Hydroformylation Of Propene Research Articles

Elucidation of hemilabile-coordination-induced tunable regioselectivity in single-site Rh-catalyzed heterogeneous hydroformylation

Revealing key factors that modulate the regioselectivity in heterogeneous hydroformylation requires identifying and monitoring the dynamic evolution of the truly active center under real reaction conditions. However, unambiguous in situ characterizations are still lacking. Herein, we elaborately construct a series of Rh-POPs catalysts for propylene hydroformylation which exhibited tunable regioselectivity. Multi-technique approaches reveal the unique microenvironment of the diverse HRh(CO)(PPh3-frame)2 sites with distinct P-Rh-P bite angles ranging from 90° to 120° and 158° to 168°, respectively. In situ time-resolved XAFS, FT-IR, and quasi-in situ Solid-state NMR experiments combined with DFT calculations explain the dynamic evolution of the electronic and coordinate state of the distinct active sites induced by hemilabile PPh3-frame ligands and further disclose the regulatory mechanism of regioselectivity. These state-of-the-art techniques and multiscale analysis advance the understanding of how hemilabile coordination influences regioselectivity and will provide a new thought to modulate the regioselectivity in future industrial processes.

Atomically dispersed Rh catalysts formed on defective CeO2 surfaces with hydroformylation activity

The electron density of the metal active sites depends on the surface properties of the support. This study aimed to demonstrate that the formation of atomically dispersed Rh on ceria and the corresponding Rh electron density can be tuned depending on ceria concentration. The highly optimized Rh/CeO2-Al2O3 catalyst exhibited the highest activity during propylene hydroformylation, which was similar to that of the commercially available homogeneous catalyst RhCl(PPh3)3. Combined analytical results and theoretical calculations demonstrated that the increased Ce3+ fraction promoted high Rh electron density and attenuated CO adsorption strength, resulting in an increased hydroformylation activity. Additionally, the catalyst achieved separation and high added value by converting olefins to aldehydes through hydroformylation of olefins in a mixed C2–C4 olefin/paraffin gas. This study showed that atomically dispersed metal supported catalysts can be designed as recyclable heterogeneous catalysts by tailoring the local environment and corresponding electron density of the metal to achieve high activity similar to that of the homogeneous catalysts that manipulate ligands around the metal.

A comprehensive study on the steric impact of phosphine ligands on propene hydroformylation

This research examines the steric impact of ligand structure on Rhodium-catalyzed hydroformylation, specifically, the significant impact of substituent positioning of monodentate phosphine ligands on the catalytic activity in propene hydroformylation. Focusing on methyl-substituted triphenylphosphine ligands, it explores how the placement of methyl groups influences the selection between mono- and bis-ligated coordination modes and, consequently, the selectivity towards linear versus branched aldehydes. Findings highlight that substituents' proximity to the ligand's phosphorus atom alters the dominant reaction step, depending on the coordination mode favored by the ligand's structural configuration. Substituents positioned further from the phosphorus atom tend to favor a bis-ligated coordination mode, wherein olefin insertion predominantly influences the aldehyde product profile. Conversely, closer substituents lead to a preference for a mono-ligated mode, shifting the decisive step from olefin insertion to other reactions, changing selectivity and catalytic activity. The result refined understanding facilitates catalyst optimization through targeted modifications of ligand structures, advancing the more effective design of hydroformylation catalysis.

Regioselective hydroformylation of propene catalysed by rhodium-zeolite.

Hydroformylation is an industrial process for the production of aldehydes from alkenes1,2. Regioselective hydroformylation of propene to high-value n-butanal is particularly important, owing to a wide range of bulk applications of n-butanal in the manufacture of various necessities in human daily life3. Supported rhodium (Rh) hydroformylation catalysts, which often excel in catalyst recyclability, ease of separation and adaptability for continuous-flow processes, have been greatly exploited4. Nonetheless, they usually consist of rotationally flexible and sterically unconstrained Rh hydride dicarbonyl centres, only affording limited regioselectivity to n-butanal5-8. Here we show that proper encapsulation of Rh species comprising Rh(I)-gem-dicarbonyl centres within a MEL zeolite framework allows the breaking of the above model. The optimized catalyst exhibits more than99% regioselectivity to n-butanal and more than99% selectivity to aldehydes at a product formation turnover frequency (TOF) of 6,500 h-1, surpassing the performance of all heterogeneous and most homogeneous catalysts developed so far. Our comprehensive studies show that the zeolite framework can act as a scaffold to steer the reaction pathway of the intermediates confined in the space between the zeolite framework and Rh centres towards the exclusive formation of n-butanal.

