On the Acid Sites of Phosphorous Modified Zeosils

The acid sites of phosphorus-containing zeosils were probed through a combination of solid acid characterization, density functional theory calculations, and kinetic interrogations, establishing their weakly Brønsted acidic character. Due to the disparity in acid-site strength, P-zeosils catalyzed the probe chemistry of isopropanol dehydration slower than aluminosilicate zeolites by an order of magnitude on an active site basis. Propene selectivity during isopropanol dehydration remained 20-30% higher than that of aluminosilicates, illustrating the distinct nature of the weakly acidic phosphorus active sites that favored unimolecular dehydration routes. Regardless of the confining siliceous environment, the nature of phosphorous active sites was unchanged, indicated by identical apparent uni- and bi-molecular dehydration energy barriers. Kinetic isotope experiments with deuterated isopropanol feeds implicated an E2-type elimination to propene formation on phosphorus-containing materials. Comparison of KIEs between phosphorus-containing zeosils and aluminosilicates pointed to an unchanged isopropanol dehydration mechanism, with changes in apparent energetic barriers attributed to weaker binding on phosphorous-active sites that lead to a relatively destabilized alcohol dimer adsorbate. Both ex-situ alkylamine Hofmann elimination and in-situ pyridine titration characterization methods exhibited phosphorous acid site counts dependent on probe molecules identity and/or concentration, underpinning the limitations of extending common characterization techniques for Brønsted-acid catalysis to weakly acidic materials.

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On the Acid Sites of Phosphorous Modified Zeosils

10.26434/chemrxiv.14225942 ◽

2021 ◽

Author(s):

Gaurav Kumar ◽

Limin Ren ◽

Yutong Pang ◽

Xinyu Li ◽

Han Chen ◽

...

Keyword(s):

Acid Site ◽

Active Sites ◽

Density Functional ◽

Phosphorous Acid ◽

Density Functional Theory Calculations ◽

Acid Sites ◽

Ex Situ ◽

Characterization Methods ◽

Isopropanol Dehydration ◽

Phosphorus Containing

The acid sites of phosphorus-containing zeosils were probed through a combination of solid acid characterization, density functional theory calculations, and kinetic interrogations, establishing their weakly Brønsted acidic character. Due to the disparity in acid-site strength, P-zeosils catalyzed the probe chemistry of isopropanol dehydration slower than aluminosilicate zeolites by an order of magnitude on an active site basis. Propene selectivity during isopropanol dehydration remained 20-30% higher than that of aluminosilicates, illustrating the distinct nature of the weakly acidic phosphorus active sites that favored unimolecular dehydration routes. Regardless of the confining siliceous environment, the nature of phosphorous active sites was unchanged, indicated by identical apparent uni- and bi-molecular dehydration energy barriers. Kinetic isotope experiments with deuterated isopropanol feeds implicated an E2-type elimination to propene formation on phosphorus-containing materials. Comparison of KIEs between phosphorus-containing zeosils and aluminosilicates pointed to an unchanged isopropanol dehydration mechanism, with changes in apparent energetic barriers attributed to weaker binding on phosphorous-active sites that lead to a relatively destabilized alcohol dimer adsorbate. Both ex-situ alkylamine Hofmann elimination and in-situ pyridine titration characterization methods exhibited phosphorous acid site counts dependent on probe molecules identity and/or concentration, underpinning the limitations of extending common characterization techniques for Brønsted-acid catalysis to weakly acidic materials.

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Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes

10.26434/chemrxiv.8150660 ◽

2019 ◽

Author(s):

Yan Wang ◽

Sagar Udyavara ◽

Matthew Neurock ◽

C. Daniel Frisbie

Keyword(s):

Electric Field ◽

Hydrogen Evolution ◽

Active Sites ◽

Density Functional ◽

Electrode Materials ◽

Density Functional Theory Calculations ◽

Electronic Charge ◽

Back Side ◽

Gate Electrode ◽

Conventional Manner

<div> <div> <div> <p> </p><div> <div> <div> <p>Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140-mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of 4 to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced electronic charge on Mo metal centers adjacent the S vacancies (the active sites), leading to enhanced Mo-H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.</p></div></div></div><br><p></p></div></div></div>

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Towards a Design of Active Oxygen Evolution Catalysts: Insights from Automated Density Functional Theory Calculations and Machine Learning

