TiO2 Nanotubes for Hydroformylation of Vinyl Acetate from Syngas
Hongyuan Chuai1*
Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, 999077, China
*Corresponding author: Hongyuan Chuai, Department of Applied Physics, Hong Kong Polytechnic University, Hong Kong, 999077, China.
Received: 18 June 2025; Accepted: 26 June 2025; Published: 30 June 2025
Article Information
Citation:
Hongyuan Chuai. TiO2 Nanotubes for Hydroformylation of Vinyl Acetate from Syngas. Journal of Nanotechnology Research. 7 (2025): 10-12.
DOI: 10.26502/jnr.2688-85210047
View / Download Pdf Share at FacebookAbstract
TiO2 nanotubes (TNTs) have emerged as promising supports for heterogeneous catalysts due to their unique physicochemical properties, including high surface area, ion-exchange capacity, and structural stability. This review focuses on the work of Chuai et al., who systematically explored TNTs as supports for Rh-based catalysts in the hydroformylation of functionalized olefins, particularly vinyl acetate, using syngas (CO/H2). Their studies demonstrated that modifying TNTs with transition metal (Ru), alkali/alkaline earth cations (Li+, Na+, K+, Mg2+, Ca2+, Sr2+), and rare-earth metal (La3+) significantly enhances catalytic activity, selectivity, and turnover frequency (TOF). Key findings include the synergistic effects of Rh-Ru systems, the promotional role of alkali cations in CO adsorption, and the exceptional performance of La-decorated Rh/TNTs (TOF = 5796 h-1). Beyond hydroformylation, the potential applications of TNTs in other catalytic processes, such as Fischer-Tropsch synthesis, hydrogenation, and environmental catalysis, are discussed. This review highlights the versatility of TNTs as catalyst supports and provides insights into future research directions.
Keywords
Hydroformylation; TiO2 Nanotubes; Vinyl Acetate; Syngas
Hydroformylation articles; TiO2 Nanotubes articles; Vinyl Acetate articles; Syngas articles
Article Details
Introduction
Hydroformylation, the addition of syngas (CO/H2) to olefins to form aldehydes, is a cornerstone of industrial chemistry, with annual production exceeding 22 million tons [1]. Rhodium-based catalysts dominate this field due to their high activity and selectivity under mild conditions [2]. However, challenges persist, including the high cost of Rh, its deactivation by functionalized olefins (e.g., vinyl acetate), and the requirement for efficient heterogeneous catalytic systems. TiO2 nanotubes (TNTs), synthesized via hydrothermal methods, offer a compelling solution as catalyst supports. Their high surface area (up to 300 m2/g), nanotubular morphology, and tunable surface acidity make them ideal for stabilizing metal nanoparticles and facilitating reactant adsorption [3]. Chuai et al. explored the use of TNTs in hydroformylation, demonstrating their efficacy in enhancing Rh catalyst performance through strategic modifications.
This review synthesizes Chuai et al.’s contributions, covering:
- Rh/TNTs and bimetallic systems(Rh-Ru) for vinyl acetate
- Alkali/alkaline earth cation-modified TNTsto improve CO adsorption and Lewis acid-base interactions.
- Rare-earth metal promotion(La3+) for creating LaOx–Rh active sites.
- Prospects for TNTsin other catalytic applications.
Rh/TNTs and Bimetallic Systems for Vinyl Acetate Hydroformylation
Rh/TNTs: Baseline Performance
Chuai et al. prepared Rh/TNTs via impregnation-photoreduction, achieving Rh nanoparticles uniformly dispersed on TNTs [4]. In vinyl acetate hydroformylation, Rh0.25/TNTs showed 60% conversion and 60% aldehyde selectivity (TOF = 3168 h-1). The regioselectivity for 2-acetoxypropanal (branched aldehyde) was 100%, attributed to the stability of a five-membered ring intermediate [5].
