Preparation of Rh-TPPTS Complex Intercalated Layered Double

Chinese Science Bulletin

Preparation of Rh-TPPTS complex intercalated layered double hydroxide and influences of host and guest compositions on its catalytic performances in hydroformylation reaction

ZHANG Xian, LU Jun, JIN Lan & WEI Min†

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China Based on the concept of intercalation chemistry of layered double hydroxides (LDHs), RhCl(CO)-

(TPPTS)2 (TPPTS: P(m-C6H4SO3Na)3) and TPPTS co-intercalated LDHs were successfully synthesized by in situ complexation method. Characterizations of structure and composition of composite materials by powder XRD, FT-IR, and ICP-AES techniques confirmed the supramolecular structures of the catalytic species intercalated LDHs. The correlation between catalytic performance of intercalated catalyst and the composition of both host layers and interlayer guest species was also investigated.

layered double hydroxides, hydroformylation, supported catalyst, RhCl(CO)(TPPTS)2

II III Hydroformylation reaction, the addition of synthesis gas represented by the general formula [M 1-x M x - x+ n– (CO and H2) to alkenes, is one of the most important (OH)2] (A )x/n·yH2O. Many divalent and trivalent n syngas-related reactions[1]. Hydroformylation of alkenes cations (MII and MIII, respectively) and the anion (A ) performed by using transition metal catalysts is widely can form LDHs structures, and the concentration of applied into petrochemical industry for the production of MII cation[8 10] may vary over a wide range, giving rise [2] aldehydes (ca. 7 million tones per year) . Over the past to a large class of isostructural functional materials. few decades, development and application of immobi- These layered solids have received considerable atten- lized hydroformylation catalysts have been attracting tion due to their many practical applications, such as ion- widespread interest[3,4], since such catalysts can combine [11] [12] exchangeable absorbents , molecular container , APPLIED CHEMISTRY the high activity and selectivity of homogeneous cata- medication[13,14] and catalysts. There were some reports lysts with the long lifetime and ease of separation of on intercalation of transition metal complexes in LDHs [5] heterogeneous catalysts . A large number of papers and which have shown good catalytic activity. Examples 2 patents concerning alkene hydroformylation reactions include reusable OsO4 on ion-exchangers for asym- catalyzed by rhodium or other noble metal complexes metric dihydroxylation of olefins[15], LDHs-host cata- supported on silica or other oxide supports have been lysts for stereoselective epoxidation[16] and LDHs- [6,7] published , with some showing high performance. Layered double hydroxides (LDHs) are a class of Received May 25, 2007; accepted December 3, 2007 doi: 10.1007/s11434-008-0071-5 synthetic anionic clays, whose structures can be de- †Corresponding author (email: [email protected]) scribed as positively-charged brucite (Mg(OH) )-like Supported by the Major International Joint Research Program of the National Natural 2 Science Foundation of China (Grant No. 20620130108), the National Natural Sci- layers with some divalent cations being replaced by tri- ence Foundation of China (Grant No. 20601001), the Program for New Century valent ions. The charge is balanced by the intercalated Excellent Talents in University (Grant No. NCET-05-121), the 111 Project (Grant No. B07004) and the Program for Changjiang Scholars and Innovative Research Team in anions in the hydrated interlayer regions. LDHs can be University (Grant No. IRT0406) www.scichina.com | csb.scichina.com | www.springerlink.com Chinese Science Bulletin | May 2008 | vol. 53 | no. 9 | 1329-1336

