Key Takeaways & Executive Findings
- •• • Rh1/CeO2 catalysts exhibit morphology-dependent activity, with specific facets enhancing hydroformylation performance, as demonstrated by molecular-level studies (ACS Catal. 2024, 14, 15956). • • Rh/activated carbon catalysts modified with surface oxygen-containing groups achieve improved catalytic performance in 1-hexene hydroformylation, with enhanced activity and selectivity (Appl. Catal. A 2016, 527, 53). • • Porous monophosphine polymers confine atomically dispersed Rh, enabling regioselective hydroformylation of alkenes with high linear aldehyde selectivity (J. Catal. 2021, 401, 321). • • Dual-active-site catalysts comprising Rh-N4 single atoms and Rh clusters on supports achieve ultra-high turnover frequency (TOF) in heterogeneous hydroformylation, demonstrating synergistic effects (Chem. Eng. J. 2024, 479, 147505).
Abstract
Olefin hydroformylation is a pivotal process for synthesizing high-value-added aldehydes, with applications extending from short-chain to long-chain olefins (C6+). Traditional homogeneous catalytic systems suffer from difficulties in separating and recovering precious rhodium (Rh), driving research toward heterogeneous catalytic systems. This review summarizes recent progress in supports for heterogeneous Rh-based catalysts, focusing on the influence of structural regulation strategies of inorganic oxide-supported, porous carbon-supported, organic porous polymer-based, zeolite-supported, and composite-supported catalysts on active site dispersion, regioselectivity, and cycle stability. Key findings include enhanced linear-to-branched (n/i) ratios and turnover frequencies (TOF) achieved through tailored support design. For instance, Rh1/CeO2 with morphology effects demonstrates molecular-level understanding of support effects, while Rh/activated carbon with surface oxygen groups improves catalytic performance in 1-hexene hydroformylation. Porous monophosphine polymers confine atomically dispersed Rh, achieving regioselective hydroformylation. Additionally, Rh-N4 single atoms and Rh clusters dual-active sites on supports yield ultra-high TOF. The review aims to provide insights for rational design of high-performance heterogeneous hydroformylation catalysts, addressing industrial challenges of catalyst recovery and stability.
1. Introduction
Olefin hydroformylation, a cornerstone for aldehyde production, has evolved from cobalt-based homogeneous systems to rhodium-based heterogeneous processes. However, commercial homogeneous catalysts suffer from severe rhodium leaching and difficult separation, escalating costs and limiting industrial scalability, particularly for long-chain olefins (C6+). Heterogeneous catalysts offer a solution, but their performance hinges on support design, which governs metal dispersion, electronic properties, and mass transport. Early supports like silica and alumina often led to poor regioselectivity and rapid deactivation. The challenge is to engineer supports that stabilize Rh species, enhance linear aldehyde selectivity, and maintain activity over multiple cycles.
This review systematically analyzes recent advances in support engineering for Rh-based heterogeneous hydroformylation catalysts. It critically evaluates inorganic oxides, porous carbons, organic polymers, zeolites, and composites, focusing on how structural regulation—such as surface functionalization, pore confinement, and single-atom dispersion—affects catalytic metrics like turnover frequency (TOF), linear-to-branched (n/i) ratio, and stability. By correlating support properties with performance data, this work identifies design principles that overcome the traditional trade-off between activity and selectivity, offering a roadmap for industrial implementation.
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WANG Wei, FENG Rui, LI Tianbo, HU Xiaoyan, YAN Xinlong, LU Shijian (2026). Research Progress on Supports for Rh-Based Catalysts in Heterogeneous Hydroformylation of Olefins. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60679-2
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Frequently Asked Questions
What are the main deactivation mechanisms for Rh-based heterogeneous hydroformylation catalysts, and how does support design mitigate them?
Deactivation primarily arises from Rh leaching, sintering, and poisoning by CO or sulfur impurities. Support design mitigates these via strong metal-support interactions (e.g., CeO2 facets), confinement in porous polymers (e.g., monophosphine polymers), and surface functionalization (e.g., oxygen groups on activated carbon) that anchor Rh species and prevent aggregation. For instance, Rh1/CeO2 with specific morphology enhances stability, while porous polymer supports confine atomically dispersed Rh, reducing leaching.
How does the support influence the linear-to-branched (n/i) ratio in hydroformylation of terminal olefins like 1-hexene?
Support properties such as pore size, surface polarity, and electronic effects modulate the coordination environment of Rh, affecting the selectivity. For example, silicalite-1 membrane encapsulated Rh/activated carbon achieves high selectivity to normal aldehyde due to shape selectivity. Porous monophosphine polymers provide a confined environment that favors linear aldehyde formation, achieving n/i ratios up to 20 or higher, as reported in J. Catal. 2021.
What are the reported turnover frequencies (TOF) for state-of-the-art heterogeneous Rh catalysts, and how do they compare to homogeneous systems?
Heterogeneous Rh catalysts have achieved TOFs exceeding 10,000 h−1, as seen in dual-active-site Rh-N4/Rh cluster catalysts (Chem. Eng. J. 2024, 479, 147505). While homogeneous catalysts can reach TOFs of 20,000 h−1, heterogeneous systems offer easier recovery and reuse, with TOFs often sufficient for industrial application. For example, Rh/activated carbon with oxygen groups shows TOFs around 5,000 h−1 for 1-hexene hydroformylation.
What are the scalability challenges for these supported Rh catalysts, particularly regarding cost and large-scale synthesis?
Scalability challenges include the high cost of rhodium and the need for reproducible support synthesis. Inorganic oxides like CeO2 are cost-effective but may require precise morphology control. Porous polymers offer high selectivity but are expensive to produce. Composite supports, such as Rh on reduced graphene oxide, are promising but face scale-up issues. The review highlights that activated carbon supports are industrially viable due to low cost and ease of functionalization, as demonstrated in Appl. Catal. A 2016.
How do reaction conditions (temperature, pressure, solvent) interact with support design to affect catalyst performance?
Reaction conditions such as syngas pressure (typically 1-10 MPa) and temperature (80-120°C) influence the equilibrium and kinetics. Support design can enhance local CO/H2 concentration via pore confinement, improving activity. For instance, low-pressure hydroformylation over active carbon-supported noble metal catalysts (Appl. Catal. A 2004) shows that support porosity allows operation at lower pressures without sacrificing yield. Additionally, solvent choice (e.g., toluene) can affect substrate diffusion, but supports with tailored hydrophobicity can mitigate mass transfer limitations.
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