10.26434/chemrxiv.7926869 ◽

2019 ◽

Author(s):

Seoin Back ◽

Kevin Tran ◽

Zachary Ulissi

Keyword(s):

Machine Learning ◽

Oxygen Evolution ◽

Active Sites ◽

Density Functional ◽

Chemical Space ◽

Density Functional Theory Calculations ◽

Catalyst Design ◽

Transition Metal Catalysts ◽

Oxide Materials ◽

Design Strategies

<div> <div> <div> <div><p>Developing active and stable oxygen evolution catalysts is a key to enabling various future energy technologies and the state-of-the-art catalyst is Ir-containing oxide materials. Understanding oxygen chemistry on oxide materials is significantly more complicated than studying transition metal catalysts for two reasons: the most stable surface coverage under reaction conditions is extremely important but difficult to understand without many detailed calculations, and there are many possible active sites and configurations on O* or OH* covered surfaces. We have developed an automated and high-throughput approach to solve this problem and predict OER overpotentials for arbitrary oxide surfaces. We demonstrate this for a number of previously-unstudied IrO2 and IrO3 polymorphs and their facets. We discovered that low index surfaces of IrO2 other than rutile (110) are more active than the most stable rutile (110), and we identified promising active sites of IrO2 and IrO3 that outperform rutile (110) by 0.2 V in theoretical overpotential. Based on findings from DFT calculations, we pro- vide catalyst design strategies to improve catalytic activity of Ir based catalysts and demonstrate a machine learning model capable of predicting surface coverages and site activity. This work highlights the importance of investigating unexplored chemical space to design promising catalysts.<br></p></div></div></div></div><div><div><div> </div> </div> </div>

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Study on the adsorption selection of CH$$_4$$ on CuO (110) versus (111) surfaces: a density functional theory study

SN Applied Sciences ◽

10.1007/s42452-021-04386-x ◽

2021 ◽

Vol 3 (4) ◽

Author(s):

Long Lin ◽

Linwei Yao ◽

Shaofei Li ◽

Zhengguang Shi ◽

Kun Xie ◽

...

Keyword(s):

Density Functional Theory ◽

Adsorption Capacity ◽

Active Sites ◽

Density Functional ◽

Oxygen Vacancies ◽

Density Functional Theory Calculations ◽

Density Functional Theory Study ◽

Functional Theory ◽

Strong Adsorption ◽

Selection Of

AbstractFinding the active sites of suitable metal oxides is a key prerequisite for detecting CH$$_4$$ 4 . The purpose of the paper is to investigate the adsorption of CH$$_4$$ 4 on intrinsic and oxygen-vacancies CuO (111) and (110) surfaces using density functional theory calculations. The results show that CH$$_4$$ 4 has a strong adsorption energy of −0.370 to 0.391 eV at all site on the CuO (110) surface. The adsorption capacity of CH$$_4$$ 4 on CuO (111) surface is weak, ranging from −0.156 to −0.325 eV. In the surface containing oxygen vacancies, the adsorption capacity of CuO surface to CH$$_4$$ 4 is significantly stronger than that of intrinsic CuO surface. The results indicate that CuO (110) has strong adsorption and charge transfer capacity for CH$$_4$$ 4 , which may provide experimental guidance.

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Theoretical Study of Zirconium Isomorphous Substitution into Zeolite Frameworks

Molecules ◽

10.3390/molecules24244466 ◽

2019 ◽

Vol 24 (24) ◽

pp. 4466

Author(s):

Duichun Li ◽

Bin Xing ◽

Baojun Wang ◽

Ruifeng Li

Keyword(s):