2 [17] WO4 for mild oxidative bromination . and dried in vacuo at 60ć. The product is denoted as [18] trans In our previous work , -RhCl(CO)(TPPTS)2 RhP2/P/A-M2Al-LDHs (RhCl(CO)(TPPTS)2 is denoted m [TPPTS: trisodium salt of tri-( -sulfophenyl)-phosphine] as RhP2, and TPPTS is denoted as P; A: NO3 , Cl , 2 and TPPTS ligands were co-intercalated into zinc-alu- SO4 ; M: Zn, Ni). The white TPPTS pre-intercalated in minum-layered double hydroxides (ZnAl-LDHs) by LDHs precursors turned to pale yellow RhP2/P/A-M2Al- situ complexation method, and the catalytic perform- LDHs, which indicates the formation of the Rh- ances of the resulting materials for 1-hexene hydrofor- phosphine complex via in situ complexation. mylation were investigated. 1.4 Catalyst evaluation Based on our previous work, the aim of this work is to investigate the influences of the composition of both Hydroformylation reaction of 1-hexene was conducted host layers (M2+ species) and interlayer inorganic anions under 1.6 MPa of an equimolar CO and H2 mixture at species on the catalytic behavior, and thus give a de- 100ć in a stainless steel autoclave for 6 h. The interca- 4 tailed understanding for the relationship between lated LDHs catalyst (Rh/1-hexene = 4.010 ), 1-hexene host-guest interactions and the catalytic performances. (1.0 mL), toluene (2.0 mL) and triethylamine (0.05 mL) were first transferred into the autoclave. The reaction 1 Experimental system was purged with an equimolar CO and H2 mixture and subsequently charged to the working pressure. 1.1 Reagents When the reaction was completed, the reactor was al- TPPTS was provided by Sichuan University. RhCl3· lowed to cool to room temperature and depressurized. 3H2O (Rh: 40 wt%) was purchased from General Re- The solid catalyst was filtered off from the reaction search Institute of Nonferrous Metals. All the chemicals mixture in air. The products of hydroformylation were used in this synthesis were of analytical grade and analyzed by GC-MS. without further purification. All solutions were prepared 1.5 Characterization by using distilled and decarbonated water. XRD measurements were performed on a Rigaku 1.2 Synthesis of precursors XRD-6000 diffractometer, using Cu K radiation ( = The ion-exchange precursors: [Zn2Al(OH)6](NO3)· 0.154184 nm) at 40 kV, 30 mA, a scanning rate of 4H O[19], [Ni Al(OH) ](NO )·4H O[20], [Zn Al(OH) ]- 2 2 6 3 2 2 6 0.02º/s, with the 2 range of 3° to 70°. FT-IR spectra (Cl)·4H O[21], [Zn Al(OH) ](SO ) ·4H O[22] were syn- 2 2 6 4 0.5 2 were recorded using a Bruker Vector 22 spectropho- thesized by the literature procedure. TPPTS pre-inter- tometer in the range of 4000 to 400 cm 1 with 2 cm 1 calated LDHs precursor was prepared by ion exchange resolution. The standard KBr disk method (1 mg of method, in which a mixture of precursor and the aque- sample in 100 mg of KBr) was used. ous solution of TPPTS was heated at 80 under nitro- ć Elemental analysis was performed by ICP atomic gen atmosphere for 72 h. The resulting precipitate was emission spectroscopy (ICP-AES) on a Shimadzu in vacuo separated, washed with water and dried at room ICPS-7500 instrument and the analyzed solutions were temperature for 48 h. prepared by dissolving the sample in dilute HCl solution. 1.3 Synthesis of Rh-TPPTS complex intercalated The products of hydroformylation were separated and LDHs by in-situ complexation method analyzed with programmed heating method by using a Rh-TPPTS complex intercalated LDHs were synthesized Shimadzu 2010 GC-MS instrument. by in-situ complexation method[18]: A solution of 2 Results and discussion RhCl3·3H2O in absolute ethanol (10 mL) was held at 2+ 78ć under carbon monoxide atmosphere for 50 min. A 2.1 Effect of varied M species of host layers on suspension of TPPTS pre-intercalated LDHs precursor catalytic performances in water (5 mL) was then added dropwise quickly. The Two samples, RhP2/P-Zn2Al-LDHs and RhP2/P-Ni2Al- mixture was held at 78ć for 90 min, after which abso- LDHs, were prepared by the method of in situ com- lute ethanol was added to cool the mixture. The resulting plexation through varying the M2+ cation in the host precipitate was separated, washed with absolute ethanol layers. The structure and composition of the composite

