B. Wang, H. Liu
alloy is actually a reactant, reacting with dilute alkaline to produce hydrogen in situ
for subsequent reduction of 1-naphthol. In comparison with catalytic reaction over
metal catalyst, this method consumes a larger amount of Ni–Al alloy per product
molecule, restricting its application for industrial-scale production. Furthermore, as
reported by Zhang and Wang [3], reduction of 1-naphthol in dilute aqueous KOH
using Ni–Al alloy gave 1-tetralone and 1,2,3,4-THNOL as major products, besides
formation of minor 5,6,7,8-THNOL. Recently, Shirai et al. [4] reported hydro-
genation of 1-naphthol over Ru catalysts in supercritical carbon dioxide solvent with
5,6,7,8-THNOL yield of 31% at 323 K and 130 bar. This process uses environ-
mentally benign carbon dioxide as solvent, eliminating use of organic solvents and
simplifying product separation. However, the high equipment cost associated with
high-pressure operation represents a drawback.
In sum, previous work on synthesis of 5,6,7,8-THNOL suffers from several
drawbacks such as high cost of noble-metal (Pt, Pd, and Ru) catalysts, low catalyst
efficiency, and high equipment investment. Thus, efficient means to produce
5,6,7,8-THNOL are highly desired. We report herein selective hydrogenation of
1-naphthol over several Ni- and Pd-based catalysts such as supported Ni/Al2O3, Pd/
C, and NiB/USY catalysts.
Experimental
Catalyst preparation
Ni/c-Al2O3 with 5 wt% Ni loading was prepared by wet impregnation method using
c-Al2O3 (Alfa Aesar, 220 m2/g) as support and aqueous Ni(NO3)2Á6H2O solution
[5]. Prior to use, it was reduced in flowing hydrogen at 400 °C. 5 wt% Pd/C was
purchased from Sinopharm Chemical Reagent Co. NiB nanocatalyst was prepared
by reducing nickel acetate [Ni(CH3COO)2Á4H2O] with potassium borohydride
(KBH4) in water-in-oil microemulsion [6–11]. Two microemulsions of 200 ml,
namely Ni(CH3COO)2 and KBH4 microemulsions, were first prepared by dissolving
Ni(CH3COO)2 and KBH4 into corresponding microemulsions consisting of
hexadecyltrimethylammonium bromide (CTAB)/1-butanol/cyclohexane/water with
weight percentage of 11/8/58/23, respectively. Then, KBH4 microemulsion was
added into Ni(CH3COO)2 microemulsion at feed rate of 1.5 ml/min using a
metering pump at 0 °C under vigorous stirring and Ar protection. The molar ratio of
KBH4 to Ni2? was kept at 3:1.
Ultrastable Y zeolite (USY, 700 m2/g, SiO2/Al2O3 = 7) was purchased from
Tianjin Nankai catalyst company. USY support was firstly calcined and stored in a
drier. It was then added to NiB nanoparticle suspension to Ni loading of 5 wt% on
USY support under vigorous stirring, after which 600 ml tetrahydrofuran solvent
was introduced into the microemulsion at flow rate of 1.5 ml/min using a peristaltic
pump to slowly break the microemulsion and allow the particles to deposit on the
support. Upon addition of tetrahydrofuran, the liquid gradually changed color from
black to gray, and finally became colorless, indicating complete deposition of NiB
on the support. Then, the catalysts were filtered, and washed with tetrahydrofuran,
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