FeOx–TiO2 catalyst for liquid phase selective hydrogenation of phthalic anhydride to phthalide

Journal of Industrial and Engineering Chemistry 23 (2015) 321–327

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Performance of Au/FeOx–TiO2 catalyst for liquid phase selective hydrogenation of phthalic anhydride to phthalide Yingxin Liu a,*, Zuojun Wei b, Tiefeng Xing a, Meng Lu a, Xiaonian Li c,* a

Research and Development Base of Catalytic Hydrogenation, College of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou 310014, China Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China c Institute of Industrial Catalysis, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China b

A R T I C L E I N F O

Article history: Received 11 November 2013 Received in revised form 21 August 2014 Accepted 28 August 2014 Available online 6 September 2014 Keywords: Au/FeOx–TiO2 catalyst Phthalic anhydride Liquid phase selective hydrogenation Phthalide

A B S T R A C T

Gold catalysts supported on FeOx–TiO2 with various Fe2O3 contents were prepared by deposition– precipitation method and used for phthalic anhydride hydrogenation to phthalide. The effect of Fe2O3 on the physico-chemical property and the performance of Au/TiO2 were investigated. The reaction conditions were optimized. Adding 5 wt.% Fe2O3 on Au/TiO2 could enhance the activity and stability, which was contributed to the increase in the strength of the catalyst structure and the decrease in the loss of gold from catalyst. Using Au/5%FeOx–TiO2, phthalic anhydride conversion and phthalide selectivity reached 95.4% and 94.5%, respectively, at 190 8C and 3.0 MPa H2 for 7 h. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Introduction Phthalide is an important industrial intermediate for pharmaceuticals, fine chemicals and organic synthesis. Selective hydrogenation of phthalic anhydride in liquid phase with H2 is a promising routine for the production of phthalide, owing to its reduced pollutant production. Usually, nickel catalysts are used for the hydrogenation reaction and show high activity [1–4]. However, the selectivity to phthalide is low (<89%), with varying amounts of hydrogenation byproducts such as o-toluic acid, aromatic ringhydrogenated derivatives of the components of the reaction mixture (such as o-methylcyclohexanecarboxylic acid, hexahydrophthalide and 1,2-cyclohexanedicarboxylic acid), and o-phthalic acid (formed from unconverted phthalic anhydride and water of reaction). It is therefore desirable to develop an efficient catalyst with high activity and selectivity to phthalide. Recently, it is found that supported gold catalysts exhibit a remarkable selectivity for the hydrogenation of oxygen-containing unsaturated groups such as nitro group in the presence of other reducible functional groups [5–21] and carbonyl group in the a,

b-unsaturated aldehydes or ketones [22–46]. In our previous work, we studied the liquid phase selective hydrogenation of phthalic anhydride to phthalide using Au/TiO2 catalyst and found that the gold catalyst showed high activity and selectivity for this reaction, but deactivated rapidly [47]. In order to enhance the stability of Au/TiO2 catalyst for the selective hydrogenation of phthalic anhydride, we then prepared several metal oxide (Fe2O3, Sm2O3 CeO2 or MgO) modified TiO2 supported gold catalysts and found that Fe2O3 modified TiO2 supported gold catalyst showed high activity and selectivity for this reaction [48]. In this work, a series of gold catalysts supported on FeOx–TiO2 with various Fe2O3 contents were prepared by deposition–precipitation method and used for the hydrogenation of phthalic anhydride to phthalide. A detail study was carried out to know the effect of Fe2O3 on the physico-chemical, the catalytic performance and the stability of Au/TiO2 catalyst. In addition, the effects of reaction conditions of phthalic anhydride hydrogenation over Au/FeOx–TiO2 catalyst were investigated. Experimental Catalyst preparation

* Corresponding authors at: Zhejiang University of Technology, College of Pharmaceutical Science, Research and Development Base of Catalytic Hydrogenation, Chaowang Road 18, Hangzhou 310014, China. Tel.: +86 571 88320064/+86 571 88320002; fax: +86 571 88320064. E-mail addresses: [email protected] (Y. Liu), [email protected] (X. Li).