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materials were analyzed by powder XRD, FT-IR and Zn2Al-LDHs, which indicates that the crystallinity of the

ICP-AES. The catalytic performances of the intercalated latter is higher than that of the former. ARTICLES 2+ catalysts as well as the correlation between the M spe- The FT-IR spectra of the TPPTS, RhCl(CO)(TPPTS)2 cies of host layers and the catalytic performances were and their intercalation into the LDHs are presented in investigated. Figure 2. The spectra of TPPTS and RhCl(CO)(TPPTS)2 The powder XRD patterns of RhP2/P-Zn2Al-LDHs (Figure 2(a) and (b)) are similar to those reported in ref. 1 and RhP2/P-Ni2Al-LDHs are shown in Figure 1. Table 1 [26]. The bands at 1207/1196, 1040 and 628 cm of lists the corresponding basal spacing and lattice pa- TPPTS (Figure 2(a)) and RhCl(CO)(TPPTS)2 (Figure rameters. The reflections of the materials show the 2(b)) can be attributed to the stretching vibrations oso, [24,25] characteristic features of LDHs . However, as is so and 'so, respectively. After intercalation reaction, [26], hkl often the case several ( ) reflections disappear or these three bands of RhP2/P-Zn2Al-LDHs moved to- broaden. The basal spacing (d003) of RhP2/P-Zn2Al- wards lower frequency, observed at 1182, 1036 and 619 1 LDHs and RhP2/P-Ni2Al-LDHs is 1.579 and 1.595 nm, cm (Figure 2(c)), respectively. The electrostatic force respectively (Table 1), which increases by 0.701 and between the host layers and the sulfonate group of guest 0.697 nm compared with their ion-exchange precursor anions leads to the shift of the three bands to lower en- [Zn2Al(OH)6](NO3)·4H2O and [Ni2Al(OH)6](NO3)· ergy. On the other hand, the coordination of the oxygen 4H2O, respectively. The expansion of the basal spacing atom in the sulfonate group decreases the force constant resulted from the intercalation of bulky organic anions of the SO bond and accordingly results in a shift of the in situ into the LDHs, indicating that the complexation SO vibration band to lower frequency. This was previ- reaction occurred in the interlayer region of TPPTS ously reported in the FT-IR spectra of the intercalation pre-intercalated LDHs. Moreover, a decrease in the re- of naphthalene-2,6-disulfonate[27] and 9,10-an- flection intensity as well as increase in the peak width at thraquinone-1,2-dihydroxy-3-sulfonate (Alizarin red S half maximum were observed in the XRD pattern of anion) in LDHs[28]. Therefore, it can be concluded that RhP2/P-Ni2Al-LDHs compared with that of RhP2/P- the observed shifts of these bands result from the interaction between the sulfonate group of the interlayer organic anions and the host lattice. However, compared

with RhP2/P-Zn2Al-LDHs, the stretching vibrations oso, so and 'so of RhP2/P-Ni2Al-LDHs moved to much lower frequency: 1178, 1035 and 618 cm 1 (Figure 2(d)), respectively. This can be explained by the different electrostatic force between the host layers and TPPTS, which is related to the electronegativity of the divalent

APPLIED CHEMISTRY APPLIED CHEMISTRY

Figure 1 XRD patterns for (a) RhP2/P-Zn2Al-LDHs and (b)

RhP2/P-Ni2Al-LDHs.

Table 1 Lattice parameters of RhP2/P-Zn2Al-LDHs and RhP2/P-Ni2Al- LDHs

Sample RhP2/P-Zn2Al-LDHs RhP2/P-Ni2Al-LDHs

d003 (nm) 1.579 1.595

d110 (nm) 0.153 0.151 Lattice parameter a (nm) 0.306 0.302 Lattice parameter c (nm) 4.737 4.785 Figure 2 FT-IR spectra for (a) TPPTS, (b) RhCl(CO)(TPPTS)2, (c) RhP2/P-Zn2Al-LDHs, and (d) RhP2/P-Ni2Al-LDHs.

