___________________________________________________________________________www.paper.edu.cn Catalysis Today 74 (2002) 5–13 Structure aspects and hydroformylation performance of water-soluble HRh(CO)[P(m-C6H4SO3Na)3]3 complex supported on SiO2 Youzhu Yuan∗, Hongbin Zhang, Yiquan Yang, Yu Zhang, Khirui Tsai State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen 361005, PR China Abstract The solution NMR (31P and 1H) and FTIR spectroscopies were employed to investigate the structure information of water-soluble complex HRh(CO)[P(m-C6H4SO3Na)3]3 (1) [P(m-C6H4SO3Na)3: trisodium salt of tri-(m-sulfophenyl)- 31 1 phosphine, TPPTS] supported on SiO2 (1/SiO2). The P( H) NMR spectra showed that a pair of new twin-peak at about 31.5, 32.1 ppm while no typical twin-peak at 44.0, 44.7 ppm for the phosphorus species ascribed to the complex 1 were ob- served at 1/SiO2. However, the typical phosphorus peaks for the complex 1 appeared in the case of using TPPTS or Na2CO3- preimpregnated SiO2 as supports. Moreover, the immobilization caused a considerable oxidation of the liberated TPPTS to OTPPTS (OTPPTS, i.e. OP(m-C6H4SO3Na)3: trisodium salt of tri-(m-sulfophenyl)-phosphine oxide) species as evidenced 31 1 by P( H) NMR spectroscopy. The phosphorus-31 peaks at 31.5, 32.1 ppm at 1/SiO2 were found to be unchanged before and −1 after the propene hydroformylation. The FTIR results revealed that the CO band appeared at about 1870 cm for the 1/SiO2 catalyst, which was lower than that for the precursor complex 1. It is concluded that there exists a strong interaction between the complex 1 and the acidic support of SiO2, resulting in the deformation of the Rh–phosphine complex containing less than three TPPTS ligands, which further transformed by dehydrogenation and dimerization under evacuation to form a species likely [Rh(CO)(TPPTS)2]2 as a main surface complex species at the catalyst 1/SiO2. © 2002 Elsevier Science B.V.All rights reserved. Keywords: Water-soluble Rh-complex; NMR; Hydroformylation; FTIR; Supported aqueous-phase catalyst 1. Introduction catalysts (SAPC) [6] are known as attractive alter- natives for heterogenized catalysts for olefin hydro- Research into heterogenization of HRh(CO) formylation. The SAPC where the complex 1 or [P(C6H4)3]3 (P(C6H4)3: triphenylphosphine) for hy- rhodium complex precursor and water-soluble ligand droformylation and selective hydrogenation has re- like TPPTS are immobilized in a thin water layer ad- ceived high attention in the past several decades from hered within the pores of a high surface-area silicates both academic and industrial interests [1]. Besides [7] makes the separation of catalyst from reaction the milestone preparation of water-soluble TPPTS mixture to be greatly simplified, thus, facilitating and corresponding Rh–phosphine complexes such as successive operation. Using this system higher alkenes HRh(CO)(TPPTS)3 (1) [2,3], supported liquid-phase can be converted at a relatively high rate without metal catalysts (SLPC) [4,5] and supported aqueous-phase leaching. It still faces the problems, however, how to improve the lower regioselectivity to the product ∗ Corresponding author. Fax: +86-592-2183047. aldehydes (i.e. molar ratio of normal:branched (n:i) E-mail address: [email protected] (Y. Yuan). aldehydes) and also the catalytic stability due to the 0920-5861/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S0920-5861(01)00525-9 ___________________________________________________________________________中国科技论文在线 www.paper.edu.cn 6 Y. Yuan et al. / Catalysis Today 74 (2002) 5–13 oxidation of water-soluble phosphine ligands [8,9]. In A water solution of 1 (0.01 mmol ml−1) was poured literature, the results on SAPC for hydroformylation, into a Schlenk flask containing 0.1 g degassed SiO2. thus, far were mostly based on rhodium, cobalt and After further degassing the mixture by vacuum boiling, platinum/nickel with TPPTS as the ligand [10,11] argon was introduced and the slurry was kept at room or sulfonated diphosphines including those with a temperature for 1 h while vibration. The water was large bite angle as ligands [12], limited attention has removed under vacuum at room temperature. The final been paid on the structure information in the SAPC product was a dry, free-flowing yellow powder and system [13]. denoted as 1/SiO2, which was stored under Ar at room It is well documented in the relationship of temperature. The water content was analyzed by TGA structure-performance in homogeneous and biphasic to be 8–10%. catalytic systems due to the easy characterization and Solution 31P(1H) NMR spectra were recorded on well-defined structure as compared to the correspond- a Varian FT