Confined Catalysis in the g-C3N4/Pt(111) Interface: Feasible Molecule Intercalation, Tunable Molecule-Metal Interaction, and Enhanced Reaction Activity of CO Oxidation

Confinement Effects of Two-Dimensional Surfaces on Water Adsorption and Dissociation over Pt(111)

It has been established that the confined space created by stacking a two dimensional (2D) surface atop a metal catalyst serves as a nano-reactor. According to recent research, when a graphene (Gr) overlayer encloses a catalyst from above, the activation barrier for the water dissociation reaction, a process with major industrial significance, decreases. In order to investigate how the effect of confinement varies among different two-dimensional (2D) materials, we study the adsorption and dissociation barriers of water molecule on (111) under graphene, hexagonal boron nitride (h-BN), and heptazine-based graphitic carbon nitride (g-C3N4) layers using density functional theory calculations. Our findings reveal that the strength of adsorption does not decrease consistently with a reduction in the height of the 2D overlayer. Furthermore, a smaller barrier is not always the consequence of poorer adsorption of the reactant. We also examine the effect of confinement on the shape of the reaction path, on the frequencies of vibrational modes, and on the rate constants derived using the harmonic transition state theory. Overall, all three 2D surfaces cause a decrease in barrier height and a weakening of adsorption, though to differing degrees due to a mix of mechanical, geometric and electronic variables.

Porous 2D Catalyst Covers Improve Photoelectrochemical Water-Oxidation Performance

Confined catalysis under the cover of 2D materials has emerged as a promising approach for achieving highly effective catalysts in various essential reactions. In this work, a porous cover structure is designed to boost the interfacial charge and mass transfer kinetics of 2D-covered catalysts. The improvement in catalytic performance is confirmed by the photoelectrochemical oxidation evolution reaction (OER) on a photoanode based on an n-Si substrate modified with a NiOx thin-film model electrocatalyst covered with a porous graphene (pGr) monolayer. Experimental results demonstrate that the pGr cover enhances the OER kinetics by balancing the charge and mass transfer at the photoanode and electrolyte interface compared to the intrinsic graphene cover and cover-free control samples. Theoretical investigations further corroborate that the pore edges of the pGr cover boost the intrinsic catalytic activity of active sites on NiOx by reducing the reaction overpotential. Furthermore, the optimized pores, which can be easily controlled by plasma bombardment, allow oxygen molecules produced in the OER to pass through without peeling off the pGr cover, thus ensuring the structural stability of the catalyst. This study highlights the significant role of the porous cover structure in 2D-covered catalysts and provides new insight into the design of high-performance catalysts.

The confined surface C2N/Pt(111) as a highly efficient catalyst for CO oxidation

The problem of poisoning on the surface of catalysts used in CO oxidation reactions, such as Pt, needs to be solved. In this work, we constructed lattice-matched C2N/Pt(111) catalysts with different configurations (top/fcc/hcp) and found that, within the confined space between the cover and the substrate, the adsorption energy of CO is reduced by 0.35 eV to 0.43 eV, while the adsorption of other reactants O/O2 is strengthened and the adsorption energy of the product CO2 is positive, indicating that the constraint effect produced by C2N and Pt(111) is beneficial to CO oxidation, when compared to the pure Pt(111). Our work suggests that the C2N cover not only protects the Pt surface under harsh conditions but also allows gaseous molecules CO and O2 to approach the Pt surface through a facile intercalation process, with enhanced surface reactivity for CO oxidation and reduced catalyst poisoning.

Optimizing Intermediate Adsorption on Pt Sites via Triple-Phase Interface Electronic Exchange for Methanol Oxidation

For the most commonly applied platinum-based catalysts of direct methanol fuel cells, the adsorption ability toward reaction intermediates, including CO and OH, plays a vital role in their catalytic activity and antipoisoning in anodic methanol oxidation reaction (MOR). Herein, guided by a theoretical mechanism study, a favorable modulation of the electronic structure and intermediate adsorption energetics for Pt active sites is achieved by constructing the triple-phase interfacial structure between tin oxide (SnO2), platinum (Pt), and nitrogen-doped graphene (NG). From the strong electronic exchange at the triple-phase interface, the adsorption ability toward MOR reaction intermediates on Pt sites could be efficiently optimized, which not only inhibits the adsorption of CO* on active sites but also facilitates the adsorption of OH* to strip the poisoning species from the catalyst surface. Accordingly, the resulting catalyst delivers excellent catalytic activity and antipoisoning ability for MOR catalysis. The mass activity reaches 1098 mA mg-1Pt, 3.23 times of commercial Pt/C. Meanwhile, the initial potentials and main peak for CO oxidation are also located at a much lower potential (0.51 and 0.74 V) against commercial Pt/C (0.83 and 0.89 V).

