Supported metal nanoparticles are widely used as catalysts in the industrial production of chemicals, but still suffer from deactivation because of metal leaching and sintering at high temperature. ...In recent years, serious efforts have been devoted to developing new strategies for stabilizing metal nanoparticles. Recent developments for preparing sinter‐resistant metal‐nanoparticle catalysts via strong metal–support interactions, encapsulation with oxide or carbon layers and within mesoporous materials, and fixation in zeolite crystals, are briefly summarized. Furthermore, the current challenges and future perspectives for the preparation of highly efficient and extraordinarily stable metal‐nanoparticle‐based catalysts, and suggestions regarding the mechanisms involved in sinter resistance, are proposed.
Recent advancements in the design and application of sinter‐resistant metal nanoparticles are reviewed. Several strategies are proposed for stabilizing metal nanoparticle catalysts. The exciting progress of sinter‐resistant supported metal‐nanoparticle catalysts is achieved via various methodologies, including strong metal–support interactions, encapsulation with oxide or carbon layers and within mesoporous materials, and fixation in zeolite crystals.
The adsorption of molecules on metal nanoparticles can be sterically controlled through the use of zeolite crystals, which enhances the product selectivity in hydrogenations of reactants with more ...than one reducible group. Key to this success was the fixation of Pd nanoparticles inside Beta zeolite crystals to form a defined structure (Pd@Beta). In the hydrogenation of substituted nitroarenes with multiple reducible groups as a model reaction, the Pd@Beta catalyst exhibited superior selectivity for hydrogenation of the nitro group, outperforming both conventional Pd nanoparticles supported on zeolite crystals and a commercial Pd/C catalyst. The extraordinary selectivity of Pd@Beta was attributed to the sterically selective adsorption of the nitroarenes on the Pd nanoparticles controlled by the zeolite micropores, as elucidated by competitive adsorption and adsorbate displacement tests. Importantly, this strategy is general and was extended to the synthesis of selective Pt and Ru catalysts by fixation inside Beta and mordenite zeolites.
Pitaya‐like catalysts: Pd nanoparticles were fixed inside Beta zeolite crystals (Pd@Beta) to obtain a catalyst that displayed superior selectivity in the hydrogenation of substituted nitroarenes with multiple reducible groups. The high selectivity was attributed to the sterically controlled adsorption of the nitroarenes on the Pd nanoparticles within the zeolite micropores.
Green chemistry is used to investigate the synthesis of zeolites. Ionic liquids can be used to prepare zeolites, while zeolite seeds can enhance the crystallization rate of zeolites.
Abstract
The reaction pathways on supported catalysts can be tuned by optimizing the catalyst structures, which helps the development of efficient catalysts. Such design is particularly desired for ...CO
2
hydrogenation, which is characterized by complex pathways and multiple products. Here, we report an investigation of supported cobalt, which is known for its hydrocarbon production and ability to turn into a selective catalyst for methanol synthesis in CO
2
hydrogenation which exhibits good activity and stability. The crucial technique is to use the silica, acting as a support and ligand, to modify the cobalt species via Co‒O‒SiO
n
linkages, which favor the reactivity of spectroscopically identified *CH
3
O intermediates, that more readily undergo hydrogenation to methanol than the C‒O dissociation associated with hydrocarbon formation. Cobalt catalysts in this class offer appealing opportunities for optimizing selectivity in CO
2
hydrogenation and producing high-grade methanol. By identifying this function of silica, we provide support for rationally controlling these reaction pathways.
In many reactions restricted by water, selective removal of water from the reaction system is critical and usually requires a membrane reactor. We found that a simple physical mixture of hydrophobic ...poly(divinylbenzene) with cobalt-manganese carbide could modulate a local environment of catalysts for rapidly shipping water product in syngas conversion. We were able to shift the water-sorption equilibrium on the catalyst surface, leading to a greater proportion of free surface that in turn raised the rate of syngas conversion by nearly a factor of 2. The carbon monoxide conversion reached 63.5%, and 71.4% of the hydrocarbon products were light olefins at 250°C, outperforming poly(divinylbenzene)-free catalyst under equivalent reaction conditions. The physically mixed CoMn carbide/poly(divinylbenzene) catalyst was durable in the continuous test for 120 hours.
Channeling water away
Heterogeneous catalytic reactions that produce water as a by-product can be inhibited by its presence on the surface. Fang
et al
. found that for the production of light olefins from syngas (a 2:1 mixture of hydrogen and carbon monoxide) with a cobalt manganese carbide catalyst at 250°C, the addition of the hydrophobic polymer polydivinylbenzene as part of a physical mixture almost doubled the conversion of carbon monoxide (see the Perspective by Ding and Xu). Theoretical models suggest that the polymer formed channels that accelerated water diffusion away from the catalyst. —PDS
Mixing a hydrophobic polymer with a solid catalyst improves performance by accelerating the escape of product water.
