Au/FeOx-TiO2 as an efficient catalyst for the selective hydrogenation of phthalic anhydride to phthalide

Article abstract of DOI:10.1016/j.cclet.2010.06.042

Au/FeO_x-TiO₂, prepared by deposition-precipitation method, is an efficient and stable catalyst for the liquid phase selective hydrogenation of phthalic anhydride to phthalide under mild reaction conditions.

Full text of DOI:10.1016/j.cclet.2010.06.042

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 1322–1325
www.elsevier.com/locate/cclet
Au/FeOx–TiO2 as an efficient catalyst for the selective
hydrogenation of phthalic anhydride to phthalide
Ying Xin Liu a,b, Tie Feng Xing a, Yi Ming Luo a, Xiao Nian Li b,*, Wei Yan a,b
a Research and Development Base of Catalytic Hydrogenation, Zhejiang University of Technology, Hangzhou 310032, China
b State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, Zhejiang University of Technology, Hangzhou 310032, China
Received 23 March 2010
Abstract
Au/FeOx–TiO2, prepared by deposition–precipitation method, is an efficient and stable catalyst for the liquid phase selective
hydrogenation of phthalic anhydride to phthalide under mild reaction conditions.
# 2010 Xiao Nian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Au/FeOx–TiO2 catalyst; Phthalic anhydride; Liquid phase hydrogenation; Phthalide
Phthalide is an important industrial intermediate for pharmaceuticals, fine chemicals and organic synthesis. It can be
produced by several methods, such as the reaction of phthalimide and sodium hydroxide, and the chemical reduction of
phthalic anhydride. Nevertheless, these processes are of low yield and serious environmental pollution. Now it is highly
desirable to produce phthalide by the selective hydrogenation of phthalic anhydride in liquid phase with H2. Usually,
RaneyNiorsupportednickel catalystsareusedforthehydrogenationreactionandshowhighactivity[1–4]. However, the
selectivity of the nickel catalysts tophthalide islow. Itistherefore desirable todevelop an efficientheterogeneouscatalyst
with high activity and high selectivity for the selective hydrogenation of phthalic anhydride to phthalide.
Supported gold catalysts show unique catalytic performance for many reactions and have attracted more and more
considerable attention [5,6]. Recently, it is found that gold catalysts exhibit a remarkable selectivity for the
hydrogenation of oxygen-containing unsaturated groups such as nitro group [7], and carbonyl group [8]. In our
previous work, we studied the liquid phase hydrogenation of phthalic anhydride to phthalide using Au/TiO2 catalyst
and found that the catalyst had high activity and selectivity for this reaction, but deactivated rapidly [9]. Herein, we
report that Fe2O3-modified TiO2 supported gold catalyst can enhance the stability of Au/TiO2 catalyst, and can
efficiently and selectively catalyze the liquid phase hydrogenation of phthalic anhydride to phthalide.
1. Experimental
TiO2 (Hongsheng Material, 220 m2/g) supported Au catalyst was prepared by deposition–precipitation method
according to [9]. Metal oxide (Fe2O3, Sm2O3 CeO2 or MgO) modified TiO2 supported gold catalysts were prepared as
* Corresponding author.
E-mail address: xnli@zjut.edu.cn (X.N. Li).
1001-8417/$ – see front matter # 2010 Xiao Nian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.06.042

Y.X. Liu et al. / Chinese Chemical Letters 21 (2010) 1322–1325
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follows. A calculated amount of metal oxide precursor (metal nitrate, analytical reagent) was dissolved in distilled
water, and TiO2 was added and impregnated for 12 h at room temperature. Then, the sample was dried at 110 8C for
12 h and calcined at 500 8C for 4 h. The resulting metal oxide-modified TiO2 supported gold catalysts were prepared
by the method as Au/TiO2. The catalysts were 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. The metal oxide content was 5 wt.% and Au content was 2 wt.%. The morphology
and the gold particle size of the catalysts were obtained by high-resolution transmission electron microscopy
(HRTEM), in a JEM-1200EX equipment. Au loading in the catalysts was measured by an Elan DRC-e ICP-MS
instrument of PE Inc. USA.
Experiment of the liquid phase hydrogenation of phthalic anhydride was carried out in a 100 mL stainless steel
autoclave equipped with magnetic stirring at 180 8C and 3.0 MPa H2. The following conditions were applied: phthalic
anhydride 5.0 g, solvent g-butyrolactone 50 mL and catalyst 1.0 g. 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.
2. Results and discussion
Table 1 shows the hydrogenation results of phthalic anhydride over several metal oxides modified TiO2 supported
gold catalysts as well as Au/TiO2. All the supported gold catalysts used in this work gave >91% selectivity to
phthalide, with only traces of o-toluic acid and o-phthalic acid (formed from unconverted phthalic anhydride and water
of reaction) byproducts, and without any aromatic ring-hydrogenated derivatives which were usually detected when
nickel catalysts were used [10]. The results indicated clearly that further hydrogenation of the desired product
phthalide usually observed over nickel-based catalysts, could be successfully inhibited over the supported gold
catalysts. Compared with Au/TiO2, the addition of Sm2O3, MgO and CeO2 decreased the activity of the catalyst. It was
excited that the addition of Fe2O3 increased the activity and the selectivity of Au/TiO2, giving 97.6% conversion and
95.2% selectivity to phthalide. To the best of our knowledge, Au/FeOx–TiO2 is the most selective and active catalyst
for the liquid phase hydrogenation of phthalic anhydride up to now. From HRTEM results of the two catalysts (Fig. 1a
and b) it can be seen that the gold nanoparticles were evenly dispersed on the surfaces of the supports, with diameters
Table 1
Catalytic results of phthalic anhydride hydrogenation over different gold catalystsa.
[
Catalyst
Conversion (%)
Selectivity (%)
Phthalide
Othersb
Au/FeOx–TiO2
Au/Sm2O3–TiO2
Au/CeO2–TiO2
Au/MgO–TiO2
Au/TiO2
97.6
89.1
85.5
87.5
94.7
95.2
93.2
95.5
91.3
94.2
4.8
6.8
4.5
8.7
5.8
a
Reaction conditions: 1.0 g catalyst, 180 8C, 5.0 g phthalic anhydride in 50 mL g-butyrolactone (solvent), 3.0 MPa H2, and reaction time 9 h.
o-Toluic acid and o-phthalic acid.
b
[(Fig._1)TD$FIG]
Fig. 1. HRTEM images of (a) fresh Au/TiO2, (b) fresh Au/FeOx–TiO2, (c) used Au/TiO2 and (d) used Au/FeOx–TiO2 catalysts.