FeOx–TiO2 with various Fe2O3 contents (0–15 wt.%), which were used as supports for the gold catalysts in this work, were prepared via the incipient-wetness impregnation method. The

http://dx.doi.org/10.1016/j.jiec.2014.08.036 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

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preparation procedure was as follows: TiO2 (Hongsheng Material, 220 m2 g 1) were saturated in aqueous solutions of Fe(NO3)3
9H2O (Shanghai Yuejing Chemical, Analytically pure) at room temperature, and then dried at 110 8C for 12 h and calcined in air at 500 8C for 4 h. FeOx–TiO2 supported gold catalyst with a nominal gold loading of 2 wt.% was prepared by deposition–precipitation method according to our previous work [47]. The sample was dried at 100 8C for 12 h, calcined at 300 8C in air for 4 h and reduced at 200 8C in hydrogen flow for 3 h.

O H2

COOH

O

H2

CH 3

O O O

H2O COOH COOH

Scheme 1. Proposed reaction pathway of phthalic anhydride hydrogenation catalyzed by Au/FeOx–TiO2 catalysts.

Catalyst characterization

Catalytic activity test The liquid phase selective hydrogenation of phthalic anhydride was carried out in a 100 ml stainless steel autoclave equipped with magnetic stirring at the reaction temperature in the range of 160–200 8C and the hydrogen pressure in the range of 2.5–4.0 MPa. 5.0 g of phthalic anhydride, 50 ml of g-butyrolactone and 0.25–1.5 g of the as-prepared catalyst were loaded into the autoclave. The stirring rate was 1000 rpm. The reaction products were analyzed using a gas chromatograph equipped with a HP-5 capillary column and a flame ionization detector. Product identification was performed with an Agilent 6890 gas chromatograph equipped with an Agilent 5973 mass selective detector. Results and discussion Catalytic performance test Table 1 shows the results of the liquid phase selective hydrogenation of phthalic anhydride over Au/FeOx–TiO2 catalysts with Fe2O3 content of 0–15 wt.%. The reaction conditions were as follows: 3.0 MPa H2, 180 8C, 1.0 g of catalyst, 5.0 g of phthalic anhydride, 50 ml of g-butyrolactone and 9 h of reaction time. It can be seen that all the gold catalysts used in this work exhibited excellent catalytic performance, giving >92% selectivity to phthalide with a high conversion. The evolution of the reaction products showed only traces of o-toluic acid and o-phthalic acid byproducts. According to the distribution of products during the Table 1 Results of phthalic anhydride hydrogenation to phthalide over Au/FeOx–TiO2 catalysts with various Fe2O3 contentsa. Catalyst

Au/TiO2 Au/2.5%FeOx–TiO2 Au/5%FeOx–TiO2 Au/7.5%FeOx–TiO2 Au/10%FeOx–TiO2 Au/15%FeOx–TiO2 a

Conversion (%)

94.7 97.2 97.6 91.3 92.7 92.8

Phthalide

Othersb

94.2 94.7 95.2 93.4 92.6 94.4

5.8 5.3 4.8 6.6 7.4 5.6

Catalyst characterization Fig. 1 shows the XRD patterns of Au/FeOx–TiO2 catalysts with different Fe2O3 contents. All the catalysts showed the diffraction peaks of both anatase and rutile phases in TiO2. The addition of Fe2O3 did not obviously change the crystalline phase of TiO2. No significant diffraction peaks of FeOx were observed for Au/FeOx– TiO2 catalysts with low Fe2O3 contents (10 wt.%), indicating fine dispersion and amorphous nature of FeOx on the surface of TiO2. For Au/15%FeOx–TiO2, the weak diffraction peaks of hematite Fe2O3 were observed, indicating that FeOx particle size increased with the increase in Fe2O3 content. No distinct signals attributed to gold species were observed for all the catalysts, indicating that the particle size of gold were too small (<5 nm) to be detected by XRD. Fig. 2 shows the HRTEM results of Au/TiO2 and Au/5%FeOx–TiO2 catalysts (Fig. 2(a) and (b)). It can be seen that the gold nanoparticles were evenly dispersed on the surfaces of the supports for both the catalysts, with diameters in the range of 2–4 nm. These results are in good agreement with the XRD results.

