Catalyst Screening Research Articles

High throughput screening of single atomic catalysts with optimized local structures for the electrochemical oxygen reduction by machine learning

Single atomic catalysts (SACs), especially metal-nitrogen doped carbon (M−NC) catalysts, have been extensively explored for the electrochemical oxygen reduction reaction (ORR), owing to their high activity and atomic utilization efficiency. However, there is still a lack of systematic screening and optimization of local structures surrounding active centers of SACs for ORR as the local coordination has an essential impact on their electronic structures and catalytic performance. Herein, we systematic study the ORR catalytic performance of M−NC SACs with different central metals and environmental atoms in the first and second coordination sphere by using density functional theory (DFT) calculation and machine learning (ML). The geometric and electronic informed overpotential model (GEIOM) based on random forest algorithm showed the highest accuracy, and its R2 and root mean square errors (RMSE) were 0.96 and 0.21, respectively. 30 potential high-performance catalysts were screened out by GEIOM, and the RMSE of the predicted result was only 0.12 V. This work not only helps us fast screen high-performance catalysts, but also provides a low-cost way to improve the accuracy of ML models.

Kinetic Understanding of Catalytic Selectivity and Product Distribution of Electrochemical Carbon Dioxide Reduction Reaction.

CO2 can be electrochemically reduced to different products depending on the nature of catalysts. In this work, we report comprehensive kinetic studies on catalytic selectivity and product distribution of the CO2 reduction reaction on various metal surfaces. The influences on reaction kinetics can be clearly analyzed from the variation of reaction driving force (binding energy difference) and reaction resistance (reorganization energy). Moreover, the CO2RR product distributions are further affected by external factors such as electrode potential and solution pH. A potential-mediated mechanism is found to determine the competing two-electron reduction products of CO2 that shifts from thermodynamics-controlled product formic acid at less negative electrode potentials to kinetic-controlled product CO at more negative electrode potentials. Based on detailed kinetic simulations, a three-parameter descriptor is applied to identify the catalytic selectivity of CO, formate, hydrocarbons/alcohols, as well as side product H2. The present kinetic study not only well explains the catalytic selectivity and product distribution of experimental results but also provides a fast way for catalyst screening.

A re-useable microreactor for dynamic and sensitive photocatalytic measurements: Exemplified by the photoconversion of ethanol on Pt-loaded titania P25.

Despite numerous advancements in synthesizing photoactive materials, the evaluation of their catalytic performance remains challenging since their fabrication often involves tedious strategies, yielding only low quantities in the μ-gram scale. In addition, these model catalysts exhibit different forms, such as powders or film(-like) structures grown on various supporting materials. Herein, we present a versatile gas phase μ-photoreactor, compatible with different catalyst morphologies, which is, in contrast to existing systems, re-openable and -useable, allowing not only post-characterization of the photocatalytic material but also enabling catalyst screening studies in short experimental time intervals. Sensitive and time-resolved reaction monitoring at ambient pressure is realized by a lid-integrated capillary, transmitting the entire gas flow from the reactor chamber to a quadrupole mass spectrometer. Due to the microfabrication of the lid from borosilicate as base material, 88% of the geometrical area can be illuminated by a light source, further enhancing sensitivity. Gas dependent flow rates through the capillary were experimentally determined to be 1015-1016 molecules s-1, and in combination with a reactor volume of 10.5 μl, this results in residence times below 40s. Furthermore, the reactor volume can easily be altered by adjusting the height of the polymeric sealing material. The successful operation of the reactor is demonstrated by selective ethanol oxidation over Pt-loaded TiO2 (P25), which serves to exemplify product analysis from dark-illumination difference spectra.