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Y.X. Liu et al. / Chinese Chemical Letters 21 (2010) 1322–1325
Table 2
Stability of Au/FeOx–TiO2 and Au/TiO2 catalysts for the selective hydrogenation of phthalic anhydridea.
Catalyst
Au/TiO2
Cycle
Conversion (%)
Selectivity (%)
Au loading (wt.%)b
1
2
3
4
5
97.9
89.1
84.0
81.3
79.9
92.9
88.6
86.4
93.6
94.1
1.35
–
–
–
0.87
Au/FeOx–TiO2
1
2
3
4
5
98.2
92.3
87.8
88.0
87.2
94.6
92.9
93.2
93.2
92.4
1.48
–
–
–
1.04
a
Reaction conditions: 1.0 g catalyst, 180 8C, 5.0 g phthalic anhydride in 50 mL g-butyrolactone (solvent), 3.0 MPa H2, and 11 h.
Obtained by ICP-MS.
b
in the range of 2–4 nm. In addition, the addition of Fe2O3 increased the dispersion degree of gold particles, which may
be the reason for the increase in the catalytic performance of Au/TiO2.
The stability of Au/FeOx–TiO2 as well as Au/TiO2 in phthalic anhydride hydrogenation was checked. The
hydrogenation reaction was performed for 11 h to ensure an almost complete substrate conversion and the catalyst was
recovered, filtered and washed with g-butyrolactone. As can be seen in Table 2, Au/TiO2 showed continued loss of
activity after each reuse. In contrast, Fe2O3-modified TiO2 supported gold catalyst exhibited a much better stability for
the reaction. After having reused five times, Au/FeOx–TiO2 catalyst still kept high activity and selectivity, with 87.2%
conversion of phthalic anhydride and 92.4% selectivity to phthalide. The results suggested that Fe2O3 significantly
improved the stability of the gold catalyst. As can be seen from the HRTEM image of the used Au/TiO2 and Au/FeOx–
TiO2 catalysts (Fig. 1c and d), the amounts of gold particles on the surface of the used catalysts decreased compared
with the fresh catalysts (Fig. 1a and b). ICP-MS results (Table 2) showed that the gold content decreased from 1.35% to
0.87% for Au/TiO2 and from 1.48% to 1.04% for Au/FeOx–TiO2 after five cycles. It suggested a leaching of gold from
the catalyst, which might contribute to the decay of the catalyst activity. On the other hand, the HRTEM and ICP-MS
results showed that the percentage of gold leaching from Au/FeOx–TiO2 was smaller than that from Au/TiO2,
suggesting that Fe2O3 promoter 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. 1b, the addition of Fe2O3 produces locally
clustered Fe2O3 film on TiO2, and this film and TiO2 jointly anchor the gold particles, which can improve the gold
binding energy [11], and therefore increase the stability of gold particles. This result was similar to the early work of
Carrettin et al. [12] 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.
3. Conclusion
In conclusion, we successfully achieved the liquid phase hydrogenation of phthalic anhydride using gold catalysts.
Fe2O3-modified TiO2 supported gold catalyst with highly dispersed gold nanoparticles has a catalytic activity and
selectivity to phthalide superior to those of the most active catalysts yet reported [1–4]. This gold catalyst is expected to
find wide applications in other hydrogenation reactions, especially in selective hydrogenations under mild conditions.
Acknowledgments
We gratefully acknowledge the financial support provided by Zhejiang Provincial Natural Science Foundation of
China (No. Y405108) and the Department of Education of Zhejiang Province of China (No. 20051409).
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