 reduction capabilities of TiO2. In-depth mechanistic analysis conducted using in-situ DRIFTS for identifying the key reaction intermediates, highlights that the catalytic performance, both in terms of activity and product selectivity, is tightly linked to the underlying reaction mechanisms route, optoelectronic properties, and substrate’s (CO2 and H2O) affinities to the catalyst surface. Enhanced light absorption and reduced charge recombination (lifetime enhancement from 0.21 ns to ∼1.2 ns) in case of metal incorporated resulted in enhanced overall photocatalytic performance. With Au as dopant, demonstrated highest electron selectivity for H2 (>97%) compared to Ag and Cu, which showed relatively higher CO2 reduction electron selectivity (∼20% for Cu). The study reveals the crucial interplay of intermediate stabilization, demonstrating its critical role in governing the reaction pathways i.e., carbene or formaldehyde routes as observed in case of Ag and Cu respectively and thus the specific final products. For enhancing the selectivity of CO, engineering the catalyst surface to favour weak CO adsorption is vital. Observations in the CO-TPD measurements demonstrated that Ag sites were effective in promoting the weaker CO* stabilization thus displayed more selectivity towards CO as compared to Cu. While higher CH3OH formation rates in case of Cu, were found to be related to the augmented reactive M=O species stabilization which promotes the oxidation of CH4 to CH3OH. Additionally, in case of Cu, the CH3O* intermediates stabilized effectively, which contributed to more Methanol selectivity through favoured formaldehyde route. While in case of Ag, the CH2* stabilization suggests more probability of the carbene pathway in comparison to the formaldehyde route (as in case of Cu) for producing the CH4 as the final hydrogenated C1 product. These insights guide the strategic design of catalysts for controlling the reaction pathways and thus selective C1 product production in photocatalytic CO2 reduction, offering insights for advanced catalyst design.

Adjacent MnOx clusters enhance the hydroformylation activity of rhodium single-atom catalysts

Hydroformylation reactions promoted by Rh single-atom catalysts typically exhibit a negative reaction order for CO and a positive reaction order for H2 and alkenes. To enhance the catalytic activity, efforts have been concentrated on reducing the CO adsorption strength and/or enhancing the hydrogenation capacity at Rh sites. This report introduces an optimized Rh single-atom catalyst, utilizing positively charged Mn species to weaken the CO adsorption strength. Our strategy involves placing MnOx clusters in the proximity to the Rh single atom. This arrangement allows the reduction of Rh3+ to produce electronically deficient Rhδ+ species (1 < δ < 2), rather than the usual formation of the lower valence state Rh+ species. The weakened CO adsorption strength on the more positively charged Rhδ+ results in reduced CO coverage on the Rh active site, and enhanced adsorption of propylene. Our mechanistic study reveals that H2 and CO adsorption on Rh catalyzes the reduction of adjacent Mn(IV) species, inducing the formation of a Rh-MnOx paired active site. The neighboring MnOx clusters hinder the extensive reduction of Rh3+ to Rh+. This study presents MnOx as an inorganic ligand in Rh-MnOx pair site modifies the electronic properties of Rh sites to modulate the hydroformylation activity of Rh single-atom catalysts.

CO2 hydrogenation to methanol over the copper promoted In2O3 catalyst

The metal promoted In2O3 catalysts for CO2 hydrogenation to methanol have attracted wide attention because of their high activity with high methanol selectivity. However, there was still no experimental confirmation if copper could be a good promoter for In2O3. Herein, the Cu promoted In2O3 catalyst was prepared using a deposition-precipitation method. Such prepared Cu/In2O3 catalyst shows significantly higher CO2 conversion and space time yield (STY) of methanol, compared to the un-promoted In2O3 catalyst. The loading of Cu facilitates the activation of both H2 and CO2 with the interface between the Cu cluster and defective In2O3 as the active site. The Cu/In2O3 catalyst takes the CO hydrogenation pathway for methanol synthesis from CO2 hydrogenation. It exhibits a unique size effect on the CO adsorption. At temperatures below 250 °C, CO adsorption on Cu/In2O3 is stronger than that on In2O3, causing higher methanol selectivity. With increasing temperatures, the Cu catalyst aggregates, which leads to the formation of weak CO adsorption site and causes a decrease in the methanol selectivity. Compared with other metal promoted In2O3 catalysts, it can be concluded that the catalyst with stronger CO adsorption possesses higher methanol selectivity.

