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Preparation of Nanostructural ZrO2/SiO2 and Study on Catalytic ...

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<str<strong>on</strong>g>Preparati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>Nanostructural</str<strong>on</strong>g> <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>Study</str<strong>on</strong>g> <strong>on</strong> <strong>Catalytic</strong> Activity <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

its Superacid Catalyst<br />

Shao-Y<strong>on</strong>g Huang ( ), Ru-Fen Chen ( ),<br />

Xu-H<strong>on</strong>g Zhang ( ) <str<strong>on</strong>g>and</str<strong>on</strong>g> Xiu-Qin S<strong>on</strong>g* ( )<br />

College <str<strong>on</strong>g>of</str<strong>on</strong>g> Chemistry <str<strong>on</strong>g>and</str<strong>on</strong>g> Material Science, Hebei Normal University,<br />

Shijiazhuang, Heibei, 050016, P. R. China<br />

A novel material <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> was synthesized <strong>on</strong> <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support by means <str<strong>on</strong>g>of</str<strong>on</strong>g> electrostatic self-assembly<br />

technique <str<strong>on</strong>g>and</str<strong>on</strong>g> sol-gel method. After treating this material with 0.7 mol·L -1 H2SO4, a nanostructural solid<br />

superacid catalyst SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> was prepared. The material was characterized by Scanning Electr<strong>on</strong><br />

Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Brunauer Emmett Teller method (BET) <str<strong>on</strong>g>and</str<strong>on</strong>g><br />

Hammett indicator method. The catalytic activity <str<strong>on</strong>g>of</str<strong>on</strong>g> the catalyst was carried out for the esterificati<strong>on</strong> between<br />

acetic acid <str<strong>on</strong>g>and</str<strong>on</strong>g> butanol. Results show that the catalytic activity <str<strong>on</strong>g>of</str<strong>on</strong>g> this catalyst was much higher<br />

than that <str<strong>on</strong>g>of</str<strong>on</strong>g> powdered superacid catalyst SO4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>. Due to the <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> spherical support, the solid superacid<br />

catalyst could be separated <str<strong>on</strong>g>and</str<strong>on</strong>g> recovered easily. The nanostructural <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> will be a promising material<br />

for the chemical industry in the future.<br />

Keywords: <str<strong>on</strong>g>Nanostructural</str<strong>on</strong>g> <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g>; Sol-gel method; Self-assembly; Solid superacid catalyst;<br />

Esterificati<strong>on</strong>.<br />

INTRODUCTION<br />

Super acid, as a novel catalyst, has been the focus <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

studies since it was successfully synthesized in 1979. 1 Due<br />

to its high specific surface area <str<strong>on</strong>g>and</str<strong>on</strong>g> high acidity, the superacid<br />

catalyst is widely used in many fields. SO4 2- /MxOy is<br />

the most used superacid catalyst because <str<strong>on</strong>g>of</str<strong>on</strong>g> its advantages,<br />

such as high catalytic activity, high selectivity, easy preparati<strong>on</strong>,<br />

good stabilizati<strong>on</strong>, no corrosi<strong>on</strong> <str<strong>on</strong>g>and</str<strong>on</strong>g> no polluti<strong>on</strong>. In<br />

industry, it is used <strong>on</strong> a large scale in cracking, isomerizati<strong>on</strong>,<br />

alkylati<strong>on</strong>, esterificati<strong>on</strong>, acylati<strong>on</strong>, polymerizati<strong>on</strong><br />

<str<strong>on</strong>g>and</str<strong>on</strong>g> so <strong>on</strong>. 2-8 Am<strong>on</strong>g SO4 2- /MxOy catalysts, SO4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> is<br />

used extensively. However, when it is used as a powder<br />

SO4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> is <str<strong>on</strong>g>of</str<strong>on</strong>g>ten difficult to be separated <str<strong>on</strong>g>and</str<strong>on</strong>g> recycled<br />

from the reacti<strong>on</strong> system. 4,9-11 In this paper, we have successfully<br />

assembled nano-zirc<strong>on</strong>ia <strong>on</strong> the <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> spherical<br />

support whose diameter is approximately 1.0 mm by using<br />

the sol-gel technique <str<strong>on</strong>g>and</str<strong>on</strong>g> layer by layer self-assembly<br />

method. ZrOCl2·8H2O was the raw material <str<strong>on</strong>g>and</str<strong>on</strong>g> sodium<br />

dodecyl sulphate (C12H24SO4Na, SDS) aqueous soluti<strong>on</strong><br />

was used as the organic self-assembly medium. After treatment<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> with H2SO4 soluti<strong>on</strong>, a novel superacid<br />

catalyst SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> was prepared <str<strong>on</strong>g>and</str<strong>on</strong>g> its activity was<br />

