Tandem Catalysis by Palladium Nanoclusters Encapsulated in Metal-Organic Frameworks
Abstract not provided
Li, Xinle↗
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Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism
In this work, the scope and mechanism of thermodynamically leveraged ester RC(O)O–R' bond hydrogenolysis by tandem metal triflate + supported Pd catalysts are investigated both experimentally and theoretically by DFT and energy span analysis. This catalytic system has a broad scope, with relative cleavage rates scaling as, tertiary > secondary > primary ester at 1 bar H 2 , yielding alkanes and carboxylic acids with high conversion and selectivity. Benzylic and allylic esters display the highest activity. The rate law is ν = k [M(OTf) n ] 1 [ester] 0 [H 2 ] 0 with an H/D kinetic isotope effect = 6.5 ± 0.5, implying turnover-limiting C–H scission following C–O cleavage, in agreement with theory. Intermediate alkene products are then rapidly hydrogenated. Applying this approach with the very active Hf(OTf) 4 catalyst to bio-derived triglycerides affords near-quantitative yields of C 3 hydrocarbons rather than glycerol. From model substrates, it is found that RC(O)O–R' cleavage rates are very sensitive to steric congestion and metal triflate identity. For triglycerides, primary/external glyceryl CH 2 –O cleavage predominates over secondary/internal CH–O cleavage, with the latter favored by less acidic or smaller ionic radius metal triflates, raising the diester selectivity to as high as 48% with Ce(OTf) 3 .
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Compartmentalisation of molecular catalysts for nonorthogonal tandem catalysis
The development of nonorthogonal tandem catalysis enables the use of a combination of arbitrary catalysts to rapidly synthesize complex products in a substainable, efficient, and timely manner. The key is to compartmentalise the molecular catalysts, thereby overcoming inherent incompatibilities between individual catalysts or reaction conditions. This tutorial review analyses the development of the past two decades in the field of nonorthogonal tandem catalysis with an emphasis on compartmentalisation strategies. Here, we highlight design principles of functional materials for compartmentalisation and suggest future directions in the field of nonorthogonal tandem catalysis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Dual active site tandem catalysis of metal hydroxyl oxides and single atoms for boosting oxygen evolution reaction
We report the high voltage in oxygen evolution reaction (OER) often causes structural change in electrocatalysts and forms multiple active sites. Therefore, exploring the synergy of various active sites is extremely significant to develop catalysts for OER with multiple elementary steps. Herein, we adopt the physically adsorbed metal ions method to successfully synthesize a highly-efficient electrocatalyst containing the dual active sites of Fe-NiOOH and NiC4 single atoms (marked as Ni SAs/Fe-NiOOH). The Ni SAs/Fe-NiOOH displays outstanding OER performance with an overpotential of 269 mV to deliver current density of 10 mA/cm 2 that shows 55 mV superior to commercial IrO 2 /CB at the same condition. Experiments and density functional theory calculations indicate that the excellent OER activity of Ni SAs/Fe-NiOOH catalyst is attributed to the synergy of dual active sites of NiC 4 SAs and Fe-NiOOH. A tandem catalysis mechanism is also proposed to reveal the synergism of two active centers, which makes the potential-determining step more facile and accordingly decreases the OER overpotential. This work offers a new concept of tandem catalysis to develop the electrocatalysts with many elemental steps, like OER and oxygen reduction reaction catalysts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Correction: Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism
Correction for ‘Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism’ by Tracy L. Lohr et al. , Energy Environ. Sci. , 2016, 9 , 550–564.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Tandem Catalysis for CO 2 Hydrogenation to C 2 –C 4 Hydrocarbons