Acid Site ◽

Density Functional ◽

Theoretical Study ◽

Atomic Radius ◽

Acid Sites ◽

Isomorphous Substitution ◽

Dispersion Correction ◽

Brønsted Acidity ◽

Functional Theory ◽

Brönsted Acidity

Systematic periodic density functional theory computations including dispersion correction (DFT-D) were carried out to determine the preferred location site of Zr atoms in sodalite (SOD) and CHA-type topology frameworks, including alumino-phosphate-34 (AlPO-34) and silico-alumino-phosphate-34 (SAPO-34), and to determine the relative stability and Brönsted acidity of Zr-substituted forms of SOD, AlPO-34, and SAPO-34. Mono and multiple Zr atom substitutions were considered. The Zr substitution causes obvious structural distortion because of the larger atomic radius of Zr than that of Si, however, Zr-substituted forms of zeolites are found to be more stable than pristine zeolites. Our results demonstrate that in the most stable configurations, the preferred favorable substitutions of Zr in substituted SOD have Zr located at the neighboring sites of the Al-substituted site. However, in the AlPO-34 and SAPO-34 frameworks, the Zr atoms are more easily distributed in a dispersed form, rather than being centralized. Brönsted acidity of substituted zeolites strongly depends on Zr content. For SOD, substitution of Zr atoms reduces Brönsted acidity. However, for Zr-substituted forms of AlPO-34 and SAPO-34, Brönsted acidity of the Zr-O(H)-Al acid sites are, at first, reduced and, then, the presence of Zr atoms substantially increased Brönsted acidity of the Zr-O(H)-Al acid site. The results in the SAPO-34-Zr indicate that more Zr atoms substantially increase Brönsted acidity of the Si-O(H)-Al acid site. It is suggested that substituted heteroatoms play an important role in regulating and controlling structural stability and Brönsted acidity of zeolites.

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Mechanism of selective benzene hydroxylation catalyzed by iron-containing zeolites

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1813849115 ◽

2018 ◽

Vol 115 (48) ◽

pp. 12124-12129 ◽

Cited By ~ 3

Author(s):

Benjamin E. R. Snyder ◽

Max L. Bols ◽

Hannah M. Rhoda ◽

Pieter Vanelderen ◽

Lars H. Böttger ◽

...

Keyword(s):

High Activity ◽

Active Site ◽

Active Sites ◽

High Performance ◽

Density Functional ◽

Catalyst Deactivation ◽

Density Functional Theory Calculations ◽

Oxidation Catalysis ◽

Spectroscopic Techniques ◽

Benzene Hydroxylation

A direct, catalytic conversion of benzene to phenol would have wide-reaching economic impacts. Fe zeolites exhibit a remarkable combination of high activity and selectivity in this conversion, leading to their past implementation at the pilot plant level. There were, however, issues related to catalyst deactivation for this process. Mechanistic insight could resolve these issues, and also provide a blueprint for achieving high performance in selective oxidation catalysis. Recently, we demonstrated that the active site of selective hydrocarbon oxidation in Fe zeolites, named α-O, is an unusually reactive Fe(IV)=O species. Here, we apply advanced spectroscopic techniques to determine that the reaction of this Fe(IV)=O intermediate with benzene in fact regenerates the reduced Fe(II) active site, enabling catalytic turnover. At the same time, a small fraction of Fe(III)-phenolate poisoned active sites form, defining a mechanism for catalyst deactivation. Density-functional theory calculations provide further insight into the experimentally defined mechanism. The extreme reactivity of α-O significantly tunes down (eliminates) the rate-limiting barrier for aromatic hydroxylation, leading to a diffusion-limited reaction coordinate. This favors hydroxylation of the rapidly diffusing benzene substrate over the slowly diffusing (but more reactive) oxygenated product, thereby enhancing selectivity. This defines a mechanism to simultaneously attain high activity (conversion) and selectivity, enabling the efficient oxidative upgrading of inert hydrocarbon substrates.

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First-Principles DFT Insights into the Mechanisms of CO2 Reduction to CO on Fe (100)-Ni Bimetals

10.21203/rs.3.rs-540311/v1 ◽

2021 ◽

Author(s):

Caroline Kwawu ◽

Albert Aniagyei ◽

Destiny Konadu ◽

Elliot Menkah ◽

Richard Tia

Keyword(s):