Unity+ 500 spectrometer at 200 MHz at ing SAPC system [14]. Use of high resolution MAS room temperature. Phosphorous-31 NMR chemical NMR technique is one of the efficient ways to clar- shifts are reported relative to 85% H3PO4. Samples of ify the coordination chemistry in the SAPC system SAPC in the NMR tube were introduced about 40% [8,13,15]. However, the measurements of MAS NMR D2O before measurements. FTIR spectra were mea- spectra are time-consuming and usually MAS spectra sured on a Nicolet-740 spectrometer with a resolution with lower resolution are far from satisfactory for cat- of 4 cm−1. The surface-areas of the samples were alyst characterization. Alternatively, when the dried measured by a conventional BET nitrogen adsorp- supported catalyst of SAPC is exposed to water it is tion method at 77 K using a SORPTOMATIC-1900 possible to record a 31P NMR spectrum using conven- machine. tional solution NMR techniques [15]. The objective of The propene hydroformylation reaction was per- this work is to investigate the structural information formed in a high-pressure fixed-bed flow reactor at SiO2-supported water-soluble TPPTS–Rh-complex connecting an on-line gas chromatgraph (102-GD, catalysts in connection to the hydroformylation per- Shanghai Analysis Factory, China) equipped with formance by means of solution NMR with the com- FID detector and a column of Porapak Q (2 m). The bination of pyridine–TPD and FTIR spectra. propene:CO:H2 ratio used here was always 1:1:1. The results showed the total hydrogenation products were lower than 1% under present experiment condition. 2. Experimental A commercial available SiO2 was washed by 3. Results distilled water and sieved to 80–100 mesh which has pore diameter of 6–12 nm, pore volume of 3.1. Pyridine–TPD 1.03 cm3 g−1 and BET surface-area of 380 m2 g−1. For comparison, SiO2 was preimpregnated with 2% It is known that the hydrophilic SiO2 support pos- Na2CO3 followed by drying in an oven at 393 K for sesses acidity at the surface. Pyridine–TPD spectra over night. TPPTS was synthesized by the known for SiO2 and Na2CO3/SiO2 are shown in Fig. 1. The 31 1 method [2,16–18]. P( H) NMR spectroscopy pyridine–TPD for the SiO2 showed a peak at about showed it consisted of 15% OTPPTS (trisodium salt 420 K, whereas that for Na2CO3/SiO2 showed no peak of tri-(m-sulfophenyl)-phosphine oxide). Thermo- in the same temperature range. In fact the pyridine ad- gravometric analysis (TGA) on the TPPTS showed sorption on Na2CO3/SiO2 sample was negligible. a 10% weight loss attributed to the residual water. − The TPPTS had a solubility of 0.63 g ml 1 at room 3.2. Solution 31P (1H ) NMR spectra of temperature and the same IR bands as reported in SiO2-supported 1 [16–18]. The complex 1 was synthesized according to the literature method [15]. 31P(1H) NMR: 44.7, The solution 31P(1H) NMR spectra for TPPTS, 1, −1 44.0 ppm; IR (cm ): 2010s, 1928s. and a SiO2-supported TPPTS and a SAPC sample ___________________________________________________________________________中国科技论文在线 www.paper.edu.cn Y. Yuan et al. / Catalysis Today 74 (2002) 5–13 7 at 35.2 ppm significantly increased from 10 mol% in the precursor 1 to about 30 mol% in the SAPC sam- ple, probably due to an oxidation of the phosphorous ligands liberated from the complex during the impreg- nation. The new peaks at 32.1 and 31.5 ppm contained 60 mol% amount of phosphorous species. Taking the weak or no coordination ability of OTPPTS to rhodium atom into account, we estimated the ratio of the phosphorous in the new peak to rhodium atom to be closely to 2:1 (mol). Further NMR experimental results revealed that the newly formed Rh–TPPTS species at SiO2 surface strongly interacted with SiO2 so that it was impossible to be simply removed from the SiO surface by washing with D O. Fig. 1. TPD spectra of pyridine adsorbed on SiO (a) and 2 2 2 To investigate the property of the interaction be- Na2CO3/SiO2 (b). tween the Rh-complex 1 and SiO2 support and clarify the reason why the interaction generated, containing about 40 wt.% D2O are shown in Fig. we chose several supports, such as GDX-102 2a–c, respectively. When TPPTS was supported on (a copolymer of ethylene benzen and xylene), 31 1 SiO2, the P( H) NMR showed two peaks at 5.1 Na2CO3-preimpregnated SiO2 (Na2CO3/SiO2), and 35.2 ppm straightforwardly assignable to the free TPPTS-impregnated SiO2 (TPPTS/SiO2) to immobi- TPPTS and OTPPTS, respectively. However, no typ- lize the Rh-complex 1 and characterize the structure ical twin phosphorus-31 peaks at 44.7, 44.0 ppm for information by the solution NMR. All the samples for the complex 1 but another pair of twin-peaks with the NMR measurements contained about 40% D2O.