Conversion of carbon dioxide to C 2 -C 4 hydrocarbons is a major pursuit in clean energy research. Despite tremendous efforts, the lack of well-defined catalysts in which the spatial arrangement of interfaces is precisely controlled hinders the development of more efficient catalysts and in-depth understanding of reaction mechanisms. Herein, we utilized the strategy of tandem catalysis to develop a well-defined nanostructured catalyst CeO 2 -Pt@mSiO2-Co for converting CO 2 to C 2 -C 4 hydrocarbons using two metal-oxide interfaces. C 2 -C 4 hydrocarbons are found to be produced with high (60%) selectivity, which is speculated to be the result of the two-step tandem process uniquely allowed by this catalyst. Namely, the Pt/CeO 2 interface converts CO 2 and H 2 to CO, and on the neighboring Co/mSiO 2 interface yields C 2 -C 4 hydrocarbons through a subsequent Fischer-Tropsch process. In addition, the catalysts show no obvious deactivation over 40 h. The successful production of C 2 -C 4 hydrocarbons via a tandem process on a rationally designed, structurally well-defined catalyst demonstrates the power of sophisticated structure control in designing nanostructured catalysts for multiple-step chemical conversions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Compartmentalization and Photo-Regulating Pathways for Incompatible Tandem Catalysis
This contribution describes an advanced compartmentalized micellar nanoreactor that possesses a reversible photoresponsive feature and its application towards photo-regulating reaction pathways for incompatible tandem catalysis under aqueous conditions. The smart nanoreactor is based on multi-functional amphiphilic poly(2-oxazoline)s and covalently crosslinked with spiropyran upon micelle formation in water. It responds to light irradiation in a wavelength-selective manner switching its morphology as confirmed by dynamic light scattering and cryo-transition electron microscopy. The compartmental structure renders distinct nanoconfinements for two incompatible enantioselective transformations: a rhodium-diene complex-catalyzed asymmetric 1,4-addition occurs in the hydrophilic corona while a Rh-TsDPEN-catalyzed asymmetric transfer hydrogenation proceeds in the hydrophobic core. Control experiments and kinetic studies showed that the gated behavior induced by the photo-triggered reversible spiropyran to merocyanine transition in the cross-linking layer is key to discriminate among substrates/reagents during the catalysis. Here, the smart nanoreactor realized photo-regulation to direct the reaction pathway to give a multi-chiral product with high conversions and perfect enantioselectivities in aqueous media. Our SCM catalytic system, on a basic level, mimics the concepts of compartmentalization and responsiveness Nature uses to coordinate thousands of incompatible chemical transformations into streamlined metabolic processes.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Computational and experimental demonstrations of one-pot tandem catalysis for electrochemical carbon dioxide reduction to methane
Electroreduction of carbon dioxide to hydrocarbons and oxygenates on copper involves reduction to a carbon monoxide adsorbate followed by further transformation to hydrocarbons and oxygenates. Simultaneous improvement of these processes over a single reactive site is challenging due to the linear scaling relationship of the binding strength of key intermediates. Herein, we report improved electroreduction of carbon dioxide by exploiting a one-pot tandem catalysis mechanism based on computational and electrochemical investigations. By constructing a well-defined copper-modified silver surface, adsorbed carbon monoxide generated on the silver sites is proposed to migrate to surface copper sites for the subsequent reduction to methane, which is consistent with insights gained from operando attenuated total reflectance surface enhanced infrared absorption spectroscopic investigations. Our results provide a promising approach for designing carbon dioxide electroreduction catalysts to enable one-pot reduction of products beyond carbon monoxide and formate.