Journal <str<strong>on</strong>g>of</str<strong>on</strong>g> the Chinese Chemical Society, 2007, 54, 997-1002 997<br />

also discussed.<br />

EXPERIMENTAL<br />

* Corresp<strong>on</strong>ding author. E-mail: s<strong>on</strong>gxq@mail.hebtu.edu.cn<br />

Project supported by the Natural Science Foundati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Hebei Province (No. 503167)<br />

<str<strong>on</strong>g>Preparati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>Nanostructural</str<strong>on</strong>g> <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> 12<br />

Cleanness <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support<br />

The <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support was purchased in China <str<strong>on</strong>g>and</str<strong>on</strong>g> the diameter<br />

is about 1 mm. The washing process was as follows:<br />

Washed the spherical <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support with (1) HCl +<br />

H2O2 (2) NH3·H2O+H2O2 (3) dei<strong>on</strong>ized water (4) absolute<br />

alcohol in turn, then dried it in a vacuum drying oven at 70<br />

C.<br />

<str<strong>on</strong>g>Preparati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> zirc<strong>on</strong>ium sol<br />

Mixed the ZrOCl2 soluti<strong>on</strong> <str<strong>on</strong>g>and</str<strong>on</strong>g> an acetic acid soluti<strong>on</strong><br />

in a beaker which was heated in a water-bath at 70 C,<br />

added 1:1 (v/v) NH3·H2O slowly under vigorous stirring to<br />

an appropriate pH till transparent sol was generated.<br />

The self-assembly process <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g><br />

The self-assembly process <str<strong>on</strong>g>of</str<strong>on</strong>g> nano-zirc<strong>on</strong>ia <strong>on</strong> <str<strong>on</strong>g>SiO2</str<strong>on</strong>g><br />

support (see the schematic diagram Fig. 1).<br />

1) Added the cleaned <str<strong>on</strong>g>and</str<strong>on</strong>g> dried <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support into the


998 J. Chin. Chem. Soc., Vol. 54, No. 4, 2007 Huang et al.<br />

zirc<strong>on</strong>ium sol then treated it in the processes <str<strong>on</strong>g>of</str<strong>on</strong>g> ultrasound,<br />

aging, washing <str<strong>on</strong>g>and</str<strong>on</strong>g> drying. After the first self-assembly<br />

process, Zr(OH)4/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> was fabricated.<br />

2) Added Zr(OH)4/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> into a SDS soluti<strong>on</strong>, followed<br />

by ultras<strong>on</strong>ic dispersi<strong>on</strong> for 30 min, then filtrated,<br />

washed <str<strong>on</strong>g>and</str<strong>on</strong>g> dried it in turn. We called this product SDS/<br />

Zr(OH)4/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g>.<br />

3) Added SDS/Zr(OH)4/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> into the zirc<strong>on</strong>ium sol<br />

then treated it with the processes <str<strong>on</strong>g>of</str<strong>on</strong>g> ultrasound, aging, washing,<br />

<str<strong>on</strong>g>and</str<strong>on</strong>g> drying.<br />

4) By repeating (2), (3) steps <str<strong>on</strong>g>and</str<strong>on</strong>g> calcining it at an appropriate<br />

temperature, we could prepare a multilayer selfassembly<br />

<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> material.<br />

<str<strong>on</strong>g>Preparati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>Nanostructural</str<strong>on</strong>g> Superacid Catalyst<br />

SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g><br />

Firstly, dried the sample Zr(OH)4/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> at 110 C for<br />

6 h; Sec<strong>on</strong>dly, impregnated the Zr(OH)4/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> with 0.7<br />

mol·L -1 H2SO4 for 1 h; Thirdly, filtrated <str<strong>on</strong>g>and</str<strong>on</strong>g> dried it at 110<br />