Controlling the spacing of the linked graphene oxide system with dithiol linkers under confinement

2D nanoscale confined systems exhibit behavior that is markedly different from that observed at the macroscale. Confinement can be tuned by controlling the interlayer spacing between confining layers using organic dithiol linkers. Adjusting spacing and selective intercalation have important impacts for catalysis, superconductivity, spin engineering, sodium ion batteries, 2D magnets, optoelectronics, and many other applications. In this study, we report how reaction conditions and organic linkers can be used to create variable, reproducible spacings between graphene oxide to provide confinement systems. We determined the conditions under which the spacing can be variably adjusted by the type of linker used, the concentration of the linker, and the reaction conditions. Employing dithiol linkers of different lengths, such as three (TPDT) and four (QPDT) aromatic rings, we can adjust the spacing between graphene oxide layers under varied reaction conditions. Here, we show that by varying dithiol linker length and using different reaction conditions, we can reproducibly control the spacing between graphene oxide layers from 0.37 nm to over 0.50 nm.

Rational optimization of g-C3N4/Co3O4 nanocomposite for enhanced photodegradation of Rhodamine B dye under visible light

Heterogeneous catalysis is widely known as an efficient, clean, and low-cost technology to mitigate the environmental pollution of industrial effluents. This research aimed at optimizing the preparation and characterization of efficient g-C₃N₄/Co₃O₄ nanocomposite for catalytic removal of Rhodamine B (Rh B) dye. The detected XRD peaks for the prepared nano-Co₃O₄ are matched with the cubic crystal structure. In contrast, the broad peak at 27.3° corresponding to the graphite reflection of hkl (002) was noticeably weakened in the XRD pattern of the g-C₃N₄/Co₃O₄ composite. FTIR spectra of g-C₃N₄/Co₃O₄ nanocomposites revealed the active vibrational modes of each Co₃O₄ and g-C₃N₄ component. The microstructure study of g-C₃N₄ showed the strong interlayer stacking of carbon nitride nanosheets, while the surface morphology of g-C₃N₄/Co₃O₄ nanocomposite revealed a hybrid particulate system. EDS analysis indicated that the spot area of g-C₃N₄/Co₃O₄ confirmed the chemical ratios of carbon, nitrogen, cobalt, and oxygen. BET measurements of g-C₃N₄/Co₃O₄ showed a significant increase in the surface area and pore volume of single components due to the lamination of stacked g-C₃N₄ nanosheets by the intercalated Co₃O₄ nanoparticles. The prepared 30% g-C₃N₄/Co₃O₄ revealed the lowest value of E_g ~1.2 eV and the highest light absorptivity suggesting strong promotion for the photocatalytic performance under visible light. The maximum photocatalytic activity of about 87% was achieved by 30% g-C₃N₄/Co₃O₄ due to the photonic enhancement, which reduces the recombination of excited electrons. The developed nanocomposite with a g-C₃N₄/Co₃O₄ ratio of 0.3 exhibited high stability in its photocatalytic performance after four recycling times, and a slight decrease of about 7% was estimated after the 5th reuse test.

Promotion Effect of Well-Defined Deposited Water Layer on Carbon Monoxide Oxidation Catalyzed by Single-Atom Alloys

Single-atom alloys (SAAs) exhibit excellent catalytic performance and unique electronic structures, emerging as promising catalysts for potential industrial reactions. While most of them have been widely employed under reducing conditions, few are applied in oxidation reactions. Herein, using density functional theory calculations and microkinetic simulations, we demonstrate that a well-defined one water layer can improve CO oxidation on model SAAs, with reaction rates increased by orders of magnitude. It is found that the formation of hydrogen bonds and the transfer of charges effectively enhance the adsorption and activation of oxygen molecules at the H₂O/SAA interfaces, which not only increases the surface coverage of O₂ species but also reduces the energy barrier of CO oxidation. The proposed strategy in this work would extend the application range of SAA catalysts to oxidation reactions.