Tunable Syngas Formation at Industrially Relevant Current Densities via CO2 Electroreduction and Hydrogen Evolution over Ni and Fe-derived Catalysts obtained via One-Step Pyrolysis of Polybenzoxazine Based Composites.

Simultaneous electroreduction of CO2 and H2O to syngas can provide a sustainable feed for established processes used to synthesize carbon-based chemicals. The synthesis of MOx/M-N-Cs (M = Ni, Fe) electrocatalysts reported via one-step pyrolysis that shows increased performance during syngas electrosynthesis at high current densities with adaptable H2/CO ratios, e.g., for the Fischer-Tropsch process. When embedded in gas diffusion electrodes (GDEs) with optimized hydrophobicity, the NiOx/Ni-N-C catalyst produces syngas (H2/CO = 0.67) at -200mA cm-2 while for the FeOx/Fe-N-C syngas production occurs at ≈-150mA cm-2. By tuning the electrocatalyst's microenvironment, stable operation for >3h at -200mA cm-2 is achieved with the NiOx/Ni-N-C GDE. Post-electrolysis characterization revealed that the restructuring of the catalyst via reduction of NiOx to metallic Ni NPs still enables stable operation of the electrode at -200mA cm-2, when embedded in an optimized microenvironment. The ionomer and additives used in the catalyst layer are important for the observed stable operation. Operando Raman measurements confirm the presence of NiOx during CO formation and indicate weak adsorption of CO on the catalyst surface.

Size-dependent catalytic activity for CO oxidation over sub-nano-Au clusters.

Gold (Au) nanocatalysts present outstanding activity for many reactions and have long attracted much attention, but the size effect of sub-nano-clusters on catalytic activity lacks systematic research. Using CO oxidation as a probe reaction, the size-dependent catalytic capability of sub-nano-Au clusters was explored. The global-minimum (GM) structures of AuN (N = 2-300, <2.5 nm) were obtained utilizing revised particle swarm optimization (RPSO) combined with density functional theory (DFT) calculations and the Gupta empirical potential. Geometric structural descriptors built a bridge among geometric features, adsorption energy, and the CO oxidation rate of each site of any given sub-nano-Au clusters, making it possible for high-throughput evaluation of the adsorption energy and catalytic activity of the whole sub-nano-Au cluster. The activity per unit mass of sub-nano-Au clusters shows a volcano-shaped relationship with the cluster size, where the sub-nano-Au clusters with a 0.75 nm diameter possess the highest CO2 formation rate per unit mass. The Edge and Kink sites have a higher turnover frequency (approximately 106) than the Face sites (approximately 102), which contribute the most to CO2 formation. The weak adsorption of CO and O2 was found to be a crucial factor determining the inferior activity of the Face site to the Kink and Edge sites. The adsorption process rather than the surface reaction step becomes the rate-determining step on the Face site, attributed to the decreased activity per unit mass of sub-nano-Au clusters. This work provides an in-depth mechanistic understanding of size-dependent catalytic activity for Au clusters at the sub-nano level.

DFT study on the mechanism of methanol dehydrogenation over RuxPy surfaces.

Methanol dehydrogenation (MD) is highly valuable in hydrogen energy production, and the introduction of nonmetals has received much attention to improve the activity and stability of the MD catalysts, but the understanding of the role of non-metallic elements in catalyzing the MD reaction is rather limited. Density functional theory (DFT) is employed to investigate the mechanism of methanol dehydrogenation on RuxPy surfaces. In this work, the P element is introduced into the Ru-based catalyst to obtain dispersed Ru sites and RuxPy (x/y = 2 : 1, 1 : 1, and 1 : 2) catalysts are designed. CH3OH adsorption, electronic structure of the catalyst, energy barriers for carbon accumulation reactions, and the mechanism of methanol decomposition are systematically calculated. The results of the effective reaction barrier (Eeffa) reveal that the order of the activity of the MD reaction is RuP(112) > Ru(0001) > Ru2P(210) > RuP2(110). The most preferable pathway on RuP(112) is pathway 1 (CH3OH* → CH3O* → CH2O* → CHO* → CO*). After the introduction of P, the weakened CO adsorption enhanced the resistance of catalysts to CO poisoning, and the activation energy of the carbon accumulation reaction increased, indicating that the anti-coking ability of the catalysts is improved. This theoretical study contributes to the design and modulation of highly active and stable metal catalysts for MD reactions.