- Anatase TiO2 - Rutile TiO2 - Fe2O3

(d) (c) (b) (a) 20

30

40

50 60 2θ (degree)

70

80

Reaction conditions: 1.0 g catalyst, 180 8C, 5.0 g phthalic anhydride in 50 ml

g-butyrolactone, 3.0 MPa H2, 9 h. b

Selectivity (%)

hydrogenation, the reaction pathway of phthalic anhydride hydrogenation over Au/FeOx–TiO2 catalysts was proposed as Scheme 1. Compared with Au/TiO2, the addition of lower Fe2O3 content (2.5–5 wt.%) increased the activity, with almost the same selectivity to phthalide. When Fe2O3 content varied from 0 to 5.0 wt.%, the conversion of phthalic anhydride increased from 94.7% to 97.6%. With further increasing Fe2O3 content beyond 5 wt.%, however, the conversion of phthalic anhydride and the selectivity to phthalide decreased obviously. It may be due to that the surface areas and pore volumes of the catalysts decrease with increasing of Fe2O3 content, which could lead to gold particle aggregation and correspondingly decrease the active surface areas of the catalysts.

Intensity

X-ray diffraction (XRD) patterns of the catalysts were measured with a Thermo X’TRA X-ray diffractometer using Cu Ka radiation. The morphology and the gold particle size were obtained by highresolution transmission electron microscopy (HRTEM) in a JEM1200EX equipment. BET specific surface areas and pore structures of the catalysts were measured by pulsed nitrogen adsorption– desorption method at 77 K using a Micromeritics ASAP 2010 instrument. Gold loading in the catalyst was measured by an Elan DRC-e ICP–MS instrument of PE Inc., USA.

o-Toluic acid and o-phthalic acid.

Fig. 1. XRD patterns of Au/FeOx–TiO2 catalysts with various Fe2O3 contents: (a) Au/ TiO2, (b) Au/5%FeOx–TiO2, (c) Au/10%FeOx–TiO2, and (d) Au/15%FeOx–TiO2.

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Fig. 2. HRTEM images of (a) fresh Au/TiO2, (b) fresh Au/5%FeOx–TiO2, (c) used Au/TiO2 and (d) used Au/5%FeOx–TiO2 catalysts.

The N2 adsorption–desorption isotherms and pore size distributions of the fresh Au/TiO2 and Au/5%FeOx–TiO2 catalysts are shown in Fig. 3, and BET specific surface areas, pore volume and pore size of the samples are given in Table 2. A type IV isotherm and an H1 hysteresis loop as shown in Fig. 3 clearly indicated the mesoporous nature of the catalysts. The pore size distribution of Au/5%FeOx–TiO2 obtained with BJH method was narrower than Au/ TiO2, confirming better quality of the sample. The results may be due to the formation of iron titania composite oxides, which effectively stabilized the structure of TiO2 [49]. The BET specific surface area, pore volume and pore size of Au/5%FeOx–TiO2 were relatively high compared with Au/TiO2. Large surface area and pore size are beneficial to the molecular transport of reactants and products. So the Au/5%FeOx–TiO2 catalyst exhibited better catalytic performance than Au/TiO2. Fig. 4 shows the XPS spectra of Au 4f (Fig. 4(a)) and Fe 2p (Fig. 4(b)) in the Au/5%FeOx–TiO2 catalyst. It can be seen from Fig. 4(a) that three peaks were observed at 83.4 eV, 87.1 eV and 88.2 eV, respectively. The above two peaks are attributed to d metallic gold (Au0) and the last one is assigned to Au + [50], which suggests that the Au species on the surface of Au/5%FeOx–TiO2

