Heterogeneous catalysis plays a significant role in the modern chemical industry. Towards the rational design of novel catalysts, understanding reactions over surfaces is the most essential aspect. ...Typical industrial catalytic processes such as syngas conversion and methane utilisation can generate a large reaction network comprising thousands of intermediates and reaction pairs. This complexity not only arises from the permutation of transformations between species but also from the extra reaction channels offered by distinct surface sites. Despite the success in investigating surface reactions at the atomic scale, the huge computational expense of
ab initio
methods hinders the exploration of such complicated reaction networks. With the proliferation of catalysis studies, machine learning as an emerging tool can take advantage of the accumulated reaction data to emulate the output of
ab initio
methods towards swift reaction prediction. Here, we briefly summarise the conventional workflow of reaction prediction, including reaction network generation,
ab initio
thermodynamics and microkinetic modelling. An overview of the frequently used regression models in machine learning is presented. As a promising alternative to full
ab initio
calculations, machine learning interatomic potentials are highlighted. Furthermore, we survey applications assisted by these methods for accelerating reaction prediction, exploring reaction networks, and computational catalyst design. Finally, we envisage future directions in computationally investigating reactions and implementing machine learning algorithms in heterogeneous catalysis.
Machine learning algorithms can facilitate the reaction prediction in heterogeneous catalysis.
To explore high-performance electrocatalysts, electronic regulation on active sites is essentially demanded. Herein, we propose controlled phosphorus doping to effectively modify the electronic ...configuration of nanostructured Mo2C, accomplishing a benchmark performance of noble-metal-free electrocatalysts in the hydrogen evolution reaction (HER). Employing MoOx–phytic acid–polyaniline hybrids with tunable composition as precursors, a series of hierarchical nanowires composed of phosphorus-doped Mo2C nanoparticles evenly integrated within conducting carbon (denoted as P-Mo2C@C) are successfully obtained via facile pyrolysis under inert flow. Remarkably, P-doping into Mo2C can increase the electron density around the Fermi level of Mo2C, leading to weakened Mo–H bonding toward promoted HER kinetics. Further density functional theory calculations show that the negative hydrogen-binding free energy (ΔGH*) on pristine Mo2C gradually increases with P-doping due to electron transfer and steric hindrance by P on the Mo2C surface, indicating the effectively weakened strength of Mo–H. With optimal doping, a ΔGH* approaching 0 eV suggests a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, the P-Mo2C@C nanowires with controlled P-doping (P: 2.9 wt%) deliver a low overpotential of 89 mV at a current density of −10 mA cm−2 and striking kinetic metrics (onset overpotential: 35 mV, Tafel slope: 42 mV dec−1) in acidic electrolytes, outperforming most of the current noble-metal-free electrocatalysts. Elucidating feasible electronic regulation and the remarkably enhanced catalysis associated with controlled P-doping, our work will pave the way for developing efficient noble-metal-free catalysts via rational surface engineering.
An atomistic understanding of the initial hydrothermal growth of titania remains crucial for the development of nanosized materials, where the presence of water strongly affects the particle growth ...in comparison to the vapor-phase growth. Herein, we explore the structural evolution of aqueous titania from its salt precursors and determine the nanoparticle configurations in the practical environment by invoking ab initio molecular dynamic simulations and a machine-learning accelerated structural search. Thermodynamically, Ti(OH) 4 ·2H 2 O serving as the hydrated monomer undergoes planar-to-tubular-to-spherical multistage growth in the Ti(OH) 4 /H 2 O hydrothermal system, in which large-sized (TiO 2 ) n (H 2 O) m particles ( n = 1–20) are generated via the olation/oxolation reaction. Importantly, in a mixture of particles of different sizes, we identify that (TiO 2 ) 8 (H 2 O) 16 is one of the most abundant species in solution with peculiar metastability and exhibits extraordinary visible-light absorption ability, which may be the smallest aqueous titania subnanoparticle in the form of suspension and worth exploring for photocatalytic applications.
Abstract
The integrated CO
2
capture and conversion (iCCC) technology has been booming as a promising cost-effective approach for Carbon Neutrality. However, the lack of the long-sought molecular ...consensus about the synergistic effect between the adsorption and in-situ catalytic reaction hinders its development. Herein, we illustrate the synergistic promotions between CO
2
capture and in-situ conversion through constructing the consecutive high-temperature Calcium-looping and dry reforming of methane processes. With systematic experimental measurements and density functional theory calculations, we reveal that the pathways of the reduction of carbonate and the dehydrogenation of CH
4
can be interactively facilitated by the participation of the intermediates produced in each process on the supported Ni–CaO composite catalyst. Specifically, the adsorptive/catalytic interface, which is controlled by balancing the loading density and size of Ni nanoparticles on porous CaO, plays an essential role in the ultra-high CO
2
and CH
4
conversions of 96.5% and 96.0% at 650 °C, respectively.