Highly dispersed copper catalysts for CO preferential oxidation in hydrogen-rich atmosphere

CeO2 and ZnO with finely rod shape were used as carriers to support copper. High-resolution transmission electron microscopy demonstrated that copper species were existed mostly in bilayer clusters containing underlying Cu+ and upper Cu0 on CeO2, but in big particles of 5–10 nm consisting of only Cu0 on ZnO. The amounts of underlying Cu+ in bilayers and oxygen vacancies (Ov) at copper-ceria interface reached maximum when copper loading was about 10 wt%. In CO preferential oxidation reaction, the 10-Cu/CeO2 catalyst showed the highest activity suggesting that CO adsorbed on Cu+ in bilayer clusters reacted rapidly with O2 absorbed on adjacent Ov. The near synergistic effect not only reduced the CO reaction temperature but also enhanced the CO conversion. The Cu/ZnO catalyst had weak CO adsorption and long distance of Cu0 and Ov, thus it showed much low activity. By filling the 10-Cu/CeO2 catalysts in a two-stage reactor, 1 % CO in the methanol steam reforming gas could be removed to 2 ppm after two successive CO oxidation processes, which provided a new solution for H2 purification.

Cu Tailoring Pt Enables Branched-Structured Electrocatalysts with High Concave Surface Curvature Toward Efficient Methanol Oxidation.

Surface engineering offers opportunities for the design and synthesis of Pt-based alloyed electrocatalysts with high mass activity and resistance to CO poisoning, which is of great significance for methanol electrooxidation. Surface curvature regulation may endow electrocatalysts with enhanced atomic utilization and abundance of unsaturated atoms; however, a reliable synthetic route for controlled construction of tailorable curved surface is still lacking. Here, a colloidal-chemical method to synthesize two types of PtCu branched-structured electrocatalysts, where the concave curvature can be customized is reported. These studies show that, among various synthesis parameters, the concentration of CuCl2·2H2O precursor is the key factor in manipulating the reaction kinetics and determining the concave surface curvature. Significantly, PtCu branched nanocrystals with long and sharp arms (PtCu BNCs-L), featuring a high concave surface curvature, exhibit remarkable activity and stability toward MOR, which is mainly attributed to advanced features of a highly concave surface and the synergistically bifunctional effect from introduced oxophilic Cu metal. In situ Raman spectroscopy and CO stripping test demonstrates weakened CO adsorption and accelerated CO removal on PtCu BNCs-L. This work highlights the importance of surface curvature, opening up an appealing route for the design and synthesis of advanced electrocatalysts with well-defined surface configurations.

Mixture Adsorption in Nanoporous Zeolite and at Its External Surface: In-Pore and Surface Selectivity.

Using toluene, ethylene, and water as gas compounds with different representative molecular interactions, we perform atom-scale simulations for their mixtures to investigate the selectivity of the core nanoporosity and external surface in a prototypical zeolite. As expected, the overall behavior suggests that increasing the pressure of a given component promotes the desorption of the coadsorbing species. However, for water-toluene mixtures, we identify that the pseudohydrogen bonding between water and toluene leads to beneficial coadsorption as toluene adsorption in the low-pressure range promotes water adsorption. Moreover, when the zeolite is completely filled with water, toluene adsorption does not occur due to steric repulsion, and ethylene shows oversolubility as the amount of ethylene per water molecule is significantly larger than in bulk water. The underlying oversolubility mechanism is found to be due to localized ethylene adsorption in the density minima arising from the layering of water in nanoconfinement. Despite these specific effects, the relatively weak coadsorption effects in the zeolite nanoporosity, which are found to be reasonably captured using the ideal adsorbed solution theory, arise from the fact that adsorption of these gases having different molecular sizes occurs in distinct pore regions (channel type, channel intersection). Finally, in contrast to confinement in the nanoporosity, mixture adsorption at the external surface does not show coadsorption effects as it mostly follows the Henry regime. These results show that selectivity is mostly governed by the confinement effects as the external surface leads to a selectivity loss.