Dynamic Construction and Maintenance of Confined Nanoregions via Hydrogen-Bond Networks between Acetylene Reactants and a Polyoxometalate-Based Metal-Organic Framework

The nanoconfinement effect in catalysis has attracted much attention because it provides a novel means of regulating the molecular properties and related reactions. Confined nanoregions composed of both reactants and catalysts through weak interactions are expected to improve the catalytic performance and promote the mass transport of relevant molecules simultaneously. However, at reaction temperatures, the structural variation of such confined spaces constructed via weak interactions remains unclear. Herein, through density functional theory calculations combined with ab initio molecular dynamics simulations, we have systematically investigated the dynamic structural evolution of the confined space constructed by acetylene reactants and a polyoxometalate-based metal-organic framework (POMOF) via hydrogen-bond networks. It is found that, at the reaction temperature of acetylene semihydrogenation, the hydrogen-bond networks and generated confined nanoregions are not rigid but are constantly changing and dynamically maintained. The steering role played by the O atoms at the surfaces of the polyoxometalate clusters is essential for generation of the hydrogen-bond networks and maintenance of the nanoregions. Upon confinement, the acetylene reactants can be better activated than those in an unconstrained atmosphere, which is reflected by the different dynamic distributions of the ∠CHC bending magnitude. Moreover, from a comparison of the distinct interaction characteristics between acetylene/ethylene and POMOF, the different manifestations in the adsorption energy variations of the confined molecules can be interpreted. This work helps to elucidate the underlying mechanisms of confined catalysis and may promote its application in practical catalytic processes.

Construction of frustrated Lewis pairs on carbon nitride nanosheets for catalytic hydrogenation of acetylene

Here, we studied Al or B atom-doped carbon nitride (g-C₃N₄ and C₂N) as catalysts for H₂ activation and acetylene hydrogenation using density functional theory calculations. The Al or B could be assembled with the surface N atoms of carbon nitride to form diverse frustrated Lewis pairs (FLPs). The results show that Al-N FLPs had lower barriers of H₂ activation in comparison with B-N FLPs. The heterolytic H₂ dissociation catalyzed by Al-N FLPs led to the formation of Al-H and N-H species. The Al-H species were highly active in the first hydrogenation of acetylene to C₂H₃*, yielding a mild barrier, while in the second hydrogenation step, the reaction between C₂H₃ and the H of N-H species caused a relatively high barrier. Electronic structure analysis demonstrated the electron transfer in the heterolytic H₂ cleavage and explained the activity differences in various FLPs. The results suggest that Al with the surface N of carbon nitride can act as an FLP to catalyze the H₂ activation and acetylene hydrogenation, thus providing a new strategy for the future development of noble metal-free hydrogenation catalysts.

Single transition metal anchored C9N4 sheets as an efficient catalyst for CO oxidation: a first-principles study

Single Ni/Co anchored C₉N₄ sheet works as an efficient catalyst for CO oxidation.

Metal single-atom coordinated graphitic carbon nitride as an efficient catalyst for CO oxidation

Single-atom catalysts (SACs) often present outstanding activity due to their high ratio of low-coordinated metal atoms and can be applied to the activation of strong chemical bonds such as C[triple bond, length as m-dash]O. Herein, we investigate the potential usage of a single-atom catalyst, in which isolated cobalt atoms are supported on porous graphitic carbon nitride (Co/g-C₃N₄), for CO oxidation. Based on the adsorption/co-adsorption energies of O₂, CO, 2O₂, CO + O₂ and 2CO, the screening criteria and the reaction mechanisms of CO oxidation, including the Eley-Rideal, New Eley-Rideal, Langmuir-Hinshelwood, and termolecular Eley-Rideal mechanisms, are established and compared. In particular, the energy barriers of the rate-limiting steps for the CO oxidation process by all possible reaction pathways are in a range from 0.21 to 0.59 eV, suggesting that the Co/g-C₃N₄ catalyst can boost CO oxidation at low temperature. Moreover, the preparation of the SAC (Co/g-C₃N₄) by using CoCl₂ as an appropriate metal precursor and the stability (up to 600 K) are evaluated by ab initio molecular dynamics simulations. The high stability and excellent activity of the Co/g-C₃N₄ SAC for CO oxidation offer a high possibility of clean energy production.