C for 10 h. After calcined at 550 C for 3 h, the SO4 2- -<br />

<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> superacid catalyst was prepared.<br />

Evaluati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>Catalytic</strong> Activity<br />

The activity <str<strong>on</strong>g>of</str<strong>on</strong>g> the so-prepared SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> catalyst<br />

was tested for the esterificati<strong>on</strong> reacti<strong>on</strong> between acetic<br />

acid <str<strong>on</strong>g>and</str<strong>on</strong>g> butanol. The catalytic activity was studied in a<br />

stirred batch reflux system at a temperature <str<strong>on</strong>g>of</str<strong>on</strong>g> 120 C. A<br />

three-necked flask equipped with a c<strong>on</strong>denser <str<strong>on</strong>g>and</str<strong>on</strong>g> a water<br />

knockout trap was charged with a certain amount <str<strong>on</strong>g>of</str<strong>on</strong>g> acetic<br />

acid (10 mL, 0.18 mol) <str<strong>on</strong>g>and</str<strong>on</strong>g> butanol (20 mL, 0.22 mol). The<br />

Fig. 1. The schematic diagram <str<strong>on</strong>g>of</str<strong>on</strong>g> the self-assembly processes.<br />

amount <str<strong>on</strong>g>of</str<strong>on</strong>g> SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> used in experiments was calculated<br />

from that <str<strong>on</strong>g>of</str<strong>on</strong>g> the powder superacid catalyst. We kept<br />

the zirc<strong>on</strong>ium c<strong>on</strong>tent equal to the powdered superacid catalyst.<br />

1gSO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> catalyst was used in the experiments.<br />

Sufficient stirring <str<strong>on</strong>g>of</str<strong>on</strong>g> the mixture was applied to<br />

avoid external mass or heat transport limitati<strong>on</strong>s. The reacti<strong>on</strong><br />

temperature was maintained by means <str<strong>on</strong>g>of</str<strong>on</strong>g> a thermostatic<br />

oil bath in which the reactor was immersed. For comparis<strong>on</strong>,<br />

a powdered superacid catalyst SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> was<br />

also prepared by the sol-gel method. In the experiment, the<br />

c<strong>on</strong>versi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> acetic acid can be regarded as the activity <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

the catalyst. 13<br />

Formula is as follows:<br />

C<strong>on</strong>versi<strong>on</strong> ratio = (1 V1/V0) 100%<br />

In this formula: V0 denotes the original volume <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

NaOH neutralizing the total acetic acid added to the reacti<strong>on</strong><br />

system; V1 represents the volume <str<strong>on</strong>g>of</str<strong>on</strong>g> NaOH neutralizing<br />

the acetic acid extracted from the reacti<strong>on</strong> device in the<br />

experiment.<br />

Characterizati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the Catalyst <str<strong>on</strong>g>and</str<strong>on</strong>g> Reacti<strong>on</strong> Product<br />

The catalyst was characterized by SEM (HITACHI<br />

S-570), EDS (HOLAND EDAX PV-9900), BET (MICRO-<br />

MERITICS ASAP 2010, -196 C) <str<strong>on</strong>g>and</str<strong>on</strong>g> the Hammett indicator<br />

method. 14,15 The products were analyzed by Gas Chromatography<br />

(GC, Shanghai Tianmei 7890F, detector: FID,<br />

column: AT.SE-54 15 m, column temperature:100 C, injector<br />

temperature: 150 C).


<str<strong>on</strong>g>Preparati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>Study</str<strong>on</strong>g> <strong>on</strong> Nano <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> Catalyst J. Chin. Chem. Soc., Vol. 54, No. 4, 2007 999<br />

