Synthesis and Characterization of Rh/B–TNTs as a Recyclable Catalyst for Hydroformylation of Olefin Containing –CN Functional Group

Abstract

The TiO2-based nanotubes (TNTs, B–TNTs) of different surface acidities and their supported Rh catalysts were designed and synthesized. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometer (XPS), tempera–ture–programmed desorption of ammonia (NH3–TPD), atomic emission spectrometer (ICP), and Brunauer–Emmett–Tellerv (BET) surface-area analyzers. Images of SEM and TEM showed that the boron-decorated TiO2 nanotubes (B–TNTs) had a perfect multiwalled tubular structure; their length was up to hundreds of nanometers and inner diameter was about 7 nm. The results of NH3-TPD analyses showed that B–TNTs had a stronger acid site compared with TNTs. For Rh/TNTs and Rh/B–TNTs, Rh nanoparticles highly dispersed on B–TNTs were about 2.79 nm in average diameter and much smaller than those on TNTs, which were about 4.94 nm. The catalytic performances of catalysts for the hydroformylation of 2-methyl-3-butennitrile (2M3BN) were also evaluated, and results showed that the existence of B in Rh/B–TNTs had a great influence on the catalytic performance of the catalysts. The Rh/B–TNTs displayed higher catalytic activity, selectivity for aldehydes, and stability than the Rh/TNTs.

Preparation and Characterization of Rh/MgSNTs Catalyst for Hydroformylation of Vinyl Acetate: The Rh0 was Obtained by Calcination

“…Figure 3C,D show the XRD pattern of Rh/MgSNTs-300(b 2 ) and Rh/MgSNTs-300(b 3 ). The intensities of the peaks decrease with the increase of the calcination temperature, which indicates that the optimum calcination temperature for catalyst preparation is 300 • C. There were no peaks relevant to Rh found in Figure 2C,D, due to the relatively low content and very small size of Rh particles, which was similar to that observed by our previous reports [30].…”

“…The surface area of the catalysts are calculated to be 238.2, 236.7 and 229.6 m 2 g -1 for Rh/MgSNTs-300(a1), Rh/MgSNTs-300(a2), and Rh/MgSNTs-300(a3), respectively. The SSAs of all catalysts are significantly lower than that of pure supports (250.6 m 2 g -1 ), which may be ascribed to those metal nanoparticles deposited on the outer and inner surface in MgSNTs like the TNTs catalysts [17,30,31]. The nanotubular structures are readily accessible, favorable to adsorption and release of reactants.…”

“…The higher binding energy state should have relevance to the partially oxidized Rh 2+ ions [25]. It is well-known that Rh 0 is the active site for the hydroformylation of olefins [30]. The percentage of Rh 0 in rhodium is calculated based on the area of the fitted Gauss peaks, with the proportions of Rh 0 in Rh/MgSNTs-300(a 1 ) at 89.79%.…”

Polymeric Heterogeneous Catalysts in the Hydroformylation of Unsaturated Compounds

“…For historical perspective, mention should be made of the scientifi c studies where different types of inorganic carriers such as silicon oxide [4][5][6][7], zeolites [8][9][10], and activated carbon [11,12] were used as materials for immobilization of metal complexes. The range of insoluble carriers used in the processes was considerably expanded thereafter, and at present the main metal fi xing methods include: incorporation of metal nanoparticles into the structures of various materials [13,18]; fi xing the rhodium complexes in the structure of the material by intercalation [19]; encapsulation of phosphine or a phosphine complex into mesopores or nanopores of the carrier [20,21]; the sol-gel method, "grafting" of a phosphine-containing hydrocarbon radical onto the carrier surface, and other methods of covalent bonding of phosphine fragments on an inorganic, hybrid or organic substrate, wherein rhodium is subsequently introduced [22][23][24][25][26][27][28]; fi xing of phosphine or a phosphine complex on the surface by means of ionic interactions [29]; fi xing of catalysts soluble in polar liquids (water and ionic liquid) in the thin hydrophilic layer of the carrier, which most frequently is silica gel SAPC/SIPC (Supported Aqueous/Ionic Liquid Phase Catalysts) [30,31]; creation of structures containing single rhodium atoms, as per the "single atom" concept [32], such as the cases in which nano-objects (nanosheets and nanofi bers) made of cobalt oxide [33] or zirconium oxide [34] were obtained and their catalytic properties were studied. Heterogeneous modifi ed rhodium clusters [35] and an iron-based catalyst [36] are also reported to have been used.…”

Advances in Heterocatalysis by Nanomaterials

“…Su et al [19] synthesized Rh nanoparticle catalysts dispersed on TiO 2 and boron-decorated TiO 2 nanotube supports (Rh/TNTs, Rh/B-TNTs), which were evaluated on the hydroformylation of 2-methyl-3-butennitrile (2M3BN). Given that 2M3BN can be used for the preparation of adiponitrile after isomerization, and the hydroformylation of 2M3BN is an industrially important and scientific research subject, in addition to the fact that hydroformylation processes are related with difficulties upon recovery of the homogeneous catalysts employed in industrial practice, the present study, employing heterogeneous catalysts, is of considerable interest.…”