MXene-based single atom catalysts for efficient CO2RR towards CO: A novel strategy for high-throughput catalyst design and screening

A top-down strategy is performed to design Ti3C2O2 MXene-based single atom catalysts (SACs) considering the coordination environment and active metal center. A total of 50 SAC candidates composed of 25 transition metals (TMs) on N, S or N, N co-coordinated Ti3C2O2 (NS/NN-Ti3C2O2) are designed and screened for electrochemical CO2 reduction reaction (CO2RR) to CO. Consequently, 36 TM-NS/NN-Ti3C2O2 structures with considerable stability show stable side-on/end-on CO2 chemisorption, which are then selected for further investigation of CO2RR performance. Analysis on the limiting potential of CO production and the competition with HCOOH production, CO reduction, and hydrogen evolution reaction indicates Ru-NS-Ti3C2O2 and Co-NN-Ti3C2O2 as outstanding catalysts for CO2RR to CO. In actual electrocatalysis, Ru-NS-Ti3C2O2 exhibits an excellent electric field responding effect with ultra-low reaction energies at potentials of −0.80–0 V vs SHE, thus surpassing most of the reported catalysts by far. The two-dimensional descriptor corresponding to the relationship between SACs-intermediate interaction and CO2RR performance, within the near-optimal region of −0.30 < binding energy (Eb(COOH)) < 0.19 eV and −0.30 < Eb(CO) < 0 eV, is demonstrated for rapid screening of candidate catalysts. This work highlights Ti3C2O2 based N, S co-coordination Ru SAC as an outstanding electrocatalyst for CO2RR to CO, and provides a feasible strategy for rational design and screening of CO2RR catalysts.

Hydrophobic Polyhedral Oligomeric Silsesquioxane Support Enhanced Methanol Production from CO2 Hydrogenation.

The abundance of CO2 from the cement industry, power generation, petroleum production, and combustion of biomass makes it a readily available feedstock to produce chemicals and materials, although it has yet to achieve optimal development. Even though syngas (CO + H2) hydrogenation to methanol is an established industrial process, when the same catalytic system based on Cu/ZnO/Al2O3 is employed with CO2, the water formed as a byproduct reduces the activity, stability, and selectivity of the process. Here, we explored the potential of phenyl polyhedral oligomeric silsesquioxane (POSS) as a hydrophobic support of Cu/ZnO for direct CO2 hydrogenation to methanol. Mild calcination of the copper-zinc-impregnated POSS material affords the formation of CuZn-POSS nanoparticles with Cu and ZnO homogeneously dispersed with an average particle size of 7 and 15 nm supported on O-POSS and D-POSS, respectively. The composite supported on D-POSS was able to reach a 3.8% yield of methanol with a 4.4% of CO2 conversion and with selectivity as high as 87.5% within 18 h. The structural investigation of the catalytic system reveals that CuO/ZnO are electron withdrawers in the presence of the siloxane cage of POSS. The catalytic system metal-POSS is stable and recyclable under H2 reduction and CO2/H2 conditions. We tested the use of microbatch reactors in heterogeneous reactions as a rapid and effective tool for catalyst screening. The increased number of phenyls in the structure of POSS results in an increased hydrophobic character that plays a decisive role in the methanol formation after comparison with CuO/ZnO supported on reduced graphene oxide with 0% selectivity to methanol under the study conditions. The materials were characterized using scanning electron microscopy, transmission electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, powder X-ray diffraction, Fourier transform infrared analysis, Brunauer-Emmett-Teller specific surface area analysis, contact angle, and thermogravimetry. The gaseous products were characterized by gas chromatography coupled with thermal conductivity detectors and flame ionization detectors.

Synergistic double-atom catalysts of metal-boron anchored on g-C2N for electrochemical nitrogen reduction: Mechanistic insight and catalyst screening

The rational design of a novel catalytic center with a sound basis remains both challenging and rewarding for the electrochemical reduction of N2 (eNRR), which has provided a feasible route for achieving clean and sustainable NH3 production under ambient conditions. Herein, using density functional theory calculations, we demonstrate that hybrid metal (M)-boron (B) double-atom catalysts (DACs) embedded in g-C2N substrate (M−B@C2N, M = 3d, 4d and 5d transition metals) can achieve both high catalytic activity and high selectivity in eNRR. The proposed M−B@C2N DACs have exhibited impressive feasibility and stability thanks to the resilient and robust C2N substrate with abundant pyridinic N atoms distributed among right-sized pore structures. Our results reveal that like the metal center, the embedded B atom can actively involve in NN bond activation via π*-backdonation mechanism concomitant with the substantial charge transfer to adsorbed *N2, leading to sizable NN bond elongation. Accordingly, both adsorption energy and NN bond length of *N2 can be employed as catalytic descriptors for predicting eNRR activity in terms of the limiting potentials (UL). Using high-throughput screening method, we found that six M−B@C2N candidates have stood out as the outstanding electrocatalysts for driving eNRR, namely, M = Ti (UL = 0 V), Mo (UL = 0 V), Nb (UL = -0.04 V), W (UL = -0.23 V), Zr (UL = -0.26 V), V (UL = -0.28 V). The underlying origin is attributed to the balanced and constrained N-affinity of M−B dual site working in synergy, which can thus be used as one important guide of catalyst design.