RESULTS AND DISCUSSION<br />

Fig. 2 shows the images for the samples <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g><br />

nanostructural <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g>. We can find an obvious difference<br />

between the surfaces <str<strong>on</strong>g>of</str<strong>on</strong>g> the samples before <str<strong>on</strong>g>and</str<strong>on</strong>g> after<br />

self-assembly. Fig. 2-a shows that there are many white<br />

protuberances <strong>on</strong> the surface <str<strong>on</strong>g>of</str<strong>on</strong>g> the <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support. According<br />

to the EDS pattern (result is not shown), we proposed<br />

that the white surface protuberances are some irregular<br />

<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> particles b<strong>on</strong>ding to the surface <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>SiO2</str<strong>on</strong>g> support. After<br />

self-assembly for 5 times (Fig. 2-b) the white surface protuberances<br />

were covered because <str<strong>on</strong>g>of</str<strong>on</strong>g> the adsorpti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> zirc<strong>on</strong>ium<br />

species <strong>on</strong> the support. From the SEM images, we<br />

also see that the zirc<strong>on</strong>ium species particles adsorbed <strong>on</strong><br />

the support are small <str<strong>on</strong>g>and</str<strong>on</strong>g> dense after self-assembly. The<br />

particle size <str<strong>on</strong>g>of</str<strong>on</strong>g> zirc<strong>on</strong>ium species is about 20 nm.<br />

Table 1. The zirc<strong>on</strong>ium c<strong>on</strong>tents <str<strong>on</strong>g>of</str<strong>on</strong>g> different <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> layers<br />

layer 1 3 5 7 8 9 11<br />

Zr/wt 37.56 40.08 42.69 48.12 50.53 48.99 48.87<br />

The zirc<strong>on</strong>ium c<strong>on</strong>tent was measured by EDS. Table<br />

1 shows that the zirc<strong>on</strong>ium c<strong>on</strong>tent increased with the selfassembled<br />

times then it reached a maximum value. After<br />

this point, the zirc<strong>on</strong>ium c<strong>on</strong>tent remained c<strong>on</strong>stant. In<br />

some experiments the zirc<strong>on</strong>ium c<strong>on</strong>tent even declined<br />

with the self-assembled times. The results indicate that the<br />

self-assembly process has a kinetic equilibrium, that is, a<br />

given experimental c<strong>on</strong>diti<strong>on</strong> has its special kinetic equilibrium<br />

value. Fig. 3 shows that the zirc<strong>on</strong>ium c<strong>on</strong>tent<br />

reaches 50.53 wt after self-assembly 8 times which was<br />

the maximum c<strong>on</strong>tent in the experiments. In practice, the<br />

Fig. 2. SEM images <str<strong>on</strong>g>of</str<strong>on</strong>g> samples before <str<strong>on</strong>g>and</str<strong>on</strong>g> after self-assembly. a- before self-assembly, b- after self-assembly 5 times.<br />

Fig. 3. EDS pattern <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> self-assembled 8 times.


1000 J. Chin. Chem. Soc., Vol. 54, No. 4, 2007 Huang et al.<br />

Table 2. Acid strengths <str<strong>on</strong>g>of</str<strong>on</strong>g> the solid superacid<br />

Indicator<br />

pKa<br />

1<br />

-11.99<br />

2<br />

-12.14<br />

self-assembly process, which is c<strong>on</strong>trolled by many factors<br />

not <strong>on</strong>ly in dynamics <str<strong>on</strong>g>and</str<strong>on</strong>g> thermodynamics but also in colloid<br />

<str<strong>on</strong>g>and</str<strong>on</strong>g> interface, is very complex. So there are still much<br />

research that needs to be d<strong>on</strong>e to prepare higher zirc<strong>on</strong>ium<br />

c<strong>on</strong>tent nanostructural <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g>. The EDS pattern also<br />

proves the self-assembly process to be feasible.<br />

The acidity <str<strong>on</strong>g>of</str<strong>on</strong>g> the SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> sample was measured<br />

with the Hammett indicator method. Table 2 gives the<br />

acidity <str<strong>on</strong>g>of</str<strong>on</strong>g> the sample self-assembled 1 time. It shows that<br />

the novel superacid SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> had almost the same<br />

acidity as the powdered superacid SO4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>.<br />

The catalytic activity <str<strong>on</strong>g>of</str<strong>on</strong>g> SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> was tested<br />

for the esterificati<strong>on</strong> reacti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> acetic acid <str<strong>on</strong>g>and</str<strong>on</strong>g> butanol.<br />

Results (Fig. 4) <str<strong>on</strong>g>of</str<strong>on</strong>g> the samples assembled 1,3,5 times(denoted<br />

as S-ZrSi1, S-ZrSi3, S-ZrSi5) indicate that the catalytic<br />

activities <str<strong>on</strong>g>of</str<strong>on</strong>g> these catalysts followed this order: S-<br />