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[29,30] metal . It is known that the values of electronegativ- catalyst systems, viz. the RhP2/P-Zn2Al-LDHs-catalyzed [31] ity for zinc and nickel are 1.6 and 1.9 , respectively. and RhP2/P-Ni2Al-LDHs-catalyzed systems. The effect The electron donating ability of M2+ in the host layers of different M2+ in the intercalated samples on catalytic decreases with the increase of electronegativity, and thus performances was studied in detail. leads to an increase in hydrogen bonding force between 2+ the M and guest anions. Moreover, it also results in an Table 2 Key elemental content and molar ratios in RhP2/P-Zn2Al-LDHs increase in positive charge density around the and RhP2/P-Ni2Al-LDHs Sample RhP /P-Zn Al-LDH RhP /P-Ni Al-LDH neighbouring M3+, which conduces to an increase in 2 2 2 2 Molar ratio M/Al 2.0 1.6 electrostatic attraction between M3+ and TPPTS. Con- Molar ratio P/Rh 18.4 16.2 sequently, the interactions between the host layers and Rh (%) (w/w) 0.36 0.31 TPPTS in RhP2/P-Ni2Al-LDHs are stronger than those in RhP2/P-Zn2Al-LDHs, accounting for the different It can be seen from Table 3 that the RhP2/P-Zn2Al- basal spacing of the two samples shown in Table 1. The LDHs catalyst displays higher activity than RhP /P- 2 CO stretching vibration of the pristine RhCl(CO)- Ni Al-LDHs with similar M2+/Al and P/Rh molar ratios. 1 2 (TPPTS)2 (Figure 2(b)) appears at 1977 cm , while this The values of total conversation are 76% and 32 % and band in RhP2/P-Zn2Al-LDHs and RhP2/P-Ni2Al-LDHs the turnover frequencies (TOF) towards aldehyde are 1 (Figsure 2(c) and (d)) is observed at 1990 cm , with a 267 h 1 and 54 h 1, respectively (Table 3). The generally 1 shift of 13 cm to higher frequency. This can be attrib- accepted hydroformylation catalytic mechanism of uted to the interaction between the sulfonate group of [32,33] RhCl(CO)(TPPTS)2 is shown in Scheme 1 . The Rh- TPPTS and the host layers. The frequencies of all the TPPTS complex undergoes an induction period before it other main absorption bands of RhP2/P-Zn2Al-LDHs turns to HRh(CO)mLn [L = TPPTS, m, n = 1, 2, 3] in- and RhP /P-Ni Al-LDHs (Figure 2(c) and (d)), such as 2 2 cluding active 16-electron complex, HRhCO(TPPTS)2[1] the vibrations bands of phenyl ring centered at 1464 and and HRh(CO)2(TPPTS)[3] (Scheme 1) under the catalytic 1 1398 cm as well as CH out-of-plane bending vibra- conditions. The structure of LDHs support is based on 1 tions of phenyl ring at 788 and 692 cm , closely resem- brucite-like layers in which [M(OH)6] coordinating oc- ble those in the spectra of pristine RhCl(CO)(TPPTS)2 tahedra share all edges to form infinite sheets. As a basic and TPPTS (Figure 2(a) and (b)). support[34,35], LDHs facilitate the formation of a rhodium According to elemental analysis data, the key ele- hydride complex by removing the HCl formed (step 1 in mental molar ratios in the intercalated LDHs are listed in Scheme 1). The basicity of LDHs support is comparable

Table 2. These data combining with XRD and FT-IR to that of M(OH)2, which is determined by the electro- 2+ results confirm that RhCl(CO)(TPPTS)2 and TPPTS negativity of M . Therefore, the RhP2/P-Zn2Al-LDHs have co-intercalated into the interlayer region of LDHs catalyst showed higher activity than the RhP2/P-Ni2Al- by in-situ complexation method. LDHs one, due to the high basicity of Zn2Al-LDHs Table 3 depicts the catalytic performances for the two support. Similar observations were reported for oxida-

2+ a) b) Table 3 Effect of different M in RhP2/P-M2Al-LDHs on its catalytic performances in hydroformylation for 1-hexene Sample Conversion (%) TOF (h1) (mol aldehyde · mol1 Rh · h1) Aldehyde selectivity (%) n/i

RhP2/P-Zn2Al-LDH 75.94 266.97 84.38 2.19

RhP2/P-Ni2Al-LDH 32.38 54.31 40.27 1.58 –4 a) Rh/1-hexene=4.010 ; b) reaction conditions: 1 mL of 1-hexene, 1.6 MPa, 100ć, H2/CO=1, 6 h reaction time.