Mesoporous coordinated polymers with single‐metal‐site iridium for efficient catalysis in propylene hydroformylation

AbstractHeterogeneous single‐metal‐site catalysts (SMSCs) have received increasing attention due to their outstanding stability and recyclability. In this work, a novel Ir‐based SMSC was successfully constructed through the coordination polymerization between zirconium and triphenylphosphine derivatives with carboxyl functional groups for efficient propylene hydroformylation with CO. The Ir‐based SMSC reported here can achieve a turnover number of over 20,000 (being 7.3 times higher than the most effective Ir‐base catalyst to date) with 99% selectivity and 56% yield for aldehyde. Besides, it represents the first example with a higher selectivity of isobutyraldehyde than n‐butyraldehyde (i.e., n/i = 0.62) among the reported Ir‐based catalysts. The Ir‐based SMSC can be easily reused for at least 10 cycles without losing its reactivity, whereas the homogeneous monomer catalyst quickly loses its reactivity after the second cycle. Furthermore, the catalytic mechanism of Ir‐based SMSC is proposed based on reaction explorations and in situ co‐adsorption tests by the method of diffuse reflectance infrared Fourier transform spectroscopy, which has also been revealed by theoretical calculations. This work provides a novel insight into the design of SMSCs with great potential for application in the hydroformylation field.

Enhanced regioselectivity in propylene hydroformylation using Xantphos-modified single-atom Rh/CeO2 catalyst

Single-atom Rh catalysts have been reported to exhibit high activity in olefin hydroformylation, yet with limited regioselectivity. We develop a Xantphos ligand coordinated single-atom Rh/CeO2 catalyst, which exhibits improved regioselectivity for butyraldehyde (n/i ratio equal to 13) while maintaining good activity (TOF = 476 h−1) in hydroformylation of propylene. The unique coordination environment created by Xantphos enhances steric hindrance at Rh active sites, thereby improving its regioselectivity for n-butyraldehyde. That is, two P atoms from a Xantphos ligand bind directly to Rh, while a P atom from another Xantphos attaches to an oxygen vacancy on CeO2 near Rh, achieving a P-Rh coordination number of 3. This unique structure shifts the propylene adsorption configuration from hybrid modes to the terminal mode, favoring n-butyraldehyde formation. The creation of electron-rich Rh sites with P/Rh ratio of 3 benefits the formation of Rh-H species for the rate-determining step, thus showing commendable activity.

Efficient Alkene Hydroformylation by Co-C Symmetry-Breaking Sites.

Alkene hydroformylation is one of the largest industrial reactions on an industrial scale; however, the development of nonnoble heterogeneous catalysts is usually limited by their low activities and stabilities. Herein, we constructed a 1% Co2C/SiO2 catalyst featuring Co-Cvacancy-Co-C symmetry-breaking sites, which generated a polar surface exhibiting a moderate charge density gradient at the localized Co atoms. Comparatively, this catalyst exhibited notable enhancements in the adsorption and activation of the reactants, as well as in the polarity between intermediates. Significantly, the spatial distance between the adsorption sites of intermediates was reduced, thereby effectively decreasing the energy barrier of reaction processes. As the density of the symmetry-breaking sites increased, the turnover number for propene hydroformylation soared to 18 363, exceeding the activity of heterogeneous Co-based catalysts reported thus far by 1 or 2 orders of magnitude, and the catalyst exhibited high stability during the reaction. This study provides a methodology for constructing atomically active sites, which holds great potential for the design and development of highly efficient catalysts.

Kinetic modelling of cobalt-catalyzed propene hydroformylation: a combined ab initio and experimental fitting protocol

The mechanism of propene hydroformylation is studied with quantum chemistry and kinetic modelling. This yields detailed insight into mechanisms, and reveals the essential role of a complex between hydridocobalttricabonyl and toluene.

Efficient Interfacial Sites between Metallic and Oxidized Cobalt for Propene Hydroformylation.

