Activity In Hydroformylation Research Articles

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.

Constructing Co@C nanoparticles with chainmail-structure for highly efficient hydroformylation of 1-hexene

Constructing highly active noble-metal-free heterogeneous catalysts is the crux for the hydroformylation of long-chain α-olefins. Herein, novel chainmail-structured cobalt oxide nanoparticles (CoO@C|SBA-15) are fabricated by the channel confinement strategy, which display excellent activity for the 1-hexene hydroformylation. Specifically, the obtained catalyst shows 100% 1-hexene conversion and 94% heptanal selectivity, as well as up to 2.0 linear to branch (l/b) ratio, outperforming most of heterogeneous noble metal catalysts. Remarkably, in-situ DRIFT spectra combined with density functional theory calculations disclosed the metallic Co derived from in-situ reconstruction of CoO is the key active site for 1-hexene hydroformylation. Specifically, the reconstructed Co site is responsible for the adsorption of 1-hexene, and the graphite carbon layer promotes the adsorption of H2 and CO by interacting with the reconstructed Co. Moreover, the graphite carbon layer provides a strong protective effect on the internal cobalt active sites and thus enhances the catalytic stability during the harsh condition. This work provides a new method for designing the low-cost heterogeneous catalyst and emphasizes the intrinsic active sites for 1-hexene hydroformylation reaction.

Adjacent MnOx clusters enhance the hydroformylation activity of rhodium single-atom catalysts

Hydroformylation reactions promoted by Rh single-atom catalysts typically exhibit a negative reaction order for CO and a positive reaction order for H2 and alkenes. To enhance the catalytic activity, efforts have been concentrated on reducing the CO adsorption strength and/or enhancing the hydrogenation capacity at Rh sites. This report introduces an optimized Rh single-atom catalyst, utilizing positively charged Mn species to weaken the CO adsorption strength. Our strategy involves placing MnOx clusters in the proximity to the Rh single atom. This arrangement allows the reduction of Rh3+ to produce electronically deficient Rhδ+ species (1 < δ < 2), rather than the usual formation of the lower valence state Rh+ species. The weakened CO adsorption strength on the more positively charged Rhδ+ results in reduced CO coverage on the Rh active site, and enhanced adsorption of propylene. Our mechanistic study reveals that H2 and CO adsorption on Rh catalyzes the reduction of adjacent Mn(IV) species, inducing the formation of a Rh-MnOx paired active site. The neighboring MnOx clusters hinder the extensive reduction of Rh3+ to Rh+. This study presents MnOx as an inorganic ligand in Rh-MnOx pair site modifies the electronic properties of Rh sites to modulate the hydroformylation activity of Rh single-atom catalysts.

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.

K-promoted cobalt-based catalysts for heterogeneous hydroformylation

K-promoted Co/SiO2 catalysts were developed for heterogeneous olefin hydroformylation. Through various characterization techniques, the promotional effect of the K promoter in enhancing oxygenate selectivity was investigated.

Hydroformylation of 1‐butene to N‐pentanal on Co‐based Materials Derived from ZIF‐67: Optimization of Pyrolysis Conditions and DFT Study

AbstractWe prepared the Co‐based materials via the pyrolysis of ZIF‐67 at low temperature (250 °C~350 °C), and obtained the optimum catalyst ZIF‐67‐Sg‐350‐10 with the conversion of 1‐butene, aldehyde selectivity and n/i ratio of 94.9 %, 77.1 % and 2.2, respectively. The conversion of 1‐butene and aldehyde selectivity obviously increased with the increasing pyrolysis temperature and pyrolysis time. It was found that the interaction between the Co cluster and N‐doped carbon composites could improve the hydroformylation activity. Different catalyst models were built to investigate the active centers (Co) in the derived materials. The Co‐N4 surface was the best catalyst model with the lowest hydrogen insertion reaction energy barrier (0.37 eV).

