Enrico BergamaschiVictor J. MayerhoferChristopher J. Teskey
6页
查看更多>>摘要：We report a conceptually distinct strategy for the synthesis of 1,1-diarylalkanes and triarylalkanes. Key to this approach is the use of light to simultaneously trigger (i) formation of a CoIII-H species which undergoes H atom transfer (MHAT) to styrenes, giving a carbon-centered radical, and (ii) generation of a persistent (hetero)arene radical. Selective coupling of these two species yields Markovnikov hydroarylation products under mild conditions and without precious metals. In contrast to many previous approaches, electron-defficient (hetero)arene coupling partners are favored and it is possible to construct highly congested quaternary centers, including those with three different aryl groups.
查看更多>>摘要：Understanding catalyst surface structure changes under reactive conditions has become an important topic with the increasing interest in operando measurement and modeling. In this work, we develop a workfow to build machine learning potentials (MLPs) for simulating complicated chemical systems with large spatial and time scales, in which the committee model strategy equips the MLP with uncertainty estimation, enabling the active learning protocol. The methods are applied to constructing PtOx MLP based on explored confgurations from bulk oxides to amorphous oxidized surfaces, which cover most ordered high-oxygen-coverage platinum surfaces within an accessible energy range. This MLP is used to perform large-scale grand canonical Monte Carlo simulations to track detailed structure changes during oxidations of fat and stepped Pt surfaces, which is normally inaccessible to costly ab initio calculations. These structural evolution trajectories reveal the stages of surface oxidation without laborious manual construction of surface models. We identify the building blocks of oxide formation and elucidate the surface oxide formation mechanism on Pt surfaces. The insightful interpretations would deeply help us understand the oxide formation on other metal surfaces. We demonstrate that these large-scale simulations would be a powerful tool to investigate realistic structures and the formation mechanisms of complicated systems.
Yoshifumi KondoKotaro HondaYasutaka KuwaharaMohammad H. Samha...
11页
查看更多>>摘要：Metal-organic frameworks (MOFs) are one of the most promising candidates for photocatalytic hydrogen peroxide (H2O2) production from dioxygen (O2) and water. However, MOF-driven H2O2 production from O2 and water remains a challenge because MOF photocatalysts need to exhibit high structural stability in aqueous reaction systems while suppressing H2O2 decomposition. In the present study, we demonstrate that a Hf-based UiO-66-NH2 with missing-linker deflects and Ni single atoms dramatically promotes the photocatalytic production of H2O2 from O2 and water under visible-light (λ > 420 nm) irradiation. The acetate-capped missing-linker deflects lead to suppression of the non-radiative relaxation of organic linkers and to the prevention of H2O2 decomposition, whereas the Ni single-atom cocatalysts promote the separation of photogenerated charges and selective two-electron oxidation of water to generate H2O2. The synergetic effect of missing-linker deflects and Ni single atoms dramatically improves photocatalytic H2O2 production, resulting in a 6.3-fold increase in activity compared with that of pristine Hf-UiO-66-NH2. This study provides not only new insights into deflect engineering in MOF photocatalysts but also an important strategy for achieving highly selective H2O2 production via O2 reduction and water oxidation.
Mohammad H. SamhaJulie L. H. WahlmanJacquelyne A. Read
10页
查看更多>>摘要：Hydrogen bond-based organocatalysts rely on networks of attractive noncovalent interactions (NCIs) to impart enantioselectivity. As a specifc example, aryl pyrrolidine substituted urea, thiourea, and squaramide organocatalysts function cooperatively through hydrogen bonding and difcult-to-predict NCIs as a function of the reaction partners. To uncover the synergistic efect of the structural components of this catalyst class, we applied data science tools to study various model reactions using a derivatized, aryl pyrrolidine-based, hydrogen-bond donor (HBD) catalyst library. Through a combination of experimentally collected data and data mined from previous reports, statistical models were constructed, illuminating the general features necessary for high enantioselectivity. A distinct dependence on the identity of the electrophilic reaction partner and HBD catalyst is observed, suggesting that a general interaction is conserved throughout the reactions analyzed. The resulting models also demonstrate predictive capability by the successful improvement of a previously reported reaction using out-of-sample reaction components. Overall, this study highlights the power of data science in exploring mechanistic hypotheses in asymmetric HBD catalysis and provides a prediction platform applicable in future reaction optimization.
查看更多>>摘要：It is challenging to develop an alkyne semi-hydrogenation catalyst with both high selectivity and high activity, especially at low temperatures and low pressures. Herein, a single-atom Ni-modiffed Al2O3-supported Pd is proposed as a modulation strategy to optimize the selectivity of alkyne semi-hydrogenation. Sphere-difference-corrected transmission electron microscopy and synchrotron radiation confirm that Ni single atoms enter the alumina lattice in a highly dispersed state, while Pd is loaded on the Ni-modiffed support in the form of nanoparticles. For the semi-hydrogenation of phenylacetylene, the Pd_(0.5)/ Ni_(0.5)@γ-Al2O3 catalyst with Pd and Ni loadings of 0.45 and 0.43 wt %, respectively, achieves 98% conversion and 94% selectivity at 298 K and 0.1 MPa. It also possesses good stability, as the activity remains unchanged after 10 cycles of application. The Pd_(0.5)/Ni_(0.5)@γ-Al2O3 catalyst inherits the high activity of Pd and the high selectivity of Ni to achieve efficient semi-hydrogenation of phenylacetylene at low temperatures and pressures, benefting from the synergistic effect of Pd and Ni.
