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

Abstract

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.

Hydroformylation of Alkenes over Phosphorous-Free Rhodium Supported on N-Doped Silica

“…These data are in agreement with the results reported in many articles, for example [33], using Rh nanoparticles. The developed Rh-UFSi catalyst showed excellent catalytic characteristics in the hydroformylation of alkenes of various structures, its activity is close to, and in some cases exceeds, the results obtained for catalysts similar in structure presented in the works [34][35][36][37][38].…”

Highly Efficient and Chemoselective Tandem Hydroformylation‐Hydrogenation of Alkenes to Alcohols over g‐CN Supported Bimetallic Rh and Co Nanoparticles Catalysts

“…As shown in Figure S1, it can be seen that pristine g-C 3 N 4 presents typical 2D continuous lamellar structure, which is in accordance with the relevant results of our previous report. [36][37] In contrast, g-CN exhibits typical nanosheet-like nanostructure with thin sheets as shown in Figure 3a, which will lead to the enhancement of specific surface area for g-CN nanosheets and facilitate the dispersion and transport of the supported particles and reactant, respectively. This could be attributed to the fact that the lamellar structure of network decomposes to form thin nanosheets structure and g-C 3 N 4 is converted to g-CN at high temperature.…”

“…Since it is well-known that the reaction temperature has a significant influence on the chemo-and region selectivity of the tandem hydroformylation-hydrogenation of styrene, we studied the temperature influence towards alcohol selectivity in detail (Table 3). In our previous studies, [36][37] we reported that g-CNbased heterogeneous catalysts showed excellent catalytic activity at 100 °C in hydroformylation reaction. Thus, the tandem hydroformylation-hydrogenation of styrene catalyzed by RhÀ Co/g-CN was first tested at 100 °C (Table 3, entry 1).…”

“…[35] In our previous study, graphitic carbon nitride supported Rh nanoparticles prepared via an impregnationchemical reducing process, exhibited outstanding catalytic performance for the hydroformylation of olefins, making g-CN an intriguing support for heterogeneous catalysts. [36][37][38][39] In particular, the incorporation of nitrogen atoms in the carbon nanostructure can enhance the mechanical, conducting, fieldemission, and energy-storage properties. [40][41][42] This special feature is not only beneficial to the diffusion of reactants and products, but also potential to improve the dispersibility and stability of the supported metal nanoparticles.…”

Phosphorus-free nitrogen-containing catalytic systems for hydroformylation and tandem hydroformylation-based reactions

“…Shi et al developed a method to produce monosized Rh nanoparticles using graphite-like carbon nitride g-C3N4 doped with sulfur [100] and boron [101]. These materials contain many "pyridinelike" nitrogen atoms and can therefore stabilize Rh nanoparticles to form potential active sites, whereas the doping heteroatom can modify the textural, electronic, and structural properties of g-C3N4; favor the electron transfer; and give rise to a more stable π-conjugated system, which enhances the adsorption and deposition of Rh nanoparticles and alkenes on g-C3N4.…”