The Fischer–Tropsch synthesis plays a significant role in re-forming natural resources to meet global demand for commodities, while there is ongoing oil depletion and population growth. Mechanisms ...have long been investigated, but they are still a heavily debated issue. In this work, all of the possible elementary reaction steps on a flat cobalt surface were calculated using density functional theory (DFT) with van der Waals interactions. Kinetic simulations using standard DFT data (free energies and barriers at low coverages), the so-called non-coverage-dependent kinetic model commonly used in the literature, are compared to those from a coverage-dependent kinetic model for the system. We show that the coverage-dependent kinetic model gives rise to a TOF which is approximately 6 orders of magnitude larger than the TOF calculated using the non-coverage-dependent kinetic model. Furthermore, it is found that Co(0001) is highly selective to olefin production, and it is very likely to produce long-chain hydrocarbons. Both models demonstrate that the CO insertion mechanism is the dominant mechanism on Co(0001). Our calculations also reveal that high coverage of CH x leads to the carbide mechanism being significant and low coverage of CH x results in the CO insertion mechanism being more favored. Direct CO dissociation is difficult on Co(0001), which leads to monomers CH x being unable to occupy a certain amount of surface coverage, causing the carbide mechanism to be inhibited. The reaction pathway through CO + H → CHO, CHO + H → CHOH, and CHOH → CH + OH is the main channel to form the monomer CH on the basis of the coverage-dependent kinetic model simulations. The temperature considerably affects the surface coverage and the total reaction rate, leading to the selectivity being highly temperature dependent. Our coverage-dependent kinetic model predicts that the selectivity of oxygenates is high in comparison to methane in the low-temperature region from 425 and 475 K. From 475 to 525 K, the selectivity toward CH4 increases. From 525 to 700 K, the selectivity of C2 decreases significantly and the selectivity of CH4 increases remarkably.
To understand the mechanisms and kinetics of catalytic reactions in heterogeneous catalysis, ab initio molecular dynamics is one of the powerful methods used to explore the free energy surface (FES) ...of surface elementary steps. The most significant aspect of performing such calculations is to choose the specific collective variable (CV) of the reaction. Here, we take CO oxidation on Pt(111) at 300 K as an example to demonstrate the protocol of selecting CVs guided by the free energy decomposition which quantifies individual bond free energy contributions. The basic concept is to conduct the brute-force molecular dynamics initiated from the transition state on the FES, which is refined from the one on the potential energy surface, to generate the reaction path at a finite temperature. The validity of this reaction path is further demonstrated by a 2-D free energy landscape spanned by the path-CV. By choosing CVs including other bond distances, we find that CO oxidation cannot be well understood by umbrella sampling or constrained molecular dynamics (CMD) solely along the OC–O bond distance. The free energy decomposition analysis suggests that not only the OC–O bond but also two O–Pt bonds are responsible for the free energy change. The further CMD simulations along selected CVs based on the insights from our protocol capture different reaction stages and give solid estimations of free energy barriers.
As one of the essential processes in the energy industry, acetylene hydrogenation reactions have been studied extensively in both experiment and theory. However, the fundamentals of structure ...sensitivity of acetylene hydrogenation over Pd catalysts are still debatable. Herein, a newly developed coverage-dependent microkinetic modelling is utilized to investigate the structure sensitivity of Pd catalysts. The key reaction kinetics are quantitatively examined; for example, a high ethylene activity of 3.92 s
−1
and a low selectivity of 0.2 at 300 K are calculated. It is found that the Pd(211) surface is much more active than Pd(111), but exhibits a poor selectivity toward ethylene in contrast to Pd(111) that is intrinsically selective toward ethylene. The high activity of Pd(211) is primarily due to the decisive role of the coverage effect in reducing the reaction barrier of the rate-determining step, while the poor selectivity is a consequence of the inherently high chemisorption energy of ethylene. Furthermore, the ethylene selectivity is found to be more sensitive to the desorption barrier at low temperature. This work provides an atomic-scale understanding of the intrinsic selectivity of the acetylene hydrogenation embodied in different Pd structures.
The structure sensitivity of Pd catalysed acetylene hydrogenation is quantitatively examined using a coverage-dependent microkinetic model. Pd(211) was found to be more active than Pd(111), but present a poorer selectivity toward ethylene.
A complete catalytic cycle for methane combustion on the Co3O4(110) surface was investigated and compared with that on the Co3O4(100) surface on the basis of first-principles calculations. It is ...found that the 2-fold coordinated lattice oxygen (O2c) would be of vital importance for methane combustion over Co3O4 surfaces, especially for the first two C–H bond activations and the C–O bond coupling. It could explain the reason the Co3O4(110) surface significantly outperforms the Co3O4(100) surface without exposed O2c for methane combustion. More importantly, it is found that the cooperation of homogeneous multiple sites for multiple elementary steps would be indispensable. It not only facilitates the hydrogen transfer between different sites for the swift formation of H2O to effectively avoid the passivation of the active low-coordinated O2c site but also stabilizes surface intermediates during the methane oxidation, optimizing the reaction channel. An understanding of this cooperation of multiple active sites not only might be beneficial in developing improved catalysts for methane combustion but also might shed light on one advantage of heterogeneous catalysts with multiple sites in comparison to single-site catalysts for catalytic activity.
Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon ...matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H2. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H2, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.
One stop shop: Isolated cobalt single‐atom sites stabilized on an ordered porous nitrogen‐doped carbon matrix are highly efficient catalysts for acceptorless dehydrogenation of N‐heterocycles to release H2, and the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles with a hydrogen source to store H2.
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