Non‐Isocyanate Polyurethanes by Alcoholysis of Alkyl Bisurea with Li Salt‐Assisted Melting: Synthesis and Properties

AbstractAlcoholysis of bisureas (BUs) would be of great potential among the non‐isocyanate routes for preparing polyurethanes, if the issue of the high melting temperature and the poor solubility for BUs can be solved. In this study, it is proposed to introduce Li salt to assist the melting of BUs via a eutectic system. It is found that the melting point of BUs indeed can be reduced to 170 °C or even lower by adding 40 mol% of LiCl or LiBr. In the polymerizations of BUs with diols, it is found that ZnO nanoparticles (30 ± 10 nm) are the most efficient catalyst in the catalyst screening study. Four polyurethanes are successfully synthesized and the glass transition temperature of them is detected to be 34–45 °C. PU1010 is tougher than other polymers so that it is able to be molded. The Young's modulus of PU1010 is 195.1 MPa, while the strength and the elongation at break are 36.4 MPa and 280%, respectively. The toughness calculated is 67.3 J cm−3. This Li salt‐assisted melting strategy not only realizes the synthesis of polyurethanes through alcoholysis of BUs, but can also be extended to the synthesis of other high performance polymers.

Visible-light-driven direct decarboxylative carbonylation of carboxylic acids using acridine photocatalysis in oxygen-liquid flow

Photocatalytic direct decarboxylative carbonylation of ubiquitous carboxylic acids is a promising strategy to obtain highly versatile ketone building blocks, but metal-free and efficient conversions are still lacking. Here, density functional theory calculations are used to guide the experimental screening of catalysts, highlighting the potential influence of frontier molecular orbital energy levels on the catalytic process and revealing an acridine photocatalyst capable of realizing value-added conversion of carboxylic acid at room temperature under visible light with excellent performance. The possible mechanism for this conversion was elucidated in depth by combining study of the excited state behavior of the photosensitizer and the results of detection experiments for radicals. Theoretical calculations and mechanistic studies further disclose the kinetically rate-limiting role of oxygen, including its participation in the formation of superoxide radicals for carbonylation and as an electron trapping agent for catalyst cycling. Based on these findings, a flow microreactor platform was ingeniously built to achieve previously inaccessible photocatalytic decarboxylative carbonylation promoted by acridine in concert with oxygen. Interestingly, the gas–liquid segmented microflow is found to enable a significant acceleration (from 14 to 2 h) and higher yield compared to the batch counterpart, resulting in a high space–time yield of 137.4 g/L d-1 for this transformation, which far exceeds the reported values. This study underscores the feasibility of broadening the competence of acridine photocatalysis through the involvement of kinetically adapted oxygen, thus enabling substitution of metal-dependent photocatalysis and even more efficient and high-yield decarboxylative carbonylation of carboxylic acids.

Screening of single-atom catalysts of transition metal supported on MoSe2 for high-efficiency nitrogen reduction reaction

Two-dimensional single-atom catalysts (2D SACs) have attracted much more attention in the field of ammonia synthesis via electrochemical nitrogen reduction reaction (NRR). In this work, we comprehensively study the NRR performance of 28 transition metals SACs loaded on 2D MoSe2 using density functional theory calculations. In view of thermodynamics and electrochemical stability, adsorption of N2, selectivity and activity of NRR, Mn, Os, V@MoSe2 exhibit outstanding performances with the most favorable potentials of -0.39 V, -0.36 V and -0.36 V, respectively. The excellent NRR performances are comprehensively related to the electronic states, kinetics, and NN bond length. Furthermore, aiming at three vital processes of NRR (adsorption and activation of N2, adsorption strength of intermediates, and the limiting potential), three independent descriptors (φ, ICOHP, ΔG*N) are adopted to make the activity trend clear. The results are of guiding significance to the design of high-efficiency NRR using SAC.