Performance and dynamic behavior of H2 layered-bed PSA processes using various activated carbons and zeolite LiX for steam methane reforming gas

Layered-bed pressure swing adsorption (PSA) processes using activated carbons (ACs) and zeolite LiX were investigated to elucidate the performance and dynamic behavior of each AC in H2 separation. Experimental adsorption and re-adsorption breakthrough characteristics of ACs (CAC: parent AC, KACa: KOH-activated CAC, and KACi: KOH-impregnated CAC) and zeolite LiX were compared using a steam methane reforming gas. A rigorous dynamic model was used to evaluate the performance of four and six layered-bed PSA processes in terms of purity, recovery, productivity, and impurities. The KACi bed demonstrated the longest breakthrough time of impurities, but its desorption performance was adversely affected by the strong affinity induced by intercalated potassium compounds. While KACa showed higher adsorption capacities than CAC, its slow adsorption rate resulted in the shortest breakthrough time. On the other hand, CAC presented a separation performance between KACi and KACa beds, but its weak CO adsorption affinity led to a relatively wide CO mass transfer zone. Zeolite LiX demonstrated the longest CO breakthrough time, indicating its potential to purify trace CO in the layered-bed, but its layer length must be carefully decided to prevent CO2 propagation. The four layered-bed PSA produced a fuel cell grade H2 (99.9999% purity, 81.54% recovery, 115 mol/kg/day productivity, and < 0.2 ppm CO), which was further improved by the six layered-bed PSA to 1.5% at the same H2 purity. The dynamic behaviors and sensitivity analysis (P/F ratio, adsorption time, AC/LiX ratio, AC type, and number of beds) provide valuable insights and guidelines for the design and optimization of H2 layered-bed PSA.

Sintering resistance of Pt-based oxidation catalyst via constructing Pt/MnOx interface

It is a challenge to improve the catalytic activity and hydrothermal stability of platinum-based catalyst in concurrently oxidizing CO/C3H6/NO. The construction of Pt/MnOx interface over Pt-based diesel oxidation catalyst via overlayer deposition to form partial-embedded structure, inhibiting the aggregation of platinum nanoparticles in Ostwald Ripening process. Even after hydrothermal aging, the average platinum particle size is equal to that of the fresh catalyst via traditional impregnation method. The electronic-transferring from platinum to manganese results in a weaker CO adsorption ability on Pt species and an improved oxygen activation ability with the help of the redox cycle of Pt and MnOx, as well as the formation of more active nitrate species via in situ DRIFTs. Measurement on the activity shows the lower apparent activation energy, so that the light-off temperature of CO/C3H6/NO on the partial-embedded catalyst via overlayer deposition method decreases by around 20 °C and 40% NO maximum conversion still keeps after severely aging comparing with the traditional catalyst. The work enlightens us the importance of interface sites in stabilizing platinum atoms and creating oxidize active sites.

Platinum-Lead-Bismuth/Platinum-Bismuth Core/Shell Nanoplate Achieves Complete Dehydrogenation Pathway for Direct Formic Acid Oxidation Catalysis.