Methods for the hydrogenation of CO2 into valuable chemicals are in great demand but their development is still challenging. Herein, we report the selective hydrogenation of CO2 into ethanol over ...non‐noble cobalt catalysts (CoAlOx), presenting a significant advance for the conversion of CO2 into ethanol as the major product. By adjusting the composition of the catalysts through the use of different prereduction temperatures, the efficiency of CO2 to ethanol hydrogenation was optimized; the catalyst reduced at 600 ° gave an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g−1 h−1. Operando FT‐IR spectroscopy revealed that the high ethanol selectivity over the CoAlOx catalyst might be due to the formation of acetate from formate by insertion of *CHx, a key intermediate in the production of ethanol by CO2 hydrogenation.
Just ethanol: CO2 was selectively hydrogenated into ethanol over non‐noble cobalt catalysts (CoAlOx). By adjusting the composition of the catalysts through the use of different prereduction temperatures, the efficiency of the reaction was optimized to give an ethanol selectivity of 92.1 % at 140 °C with an ethanol time yield of 0.444 mmol g−1 h−1. The high ethanol selectivity might be due to the formation of acetate from formate by *CHx insertion.
The contribution of catalyst wettability for catalytic performance has been ignored for a long time. In this Concept, we have briefly summarized recent works on the importance of catalyst wettability ...for improving catalytic activity, product selectivity, and catalyst stability. Suitable catalyst wettability is favourable for several reasons: 1) to enrich the reactants, leading to enhancement of the catalytic activity; 2) to inhibit side‐reactions, giving desirable products; 3) to reduce the poisoning of active sites and damage to catalyst framework, resulting in an increase of catalyst stability. These advantages of suitable catalyst wettability will be very important for designing and developing novel heterogeneous catalysts in the future.
When just getting wet is not enough: Preparation of highly efficient heterogeneous catalysts is mainly devoted to designing catalytic sites, and the catalyst wettability has been overlooked for a long time. Here, it is shown that the catalyst wettability is also an important factor for improving catalytic activity, product selectivity, and catalyst stability. The catalyst wettability should be considerable for designing and developing novel heterogeneous catalysts in the future.
Herein, we show how the spatial environment in the functional pores of covalent organic frameworks (COFs) can be manipulated in order to exert control in catalysis. The underlying mechanism of this ...strategy relies on the placement of linear polymers in the pore channels that are anchored with catalytic species, analogous to outer‐sphere residue cooperativity within the active sites of enzymes. This approach benefits from the flexibility and enriched concentration of the functional moieties on the linear polymers, enabling the desired reaction environment in close proximity to the active sites, thereby impacting the reaction outcomes. Specifically, in the representative dehydration of fructose to produce 5‐hydroxymethylfurfural, dramatic activity and selectivity improvements have been achieved for the active center of sulfonic acid groups in COFs after encapsulation of polymeric solvent analogues 1‐methyl‐2‐pyrrolidinone and ionic liquid.
Creating a solvation environment: The catalytic performance of sulfonic acid groups in covalent organic frameworks (COFs) can be greatly amplified by the introduction of polymeric solvent analogues, which create desired solvation environments through hydrogen‐bonding interactions. Improved activity and selectivity was demonstrated by the COF‐catalyzed dehydration of fructose to produce 5‐hydroxymethylfurfural.
Atomically dispersed supported metal catalysts are drawing wide attention because of the opportunities they offer for new catalytic properties combined with efficient use of the metals. We extend ...this class of materials to catalysts that incorporate atomically dispersed metal atoms as promoters. The catalysts are used for the challenging nitroarene hydrogenation and found to have both high activity and selectivity. The promoters are single-site Sn on TiO
supports that incorporate metal nanoparticle catalysts. Represented as M/Sn-TiO
(M = Au, Ru, Pt, Ni), these catalysts decidedly outperform the unpromoted supported metals, even for hydrogenation of nitroarenes substituted with various reducible groups. The high activity and selectivity of these catalysts result from the creation of oxygen vacancies on the TiO
surface by single-site Sn, which leads to efficient, selective activation of the nitro group coupled with a reaction involving hydrogen atoms activated on metal nanoparticles.
Zeolite nanosheets for catalysis Wang, Xiangyu; Ma, Ye; Wu, Qinming ...
Chemical Society reviews,
04/2022, Volume:
51, Issue:
7
Journal Article
Peer reviewed
Zeolites with well-defined micropores have been widely used as heterogeneous catalysts in the fields of petroleum refining, fine chemicals, and environment protection. However, the sole micropores in ...the zeolite structures usually impose diffusion constraints, which would greatly influence their catalytic performances. Therefore, it is highly desirable to shorten the diffusion pathway of zeolites and thus eliminate the diffusion constraints. One of the efficient methods is to synthesize zeolite nanosheets, which has become a hot topic in the past decades. In this tutorial review, the recent progresses in the synthesis of zeolite nanosheets and their relevant catalysis are briefly discussed. Various strategies for the synthesis of zeolite nanosheets are summarized including delamination, templated crystallization, additive-assisted synthesis, seed-directed synthesis, and gaseous expansion synthesis. In addition, the catalytic reactions of zeolite nanosheets with acidic and metal sites are also outlined. This tutorial review should be significant for the design and preparation of highly efficient zeolite catalysts.
This tutorial review briefly summarizes the recent progress in the synthetic strategies of zeolite nanosheets and their relevant catalytic applications.
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