59 BASIC BIOLOGICAL SCIENCES↗
Heterogeneous Diels–Alder tandem catalysis for converting cellulose and polyethylene into BTX
Producing biomass-derived aromatic hydrocarbons via controllable Diels–Alder reactions is a promising approach to recover energy and chemicals from waste streams. A tandem Diels–Alder catalysis consisting of SAPO-34 and Fe/HZSM-5 (stacked catalysis or mixed catalysis) was evaluated for thermochemical conversion of cellulose and polyethylene blends into benzene, toluene, and xylenes (BTX). Aromatization catalyst type significantly affected the activity of tandem catalysis, and the BTX obtained from the HZSM-5 stacked catalysis was ~2.3 times higher than that of the USY stacked one. An introduction of Fe active promoters into HZSM-5 increased the Lewis to Brønsted acid sites molar ratio (L/B) from 0.4 to 4.1. The comparison between Fe/HZSM-5 stacked catalysis and parent HZSM-5 single catalysis indicated that the former was more effective for BTX production, obtaining a nearly two-fold increase in yield with a high selectivity of 82.8%. A close proximity between Fe/HZSM-5 and SAPO-34 in the mixed catalysis increased the BTX enhancement to 1.8. A synergistic effect was provided by the coordination of Lewis and Brønsted acid sites in the Fe/HZSM-5 mixed catalysts for facilitating BTX generation, achieving a maximum of 25.9% at a Fe/HZSM-5 to SAPO-34 mass ratio of 1:1 with a theoretical L/B of 7.2. Finally, this work provides a sustainable strategy to produce biomass-derived aromatic hydrocarbons.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Nanocrystal assembly for tandem catalysis
The present invention provides a nanocrystal tandem catalyst comprising at least two metal-metal oxide interfaces for the catalysis of sequential reactions. One embodiment utilizes a nanocrystal bilayer structure formed by assembling sub-10 nm platinum and cerium oxide nanocube monolayers on a silica substrate. The two distinct metal-metal oxide interfaces, CeO.sub.2--Pt and Pt--SiO.sub.2, can be used to catalyze two distinct sequential reactions. The CeO.sub.2--Pt interface catalyzed methanol decomposition to produce CO and H.sub.2, which were then subsequently used for ethylene hydroformylation catalyzed by the nearby Pt--SiO.sub.2 interface. Consequently, propanal was selectively produced on this nanocrystal bilayer tandem catalyst.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Efficient Polyester Hydrogenolytic Deconstruction via Tandem Catalysis
Abstract Using a mechanism‐based solvent‐free tandem catalytic approach, commodity polyester plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are rapidly and selectively deconstructed by combining the two air‐ and moisture‐stable catalysts, Hf(OTf) 4 and Pd/C, under 1 atm H 2 , affording terephthalic acid (or naphthalene dicarboxylic acid for PEN) and ethane (or butane for PBT) in essentially quantitative yield. This process is effective for both laboratory grade and waste plastics, and comingled polypropylene remains unchanged. Combined experimental and DFT mechanistic analyses indicate that Hf(OTf) 4 catalyzes a mildly exergonic retro‐hydroalkoxylation reaction in which an alkoxy C−O bond is first cleaved, yielding a carboxylic acid and alkene, and this process is closely coupled to an exergonic olefin hydrogenation step, driving the overall reaction forward.
Kratish, Yosi↗
Selective Valorization of CO 2 towards Valuable Hydrocarbons through Methanol-mediated Tandem Catalysis
The thermocatalytic conversion of carbon dioxide (CO 2 ) into valuable hydrocarbons presents a promising solution for mitigating anthropogenic CO 2 emissions while producing drop-in replacements for fossil-derived products. Among the two tandem mechanisms for the direct hydrogenation of CO 2 , the methanol synthesis coupled with the methanol to hydrocarbon (MTH) reaction offers an improvement over the reverse water-gas shift coupled with Fischer-Tropsch synthesis reaction (RWGS-FTS), as it is not limited by Anderson-Schulz-Flory distribution and yields higher selectivity towards specific products (e.g., olefins, aromatics, higher hydrocarbons). Herein, we focus on the recent progress achieved through this pathway and outline the existing knowledge gaps. We discuss the challenges involved in the process and highlight the key descriptors in the selection of catalyst components. Finally, we present several potential solutions to circumvent the current challenges, aiming to expedite the advancement of this route toward an efficient CO 2 hydrogenation process.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Efficient Polyester Hydrogenolytic Deconstruction via Tandem Catalysis
Using a mechanism-based solvent-free tandem catalytic approach, commodity polyester plastics such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) are rapidly and selectively deconstructed by combining the two air- and moisture-stable catalysts, Hf(OTf) 4 and Pd/C, under 1 atm H 2 , affording terephthalic acid (or naphthalene dicarboxylic acid for PEN) and ethane (or butane for PBT) in essentially quantitative yield. This process is effective for both laboratory grade and waste plastics, and comingled polypropylene remains unchanged. Combined experimental and DFT mechanistic analyses indicate that Hf(OTf) 4 catalyzes a mildly exergonic retro-hydroalkoxylation reaction in which an alkoxy C-O bond is first cleaved, yielding a carboxylic acid and alkene, and this process is closely coupled to an exergonic olefin hydrogenation step, driving the overall reaction forward.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Advances and Challenges in Low‐Temperature Upcycling of Waste Polyolefins via Tandem Catalysis
Abstract Polyolefin waste is the largest polymer waste stream that could potentially serve as an advantageous hydrocarbon feedstock. Upcycling polyolefins poses significant challenges due to their inherent kinetic and thermodynamic stability. Traditional methods, such as thermal and catalytic cracking, are straightforward but require temperatures exceeding 400 °C for complete conversion because of thermodynamic constraints. We summarize and critically compare recent advances in upgrading spent polyolefins and model reactants via kinetic (and thermodynamic) coupling of the endothermic C─C bond cleavage of polyolefins with exothermic reactions including hydrogenation, hydrogenolysis, metathesis, cyclization, oxidation, and alkylation. These approaches enable complete conversion to desired products at low temperatures (<300 °C). The goal is to identify challenges and possible pathways for catalytic conversions that minimize energy and carbon footprints.