Currently, the hydroformylation of short olefins is operated almost exclusively by using Rh catalysts. Considering the high cost and scarcity of rhodium resources, it is important to develop non-noble metal catalysts toward hydroformylation. Herein, we report an efficient cobalt-based catalyst rich in interfacial sites between metallic and oxidized cobalt species for the hydroformylation of short olefin, propene, under a moderate syngas pressure. The catalyst exhibited a high specific activity of 252 mol molCo-1 h-1 in toluene under 2 bar of propene and 40 bar of CO/H2 mixed gas (CO/H2 = 1:1) at 160 °C. According to mechanistic studies, the interface of metallic and oxidized cobalt species promoted the adsorption of CO and propene. Moreover, the interfacial sites lowered the energy barrier for CO* hydrogenation and C-C coupling compared with metallic cobalt.

The tunable effect of the second metal site on the hydroformylation of propylene over Rh-M-BTC (M= Fe, Ru, Mn, Rh, Pt, Pd, Re, Cu, Ni)

Hydroformylation is one of the most important homogeneous reactions in industry. Cu-BTC, as a kind of MOFs material with coordinate unsaturated metal sites, has strong interaction with adsorption molecules and is widely used in adsorption and catalytic research fields. The open metal sites in it can be adjusted according to the demand. In this work, Rh-BTC was selected as the catalyst for the hydroformylation of propylene. In order to regulate the electronic properties of Rh metal center, eight Rh-M-BTC materials (M= Fe, Ru, Mn, Rh, Pt, Pd, Re, Cu, Ni) were investigated. The Mulliken charge of Rh-M metal nodes and the reaction energy barrier of the key steps of propylene hydroformylation on Rh-M-BTC were calculated, including the step of propylene insertion, CO insertion, and aldehyde formation. The results showed that on Rh-Pd-BTC, the energy barrier difference between linear and branched path for the regional decisive step propylene insertion step is the lowest, only 0.04 eV. The reaction energy barrier of the linear path for CO insertion is only half of that of the branched path. The linear path has obvious advantages. Therefore, Rh-Pd-BTC was suggested as the most suitable model studied in the work for hydroformylation of propylene.

Boosting the Hydroformylation Activity of a Rh/CeO2 Single-Atom Catalyst by Tuning Surface Deficiencies

Controlling the interactions between atomically dispersed metal atoms and the support plays significant roles in determining the activity and selectivity of single-atom catalysts. In this report, we tuned the local coordination environment of Rh single atoms on CeO2 via calcination to construct a highly active hydroformylation catalyst. Single-atom Rh/CeO2 calcined at a high temperature exhibits more oxygen vacancies, which lead to the formation of a large amount of low-coordination Rh active species that are more active for hydroformylation. Under the optimum conditions, the best Rh/CeO2 catalyst achieved a TOF at approximately 5000 h–1 with 100% aldehyde selectivity in propylene hydroformylation to butanal. In situ FTIR spectroscopy and in situ XPS characterizations provide strong evidence that Rh on 800 °C-calcined CeO2 is easily activated to form surface HRh(CO)2 active species, favoring propylene adsorption and CO insertion. This work highlights the significance of engineering metal–support interactions in tuning the hydroformylation performance of single-atom catalysts and contributes to mechanistic insights into single-atom Rh-catalyzed hydroformylation reactions.

In-situ adaptive evolution of rhodium oxide clusters into single atoms via mobile rhodium-adsorbate intermediates

It is a common phenomenon for supported metal catalysts to undergo thermally-induced or adsorbate-induced reconstruction. Great efforts have been devoted to making these reconstruction adaptive to the reaction environment instead of deactivation. Herein, we reported the evolution of initially inactive RhOx clusters on Al2O3 into the formation of catalytically active oxygen vacancies and Rh single atoms via mobile Rh-CO intermediates during hydroformylation of propene. The activated catalyst exhibited a high specific activity of 3.0 × 104 mol molRh–1 h–1 towards hydroformylation reaction. Mechanistic studies revealed the evolution paths. Specially, RhOx clusters were reduced by CO to form oxygen vacancy where the surrounding unsaturated Rh atoms enabled the chemisorption of CO*. Rh atoms that were ejected from RhOx clusters diffused on Al2O3 supports to generate Rh single atom via the formation of carbonyl or geminal dicarbonyl species. Meanwhile, the Rh atoms on clusters were also leached to the solution by the adsorbed CO molecules, followed by partial re-adsorption on the support. This work not only offers an efficient catalyst for propene hydroformylation, but also advances the understandings of dynamic evolution of catalysts.