ZrSi1 S-ZrSi3 S-ZrSi5. Am<strong>on</strong>g these catalysts, the catalytic<br />

activity <str<strong>on</strong>g>of</str<strong>on</strong>g> S-ZrSi1 was the best <str<strong>on</strong>g>and</str<strong>on</strong>g> the c<strong>on</strong>versi<strong>on</strong><br />

could reach 98.7 within 120 min. It is worth noting that<br />

the activities <str<strong>on</strong>g>of</str<strong>on</strong>g> all nanostructural superacid catalysts S-<br />

ZrSi1, S-ZrSi3 <str<strong>on</strong>g>and</str<strong>on</strong>g> S-ZrSi5 were better than the powder<br />

3<br />

-12.70<br />

4<br />

-13.16<br />

5<br />

-13.80<br />

6<br />

-14.52<br />

7<br />

-16.04<br />

SO 4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/SiO 2 <br />

SO 4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> (Powder) <br />

“” color change clear, “” color change unclear<br />

1 m-methylnitrobenzene 2 nitrobenzene 3 p-nitrochloro-benzene 4 m-nitrochloro-benzene<br />

5 2,4-dinitrotoluene 6 2,4-dinitrfluorobenzene 7 1,3,5-trinitrotoluene<br />

Fig. 4. C<strong>on</strong>versi<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> the SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> catalysts<br />

with different assembly times. 1- catalyst selfassembled<br />

1 time; 2- catalyst self-assembled 3<br />

times; 3- catalyst self-assembled 5 times; 4powder<br />

catalyst; 5- no catalyst.<br />

superacid catalyst SO4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>. Their c<strong>on</strong>versi<strong>on</strong>s were bey<strong>on</strong>d<br />

90% in all experiments. The experiment results also<br />

show that the catalytic activity decreased with the selfassembly<br />

times. In experiments, we just found a little difference<br />

in acidity am<strong>on</strong>g them. A possible explanati<strong>on</strong> for<br />

the activities decrease is that the specific surface area <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />

<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> declines with the self-assembly times (See Table<br />

3). As we all know, when the superacid catalyst was<br />

prepared, the specific surface area became smaller than that<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> the precursor. We c<strong>on</strong>sider that the <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> particles are<br />

separated from each other (less agglomerati<strong>on</strong>, less b<strong>on</strong>ding)<br />

after the first self-assembly was given, so the catalyst<br />

had a higher specific surface area which resulted in the<br />

higher activity.<br />

The catalytic repeatability <str<strong>on</strong>g>of</str<strong>on</strong>g> the SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g><br />

catalyst was tested by using S-ZrSi1 to catalyze the reacti<strong>on</strong><br />

for several runs. Fig. 5 shows that after the catalyst was<br />

used for the sec<strong>on</strong>d run, the catalytic activity was still bey<strong>on</strong>d<br />

93. The c<strong>on</strong>versi<strong>on</strong> declined sharply when the catalyst<br />

was used for the third time. This result is perhaps related<br />

to two aspects. On <strong>on</strong>e h<str<strong>on</strong>g>and</str<strong>on</strong>g>, water is a major influencing<br />

factor in catalytic activity. It deactivates the catalyst<br />

Fig. 5. C<strong>on</strong>versi<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> the SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> catalysts<br />

with different use times. 1- used 1 time; 2- used<br />

2 times; 3- used 3 times; 4- used 4 times; 5- used<br />

5 times.


<str<strong>on</strong>g>Preparati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>and</str<strong>on</strong>g> <str<strong>on</strong>g>Study</str<strong>on</strong>g> <strong>on</strong> Nano <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> Catalyst J. Chin. Chem. Soc., Vol. 54, No. 4, 2007 1001<br />

Table 3. The surface specific areas <str<strong>on</strong>g>of</str<strong>on</strong>g> the samples<br />