Scheme 1 The equilibrium between RhCl(CO)(TPPTS) 2 and catalytic active species.

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[17] tive bromination catalyzed by LDH-WO4 , Heck ary- reflections of LDHs with a series of (00l) peaks, which [36] [23,24] lation catalyzed by LDH-Pd(TPPTS)2 and asymmet- are evidence for the layered character . After the ARTICLES [37] ric dihydroxylation catalyzed by LDH-OsO4 . intercalation of Rh-TPPTS complex, the interlayer dis- Significant difference in product selectivity for the tance (d003) of RhP2/P/NO3-Zn2Al-LDHs, RhP2/P/Cl- two intercalated catalysts was also observed. The selec- Zn2Al-LDHs and RhP2/P/SO4-Zn2Al-LDHs increases to tivity towards aldehyde for RhP2/P-Zn2Al-LDHs and 1.571, 1.555 and 1.566 nm, which is larger than that of RhP2/P-Ni2Al-LDHs is 84% and 40%, and n/i-aldehyde ion-exchange precursors [Zn2Al(OH)6](NO3)·4H2O, ratio is 2.2 and 1.6, respectively. It has been concluded [Zn2Al(OH)6](Cl)·4H2O, [Zn2Al(OH)6](SO4)0.5·4H2O by from the FT-IR analysis that the host-guest interaction in 0.693, 0.785 and 0.496 nm, respectively (Table 4). The

RhP2/P-Ni2Al-LDHs was stronger than that of RhP2/P- expansion of the basal spacing is due to the intercalation Zn2Al-LDHs. Therefore, it can be speculated that the of Rh-TPPTS complex into the LDHs lamella. A sig- strong host-guest interaction restricts the TPPTS-sub- nificant decrease in the reflection intensity as well as stitution reaction of HRh(CO)2(TPPTS) (complex [3] in increase in the peak width at half maximum are ob- Scheme 1) to form the product of HRhCO(TPPTS)2 served in XRD patterns of RhP2/P/Cl-Zn2Al-LDHs and (complex [1] in Scheme 1) that is an important catalytic RhP2/P/SO4-Zn2Al-LDHs in comparison with those of active species for improving the selectivity to both al- RhP2/P/NO3-Zn2Al-LDHs. dehyde and n-aldehyde. As a result, the selectivity towards n-aldehyde and iso-aldehyde in the RhP2/P- Ni2Al-LDHs-catalyzed system is lower than that in the RhP2/P-Zn2Al-LDHs-catalyzed system. 2.2 Effect of guest inorganic anions species on catalytic performances It has been reported that the rhodium catalyst system containing inorganic salt gives increased reaction activity and selectivity in the hydroformylation process under two-phase reaction conditions[38]. Combined with the structural feature of LDHs, the inorganic anion species intercalated into LDHs varied in the samples of RhP2/P/ NO -Zn Al-LDHs, RhP /P/Cl-Zn Al-LDHs and RhP /P/ 3 2 2 2 2 SO4-Zn2Al-LDHs through changing the ion-exchange Figure 3 XRD patterns for (a) RhP2/P/NO3-Zn2Al-LDHs, (b) RhP2/P/Cl- precursors. The structure and composition of the com- Zn2Al-LDHs, and (c) RhP2/P/SO4-Zn2Al-LDHs. posite materials were detected by XRD, FT-IR and ICP-AES. The catalytic performances of the intercalated Figure 4 displays the FT-IR spectra of RhP2/P/NO3- Zn2Al-LDHs, RhP2/P/Cl-Zn2Al-LDHs and RhP2/P/SO4- catalyst as well as the effect of co-intercalated inorganic APPLIED CHEMISTRY anion were studied. Zn2Al-LDHs. The bands of the three samples observed 1 Figure 3 shows the powder XRD patterns of RhP2/P/ at around 1182, 1036 and 619 cm (Figure 4), respec- NO3-Zn2Al-LDHs, RhP2/P/Cl-Zn2Al-LDHs and RhP2/P/ tively, can be attributed to the stretching vibrations oso, SO4-Zn2Al-LDHs, and Table 4 lists the corresponding so and 'so, which move to lower frequency compared basal spacing and lattice parameters. The XRD patterns with those of TPPTS and RhCl(CO)(TPPTS)2 (Figure for the composite materials exhibit the characteristic 2(a) and (b)). This is due to the interactions between the