Designing platinum (Pt)-based formic acid oxidation reaction (FAOR) catalysts with high performance and high selectivity of direct dehydrogenation pathway for direct formic acid fuel cell (DFAFC) is desirable yet challenging. Herein, we report a new class of surface-uneven PtPbBi/PtBi core/shell nanoplates (PtPbBi/PtBi NPs) as the highly active and selective FAOR catalysts, even in the complicated membrane electrode assembly (MEA) medium. They can achieve unprecedented specific and mass activities of 25.1 mA cm-2 and 7.4 A mgPt-1 for FAOR, 156 and 62 times higher than those of commercial Pt/C, respectively, which is the highest for a FAOR catalyst by far. Simultaneously, they show highly weak adsorption of CO and high dehydrogenation pathway selectivity in the FAOR test. More importantly, the PtPbBi/PtBi NPs can reach the power density of 161.5 mW cm-2, along with a stable discharge performance (45.8% decay of power density at 0.4 V for 10 h), demonstrating great potential in a single DFAFC device. The in situ Fourier transform infrared spectroscopy (FTIR) and X-ray absorption spectroscopy (XAS) results collectively reveal a local electron interaction between PtPbBi and PtBi. In addition, the high-tolerance PtBi shell can effectively inhibit the production/adsorption of CO, resulting in the complete presence of the dehydrogenation pathway for FAOR. This work demonstrates an efficient Pt-based FAOR catalyst with 100% direct reaction selectivity, which is of great significance for driving the commercialization of DFAFC.

Synergistically Mitigating Electron Back-Donation by Single-Atomic Fe–N–C and Alloying to Boost CO-Tolerance of Pt in Hydrogen Oxidation

Developing CO-tolerant Pt-based catalysts for the hydrogen oxidation reaction (HOR) is critical for the commercialization of fuel cells and thus receiving increasing interest. Although it is known that weakening the CO adsorption on Pt can improve CO tolerance, efficient strategies are still needed. Inspired by theoretical simulations, we propose here a cascade strategy to synergistically mitigate electron back-donation of Pt 5d → CO 2π* by introducing single-atomic Fe–N–C substrate and alloying, which significantly boosts the CO-tolerance of Pt-based HOR catalysts. The obtained PtNiMo/Fe–N–C can maintain above 80% HOR current density after 2000 s in 1000 ppm CO/H2, substantially outperforming control catalysts and ranking among the state-of-the-art catalysts. The in situ surface-enhanced infrared adsorption spectroscopy validates that the effectively weakened CO adsorption contributes to improved CO tolerance. This strategy opens up opportunities for designing advanced HOR catalysts with desired CO tolerance.

Ni Single Atoms Confined in Nitrogen-Doped Carbon Nanotubes for Active and Selective Hydrogenation of CO2 to CO

Developing efficient non-precious-metal catalysts capable of selectively converting CO2 into fuels and chemicals is desirable yet remains a challenge. Ni-based catalysts usually exhibit high activity in methanation reactions but low selectivity and stability in the reverse water-gas shift (RWGS) reaction. Herein, we report a Ni single-atom catalyst with Ni–Nx motifs confined in N-doped carbon nanotubes as an active, selective, and stable catalyst for the RWGS reaction, achieving almost 100% CO selectivity with a STY of 1.88 molCO gNi–1 h–1 at 500 °C and atmospheric pressure. In addition to weak CO adsorption, strong CO2 adsorption and weak H2 adsorption at the Ni–Nx active site were found to be responsible for the high catalytic activity and CO selectivity.

Porous edge confinement: High carrier potential and low activation energy barrier synergistically boosting the efficiency of selective photocatalytic CO2 conversion

Catalysts which allow directional transfer of photogenerated electrons to catalytic sites are crucial to efficient photocatalytic CO2 reduction. Herein, 2D BiOCl porous nanosheets (BOC-PNS) are prepared by triblock polymer (F127) assisted mechanical ball milling. The main exposed plane is (001) on the BOC-PNS surface and the porous structure increases the edge (110) facet. The (001)/(110) heterojunction enhances directional migration and separation of photogenerated carriers. In situ Raman scattering, in situ Fourier transform infrared spectroscopy, 3D FDTD simulation and theoretical calculations reveal that the BOC (001) plane is enriched with directionally migrating photogenerated electrons and provides the primary active sites to bridge adsorption-activated CO2 molecules consequently producing a smaller energy barrier for the intermediate product of *COOH. Weak CO adsorption on the BOC (001) plane further promotes CO2 reduction. Upon exposure to simulated sunlight, the CO yield of BOC-PNS is enhanced by the rich edge confinement effect reaching 28.2 μmol g−1 h−1, which is 2.1 and 2.8 times that of the BOC nanosheets (13.5 μmol g−1 h−1) and nanoplates (9.9 μmol g−1 h−1), respectively.