A universal microkinetic-machine learning bimetallic catalyst screening method for steam methane reforming

With the development of first-principles computing and artificial intelligence, catalyst screening have taken remarkable steps toward machine learning (ML). However, it is difficult to explore universal features and descriptors for catalyst screening due to the high spatial freedom of catalytic materials and the lacking kinetic insights of catalytic activity metrics. In this paper, a universal microkinetic-machine learning method (Mkml) is proposed to screen bimetallic catalysts. First, microkinetic models are built based on reaction information to search for descriptors and activity ranges. Then, datasets consisting of elemental properties and adsorption site encoding are evaluated by ML to predict the reference formation energy of the descriptors to optimize the microkinetic model. Finally, activity, stability and price factors are considered to screen competitive catalysts. Mkml was applied to steam methane reforming (SMR) to prove its high accuracy and low cost. The perform best ML is XGBoost with a 0.973 R2 score, and the feature importance also provides a valuable reference for catalyst design. 48 promising candidates are selected by Mkml from the 5000 + catalytic database, which not only accelerates experimenters' discovery of efficient and cheap SMR catalysts, but also guides the search way in a larger materials space.

Support-Dependent Activity and Thermal Stability of Ru-Based Catalysts for Catalytic Combustion of Light Hydrocarbons

Ru-based catalysts are the most promising and concerned candidates for catalytic combustion of propane as one of light hydrocarbons (LHs). In this work, different supports such as SiO2, Al2O3, CeO2, and Co3O4 were investigated to unravel the nature of high activity for catalytic combustion of LHs, and effects of Ru content, high-temperature aging, high weight hourly space velocity, and H2O were focused on. The pristine CeO2 was lowly active for catalytic combustion of methane, ethane, and propane (T90C3 > 400 °C), while the pristine Co3O4 and doped Co3O4 presented high activity (T90C3 < 200 °C), the loading of Ru sharply improved the activity of CeO2 especially for ethane and propane (T90C3 < 150 °C) and observably depended on the Ru content, and the promotion of RuOx to Co3O4-based supports was inconspicuous. However, Ru/CeO2 catalysts were inferior to catalytic combustion of methane and lowly resistant to the high-temperature aging compared with Ru/Co3O4 catalysts. Based on characterization results and comparison with SiO2 supports with different surface areas, the Ru–O–M interface or highly dispersed RuOx species were determined as the main active sites for catalytic combustion of LHs and as follows: Ru–O–Ce interface > Ru–O–Co interface ≈ Co3O4 > highly dispersed RuOx ≫ CeO2. Ru-supported Co3O4 and doped Co3O4 especially Ce-doped Co3O4 demonstrated superior versatile activity, stability, and resistance to high temperature and H2O under harsh conditions close to the real full-scale applications, which showed the potential to eliminate the industrial VOC emissions. By contrast, Ru/CeO2 was considered to be promisingly practiced in the portable NMHC detection/monitoring system due to the huge difference in catalytic combustion of ethane/propane and methane. This work was considered to be attributed to the further understanding of the activation of C–H bonds, the optimization of Ru-based catalysts for catalytic combustion of LHs, and the rational screening of potential catalysts for different practical application scenarios.

Theoretical screening of synergistic transition metal dual-atom catalysts for overall water splitting

Double-atom catalysts (DACs) with bimetallic active sites can produce a synergistic effect between the neighbouring metallic sites, which can further enhance the catalytic activity. In this work, DFT calculations are used to screen lots of DACs as effective bifunctional electrocatalysts for overall water splitting. Through the comparative study between the DACs and single-atom catalysts (SACs), we found that DACs show higher overall water splitting activity than corresponding SACs counterparts, attributing to the synergistic effect between the adjacent active sites which play a vital role in fine tuning the binding strength of the reaction intermediates. The d-band center and charge transfer as descriptors are used to explain the activity origin of DACs. This work highlights that DACs with bimetallic active sites are promising for designing bifunctional catalysts for overall water splitting.