Carbon Monoxide ◽

Binding Site ◽

Active Sites ◽

Density Functional ◽

Co2 Reduction ◽

Density Functional Theory Calculations ◽

Hydrocarbon Fuel ◽

Generalized Gradient ◽

Efficient Catalyst ◽

Stepped Surface

Abstract Iron and nickel are known active sites in the enzyme carbon monoxide dehydrogenases (CODH) which catalyzes CO2 to CO reversibly. The presence of nickel impurities in the earth abundant iron surface could provide a more efficient catalyst for CO2 degradation into CO, which is a feedstock for hydrocarbon fuel production. In the present study, we have employed spin-polarized dispersion-corrected density functional theory calculations within the generalized gradient approximation to elucidate the active sites on Fe (100)-Ni bimetals. We sort to ascertain the mechanism of CO2 dissociation to carbon monoxide on Ni deposited and alloyed surfaces at 0.25, 0.50 and 1 monolayer (ML) impurity concentrations. CO2 and (CO + O) bind exothermically i.e., -0.87 eV and − 1.51 eV respectively to the bare Fe (100) surface with a decomposition barrier of 0.53 eV. The presence of nickel generally lowers the amount of charge transferred to CO2 moiety. Generally, the binding strengths of CO2 were reduced on the modified surfaces and the extent of its activation was lowered. The barriers for CO2 dissociation increased mainly upon introduction of Ni impurities which is undesired. However, the 0.5 ML deposited (FeNi0.5(A)) surface is promising for CO2 decomposition, providing a lower energy barrier (of 0.32 eV) than the pristine Fe (100) surface. This active 1-dimensional defective FeNi0.5(A) surface provides a stepped surface and Ni-Ni bridge binding site for CO2 on Fe (100). Ni-Ni bridge site on Fe (100) is more effective for both CO2 binding or sequestration and dissociation compared to the stepped surface providing the Fe-Ni bridge binding site.

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Nitrogen-rich covalent organic frameworks with multiple carbonyls for high-performance sodium batteries

Nature Communications ◽

10.1038/s41467-019-13739-5 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 32

Author(s):

Ruijuan Shi ◽

Luojia Liu ◽

Yong Lu ◽

Chenchen Wang ◽

Yixin Li ◽

...

Keyword(s):

High Performance ◽

Density Functional ◽

Specific Capacity ◽

Density Functional Theory Calculations ◽

Rechargeable Batteries ◽

High Rate ◽

Ex Situ ◽

Covalent Organic Frameworks ◽

Rate Performance ◽

Practical Applications

AbstractCovalent organic frameworks with designable periodic skeletons and ordered nanopores have attracted increasing attention as promising cathode materials for rechargeable batteries. However, the reported cathodes are plagued by limited capacity and unsatisfying rate performance. Here we report a honeycomb-like nitrogen-rich covalent organic framework with multiple carbonyls. The sodium storage ability of pyrazines and carbonyls and the up-to twelve sodium-ion redox chemistry mechanism for each repetitive unit have been demonstrated by in/ex-situ Fourier transform infrared spectra and density functional theory calculations. The insoluble electrode exhibits a remarkably high specific capacity of 452.0 mAh g−1, excellent cycling stability (~96% capacity retention after 1000 cycles) and high rate performance (134.3 mAh g−1 at 10.0 A g−1). Furthermore, a pouch-type battery is assembled, displaying the gravimetric and volumetric energy density of 101.1 Wh kg−1cell and 78.5 Wh L−1cell, respectively, indicating potentially practical applications of conjugated polymers in rechargeable batteries.

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Gold Nanoclusters Grown on MoS2 Nanosheets by Pulsed Laser Deposition: An Enhanced Hydrogen Evolution Reaction

Molecules ◽

10.3390/molecules26247503 ◽

2021 ◽

Vol 26 (24) ◽

pp. 7503

Author(s):

Yuting Jing ◽

Ruijing Wang ◽

Qiang Wang ◽

Xuefeng Wang

Keyword(s):

Active Sites ◽

Density Functional ◽

Au Nanoparticles ◽

Gold Nanoclusters ◽

Density Functional Theory Calculations ◽

Laser Deposition ◽

Mos2 Nanosheets ◽

Functional Theory ◽

The Density Functional Theory ◽

A Current

Au nanoparticles were decorated on a 2H MoS2 surface to form an Au/MoS2 composite by pulse laser deposition. Improved HER activity of Au/MoS2 is evidenced by a positively shifted overpotential (−77 mV) at a current density of −10 mA cm−2 compared with pure MoS2 nanosheets. Experimental evidence shows that the interface between Au and MoS2 provides more sites to combine protons to form an active H atom. The density functional theory calculations found that new Au active sites on the Au and MoS2 interface with improved conductivity of the whole system are essential for enhancing HER activity of Au/MoS2.

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