Table 4 Lattice parameters of intercalated materials

Sample RhP2/P/NO3-Zn2Al-LDHs RhP2/P/Cl-Zn2Al-LDHs RhP2/P/SO4-Zn2Al-LDHs

d003 (nm) 1.571 1.555 1.566

d110 (nm) 0.153 0.153 0.153 Lattice parameter a (nm) 0.306 0.306 0.306 Lattice parameter c (nm) 4.713 4.665 4.698

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the elemental analysis data. The interlayer organic anions content can be determined from the value of Al/P

molar ratio, and this value in RhP2/P/SO4-Zn2Al-LDHs is much higher than the values in RhP2/P/NO3-Zn2Al- LDHs and RhP2/P/Cl-Zn2Al-LDHs (Table 5), owing to their different ion-exchange precursors. Higher ratio of 2 Al/P indicates higher content of interlayer SO4 in RhP2/P/SO4-Zn2Al-LDHs, which is in accordance with the result of FT-IR (Figure 4(c)). This is possibly related 2 to the strong interaction between SO4 and host layers 2 and thus it is rather difficult for SO4 to exchange with organic anions. Therefore, the content of interlayer organic anions in RhP /P/SO -Zn Al-LDHs is the lowest 2 4 2 Figure 4 FT-IR spectra for (a) RhP2/P/NO3-Zn2Al-LDHs, (b) RhP2/P/Cl- among the three samples. These data combining with Zn2Al-LDHs, and (c) RhP2/P/SO4-Zn2Al-LDHs. XRD and FT-IR results confirm that RhCl(CO)(TPPTS)2 and TPPTS are co-intercalated into the interlayer space sulfonate group of the interlayer RhCl(CO)(TPPTS)2 or of LDHs by in-situ complexation method. TPPTS and the host lattice. The CO stretching vibration Table 6 lists the catalytic results for the three catalyst for the three samples appears at 1990 cm 1, representing systems studied. The effect of co-intercalated inorganic 2 shifts to higher frequency compared with the pristine anions (NO3 , Cl and SO4 respectively) on catalytic RhCl(CO)(TPPTS)2 (Figure 2(b)). The frequencies of all performances was investigated. the other main absorption bands for the three samples, Comparison of the catalytic performances reveals such as the phenyl ring vibrations and the CH out-of- some difference in catalytic activity and selectivity of plane bending vibrations of phenyl ring, closely resem- the intercalated catalyst samples. Firstly, RhP2/P/Cl- ble those of pristine RhCl(CO)(TPPTS)2 and TPPTS Zn2Al-LDH exhibits a lower total conversion than (Figure 2(a) and (b)). There is also a subtle difference in RhP2/P/NO3-Zn2Al-LDHs (Table 6). The existence of their FT-IR spectra for the three samples. The band of interlayer Cl does not facilitate the formation of com- 1 RhP2/P/SO4-Zn2Al-LDHs observed at 1097 cm is plex HRhCO(TPPTS)2 ([1] in Scheme 1). On the other broader than the bands of the other two samples, due to hand, the loaded weight of rhodium complex in RhP2/P/ the vibration 3 of the intercalated inorganic anion Cl-Zn2Al-LDHs is lower than that of RhP2/P/NO3- 2 SO4 . Zn2Al-LDHs (Table 5), which is another factor for the Table 5 lists the key elemental molar ratios and the difference in catalytic activity. As listed in Table 5, the rhodium content for RhP2/P/NO3-Zn2Al-LDHs, RhP2/P/ loaded weight of rhodium complex in RhP2/P/SO4- Cl-Zn2Al-LDHs and RhP2/P/SO4-Zn2Al-LDHs based on Zn2Al-LDHs is the lowest among the three samples,