Theoretical screening and investigation on electrocatalytic nitrogen fixation of single transition metal atom supported by monolayer SnS2

Dispersing transition metal atoms on substrates is a novel approach to constructing (photo) electrocatalysts, which has received extensive attention in electrocatalytic nitrogen reduction reaction (NRR). Two-dimensional monolayer SnS2 is an easy-to-prepare, low-cost, and low-environmental pollution material. In this work, through first-principles calculation, fifteen transition metal atoms (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, Ru, Hf, Ta, W, Os) supported on monolayer SnS2 (TM@SnS2), respectively, are investigated as an efficient NRR catalyst. The screening of the NRR catalyst is followed by a three-step method and our results indicate that a single W atom supported on top of the Sn atom of SnS2 (W@SnS2) has the best catalytic activity, with an over potential of 0.42 V along the distal pathway, which is much lower than the reported values based on SnS2. Moreover, the N2 adsorption on W@SnS2 is far superior to the hydrogen atom adsorption, which can inhibit the competitive side reaction effectively. Our results are helpful for the design of NRR catalysts based on SnS2 monolayer.

Machine Learning Assisted Understanding and Discovery of CO2 Reduction Reaction Electrocatalyst

Electrochemical CO2 reduction reaction (CO2RR) is an important process which is a potential way to recycle excessive CO2 in the atmosphere. Although the electrocatalyst is the key toward efficient CO2RR, the progress of discovering effective catalysts is lagging with current methods. Because of the cost and time efficiency of the modern machine learning (ML) algorithm, an increasing number of researchers have applied ML to accelerate the screening of suitable catalysts and to deepen our understanding in the mechanism. Hence, we reviewed recent applications of ML in the research of CO2RR by the types of electrocatalyst. An introduction on the general methodology and a discussion on the pros and cons for such applications are included.

A Recoverable PANI/α-Fe2O3 Nanocatalyst for Ultrasound-Assisted Knovenagel Condensation

In this research work, a new PANI/α-Fe2O3 (PANI = polyaniline) nanocatalyst was prepared and applied to ultrasound-assisted Knoevenagel condensation reaction using ultrasound waves at ambient temperature. The ultrasound-assisted synthesis is a quick, green and efficient C–C bond formation reaction method. Many parameters of the condensation reaction were optimized, such as irradiation time, types of solvent, screening of catalyst and its amount. The results showed that the yields from the ultrasound-assisted reactions were higher than from non-irradiated responses as well as other conventional routes of synthesis. The prepared catalyst was characterized via SEM-EDS, FTIR, DLS and XRD studies. The stability and catalytic performance of the PANI/α-Fe2O3 were good and it could be reused six times without loss in catalytic activity. The dinitrile molecules were synthesized by Knoevenagel condensation and characterized by FTIR and NMR techniques. Compared to the reported work, the present protocol has numerous benefits such as economical, simplistic workup, high yields and, an environmentally gentle method with a shorter reaction time.

ALKYLATION OF PHENOL USING TERT-BUTANOL OVER MODIFIED CLAY CATALYSTS

Fe-bentonite is used as a catalyst for the alkylation of phenol using tert-butanol. Bentonite was modified by loading with the known concentrations of Fe/Zn/Zr. Series of catalysts such as Fe-bentonite, Zn-bentonite and Zr-bentonite were prepared by ion-exchange method and were used for the synthesis of p-tert-butylphenol (PTBP) by alkylation of phenol with tert-butylalcohol (TBA) in a batch process. Fe-bentonite was found to be an excellent catalyst with 100&amp;#37; TBA conversion and 81&amp;#37; selectivity for PTBP at 80&amp;deg;C. All the catalysts have been analyzed by different characterization methods, FTIR, XRD, TEM, SEM, and BET. The effect of various parameters like catalyst screening, reaction time, temperature, and the molar ratio of the reagents have been tested to obtain the best conversion and selectivity for the desired product.

