Hierarchically porous materials: synthesis strategies and structure design

Chemical Society Reviews, Год журнала: 2016, Номер 46(2), С. 481 - 558

Опубликована: Дек. 1, 2016

This review addresses recent advances in synthesis strategies of hierarchically porous materials and their structural design from micro-, meso- to macro-length scale.

Язык: Английский

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Dynamic multinuclear sites formed by mobilized copper ions in NO _x selective catalytic reduction

Science, Год журнала: 2017, Номер 357(6354), С. 898 - 903

Опубликована: Авг. 18, 2017

Copper ions exchanged into zeolites are active for the selective catalytic reduction (SCR) of nitrogen oxides (NO x ) with ammonia (NH3), but low-temperature rate dependence on copper (Cu) volumetric density is inconsistent reaction at single sites. We combine steady-state and transient kinetic measurements, x-ray absorption spectroscopy, first-principles calculations to demonstrate that under conditions, mobilized Cu can travel through zeolite windows form ion pairs participate in an oxygen (O2)-mediated CuI→CuII redox step integral SCR. Electrostatic tethering framework aluminum centers limits volume each explore thus its capacity pair. The dynamic, reversible formation multinuclear sites from atoms represents a distinct phenomenon falls outside conventional boundaries heterogeneous or homogeneous catalyst.

Язык: Английский

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Selective anaerobic oxidation of methane enables direct synthesis of methanol

Science, Год журнала: 2017, Номер 356(6337), С. 523 - 527

Опубликована: Май 4, 2017

Direct functionalization of methane in natural gas remains a key challenge. We present direct stepwise method for converting into methanol with high selectivity (~97%) over copper-containing zeolite, based on partial oxidation water. The activation helium at 673 kelvin (K), followed by consecutive catalyst exposures to 7 bars and then water 473 K, consistently produced 0.204 mole CH3OH per copper zeolite. Isotopic labeling confirmed as the source oxygen regenerate zeolite active centers renders desorption energetically favorable. On basis situ x-ray absorption spectroscopy, infrared density functional theory calculations, we propose mechanism involving CuII oxide centers, CuI reoxidation concurrent formation hydrogen.

Язык: Английский

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Small-Pore Zeolites: Synthesis and Catalysis

Chemical Reviews, Год журнала: 2018, Номер 118(11), С. 5265 - 5329

Опубликована: Май 10, 2018

In the past decade or so, small-pore zeolites have received greater attention than large- and medium-pore molecular sieves that historically dominated literature. This is primarily due to commercialization of two major catalytic processes, NOx exhaust removal methanol conversion light olefins, take advantage properties these materials with smaller apertures. Small-pore possess pores are constructed eight tetrahedral atoms (Si4+ Al3+), each time linked by a shared oxygen These eight-member ring (8MR) provide small molecules access intracrystalline void space, e.g., during car cleaning (NOx removal) en route its into while restricting larger molecule entrance departure critical overall catalyst performance. total, there forty-four structurally different zeolites. Forty-one can be synthesized, first synthetic zeolite (KFI, 1948) was in fact material. Although field 8MR chemistry has expanded many directions, progress synthesis framework-specific, leaving insights generalizations difficult realize. review focuses on relevant details all provides some generalized findings related insights. Next, applications where either been commercialized investigations presented, aim providing structure-activity relationships. The ends summary discusses (i) both progress, (ii) list opportunities field, (iii) brief future outlook.

Язык: Английский

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The Direct Catalytic Oxidation of Methane to Methanol—A Critical Assessment

Angewandte Chemie International Edition, Год журнала: 2017, Номер 56(52), С. 16464 - 16483

Опубликована: Июнь 23, 2017

Despite the large number of disparate approaches for direct selective partial oxidation methane, none them has translated into an industrial process. The methane to methanol is a difficult, but intriguing and rewarding, task as it potential eliminate prevalent natural gas flaring by providing novel routes its valorization. This Review considers synthesis derivatives from homogeneous heterogeneous pathways. By establishing severe limitations related catalytic we highlight vastly superior performance systems which produce or incorporate specific measures, such use multicomponent catalysts stabilize methanol. We thereby identify protection being indispensable future research on catalysis.

