Heterogeneous Hydroformylation Research Articles

Balanced Rh+‐Rh0 Sites over Rh Clusters Enhance Heterogeneous Hydroformylation of Aldehyde

AbstractControlling the metal geometric and electronic structure is of significance in developing efficient catalysts for heterogeneous hydroformylation. This study examines the structural sizes of Rh and Rh+‐Rh0 distribution to construct a highly active catalyst for formaldehyde hydroformylation. The active sites for hydroformylation require several Rhn atoms, while single‐atom Rh can solely catalyze hydrogenation. The highest activity was achieved on Rh nanoclusters (0.95 nm), giving a TOF of 191 h−1 and selectivity of 82% for glycolaldehyde formation. The tunability of the electronic properties of Rh nanoclusters and the synergistic interaction between Rh+ and Rh0 are essential for enhanced activity. Pseudo‐in situ FT‐IR analysis elucidated that formaldehyde adsorbed on Rh nanocluster prefers to produce glycolaldehyde via hydroformylation, while formaldehyde adsorbed on isolated Rhδ+ sites tends to form methanol via hydrogenation. This study provides a new insight into the design of heterogeneous catalysts and guidance for understanding the reaction mechanism for aldehydes/olefins hydroformylation.

Heterogeneous Bisphosphine Ligand-Encapsulated Rh Catalysts for Heterogeneous Hydroformylation of Alkenes with CO2

Heterogeneous Bisphosphine Ligand-Encapsulated Rh Catalysts for Heterogeneous Hydroformylation of Alkenes with CO₂

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.

A highly active phosphine oxides-containing porous organic polymer supported Co catalyst for hydroformylation of 2-octene

The development of earth-abundant catalysts with high activity and selectivity is important yet challenging in hydroformylation. In this work, a stable and efficient phosphine-oxide group containing porous organic polymer was afforded, which served as a ligand and a support to fabricate a heterogeneous Co catalyst (Co/POL-POPh3) for hydroformylation of 2-octene under mild condition. A 2-octene conversion of 94.6 % and at least three recycles were achieved using Co/POL-POPh3 in the hydroformylation with a 51.1 % aldehyde selectivity under 423 K and 3.0 MPa. The experimental and characterization results elucidated that the highly dispersed Co ions was coordinated with the phosphine-oxide groups in the polymer, which was beneficial for the 2-octene isomerization and in turn led to the excellent performance for synthesis of oxygenates. Furthermore, a reaction mechanism was also suggested for 2-octene hydroformylation over the Co/POL-POPh3 catalyst. The current study delivers valuable insights into the adjustment of the catalytic efficiency of non-previous metal catalysts in the heterogeneous hydroformylation of internal olefins.

Porous Organic Polymers Supported Heterogeneous Catalysts for Hydroformylation Reactions

AbstractSince Otto Roelen revealed the accidental discovery of the hydroformylation process while exploring Fischer‐Tropsch synthesis, this chemical process of olefins with syngas has subsequently become the main source of aldehyde products. Compared to homogeneous systems, heterogeneous hydroformylation systems can avoid homogenous separation and lower the loss of valuable metals. Porous organic polymers (POPs) are one of porous materials that are interconnected by strong covalent bonds. By modifying the substrate structures, they may encapsulate various metal atoms and show remarkably high selectivity and activity for hydroformylation processes. In this review, we mainly focus on systematically summarizing recent developments, synthesis, and catalytic research on POPs supported catalysts in hydroformylation reactions. Lastly, we also discuss the prospects and challenges for future studies for the POPs supported metal catalysts.

Unravelling structure sensitivity in heterogeneous hydroformylation of aldehyde over Rh

Delineating the geometrical and electronic structure of supported metal is significant for developing heterogeneous hydroformylation catalysts. This study modulated the configuration and charge distribution of Rh to construct highly efficient Rh@SiO2 catalysts for formaldehyde hydroformylation. The structure sensitivity of Rh species reveals that single-atom Rh can solely catalyze hydrogenation, while Rh aggregates are active for hydroformylation. Moderate Rh nanoclusters (0.98 nm) offered the highest TOF (183 h−1) and selectivity (90.8 %) of glycolaldehyde. Electronic effects demonstrate that synergy between Rh0 and Rh+ sites on the cluster is essential to enhancing the reaction. The Rh0 species function as the adsorption/activation sites for H2 and formaldehyde, and the Rh+ sites act to coordinate PPh3 and CO to form Rhδ+(CO)x(PPh3)y active species. This study provides new insights into the design of heterogeneous catalysts and guidance for understanding the structure sensitivity of active metal and hydroformylation mechanism.

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.

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.