d

catalyst mainly exists as Au0, as well as a trace of Au +. The XPS spectra of Fe 2p (Fig. 4(b)) suggests that the Fe species exists in different states as Fe2+ and Fe3+. The peaks for Fe2+ were appeared at 710.6 eV (Fe 2p3/2) and 724.6 eV (Fe 2p5/2). The peaks for Fe3+ were located at 713.5 eV (Fe 2p3/2) and 725.0 eV (Fe 2p5/2). Catalyst stability and deactivation analysis The stability of Au/5%FeOx–TiO2 as well as Au/TiO2 in the liquid phase selective hydrogenation of phthalic anhydride was checked. In each experience, after hydrogenation reaction at 180 8C and 3.0 MPa H2 for 11 h to ensure an almost complete substrate conversion, the catalyst was recovered, filtered, washed with solvent and used again, completing five cycles of hydrogenation. As can be seen in Fig. 5, although Au/TiO2 and Au/5%FeOx–TiO2 exhibited similar initial activity for the hydrogenation of phthalic anhydride, Au/TiO2 showed continued loss of activity after each reuse, indicating a certain deactivation. In contrast, Fe2O3modified TiO2 supported gold catalyst exhibited better stability for the reaction. After being reused five times, Au/5%FeOx–TiO2 catalyst still kept high activity and selectivity, with 87.2%

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324

140

300

1.2

0.8 1.0

0.6

0.6

200

0.4 0.2

80

dV/dlog(D)

100

0.7

250

0.8

Vol adsorbed (cm3/g STP)

dV/dlog(D)

Vol adsorbed (cm3/g STP)

120

150

0.0 1

60

10

100

Pore diameter(nm)

0.4 0.3 0.2 0.1 0.0

100

40

0.5

1

10

100

Pore diameter(nm)

50

20 Fresh Au/TiO 2 0

0.0

0.2

0.4

0.6

0.8

Fresh Au/5%FeO x-TiO2

0 0.0

1.0

0.2

Relative pressure (P/Po)

0.8

1.0

180 160

0.40

0.25

0.35

140

40

Vol adsorbed (cm3/g STP)

dV/dlog(D)

0.20

120

0.15

100

0.10 0.05 0.00 1

10

100

Pore diameter(nm)

20

0.25 0.20 0.15 0.10 0.05

60

0.00

1

10

100

Pore diameter(nm)

40 20

Used Au/TiO 2 0

80

0.30

dV/dlog(D)

80

Vol adsorbed (cm3/g STP)

0.6

Relative pressure (P/Po)

100

60

0.4

0.0

0.2

0.4

0.6

0.8

1.0

Used Au/5%FeOx-TiO2

0 0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure (P/Po)

Relative pressure (P/Po)

Fig. 3. Nitrogen adsorption–desorption isotherms and pore size distributions of fresh and used Au/TiO2 and Au/5%FeOx–TiO2 catalysts.

conversion of phthalic anhydride and 92.4% selectivity to phthalide. The results suggested that Fe2O3 significantly improved the stability of the gold catalyst. The HRTEM images of the used Au/TiO2 and Au/5%FeOx–TiO2 catalysts are shown in Fig. 2(c) and (d). As can be seen that the amounts of gold particles on the surface of the used catalysts decreased compared with the fresh ones (Fig. 2(a) and (b)). It could also be clearly observed from the ICP–MS results (Table 2) of the two catalysts before and after used. The gold content decreased from 1.4% to 0.9% for Au/TiO2 and from 1.5% to 1.1% for Au/5%FeOx– TiO2 after five cycles. It suggested a leaching of gold from the catalyst, which might be one of the basic reasons for the deactivation of the catalysts. On the other hand, the ICP–MS results showed that the percentage of gold leaching from Au/ 5%FeOx–TiO2 was 27%, lower than that from Au/TiO2 (36%), Table 2 Physical properties of Au/TiO2 and Au/5%FeOx–TiO2 catalysts before and after five reaction cycles. Catalyst Fresh Au/TiO2 Used Au/TiO2 Fresh Au/5%FeOx–TiO2 Used Au/5%FeOx–TiO2 a

Obtained by ICP–MS.