Key limitations:
- • Functional groups (e.g., acetate in vinyl acetate) coordinate with Rh, reducing activity.
- •Low H2 adsorption capacity limits aldehyde yield.
Rh-Ru/TNTs: Synergistic Effects
To mitigate chelation effects, Chuai et al. developed Rh-Ru/TNTs, where Ru acts as a Lewis acid to attract vinyl acetate’s carboxyl group, freeing Rh for hydroformylation [4].
Key results:
- • Vinyl acetate: Conversion increased from 39% (Rh/TNTs, 1 h) to 45% (Rh-Ru/TNTs, 1 h), but aldehyde selectivity dropped from 82% to 57% due to Ru’s hydrogenation activity.
- • Cyclohexene: Ru had no promotional effect, confirming its role is specific to functionalized olefins.
Mechanism: Ru enhances CO adsorption (FT-IR peaks at 2066 cm-1 and 1997 cm-1) and weakens substrate-catalyst chelation [4].
Alkali/Alkaline Earth Cation-Modified TNTs
Design and Characterization
Chuai et al. decorated TNTs with Li+, Na+, K+, Mg2+, Ca2+, and Sr2+ via impregnation [6]. These cations:
- • Increased CO adsorption (FT-IR peak intensity at 2068 cm-1).
- • Acted as Lewis acids to attract vinyl acetate (Lewis base).
Notable catalysts:
- • Rh25/Li-TNTs-P5: 100% conversion, 67% selectivity (TOF = 3581 h-1).
- • Rh25/Mg-TNTs-P5: 99% conversion, 76% selectivity (TOF = 2826 h-1) [6].
Promotion Mechanism
- Electronic effects: Cations (e.g., Mg2+) donate electrons to Rh, facilitating CO insertion (XPS shifts in Rh 3d) [6].
- Concentration effect: Cations pre-concentrate substrates near active sites.
Trend: Smaller cations (Li+ > Na+ > K+) showed higher polarizing power and better performance [6].
Rare-Earth Metal Promotion: La-Decorated Rh/TNTs
La’s Unique Role
Chuai et al. introduced La3+ to Rh/TNTs, achieving:
- • Rh25-La/TNTs: 89% conversion, 66% selectivity, TOF = 5796 h-1 [7].
- • H2-TPD: Enhanced H2 adsorption (peak at 307°C) due to LaOx–Rh sites [7].
Mechanism
La forms highly dispersed La2O3 (XPS BE = 835.3 eV) that interacts with Rh2+, creating LaOx–Rh interfaces to boost H2 activation and CO insertion [7].
Prospects for TNTs in Other Catalytic Applications
Fischer-Tropsch Synthesis (FTS)
TNTs’ high surface area and metal-support interactions could stabilize Co or Fe nanoparticles. La-promoted TNTs may mimic Co-La/SiO2 systems, enhancing C5+ selectivity [8].
Hydrogenation Reactions
Ru/TNTs’ hydrogenation activity (observed in hydroformylation) could be leveraged for nitroarene reduction or bio-oil upgrading.
Environmental Catalysis
TNTs’ photocatalytic properties (e.g., for CO oxidation [9]) may be combined with metal sites for VOC degradation.
Conclusion
Chuai et al.’s work establishes TNTs as versatile supports for hydroformylation catalysts. Key advances include:
- • Bimetallic systems: Rh-Ru for enhanced activity in the hydroformylation of vinyl acetate.
- • Cation promotion: Alkali/alkaline earth metals optimize CO adsorption and Lewis acid-base interactions.
- • La decoration: Creates LaOx–Rh sites for higher TOFs.
Future research should explore:
- TNTs in tandem reactions(e.g., hydroformylation-hydrogenation).
- Multifunctional TNTsfor coupled redox processes.
- Scalable synthesisfor industrial adoption.
TNTs’ adaptability positions them as a platform for next-generation catalysts beyond hydroformylation.
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