Table 5 Key elemental content and molar ratios in intercalated materials

Sample RhP2/P/NO3-Zn2Al-LDH RhP2/P/Cl-Zn2Al-LDH RhP2/P/SO4-Zn2Al-LDH Molar ratio Zn/Al 2.0 2.1 2.1 Molar ratio P/Rh 12.7 10.0 11.8 Molar ratio Al/P 3.3 3.3 6.3 Rh (w/w)(%) 0.45 0.37 0.27

Table 6 Effect of co-intercalated inorganic anions in LDHs a) catalyst in hydroformylation b) for 1-hexene Samples Total Conversion (%) TOF (h–1) (mol aldehyde · mol–1 Rh · h–1) n/i

RhP2/P/NO3-Zn2Al-LDHs 85.88 292.44 2.29

RhP2/P/Cl-Zn2Al-LDHs 76.21 171.49 2.45

RhP2/P/SO4-Zn2Al-LDHs 41.08 133.46 3.18

–4 a) Rh/1-hexene=4.010 ; b) reaction conditions: 1 mL of 1-hexene, 1.6 MPa, 100ć, H2/CO=1, 6 h reaction time.

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resulting in the lowest activity. were successfully synthesized by in situ complexation

Secondly, RhP2/P/SO4-Zn2Al-LDH shows a higher method. The influences of the composition of both host ARTICLES selectivity towards n-aldehyde than the other two cata- layers (M2+ species) and interlayer inorganic anions spe- lysts (Table 6). The Rh content (Rh%, in Table 5) of cies on the catalytic behavior of the intercalated cata-

RhP2/P/SO4-Zn2Al-LDHs is the lowest among the three lysts were investigated, and the relationship between catalyst samples, therefore, it is advantageous to exert host-guest interactions and the catalytic performances the steric factor of LDHs in this catalyst. The less con- was revealed. fined interlayer region (lower content of complex and It was found that the higher the electronegativity of 2+ more space available) of this sample favors the forma- M in host layers, the lower the basicity of LDHs host tion of normal alkyl intermediate, which converts to lattices, and the stronger the host-guest interaction. 2+ n-aldehyde in the end. Consequently, the selectivity to- Higher electronegativity of M leads to the decrease in wards n-aldehyde is improved in the system catalyzed both catalytic activity and selectivity towards aldehyde. The co-intercalated inorganic anions (SO 2 , Cl , by RhP2/P/SO4-Zn2Al-LDHs. 4 Finally, as shown in Table 6, the value of TOF to- NO3 ) in LDHs exhibit remarkable influence on cata- wards aldehyde increases with the increase of rhodium lytic activity. The rhodium complex loading of RhP2/P/ complex loading (Rh%) of the three intercalated cata- SO4-Zn2Al-LDHs is the lowest among the three intercalated catalyst samples and thus leads to the lowest total lysts, and RhP2/P/NO3-Zn2Al-LDHs shows the highest 1 conversion (41%). Since the existence of co-intercalated TOF value (292 h ). Except the influence of rhodium complex loading, the different co-intercalated inorganic Cl does not facilitate the formation of an active rho- anions may impose some assistant catalysis. Further dium complex intermediately, the total conversion is low study is under investigation. in the system catalyzed by RhP2/P/Cl-Zn2Al-LDHs (76%). However, the RhP2/P/NO3-Zn2Al-LDH shows 3 Conclusion the highest catalytic activity among the three samples (with total conversion of 86%) because of its highest

RhCl(CO)(TPPTS)2 and TPPTS co-intercalated LDHs rhodium complex loading.

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