Au loading (wt.%)a

BET (m2 g

1.4 0.9 1.5 1.1

100.4 51.1 149.1 62.6

1

)

Vtotal (cm3 g 0.2 0.1 0.4 0.2

Dpore (nm) 1

) 6.4 7.7 10.2 12.8

suggesting that the addition of Fe2O3 into TiO2 could inhibit the loss of gold from the catalyst, which could be well explained by the HRTEM characterization results of the two catalysts. As shown in Fig. 2(b), the addition of Fe2O3 produced locally clustered Fe2O3 film on TiO2, and this film and TiO2 jointly anchored the gold particles, which could improve the gold binding energy [51], and therefore increased the stability of gold particles. This result was similar to the early work of Carrettin et al. [52] in which iron presented near the interfaces between the gold clusters and the TiO2 support and improved the activity and stability of the gold catalyst for CO oxidation. The results of N2 adsorption–desorption measurements of the used Au/TiO2 and Au/5%FeOx–TiO2 catalysts are shown in Table 2 and Fig. 3. The BET specific surface area and pore volume of the two catalysts dramatically diminished after five reaction cycles, and the average pore diameter became larger compared with the fresh ones. These results indicated that the pore structure of the catalysts suffered a collapse and the surface was covered by amounts of organic species, which could also be seen from the HRTEM images of the two used catalysts as shown in Fig. 2(c) and (d). It might be other basic reasons for the deactivation of the catalysts. From Fig. 3(c) it can be seen that the pore size distribution of the used Au/TiO2 catalyst was strongly shifted towards larger pores, indicating a serious collapse of the pore structure. In comparison, the pore size of the used Au/5%FeOx–TiO2 still kept a narrow distribution, suggesting that the addition of

Y. Liu et al. / Journal of Industrial and Engineering Chemistry 23 (2015) 321–327

Au 4f 5/2

Au 4f 7/2

325

Au/TiO2

100

Au/5% FeOx-TiO2

80 0

Intensity

Conversion (%)

Au

60 40 20

d +

Au

0 1 80

82

84

86

88

90

2

92

3

4

5

Run time (n)

Binding energy (eV)

(a)

Au/TiO2 Au/5% FeOx-TiO2

100 80

Fe 2p3/2

Selectivity (%)

Fe 2p5/2 3+

Intensity (a.u)

Fe

60 40 20 0

2+

Fe

1

2

3

4

5

Run time (n) 705

710

715

720

725

730

735

Binding energy (eV)

(b) Fig. 4. XPS Au 4f spectra (a) and Fe 2p spectra of Au/5%FeOx–TiO2 catalyst.

Fe2O3 could improve the thermal stability and the mechanical strength of TiO2. It could also be confirmed from Fig. 2(d) that most of the used Au/5%FeOx–TiO2 catalyst still kept a structure similar to the fresh one. Effects of reaction conditions on phthalic anhydride hydrogenation to phthalide over Au/5%FeOx–TiO2 Effect of reaction temperature Using Au/5%FeOx–TiO2 as the catalyst, the effects of reaction conditions on the liquid phase selective hydrogenation of phthalic anhydride were investigated. Fig. 6 shows the effect of reaction temperature in the range of 160–200 8C on the conversion of phthalic anhydride and the selectivity to phthalide by keeping the other reaction parameters constant. It can be noted that both phthalic anhydride conversion and phthalide selectivity significantly increased as the reaction temperature increased from 160 to 190 8C at 7 h reaction time. The results may be explained as follows: on the one hand, the hydrogenation reaction rate constants would increase with the reaction temperature; on the other hand, high reaction temperature could inhibit the generation of byproduct o-phthalic acid formed from unconverted phthalic anhydride and water of reaction, and thus the selectivity to phthalide increased with temperature. Further increasing the reaction temperature from 190 to 200 8C, phthalic anhydride

Fig. 5. Phthalic anhydride conversion and phthalide selectivity versus recycle time of the catalysts. Reaction conditions: 1.0 g catalyst, 180 8C, 5.0 g phthalic anhydride in 50 ml g-butyrolactone, 3.0 MPa H2, 11 h.