Iridium-phosphine ligand complexes as an alternative to rhodium-based catalysts for the efficient hydroformylation of propene.

Expensive rhodium (Rh)-based catalysts have been widely used for the hydroformylation of propene. To find a cheaper and effective alternative to these Rh-based catalysts, herein, a series of phosphine ligands were used to coordinate with iridium, and their catalytic reactivities for the hydroformylation of propene were systematically investigated in this study. The effects of different phosphine ligands, pressures, temperatures, and catalyst dosages on the hydroformylation of propene were investigated. Tripyridyl phosphine iridium Ir2(cod)2Cl2-P(3-py)3 (Ir(I)-L5) and its derivatives exhibit the highest catalytic reactivity. Surprisingly, the catalytic reactivity of Ir(I)-L5 is higher than that of Rh2(cod)2Cl2-P(3-py)3 (Rh(I)-L5). When the Ir(I)-L5 complex is used as the catalyst, reactions performed in a polar solvent gave higher turnover number (TON) values than those in a non-polar solvent. Up to a TON of 503 can be obtained. Different n-butyraldehyde/iso-butyraldehyde (n/i) ratios can be obtained by adjusting the phosphine ligands or the proportion of gas pressure. The catalyst showed good reusability in five recycling experiments. Furthermore, based on DFT theoretical calculations, a probable reaction mechanism was proposed. It is reliable that an Ir-based catalyst can be considered as a highly effective catalyst for the hydroformylation of propylene with CO.

Theoretical insights into the catalytic mechanism of propylene hydroformylation over Co-N-C materials.

M-N-C was recently reported to be a high activity catalyst for hydroformylation compared with a metal nanocluster. However, the nature of M-N-C sites and the dominant path of propylene hydroformylation on M-N-C sites with different structures are poorly understood. In this work, five different Co-N-C models (Co-N3-C, Co-N4-C, 0N-bridged Co2-N6-C, 1N-bridged Co2-N7-C and 2N-bridged Co2-N6-C) were constructed to simulate the Co active sites with different coordination that may exist on the surface of MOF-derived Co-based carbon materials. DFT combined with kinetic Monte Carlo (kMC) methods were used to study the catalytic performance for hydroformylation of different Co-N-C models. The results of the DFT calculations show that the coordination number and mode of N atoms could regulate the electronic density of the Co sites. The electronic density of the Co sites further affects the catalytic activity. The higher the electronic density is, the lower the energy barrier for partial hydrogenation of propylene and CO insertion reactions. Besides, the catalytic activity is also affected by the strong interaction in closer neighboring Co atoms in some Co2-Nx-C models. The strong interaction affects the adsorption state and energy of species, which also reduces the overall reaction energy barrier. The kMC simulation results further showed that the dominant path of propylene hydroformylation was the n-butylaldehyde path for the 0N-bridged model, and the isobutylaldehyde path for Co-N3-C and 2N-bridged models.

Synergistic Ligand Effect in Rhodium(I)-Catalyzed Regio-Controlled Propene Hydroformylation

Synergistic Ligand Effect in Rhodium(I)-Catalyzed Regio-Controlled Propene Hydroformylation

Achieving rhodium-like activity for olefin hydroformylation by electronic metal-support interaction of single atomic cobalt catalyst

Hydroformylation of olefins with H2 and CO is an important industrial process for aldehyde production, and developing Earth-abundant catalysts with high catalytic activity and stability remains challenging. Here, we synthesize a rhodium-like high-efficiency single-atom cobalt catalyst over β-Mo2C toward olefin hydroformylation. During the hydroformylation of propene, the single atomic cobalt catalyst achieves a turnover number of 3,834 and a turnover frequency of 749 h−1, which to our knowledge surpasses all the reported heterogeneous cobalt-based catalysts and approaches the performance of rhodium catalysts. Moreover, the catalyst can be reused five times without an obvious activity decline, confirming the excellent stability of single-atom Co supported on β-Mo2C. We demonstrate that a Co1-MoxCy motif forms on the carbide surface with electronic metal-support interaction (EMSI). Such an EMSI effect plays a pivotal role in optimizing the charge density, reducing the reaction barrier, and stabilizing the active site.