Язык: Английский

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Copper–Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity

Chemical Reviews, Год журнала: 2017, Номер 117(3), С. 2059 - 2107

Опубликована: Янв. 19, 2017

A longstanding research goal has been to understand the nature and role of copper–oxygen intermediates within copper-containing enzymes abiological catalysts. Synthetic chemistry played a pivotal in highlighting viability proposed expanding library known cores. In addition number new complexes that have synthesized since previous reviews on this topic journal (Mirica, L. M.; Ottenwaelder, X.; Stack, T. D. P. Chem. Rev. 2004, 104, 1013–1046 Lewis, E. A.; Tolman, W. B. 1047–1076), field seen significant expansion (1) range cores characterized, (2) amount mechanistic work performed, particularly area organic substrate oxidation, (3) use computational methods for both corroboration prediction intermediates. The scope review limited well-characterized examples species but seeks provide thorough picture spectroscopic characteristics reactivity trends discussed.

Язык: Английский

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Strategies for the Direct Catalytic Valorization of Methane Using Heterogeneous Catalysis: Challenges and Opportunities

ACS Catalysis, Год журнала: 2016, Номер 6(5), С. 2965 - 2981

Опубликована: Март 31, 2016

In this Perspective, we highlight the main challenges to be addressed in development of heterogeneous catalysts for direct functionalization methane. Along with our personal view on current developments field, outline mechanistic, engineering, and catalyst design issues that have hampered implementation new technologies possible paths overcome these problems.

Язык: Английский

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New trends in tailoring active sites in zeolite-based catalysts

Chemical Society Reviews, Год журнала: 2019, Номер 48(4), С. 1095 - 1149

Опубликована: Янв. 1, 2019

This review discusses approaches for tailoring active sites in extra-large pore, nanocrystalline, and hierarchical zeolites their performance emerging catalytic applications.

Язык: Английский

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Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature

ACS Central Science, Год журнала: 2016, Номер 2(6), С. 424 - 429

Опубликована: Июнь 13, 2016

The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C-H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration direct, oxidation into over copper-exchanged zeolites reaction temperatures (483-498 K). Reaction kinetics studies show sustained activity and high selectivity for variety commercially available zeolite topologies under mild conditions (e.g., 483 K atmospheric pressure). Transient steady state measurements isotopically labeled molecules confirm turnover. rates apparent energies are affected by topology, caged-based Cu-SSZ-13) showing highest rates. Although low, discovery sites will accelerate development strategies directly oxidize conditions.

Язык: Английский

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Iron and Copper Active Sites in Zeolites and Their Correlation to Metalloenzymes

Chemical Reviews, Год журнала: 2017, Номер 118(5), С. 2718 - 2768

Опубликована: Дек. 19, 2017

Metal-exchanged zeolites are a class of heterogeneous catalysts that perform important functions ranging from selective hydrocarbon oxidation to remediation NOx pollutants. Among these, copper and iron remarkably reactive, hydroxylating methane benzene selectively at low temperature form methanol phenol, respectively. In these systems, reactivity occurs well-defined molecular transition metal active sites, in this review we discuss recent advances the spectroscopic characterization sites their reactive intermediates. Site-selective spectroscopy continues play key role, making it possible focus on exist within distribution inactive spectator centers. The definition geometric electronic structures metallozeolites has advanced level bioinorganic chemistry, enabling direct comparison metallozeolite functionally analogous Fe Cu biology. We identify significant parallels differences strategies used by each achieve high reactivity, highlighting potentially interesting mechanisms tune performance synthetic catalysts.

Язык: Английский

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