查看更多>>摘要：Hydroxide-derived copper (OH/Cu) electrodes exhibit excellent performance for the electrocatalytic CO2 reduction reaction (CO2RR). However, the role of hydroxide (OH) in CO2RR remains controversial; therefore, the origin of the selectivity enhancement emerging on OH/Cu has not been fully understood. In the present work, we quantitatively evaluated surface OH by electroadsorption and established a direct correlation between the OH amount and selectivity for the production of CH4 and C_(2+) on OH/Cu with the help of computational investigations concerning work functions of the surface. Based on these findings, we demonstrated variable selectivity using OH/Cu electrodes having a controlled OH amount; three OH/Cu electrodes realized their distinct selectivity such as Faradic efficiency (FE) for the production of CH4 (CH4 FE) of 78%, C_(2+) FE of 71%, and the ratio of C_(2+)-to-CH4 >355. The proposed simple strategy for selectivity control would contribute to further quantity synthesis of value-added chemicals using CO2RR.
查看更多>>摘要：To achieve an equitable energy transition toward net-zero 2050 goals, the electrochemical reduction of CO2 (CO2RR) to chemical feedstocks through utilizing both CO2 and renewable energy is particularly attractive. However, the catalytic activity of CO2RR is limited by the scaling relation of the adsorption energies of intermediates. Circumventing the scaling relation is a potential strategy to achieve a breakthrough in catalytic activity. Herein, based on density functional theory (DFT) calculations, we designed a high-entropy alloy (HEA) system of FeCoNiCuMo with high catalytic activity for CO2RR. Machine learning models were developed by considering 1280 adsorption sites to predict the adsorption energies of COOH*, CO*, and CHO*. The scaling relation between the adsorption energies of COOH*, CO*, and CHO* is circumvented by the rotation of COOH* and CHO* on the designed HEA surface, resulting in the outstanding catalytic activity of CO2RR with the limiting potential of 0.29-0.51 V. This work not only accelerates the development of HEA catalysts but also provides an effective strategy to circumvent the scaling relation.
查看更多>>摘要：Catalytic hydrogenation is the key measure to remove traces of acetylene in ethylene in the petroleum industry. Herein we report a highly selective and stable nanocatalyst, Pd1Ag3 supported on rutile-TiO2 (r-TiO2) annealed at unusually high temperatures (>750 °C), which can purify ethylene mixed with 1% of acetylene at 97.2% selectivity and 100% acetylene conversion below 100 °C. The selectivity is more than 10% higher than that in our previous work. This advance is achieved by a rational catalyst search featuring machine learning to correlate catalyst synthesis conditions with the catalyst performance and a large-scale machine-learning atomic simulation for disclosing composite atomic structures at high temperatures. We show that Pd1Ag3 alloy crystal nanoparticles form until 727 °C and the alloy nanoparticles grow epitaxially on r-TiO2(110) via its {111} facets. The maximum exposure of the alloy {111} surface is the key to the highest selectivity among the different supports tested, as confirmed by high-resolution characterization experiments and microkinetics simulations. Our results demonstrate the power of multiscale machine-learning tools in guiding the catalyst design and clarifying the atomic nature in complex heterogeneous catalysis.
查看更多>>摘要：Polyolefins, the largest used commodity plastics in the world, fnd extensive application in many fields. However, most end up in landflls or incineration, leading to severe ecological crises, environmental pollution, and serious resource waste problems. As representatives on chemical upcycling of polyolefin plastics polyolefin waste to fluels and bulk/fne chemicals, polyolefin catalytic cracking and hydrocracking based on zeolite or metal/zeolite composite catalysts are considered the most effective paths due to their large capacity and strong adaptability to existing petrochemical equipment. After an overview of the reaction mechanisms of pyrolysis and catalytic cracking, this review aims to comprehensively discuss the influence of zeolite catalyst structure (acidity, pore structure, and morphology) on the catalytic activity, selectivity, and stability of polyolefin cracking, particularly emphasizing the importance for matching acidity and pore structure for target product formation. Subsequently, the structure-activity relationship between the metal site and zeolite's acid site in polyolefin hydrocracking is also discussed. In the end, emerging opportunities and challenges are proposed to promote a more efficient way for polyolefin chemical upcycling.
Deepti KalsiSavarithai J. Louis AnandarajManisha Durai
9页
查看更多>>摘要：The integrated one-pot synthesis of valuable allylamines and alkylamines from amines, formaldehyde, and terminal alkynes is achieved using a single catalyst material. This multifunctional catalytic system is composed of a silica support on which are jointly assembled ruthenium nanoparticles and covalently functionalized copper N-heterocyclic carbene (NHC) complexes, introducing a new generation of nanoparticles immobilized on molecularly modiffed surfaces. The textural, structural, morphological, and electronic properties of the resulting Ru@SiO2-[Cu-NHC] material were studied by a variety of techniques including N2 adsorption, solid-state NMR, electron microscopy, and X-ray photoelectron spectroscopy. Ru@SiO2-[Cu-NHC] was found active and selective for the one-pot synthesis of a wide range of allylamines and alkylamines, products of great importance in the fine chemical and pharmaceutical industry. Detailed investigations evidenced that the immobilized molecular Cu(I)-NHC complex is responsible for the atom-efficient A~3 coupling of amines, formaldehyde, and terminal alkynes, while the selective hydrogenation of the resulting propargyl amines is catalyzed by Ru(0) nanoparticles. The design strategy and the preparation method to combine molecular and nanoparticle sites on a single support are fexible, opening the way to the development of multifunctional catalytic systems capable of performing complex reaction sequences in one pot.
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