Construction of Rh-N4 single atoms and Rh clusters dual-active sites for synergistic heterogeneous hydroformylation of olefins with ultra-high turnover frequency

The design and construction of Rh-based heterogeneous catalysts with excellent catalytic activity and high atom utilization for hydroformylation of olefins is extremely important but still challenging. Herein, we report a robust dual-active sites coupling catalyst containing triphenyl phosphine-coordinated Rh clusters and Rh-N4 single atomic sites (PPh3-RhAC-SA/N-C) for hydroformylation of olefins. The PPh3-RhAC-SA/N-C exhibits ultra-high activity to the hydroformylation of 1-hexene among the reported Rh-based catalysts, achieving the turnover frequency value of 6599 h−1, which is 13-fold higher than that of conventional Wilkinson’s catalyst (508 h−1). Density functional theory calculations reveal that PPh3-coordinated Rh clusters can facilitate the adsorption and activation of olefins and H2. The adjacent Rh-N4 provides a more favorable adsorption site for CO, enabling the easy addition of CO to carbon chain. The incorporated PPh3 increases the electron cloud density of Rh clusters, reduces the energy barriers of hydrogenation step on Rh clusters, and thereby enhancing the activity of catalyst for hydroformylation. Furthermore, PPh3-RhAC-SA/N-C can be applied as a recyclable catalyst without obvious deactivation. This work provides a novel design concept for the construction of dual sites coupling catalyst from the atomic scale for synergistic heterogeneous hydroformylation.

Low-temperature hydroformylation of ethylene by phosphorous stabilized Rh sites in a one-pot synthesized Rh-(O)-P-MFI zeolite

Zeolites containing Rh single sites stabilized by phosphorous were prepared through a one-pot synthesis method and are shown to have superior activity and selectivity for ethylene hydroformylation at low temperature (50 °C). Catalytic activity is ascribed to confined Rh2O3 clusters in the zeolite which evolve under reaction conditions into single Rh3+ sites. These Rh3+ sites are effectively stabilized in a Rh-(O)-P structure by using tetraethylphosphonium hydroxide as a template, which generates in situ phosphate species after H2 activation. In contrast to Rh2O3, confined Rh0 clusters appear less active in propanal production and ultimately transform into Rh(I)(CO)2 under similar reaction conditions. As a result, we show that it is possible to reduce the temperature of ethylene hydroformylation with a solid catalyst down to 50 °C, with good activity and high selectivity, by controlling the electronic and morphological properties of Rh species and the reaction conditions.

Rh nanoparticles anchored on phosphorous-doped porous carbon for efficiently catalytic hydroformylation of alkenes

The hydroformylation of alkenes to prepare aldehydes using rhodium-based catalysts has been widely investigated, while homogeneous Rh catalysts always suffer from poor reusability. Herein, a promising solution was proposed to introduce phosphorous heteroatoms into a porous carbon support to fabricate a stable and efficient catalyst (Rh/P-mC). And the obtained Rh/P-mC had high hydroformylation activity under mild reaction conditions. The substrate expansion experiment using different alkene substrates and the catalyst cycling experiment demonstrated the universality and stability of this catalyst. The hydroformylation reaction mechanism was also proposed, and the effect of the interaction between phosphorus and rhodium on the hydroformylation reaction was verified. Thus, this work has great application prospects for the highly efficient catalytic hydroformylation of alkenes and provides an efficient method for the design of high-performance hydroformylation catalysts.

Cationic Cobalt(II) Bisphosphine Hydroformylation Catalysis: In Situ Spectroscopic and Reaction Studies.

[HCo(CO)x(bisphosphine)](BF4), x = 1-3, is a highly active hydroformylation catalyst system, especially for internal branched alkenes. In situ infrared spectroscopy (IR), electron paramagnetic resonance (EPR), and nuclear magnetic resonance studies support the proposed catalyst formulation. IR studies reveal the formation of a dicationic Co(I) paramagnetic CO-bridged dimer, [Co2(μ-CO)2(CO)(bisphosphine)2]2+, at lower temperatures formed from the reaction of two catalyst complexes via the elimination of H2. DFT studies indicate a dimer structure with square-pyramidal and tetrahedral cobalt centers. This monomer-dimer equilibrium is analogous to that seen for HCo(CO)4, reacting to eliminate H2 and form Co2(CO)8. EPR studies on the catalyst show a high-spin (S = 3/2) Co(II) complex. Reaction studies are presented that support the cationic Co(II) bisphosphine catalyst as the catalyst species present in this system and minimize the possible role of neutral Co(I) species, HCo(CO)4 or HCo(CO)3(phosphine), as catalysts.