Outlook of Cobalt-Based Catalysts for Heterogeneous Hydroformylation of Olefins: From Nanostructures to Single Atoms

Outlook of Cobalt-Based Catalysts for Heterogeneous Hydroformylation of Olefins: From Nanostructures to Single Atoms

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.

Utilizing CO2 as a Reactant for C3 Oxygenate Production via Tandem Reactions.

One possible solution to closing the loop on carbon emissions is using CO2 as the carbon source to generate high-value, multicarbon products. In this Perspective, we describe four tandem reaction strategies for converting CO2 into C3 oxygenated hydrocarbon products (i.e., propanal and 1-propanol), using either ethane or water as the hydrogen source: (1) thermocatalytic CO2-assisted dehydrogenation and reforming of ethane to ethylene, CO, and H2, followed by heterogeneous hydroformylation, (2) one-pot conversion of CO2 and ethane using plasma-activated reactions in combination with thermocatalysis, (3) electrochemical CO2 reduction to ethylene, CO, and H2, followed by thermocatalytic hydroformylation, and (4) electrochemical CO2 reduction to CO, followed by electrochemical CO reduction to C3 oxygenates. We discuss the proof-of-concept results and key challenges for each tandem scheme, and we conduct a comparative analysis of the energy costs and prospects for net CO2 reduction. The use of tandem reaction systems can provide an alternative approach to traditional catalytic processes, and these concepts can be further extended to other chemical reactions and products, thereby opening new opportunities for innovative CO2 utilization technologies.

Regioselectivity regulation of styrene hydroformylation over Rh-based Phosphides: Combination of DFT calculations and kinetic studies

Heterogeneous hydroformylation catalysts have attracted much attention to overcome the separation challenges of homogeneous systems. Herein, we proposed a semi-theoretical model to predict the apparent activity and regioselectivity over Rh-based phosphide catalysts. The density functional theory (DFT) calculations were conducted to understand the surface reaction mechanism and to determine the rate determining step (RDS) to either linear or branched aldehydes. The kinetic expressions were further studied based on equilibrium hypothesis using the information of RDS obtained from DFT calculations. The semi-theoretical model was verified by condition experiments. Using this model, the regioselectivity of products could be effectively regulated according to production requirements by simply changing the temperature and pressure conditions. The highest selectivity to branched aldehydes reached 95% at a conversion of 98% and the corresponding TOF was 204 h−1, which was comparable with the best homogeneous Rh catalysts.

A heterogeneous Rh/CPOL-BINAPa&PPh3 catalyst for hydroformylation of olefins: chemical and DFT insights into active species and the roles of BINAPa and PPh3

A reusable Rh/CPOL-BINAPa&PPh3 catalyst was used for heterogeneous hydroformylation of olefins, affording the corresponding linear aldehydes with excellent regioselectivities and high TON values. The active Rh–H species were studied in detail.

Trends and descriptors of heterogeneous hydroformylation activity and selectivity of RhM3 (M = Fe, Co, Ni, Cu and Zn) catalysts

The origin of superior C3 oxygenate selectivity of RhCo3 catalysts during hydroformylation was studied, which provided the design principles for catalyst improvements.

Understanding the facet effects of heterogeneous Rh2P catalysts for styrene hydroformylation

Rh2P (111) facets are much more active than the other facets for heterogeneous hydroformylation.

Intermetallic Nanocatalyst for Highly Active Heterogeneous Hydroformylation.

Hydroformylation is an imperative chemical process traditionally catalyzed by homogeneous catalysts. Designing a heterogeneous catalyst with high activity and selectivity in hydroformylation is challenging but essential to allow the convenient separation and recycling of precious catalysts. Here, we report the development of an outstanding catalyst for efficient heterogeneous hydroformylation, RhZn intermetallic nanoparticles. In the hydroformylation of styrene, it shows three times higher turnover frequency (3090 h-1) compared to the benchmark homogeneous Wilkinson's catalyst (966 h-1), as well as a high chemoselectivity toward aldehyde products. RhZn is active for a variety of olefin substrates and can be recycled without a significant loss of activity. Density functional theory calculations show that the RhZn surfaces reduce the binding strength of reaction intermediates and have lower hydroformylation activation energy barriers compared to pure Rh(111), leading to more favorable reaction energetics on RhZn. The calculations also predict potential catalyst design strategies to achieve high regioselectivity.

