Chemistry Reference
In-Depth Information
as well as phenol due to demethoxylation and demethylation reactions. It
was suggested that the ReS layer thickness is important for optimizing
catalyst activity. A three dimensional lamellar structure could be obtained
on the non-sulfated surface, which had weaker support interactions than
the sulfated analogue.
Yan et al.
236
studied a combination of nanoparticle (NP) catalysts (Rh,
Ru, Pd, Pt based) and Brønsted acidic ionic liquids (IL) (SO
3
H groups
covalently linked through an alkyl chain of variable length/acidity) in
HDO of lignin-derived phenols, producing cycloalkanes. The ionic liquid
was investigated as an alternative to an aqueous phase system, which is
imposing equilibrium limitations to the dehydration reactions. The NP
catalysts were found to be highly active for hydrogenation of C
¼
C, C
¼
O
and aromatic bonds in IL at mild conditions such as 130 1C (40 atm H
2
,
4 h). In contrast, the use of classical mineral acids (H
2
SO
4
,H
3
PO
4
) with IL
was not successful due to deactivation and tar formation.
Elliott and Hart
224
investigated guaiacol, furfural and acetic acid
hydrotreating in a batch reactor over 3 wt% Pd/C (in-house) and 7.8 wt%
Ru/C (Engelhard / BASF) catalysts in the temperature range 150 to 300 1C
over 4 h. The Ru/C catalyst was the most active with a potential to convert
the substrate at 50 - 100 1C lower in temperature than the Pd/C. A limi-
tation of the Ru system is methanation and aqueous phase reforming
at temperatures higher than 250 1C. With guaiacol, ring saturation
proceeded easily with the Ru catalyst. This was in contrast to the less
hydrogenation-active Pd/C catalysts that gave more 2 methoxy-cyclohexa-
none. The Pd catalyst was not very active for acetic acid conversion at
200 1C, but could be used at higher temperatures.
A new catalytic route with a bifunctional combination of a carbon-
supported noble metal catalyst and a mineral acid for conversion of
phenols, guaiacols and syringols to cycloalkanes was suggested and
demonstrated by Zhao et al.
237
Conversion of the model compound
phenol over Pd/C was studied at 80 1C for 7 h on-stream. Pd- as well as Pt-,
Ru- and Rh-based catalysts favor phenol hydrogenation to cyclohexanol.
Cyclohexanol is very stable at 100-150 1C in aqueous solutions acidified
with H
3
PO
4
. However, a minor temperature increase caused rapid and
quantitative dehydration to cyclohexene. Thus, the system enables one-
pot hydrodeoxygenation through multistep reactions consisting of hy-
drogenation, hydrolysis and dehydration. The alkane products form a
separate phase.
Gutierrez et al.
238
studied mono and bimetallic noble metals (Rh, Pd,
Pt) on a ZrO
2
support in hydrotreating 3 wt% guaiacol in n-hexadecane in
a 40mL stainless steel batch reactor. The temperature was either 100 or
300 1C and the H
2
pressure was 80 bars. The effect of time-on-stream
(TOS) was studied only with the Rh catalyst, which performed much
better than the conventional CoMoS/Al
2
O
3
system, including less carbon
formation and the avoidance of sulfur in the products. At 300 1C all noble
metals gave almost complete conversion of guaiacol towards benzene
and small amounts of cyclohexanol. At 100 1C the noble metals catalysed
methyl transfer to the hydrocarbon ring. The main difference between
mono and bimetallic systems was the activity level. Complete conversion