Unraveling template-free fabrication of carbon nitride nanorods codoped with Pt and Pd for efficient electrochemical and photoelectrochemical carbon monoxide oxidation at room temperature

The tailored synthesis of carbon nitrides (CNs) is of particular interest in multidisciplinary catalytic applications. However, their fabrication in the form of one-dimensional (1D) nanorods for electrocatalytic carbon monoxide (CO) oxidation is not hitherto reported. Herein, a facile roadmap is presented for the rational design of Pt- and Pd-codoped CN (PtPd/CNs) nanorods via protonation of melamine in an ethylene glycol solution containing Pt and Pd precursors using NaNO3 and HCl and subsequent annealing. The protonation induces the polymerization of melamine to melon nanosheets that consequently roll up to CN nanorods. This tailored the prompt high mass production of uniform 1D CN nanorods (94 ± 2 nm) with a high surface area (155.2 m2 g-1) and they were atomically codoped with Pt and Pd (1.5 wt%) without a template and/or multiple complicated steps. The electrocatalytic CO oxidation activity of PtPd/CNs is 2.01 and 23.41 times greater than that of the commercial Pt/C catalyst and metal-free CNs, respectively, at room temperature. Meanwhile, the UV-vis light irradiation enhanced the CO oxidation activity of PtPd/CNs nanorods by 1.48 fold compared to that in the dark, emanated from the coupling between the drastic inbuilt catalytic merits of PtPd and the inimitable physicochemical properties of CNs. The presented study may pave the way for using CN-based materials in gas conversion reactions.

Under-cover stabilization and reactivity of a dense carbon monoxide layer on Pt(111)

A dense CO overlayer on a Pt(111) surface under a 2D hybrid h-BN–graphene cover was studied.

The space between a metal surface and a two-dimensional cover can be regarded as a nanoreactor, where confined molecule adsorption and surface reactions may occur. In this work, we report CO intercalation and reactivity between a graphene-hexagonal boron nitride (h-BNG) heterostructure and Pt(111). By employing high resolution X-ray photoemission spectroscopy (XPS) we demonstrate the molecular intercalation of the full h-BNG overlayer and stabilization of a dense R23.4°–13CO layer on Pt(111) under ultra-high vacuum at room temperature. We provide experimental evidence of a weakened CO–metal bond due to the confinement effects of the 2D cover. Temperature-programmed XPS results reveal that CO desorption is kinetically delayed and occurs at a higher temperature than on bare Pt(111). Moreover, CO partially reacts with the h-BNG layer to form boron-oxide species, which affect repeated CO intercalation. Finally, we found that the properties of the system towards interaction with CO can be considerably recovered using high temperature treatment.

The interplay between structural perfectness and CO oxidation catalysis on aluminum, phosphorous and silicon complexes of corroles

Catalytic oxidation of carbon monoxide on perfect and defective structures of corrole complexes with aluminum, phosphorous and silicon have been investigated by performing density functional theory calculations.

Versatile Synthesis of Pd and Cu Co-Doped Porous Carbon Nitride Nanowires for Catalytic CO Oxidation Reaction

Developing efficient catalyst for CO oxidation at low-temperature is crucial in various industrial and environmental remediation applications. Herein, we present a versatile approach for controlled synthesis of carbon nitride nanowires (CN NWs) doped with palladium and copper (Pd/Cu/CN NWs) for CO oxidation reactions. This is based on the polymerization of melamine by nitric acid in the presence of metal-precursors followed by annealing under nitrogen. This intriguingly drove the formation of well-defined, one-dimensional nanowires architecture with a high surface area (120 m2 g−1) and doped atomically with Pd and Cu. The newly-designed Pd/Cu/CN NWs fully converted CO to CO2 at 149 °C, that was substantially more active than that of Pd/CN NWs (283 °C) and Cu/CN NWs (329 °C). Moreover, Pd/Cu/CN NWs fully reserved their initial CO oxidation activity after 20 h. This is mainly attributed to the combination between the unique catalytic properties of Pd/Cu and outstanding physicochemical properties of CN NWs, which tune the adsorption energies of CO reactant and reaction product during the CO oxidation reaction. The as-developed method may open new frontiers on using CN NWs supported various noble metals for CO oxidation reaction.

Cu nanocrystal enhancement of C3N4/Cu hetero-structures and new applications in photo-electronic catalysis: hydrazine oxidation and redox reactions of organic molecules

A C₃N₄/Cu hetero-structure was prepared for new applications in photo-electronic redox reactions.

Phosphomolybdic acid supported single-metal-atom catalysis in CO oxidation: first-principles calculations

Highly active phosphomolybdic acid supported single-metal-atom catalysts for CO oxidation.