Comparison of Heterogeneous Hydroformylation of Ethylene and Propylene over RhCo3/MCM-41 Catalysts

The reaction mechanisms of heterogeneous hydroformylation of ethylene and propylene were compared at 413–453 K using RhCo3/MCM-41 as catalysts. The reaction rates of propylene for both hydroformylation and the undesired side reaction of hydrogenation were found to be about one order of magnitude lower than those for ethylene in flow reactor studies. The difference in the kinetic behavior between ethylene and propylene was investigated by measuring the reaction orders and apparent activation energies, and these macrokinetic observables were analyzed using the degree of rate control (DRC) method. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were performed to characterize the surface intermediates formed during the reactions. When the reactant was changed from ethylene to propylene, the IR peak corresponding to adsorbed CO exhibited a significant increase, while the IR peaks of the alkyl group decreased in magnitude. Combined with the DRIFTS results, DRC analysis indicates that the first step of olefin hydroformylation, the formation of an alkyl group on the catalyst surface, plays a key role in the difference between ethylene and propylene. This step is kinetically nonrelevant when ethylene is the reactant, but it is one of the rate-controlling steps for propylene. The low concentration of the adsorbed propyl group, which is a common intermediate shared by both hydroformylation and hydrogenation of propylene, decreases the rates of both reaction pathways as compared to ethylene.

A recyclable CoGa intermetallic compound catalyst for the hydroformylation reaction

Metal leaching is an important obstacle for the development of CO-containing heterogeneous catalysis systems. The modulation of the metal surface could substantially influence the structural stability under a CO atmosphere. In this work, the inductively coupled plasma (ICP) results indicate that the leaching amount of cobalt in the CoGa intermetallic compound (CoGa IMC/SiO2) catalyst is notably less than that of the Co/SiO2 catalyst in hydroformylation reaction. The in situ Fourier Transform Infrared Spectroscopy (FTIR) results prove that aldehydes can be generated on CoGa IMC/SiO2 by heterogeneous hydroformylation reaction without the formation of Co carbonyl species. Moreover, the analysis of metal bond interaction proves that although the Co-Ga bond has a weaker metal interaction strength in the bulk phase, it has higher structural stability than the Co-Co bond with the adsorption of CO molecules. Above all, this work provides a strategy to suppress metal leaching for heterogeneous catalysis.

Confinement of atomically dispersed Rh catalysts within porous monophosphine polymers for regioselective hydroformylation of alkenes

Precisely controlling the regioselectivity with monophosphine ligand is a long-standing challenge in hydroformylation. Herein, we describe the one-pot encapsulation of single-atom Rh catalysts within porous monophosphine polymers for regioselective heterogeneous hydroformylation of alkenes. The optimized catalyst (Rh@POP-PTBA-HA-50) shows remarkable enhancement of regioselectivity compared with the combination of Rh(CO)2(acac) and monophosphine ligand (PTBA), and the linear aldehyde selectivity increases from 62% to 92%. In addition, this catalyst shows excellent catalytic activity (one run TON at least 60,000) and good stability. Detailed studies reveal that the encapsulation of atomically dispersed Rh catalysts within porous monophosphine polymers may endow the catalysts with high regioselectivity, while the encirclement of metal active species by abundant but dispersive phosphine ligand would strengthen the stability of the catalysts through multiple-sites-coordination. The present study provides meaningful insights for designing heterogeneous catalysts with good regioselectivity, and merging the advantages of homogeneous and heterogeneous catalysis.

Rh Particles Supported on Sulfated g-C3N4: A Highly Efficient and Recyclable Heterogeneous Catalyst for Alkene Hydroformylation

The hydroformylation of alkenes with CO and H2 to manufacture aldehydes is one of the most large-scale chemical reactions. However, an efficient and recyclable heterogeneous catalyst for alkene hydroformylation is extremely in demand in academia and industry. In this study, a sulfated carbon nitride supported rhodium particle catalyst (Rh/S-g-C3N4) was successfully synthesized via an impregnation-borohydride reduction method and applied in the hydroformylation of alkenes. The catalysts were characterized by XRD, FTIR, SEM, TEM, XPS, and nitrogen adsorption. The influence of the sulfate content, pressure of syngas, temperature, and reaction time, as well as the stability of Rh/S-g-C3N4, on the hydroformylation was examined in detail. The delocalized conjugated structure in g-C3N4 can lead to the formation of electron-deficient aromatic intermediates with alkenes. The sulphate g-C3N4 has a defected surface owing to the formation of oxygen vacancies, which increased the adsorption and dispersion of RhNPs on the surface of g-C3N4. Therefore, Rh/S-g-C3N4 exhibited an outstanding catalytic performance for styrene hydroformylation (TOF = 9000 h−1), the conversion of styrene could reach 99.9%, and the regioselectivity for the branched aldehyde was 52% under the optimized reaction conditions. The catalytic properties of Rh/S-g-C3N4 were also studied in the hydroformylation of various alkenes and displayed an excellent catalytic performance. Furthermore, the reuse of Rh/S-g-C3N4 was tested for five recycling processes, without an obvious decrease in the activity and selectivity under the optimum reaction conditions. These findings demonstrated that Rh/S-g-C3N4 is a potential catalyst for heterogeneous hydroformylation.