Sample<br />

BET/m 2 ·g -1<br />

ZrO 2/SiO 2 assembled<br />

1 time<br />

by decreasing the active sites <str<strong>on</strong>g>of</str<strong>on</strong>g> the catalyst. On the other<br />

h<str<strong>on</strong>g>and</str<strong>on</strong>g>, the effect <str<strong>on</strong>g>of</str<strong>on</strong>g> specific surface area <strong>on</strong> the activity is<br />

also relevant. The explanati<strong>on</strong> is as follows. As we all know,<br />

the specific surface area <str<strong>on</strong>g>of</str<strong>on</strong>g> a traditi<strong>on</strong>al super acid catalyst<br />

prepared with powdered <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> declines in the processes <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

catalyst preparati<strong>on</strong> <str<strong>on</strong>g>and</str<strong>on</strong>g> use. In the case <str<strong>on</strong>g>of</str<strong>on</strong>g> S-ZrSi1, it has a<br />

high specific surface area. However, the high specific surface<br />

area also makes it easy to adsorb the organic species <strong>on</strong><br />

the catalyst surface, which block the active sites <str<strong>on</strong>g>and</str<strong>on</strong>g> decrease<br />

the acid active centre numbers <str<strong>on</strong>g>of</str<strong>on</strong>g> the superacid. As a<br />

result, it decreases the catalytic activity <str<strong>on</strong>g>of</str<strong>on</strong>g> the superacid<br />

catalyst SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g>. The catalytic activity could be<br />

partly recovered by washing the catalyst with ethanol or acet<strong>on</strong>e.<br />

16<br />

The reacti<strong>on</strong> products were analyzed by a GC measurement.<br />

As can be seen from Fig. 6, <strong>on</strong>ly two peaks appeared<br />

in the GC pattern. Compared to the retenti<strong>on</strong> time <str<strong>on</strong>g>of</str<strong>on</strong>g><br />

the st<str<strong>on</strong>g>and</str<strong>on</strong>g>ard substance (acetic acid 2.298, butanol 1.345,<br />

butyl acetate 2.182), we can c<strong>on</strong>clude that after reacti<strong>on</strong><br />

there are <strong>on</strong>ly two substances in the reacti<strong>on</strong> system: butanol<br />

<str<strong>on</strong>g>and</str<strong>on</strong>g> butyl acetate. In experiments, butanol was overdosed<br />

so in the GC pattern its peak appeared. That is to say,<br />

no by-products were formed in any experiments. All these<br />

indicated that the novel superacid catalyst SO4 2- -<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g><br />

can catalyze the reacti<strong>on</strong> successfully <str<strong>on</strong>g>and</str<strong>on</strong>g> the reacti<strong>on</strong> selectivity<br />

is 100%.<br />

Fig. 6. Gas chromatography <str<strong>on</strong>g>of</str<strong>on</strong>g> the catalytic products.<br />

(Catalyst: self-assembled 1 time; Reacti<strong>on</strong> temperature:<br />

120 C, Reacti<strong>on</strong> time: 120 min).<br />

ZrO 2/SiO 2 assembled<br />

3 times<br />

CONCLUSION<br />

We have successfully synthesized a novel nanostructural<br />

<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> material by using the sol-gel technique <str<strong>on</strong>g>and</str<strong>on</strong>g><br />

layer by layer self-assembly method. After treatment with<br />

H2SO4 soluti<strong>on</strong>, a novel superacid catalyst was prepared.<br />

The experiment results show that this superacid catalyst<br />

has almost the same acidity as the traditi<strong>on</strong>al powdered<br />

superacid SO4 2- /<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>; however, the catalytic activity is<br />

higher than that <str<strong>on</strong>g>of</str<strong>on</strong>g> the powdered superacid catalyst SO4 2- /<br />

<str<strong>on</strong>g>ZrO2</str<strong>on</strong>g> used in the experiments. The significant characteristic<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> this novel superacid catalyst is that it can be used, separated<br />

<str<strong>on</strong>g>and</str<strong>on</strong>g> recovered more easily <str<strong>on</strong>g>and</str<strong>on</strong>g> c<strong>on</strong>veniently due to<br />

having a big support. Now, the research <str<strong>on</strong>g>of</str<strong>on</strong>g> this novel super<br />

acid catalyst is still in the beginning stage so there is further<br />

work to be d<strong>on</strong>e. This nanostructural <str<strong>on</strong>g>ZrO2</str<strong>on</strong>g>/<str<strong>on</strong>g>SiO2</str<strong>on</strong>g> material<br />

will play an increasingly important role in the green catalytic<br />

field in the future.<br />

Received February 24, 2006.<br />

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455 413 380 96<br />

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