conversion increased slightly, while phthalide selectivity decreased from 94.5% to 91.3%. Prolonging the reaction time to 9 h, phthalide selectivity obviously decreased at higher reaction temperature (>190 8C) due to further hydrogenation of phthalide to byproduct o-toluic acid. In the following studies, the reaction was controlled at 190 8C for 7 h. Effect of hydrogen pressure The effect of hydrogen pressure in the range of 2.5–4.0 MPa on phthalic anhydride conversion and phthalide selectivity was studied, and the results are shown in Table 3. As the hydrogen pressure increased from 2.5 to 3.0 MPa, the conversion of phthalic anhydride distinctly increased from 82.3% to 95.4%, and the selectivity to phthalide increased from 92.6% to 94.5%. The results were mainly because that higher hydrogen pressure could provide greater concentration of surface hydrogen, which was beneficial to the hydrogenation of phthalic anhydride. With further increasing the hydrogen pressure from 3.0 to 4.0 MPa, the conversion of phthalic anhydride increased continuously from 95.4% to 99.2%, while the selectivity to phthalide decreased from 94.5% to 89.7%. It was because that with the increase in hydrogen pressure, a greater concentration of surface hydrogen became available on the active sites of the catalyst, facilitating both the hydrogenation of phthalic anhydride to phthalide and the hydrogenation of phthalide to byproduct o-toluic acid, with a large loss of selectivity to phthalide. Since the 3.0 MPa hydrogen pressure gave the highest phthalide selectivity with a high phthalic anhydride conversion, it was chosen as the standard reaction pressure in the following study.

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Table 4 Effect of Au/5%FeOx–TiO2 loading on phthalic anhydride hydrogenation to phthalidea. Catalyst loading (g)

0.25 0.5 1.0 1.5

Conversion (%)

59.5 73.5 95.4 98.5

Selectivity (%) Phthalide

Othersb

87.8 91.7 94.5 93.8

12.2 8.3 5.5 6.2

a Reaction conditions: 190 8C, 5.0 g phthalic anhydride in 50 ml g-butyrolactone, 3.0 MPa H2, 7 h. b o-Toluic acid and o-phthalic acid.

Conclusions

Fig. 6. Effect of reaction temperature on phthalic anhydride hydrogenation to phthalide. Reaction conditions: 1.0 g catalyst, 5.0 g phthalic anhydride in 50 ml g-butyrolactone, 3.0 MPa H2.

Effect of Au/5%FeOx–TiO2 loading The effect of Au/5%FeOx–TiO2 loading in the range of 0.25–1.5 g on the hydrogenation of phthalic anhydride was studied by keeping the other reaction parameters constant. As shown in Table 4, at lower catalyst loading (0.25 g), the conversion of phthalic anhydride was only 59.5%, with a phthalide selectivity of 87.8%. This indicated that lower Au/5%FeOx–TiO2 catalyst could not provide enough active sites for the hydrogenation of phthalic anhydride. With an increase in Au/5%FeOx–TiO2 loading from 0.25 to 1.0 g, the conversion of phthalic anhydride increased significantly from 59.5% to 95.4%, and the selectivity to phthalide increased from 87.8% to 94.5%. Further increasing Au/5%FeOx–TiO2 loading to 1.5 g, the conversion of phthalic anhydride increased slightly, while the selectivity to phthalide decreased. It might be because that the increased catalyst loading provided more hydrogenation active sites, which was available for further hydrogenation of phthalide to byproduct o-toluic acid. Table 3 Effect of hydrogen pressure on phthalic anhydride hydrogenation to phthalide over Au/5%FeOx–TiO2 catalysta. H2 pressure (MPa)

2.5 3.0 3.5 4.0 a

Conversion (%)

82.3 95.4 97.5 99.2

Phthalide

Othersb

92.6 94.5 92.9 89.7

7.4 5.5 7.1 10.3

Reaction conditions: 1.0 g catalyst, 190 8C, 5.0 g phthalic anhydride in 50 ml

g-butyrolactone, 7 h. b

Selectivity (%)

o-Toluic acid and o-phthalic acid.