A rotating ring disc electrode study of photo(electro)catalyst for nitrogen fixation.

There are numerous reports of photo(electro)catalysts demonstrating activity for nitrogen reduction to ammonia and a few reports of photo(electro)catalysts demonstrating activity for nitrogen oxidation to nitric acid. However, progress in advancing solar-to-fertilizer applications is slow, due in part to the pace of catalyst screening. Most evaluations of photo(electro)catalysts activity occur using batch reactors. This is because common product analyses require accumulation of ammonia or nitric acid in the reactor to overcome instrument detection limits. The primary aim here is to examine the use of an electroanalytical method, rotating ring disk electrode voltammetry (RRDE), to detect ammonia produced by a nitrogen fixing photo(electro)catalyst. To examine the potential for RRDE, we investigated a photo(electro)catalyst known to reduce nitrogen to ammonia (titania), while varying the applied electrochemical potential and degree of illumination on the disk. We show that the observed ammonia oxidation at the ring electrode corresponds strongly with ammonia measurements obtained from the bulk electrolyte. Indicating that RRDE may be effective for catalyst screening. The chief limitation of this approach is the need for an alkaline electrolyte. In addition, this approach does not rule out the presence of adventitious ammonia.

New horizons of MBenes: highly active catalysts for the CO oxidation reaction.

The search for materials with high intrinsic carbon monoxide oxidation reaction (COOR) catalytic activity is critical for enhancing the efficiency of reducing CO contamination. COOR catalysts, however, have long relied heavily on noble metals and CeO2. Herein, in order to search for non-noble COOR catalysts that are more active than CeO2, 18 oxygen-functionalized MBenes with orthorhombic and hexagonal crystal structures, denoted as orth-M2B2O2 and hex-M2B2O2 (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W), were investigated in terms of their COOR catalytic activity by high-throughput first-principles calculations. Hex-Mo2B2O2, orth-Mo2B2O2, hex-V2B2O2 and hex-Cr2B2O2 were found to be more active than CeO2 and possess structural stability below 1000 K, showing the potential to replace CeO2 as the substrates of COOR catalysts. Moreover, orth-Mo2B2O2, hex-V2B2O2 and hex-Cr2B2O2 exhibit even higher COOR catalytic activity than Pt-CeO2 and Au-CeO2, and are expected to be applied as COOR catalysts directly. Further investigations showed that the formation energy of oxygen vacancies could be used as the descriptor of COOR catalytic activity, which would help to reduce the amount of calculations significantly during the catalyst screening process. This work not only reports a series of 2D materials with high COOR catalytic activity and opens up a new application area for MBenes, but also provides a reliable strategy for highly efficient screening for COOR catalysts.

Screening of steam-reforming catalysts using unsupervised machine learning

In this article, a bidirectional clustering model proposed for methanol-reforming catalysts demonstrates excellent mathematical performance and is of significance for the discovery of methanol-reforming catalysts.

Theoretical screening of a graphyne-supported transition metal single-atom catalyst for the N2 reduction reaction.

The electrocatalytic nitrogen reduction reaction (NRR) is a promising technology for the synthesis of NH3 in an ambient environment. However, developing low-cost and high-efficiency electrocatalysts still remains a long-standing challenge. In this work, density function theory (DFT) calculations are done to systematically investigate the NRR catalytic activity of transition metals (TM = Sc-Cu, Y-Ag, and Hf-Au) supported on monolayer graphyne (GY). TM@GY (TM = Sc, V, Mn, Y, Tc, and Os) with excellent NRR performance are demonstrated. The mixed pathway is the most favorable for Sc, V, Y, and Os@GY with the potentials of -0.37, -0.27, -0.40, and -0.36 V, respectively, while the distal reaction pathway is most favorable for Mn and Tc@GY with the potentials of -0.37 and -0.42 V. Most strikingly, Mn, Tc, and Os@GY exhibit high NRR selectivity. This work provides a screening scheme for exploring highly efficient electrocatalysts for the electrochemical NRR under ambient conditions.