C-C cleavage↗
Circumventing thermodynamic limitations in converting carbon dioxide into carbon nanotubes via tandem catalysis
Carbon nanotubes (CNTs) are important materials for electronics and structural composites, but their production still relies on hydrocarbon-based chemical vapor deposition, an energy-intensive and fossil-dependent process, limited by rapid catalyst deactivation. Using CO2 as a carbon feedstock offers a sustainable route for CNT synthesis, yet direct CO2 conversion to CNTs is thermodynamically unfavorable and existing CO2-to-carbon pathways mainly yield amorphous or weakly graphitized solids. Here, we demonstrate a tandem electrochemical–thermochemical (EC-TC) strategy that overcomes these limitations. CO2 is first electrochemically reduced to a tunable mixture of C2H4 and CO, which is directly fed into a thermochemical reactor and converted into CNTs with controllable morphology and high CNT-to-metal mass ratios (~200) over NiFe catalysts at 750 °C. In situ synchrotron-based characterization and density functional theory calculations reveal that CO dissociation and C2H4 decomposition on NiFe alloys cooperatively promote CNT nucleation and sustained growth. This EC-TC strategy establishes a modular route for converting CO2 into value-added carbon nanomaterials.
03 NATURAL GAS↗
Metal-organic-framework-derived carbons: Applications as solid-base catalyst and support for Pd nanoparticles in tandem catalysis
Here, the facile pyrolysis of a bipyridyl metal-organic framework, MOF-253, produces N-doped porous carbons (Cz-MOF-253), which exhibit excellent catalytic activity in the Knoevenagel condensation reaction and outperform other nitrogen-containing MOF-derived carbons. More importantly, by virtue of their high Lewis basicity and porous nature, Cz-MOF-253-supported Pd nanoparticles (Pd/Cz-MOF-253-800) show excellent performance in a one-pot sequential Knoevenagel condensation-hydrogenation reaction.
36 MATERIALS SCIENCE↗
Compartmentalization of Incompatible Catalytic Transformations for Tandem Catalysis
In Nature, incompatible catalytic transformations are being carried out simultaneously through compartmentalization that allows for the combination of incompatible catalysts in tandem reactions. Herein, we take the compartmentalization concept to the synthetic realm and present an approach that allows two incompatible transition metal catalyzed transformations to proceed in one pot in tandem. The key is the site isolation of both catalysts through compartmentalization using a core-shell micellar support in an aqueous environment. The support is based on amphiphilic triblock copolymers of poly(2-oxazoline)s with orthogonal functional groups on the side-chain that can be used to crosslink covalently the micelle and to conjugate two metal catalysts in different domains of the micelle. Here, the micelle core and shell provide different microenvironments for the transformations: Co-catalyzed hydration of an alkyne proceeds in the hydrophobic core while the Rh-catalyzed asymmetric transfer hydrogenation of the intermediate ketone into a chiral alcohol occurs in the hydrophilic shell.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