A series of Au/FeOx–TiO2 catalysts with various Fe2O3 contents were prepared by deposition–precipitation method and used for the liquid phase selective hydrogenation of phthalic anhydride to phthalide. Adding a suitable amount of Fe2O3 on Au/TiO2 could enhance the catalytic activity and the stability. The gold catalyst with 5 wt.% of Fe2O3 exhibited the best catalytic performance. After having reused five times, the Au/5%FeOx–TiO2 catalyst still kept high activity and selectivity. The characterization results showed that the addition of Fe2O3 could increase the strength of the catalyst structure and inhibit the loss of gold from the catalyst, which might be the reasons that Au/5%FeOx–TiO2 exhibited better stability than Au/TiO2. An increase in reaction temperature, hydrogen pressure and Au/5%FeOx–TiO2 catalyst loading led to an increase in phthalic anhydride conversion but a decrease in phthalide selectivity. Under the optimal conditions, the conversion of phthalic anhydride and the selectivity to phthalide could reach 95.4% and 94.5%, respectively. Acknowledgements We gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (nos. 21106134 and 21276230), Key Laboratory of Biomass Chemical Engineering of Ministry of Education and the Program for Zhejiang Leading Team of S&T Innovation. References [1] J.E. Lyons, US 4485246A, 1984. [2] H. aus der Funten, W. Vogt, US 4528385, 1985. [3] K. Massonne, R. Becker, W. Reif, H. Neuhauser, A. Gieseler, K. Mundinger, US 6028204, 2000. [4] Y.X. Liu, Z.J. Wei, J. Fu, Y. Gao, W. Yan, Chin. J. Catal. 29 (2008) 52. [5] A. Corma, P. Serna, Science 313 (2006) 332. [6] A. Corma, P. Serna, H. Garcia, J. Am. Chem. Soc. 129 (2007) 6358. [7] Y.Y. Chen, J.S. Qiu, X.K. Wang, J.H. Xiu, J. Catal. 242 (2006) 227. [8] M. Boronat, P. Concepcio´n, A. Corma, S. Gonza´lez, F. Illas, P. Serna, J. Am. Chem. Soc. 129 (2007) 16230. [9] D.P. He, H. Shi, Y. Wu, B.Q. Xu, Green Chem. 9 (2007) 849. [10] F. Ca´rdenas-Lizana, S. Go´mez-Quero, M.A. Keane, Catal. Commun. 9 (2008) 475. [11] L.Q. Liu, B.T. Qiao, Z.J. Chen, J. Zhang, Y.Q. Deng, Chem. Commun. 6 (2009) 653. [12] F. Ca´rdenas-Lizana, S. Go´mez-Quero, A. Hugon, L. Delannoy, C. Louis, M.A. Keane, J. Catal. 262 (2009) 235. [13] K. Shimizu, Y. Miyamoto, T. Kawasaki, T. Tanji, Y. Tai, A. Satsuma, J. Phys. Chem. C 113 (2009) 17803. [14] P. Serna, P. Concepcion, A. Corma, J. Catal. 265 (2009) 19. [15] F. Ca´rdenas-Lizana, S. Go´mez-Quero, N. Perret, M.A. Keane, Gold Bull. 42 (2009) 124. [16] F. Ca´rdenas-Lizana, Z.M. de Pedro, S. Go´mez-Quero, M.A. Keane, J. Mol. Catal. A: Chem. 326 (2010) 48. [17] P. Serna, M. Boronat, A. Corma, Top. Catal. 54 (2011) 439. [18] Y.F. Hao, R.X. Liu, X.C. Meng, H.Y. Cheng, F.Y. Zhao, J. Mol. Catal. A: Chem. 335 (2011) 183. [19] X.Y. Tan, Z.X. Zhang, Z.H. Xiao, Q. Xu, C.H. Liang, X.K. Wang, Catal. Lett. 142 (2012) 788. [20] F. Cardenas-Lizana, D. Lamey, N. Perret, S. Gomez-Quero, L. Kiwi-Minsker, M.A. Keane, Catal. Commun. 21 (2012) 46.

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