Quantitative ligand effect and mechanism insight of Rh-biphosphine complexes in hydroformylation of formaldehyde

Hydroformylation is one of the most important homogenous reactions with more than 10 million tons of aldehydes production each year. Due to monodentate ligands instable coordination under hydroformylation of formaldehyde, here, we introduced a range of chelating biphosphine ligands onto rhodium catalysts. Ligands, such as BINAP (TOFGA = 106.4 h−1), present higher activity relative to common monodentate ligand PPh3 (TOFGA = 73.4 h−1) with lower ligand to metal ratio. Density functional theory calculation revealed that Rh-biphosphine complexes follow the anion mechanism, with H2 oxidation addition being the rate-determining step. Activation strain analysis further demonstrated that lower H2 distortion energy resulting higher TOF of glycolaldehyde formation. Besides, the predictable quantitative structure–activity relationship model was established and suggested that both electronic and steric properties synergistically controlled formaldehyde hydroformylation activity. This combination of mathematical modeling and theoretical calculation will provide a reliable approach to activity prediction and catalyst design for important industrial hydroformylation reaction.

Rh nanoparticles supported on porous hexagonal boron nitride nanorods with hierarchical structure for highly efficient hydroformylation of olefins

Hydroformylation would be a promising alternative for partial technological process in petrochemical industry because it is a 100% atom-economical route for large-scale production of aldehydes and alcohols from olefins and synthesis gas (H2 and CO). However, there are still a few problems such as cost-intensive recycling and harsh operating conditions etc. encountering in the ligand-modified cobalt and rhodium as homogeneous catalysts in practical applications. Responding to the challenges, to exploit heterogeneous catalysts especially supported catalysts is desired and needs to make more efforts. Here, porous boron nitride (p-BN) with hierarchical structure is designed through a facile thermal polymerization procedure for catalyst support. The p-BN possesses nanorod morphology assembled by numerous highly crystallized hexagonal boron nitride (h-BN) nanoparticles with the diameter of about 20 nm as building blocks, thereby forming abundant interparticle pores. The Rh nanoparticles are then supported on p-BN by an impregnation-borohydride reduction method using RhCl3 as metal precursor, and the obtained catalyst of Rh nanoparticle supported on p-BN (Rh/p-BN) is applied in hydroformylation of styrene. The high porosity and accessible boron acid sites arising from hierarchical structure of p-BN nanorods make Rh nanoparticles homogeneously disperse on the surface of p-BN nanorods and also keep the diameter about 5 nm without further aggregations. Just for this reason, Rh/p-BN exhibits excellent activity of styrene hydroformylation with the highest turnover frequency of styrene as high as 12000 h−1, in comparison with other supported catalysts using different catalyst supports. Besides the detailed investigation of the catalytic properties of Rh/p-BN under different reaction conditions, the recycle of Rh/p-BN is also conducted for five times during which there is no significant decrease in catalytic activity. The present findings indicates that the combination of catalyst support of p-BN and metal nanoparticle catalysts could be an attractive strategy for designing heterogeneous hydroformylation catalysts.

Promising Applications of Polyethyleneimine as a Ligand in Rhodium-Catalyzed Tandem Hydroformylation/Hydrogenation of Olefins

Three rhodium-containing catalytic systems active in tandem hydroformylation/hydrogenation of unsaturated substrates were developed based on polyethyleneimine (PEI): a homogeneous system with distillation of the product; a biphasic system with segregation of the product and catalyst into a non-polar phase and a polar phase, respectively; and a solid catalyst prepared from PEI and (3-chloropropyl)triethoxysilane with its centrifugation from the product mixture. All the systems were shown to be reusable over multiple cycles in hydroformylation/hydrogenation, with the catalytic activity being partially sustained in both steps of the tandem process. Methylation of PEI (or its NH and NH2 moieties in the case of solid material) was found to be critical for the catalytic activity in hydroformylation.

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.

Ethene Hydroformylation Catalyzed by Rhodium Dispersed with Zinc or Cobalt in Silanol Nests of Dealuminated Zeolite Beta.