Single-atom catalysts: One for all or all for one?

Precious-metal thrifting through the development of single-atom catalysts is an attractive way to promote the sustainable use of precious metals in catalytic processes. In this issue of Chem Catalysis , Wei et al. demonstrate a new strategy for producing atomically dispersed gold within a S-1 zeolite framework for propene hydroformylation. Precious-metal thrifting through the development of single-atom catalysts is an attractive way to promote the sustainable use of precious metals in catalytic processes. In this issue of Chem Catalysis , Wei et al. demonstrate a new strategy for producing atomically dispersed gold within a S-1 zeolite framework for propene hydroformylation.

Single-atom gold species within zeolite for efficient hydroformylation

Various transition metals including Rh, Co, Ir, Ru, Os, Pt, Pd, Fe, and Ni have been proven to be efficient active centers for hydroformylation. Although Au is conventionally considered inactive for hydroformylation due to its intrinsic inertness, we design an atomically dispersed Au catalyst confined in zeolite with excellent activity and selectivity toward propene hydroformylation. The Au catalyst achieves 3,794 μmol of butyraldehyde and shows superior durability after 5 cycles, which is even comparable to Rh-based catalysts. Impregnating Au on the zeolite or increasing the mass loading of an encapsulated one will increase the size of active metal Au, which is unfavorable to hydroformylation. Detailed characterizations and theoretical calculations indicate that the isolated Au atoms within the zeolite matrix are stabilized via oxygen-bridge bonds. The formed Au1-O-SiOX motifs render maximum active site density and high structural stability, which are identified as the real active sites for efficient hydroformylation.

Flexible homogeneous hydroformylation: on-demand tuning of aldehyde branching with a cyclic fluorophosphite ligand

Tuning aldehyde regioselectivity via homogeneous hydroformylation of olefins using the same catalyst system remains a challenge. Here, we present flexible rhodium (Rh)-catalyzed hydroformylation of 1-octene and propylene with a bulky cyclic monofluorophosphite ligand L. Hydroformylation of 1-octene with Rh/L catalyst achieves, for the first time, turnover frequencies exceeding 75,000 mol ald.mol Rh−1.h−1 (at 30% conversion) in segmented flow, while enabling access to an unmatched tunable aldehyde branching (0.06 < linear/branched < 15) with the same ligand L. Our mechanistic studies demonstrate that L provides a viable alternative to traditional bidentate phosphine/phosphite ligands for high activity with the added benefit of tunable selectivity. The unique high flexibility feature of L over traditional linear- or branched-selective ligands allows for on-demand tuning from 90% linear to 75% branched aldehyde in a continuous flow reactor without the need for ligand/catalyst alteration. Furthermore, when starting from the internal olefins, Rh/L catalyst achieves high regioselectivity (>90%) toward the two positional aldehyde isomers. The high turnover frequencies obtained with L in flow will enhance the economics of the production of aldehydes and their isotopically labeled analogues by significantly reducing the reaction time, thereby enabling better utilization of the increasingly expensive Rh catalyst and minimizing the need for catalyst/ligand separation and recycle.

Isoselective Hydroformylation of Propylene by Iodide‐Assisted Palladium Catalysis

AbstractIsobutanal is a high value bulk material that, in principle, could be produced with 100 % atom‐economy by isoselective hydroformylation of propylene with syngas. However, leading industrial Rh‐ and Co‐catalyzed hydroformylation methods preferentially form n‐butanal over the iso‐product, and methods offering isoselectivity remain underdeveloped. Here we report an iodide‐assisted Pd‐catalyzed hydroformylation of propylene that produces isobutanal with unprecedented levels of selectivity. The method involves PdI2, simple alkyl monophosphines, such as tricyclohexylphosphine, and common green solvents, enabling the title reaction to occur with isoselectivity in up to 50 : 1 iso/n product ratios under industrially relevant conditions (80–120 °C). The catalytic and preliminary mechanistic experiments indicate a key role of the iodide anions in both the catalytic activity and the isoselectivity.