Catalysts for hydroformylation of ethene were prepared by grafting Rh into nests of ≡SiOZn-OH or ≡SiOCo-OH species prepared in dealuminated BEA zeolite. X-ray absorption spectra and infrared spectra of adsorbed CO were used to characterize the dispersion of Rh. The Rh dispersion was found to increase markedly with increasing M/Rh (M = Zn or Co) ratio; further increases in Rh dispersion occurred upon use for ethene hydroformylation catalysis. The turnover frequency for ethene hydroformylation measured for a fixed set of reaction conditions increased with the fraction of atomically dispersed Rh. The ethene hydroformylation activity is 15.5-fold higher for M = Co than for M = Zn, whereas the propanal selectivity is slightly greater for the latter catalyst. The activity of the Co-containing catalyst exceeds that of all previously reported Rh-containing bimetallic catalysts. The rates of ethene hydroformylation and ethene hydrogenation exhibit positive reaction orders in ethene and hydrogen but negative orders in carbon monoxide. In situ IR spectroscopy and the kinetics of the catalytic reactions suggest that ethene hydroformylation is mainly catalyzed by atomically dispersed Rh that is influenced by Rh-M interactions, whereas ethene hydrogenation is mainly catalyzed by Rh nanoclusters. In situ IR spectroscopy also indicates that the ethene hydroformylation is rate limited by formation of propionyl groups and by their hydrogenation, a conclusion supported by the measured H/D kinetic isotope effect. This study presents a novel method for creating highly active Rh-containing bimetallic sites for ethene hydroformylation and provides new insights into the mechanism and kinetics of this process.

Preparation of porous organic polymers containing N or P atoms and their application in hydroformylation of 1-octene

Three kinds of porous organic polymers (POPs) containing N or P atoms were prepared, named N-POP, P-POP, and N + P-POP respectively and used as the supports for Rh catalysts. Their structures and compositions were fully understood by FTIR, XRD, EDX, 13C MAS NMR, 31P MAS NMR and XPS characterizations. Rich micropores and mesopores were detected in the polymers through N2 adsorption–desorption, SEM and TEM. Because of the bulk extrusion of triphenylphosphine (TPP) unit in Rh-P-POP and Rh-N + P-POP, the Rh-N-POP showed a larger BET surface area and larger pore volume. The characterization also proved that P atoms were oxidized partly to PO species. Their catalysis performances were tested in the hydroformylation of 1-octene and syngas, with isomerization as the main competing reaction. It was interesting to see that the inactive Rh-N-POP allowed Rh to combine with free ligands more easily, thus promoting the hydroformylation activity. The existence of TPP structure in the polymers, however, greatly promoted isomerization, with a weak hydroformylation activity, partly due to the partial oxidation of P atoms. On the other hand, the strong alkalinity and coordination ability of P atoms in the polymers made the association and dissociation of Rh with other free ligands difficult.

Effect of NaY Zeolite at Different Calcination Temperatures on the Activity in Hydroformylation of Formaldehyde

AbstractThe NaY zeolites were prepared by hydrothermal synthesis method. The influence of NaY zeolite calcined at different temperatures as carriers for Rh/NaY catalysts on the hydroformylation of formaldehyde was investigated. The physical and chemical properties of Rh/NaY catalysts and their performance were characterized in details. When the zeolites were calcined at 400–700 °C, the crystal structure and morphology were kept unchanged within this range of calcination temperature. However, the surface crystallinity and surface area were reduced with increasing the temperature due to the partially collapsed of its framework, and thus reducing the confine of cages structure to rhodium species promote its participation in the coordination reaction. The reduction in the amount of surface Lewis acid can reduce the electronegativity of the carrier and change the electronic state of the surface rhodium species, which would weaken the hindrance to anionic speciation and promote CO insertion, which facilitates the hydroformylation of formaldehyde.

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.

Ultralow-Loading and High-Performing Ionic Liquid-Immobilizing Rhodium Single-Atom Catalysts for Hydroformylation.

We have developed a Keggin polyoxometalate (POM)-based ionic-liquid (IL)-immobilizing rhodium single-atom Rh catalyst (MTOA)5 [SiW11 O39 Rh] (MOTA=methyltrioctylammonium cation) that can afford exceptionally high catalytic activity for the hydroformylation of alkenes to produce aldehydes at an ultralow loading of Rh (ca. 3 ppm). For styrene hydroformylation, both the conversion and the yield of the aldehyde can reach almost 99 %, and a TOF as high as 9000 h-1 was obtained without using any phosphine ligand in the reaction process. Further characterization by FTIR, ICP and ESI-MS analysis revealed that the single Rh atom was incorporated in the lacunary POM anions. In particular, the bulky IL cation can play an additional role in stabilizing Rh species and thus prevent aggregation and leaching of Rh species. The IL catalyst was miscible with n-hexane at temperatures; this contributed to exceptionally high activity for hydroformylation even at ultra-low loading of IL catalyst.