(58a) Hydrodeoxygenation of Anisole As Bio-Oil Model Compound over Supported Non-Sulphided CoMo Catalysts: Effect of Co/Mo Ratio and Support

Hydrodeoxygenation
of anisole as bio-oil model compound over supported non-sulphided CoMo
catalysts: effect of Co/Mo ratio and support

Chanakya
Ranga^a, Rune
Lødeng^b, Vaios I. Alexiadis^a, Joris W. Thybaut^a*

^aLaboratory for
Chemical Technology, Ghent University, Technologiepark 914, B-9052 Ghent,
Belgium.

^bSINTEF
Materials & Chemistry, Department of Kinetics and Catalysis, N-7465
Trondheim, Norway.

*Corresponding
Author: Joris W. Thybaut, E-mail: Joris.Thybaut@UGent.be

Introduction

            Fast
pyrolysis is considered as one of the prominent approaches to obtain liquid
organic products with high yield from lignocellulosic biomass.  However,
pyrolysis oils (bio-oil) cannot be directly used as a fuel or fuel additive due
to the high oxygen content ¹,
 which results in undesirable properties such as low thermal and chemical
stability, low heating value, immiscibility with conventional, fossil fuels and
high acidity. These oils, hence, require upgrading via oxygen removal and increase
in hydrogen content. Catalytic hydrodeoxygenation (HDO) is one of the most promising
routes to upgrade pyrolysis oils for producing liquid transportation fuels ².

            The
complexity of fast pyrolysis oil has prompted the use of model compounds such
as phenolics, furans, ethers, acids etc. to study the intricacies of
hydrodeoxygenation ^1,
3.
Anisole, because of its methoxy group, has already been widely investigated as
a model compound for lignin derived bio-oil ⁴.
The low sulfur content in bio-oil renders the use of traditional sulfided
catalysts (NiMoS and CoMoS) for hydroprocessing less suited, as they require
the presence of sulfur to retain their activity and, hence, result in contaminated
end products. To mitigate this issue, non sulfided transition metal (Ni, Co,
Mo) catalysts on various supports have been investigated for hydrotreatment of
bio-oil model compounds ^5-8,
yet significant challenges remain in improving the catalyst activity,
selectivity and stability. Our previous work on MoO₃/ZrO₂
catalysts provided insight in the effect of catalyst structural composition
with varying preparation conditions on catalyst performance ^7-8.
The present work explores the intricacies of anisole HDO reaction pathways upon
addition of Co to the Mo catalysts by assessing their intrinsic kinetics
performance in non-sulphided form. The catalyst performance is correlated with
properties such as reducibility, active site dispersion, crystallite size, metal-support
interaction.

Results

A
series of supported CoMo catalysts were prepared with varying Co/Mo ratio (0.25,
0.58, and 1.07) while keeping the Mo loading between 8.3 – 10.2 wt%. A sequential
incipient wetness impregnation (with Mo being introduced first) method using
aqueous solutions of the corresponding precursor salts was employed during the
synthesis procedure. Two different supports, i.e., Al₂O₃
and ZrO₂, were used. Material physicochemical characteristics were
evaluated through ICP-OES, BET, (in-situ) XRD, H₂-TPR, NH₃-TPD,
CO chemisorption, (S)TEM, and XPS techniques. The performance of these CoMo
catalysts was tested for anisole HDO at gas phase conditions in a fixed bed
tubular reactor in plug flow regime. A high-throughput kinetics screening set-up
(HTK-S) ⁹
comprising 16 plug flow reactors with an internal diameter of 0.00211 m and a
length of 0.85 m was used for the acquisition of intrinsic kinetic data.

 CoMo/Al₂O₃ catalysts promote the
transalkylation and isomerization reactions whereas, ZrO₂ supported
ones promote mainly hydrodeoxygenation and transalkylation reactions. Catalyst stability
as well as anisole conversion increased with Co/Mo ratio. Figure
1
displays the anisole conversion and product selectivity for CoMo/ZrO₂
and CoMo/Al₂O₃ catalysts with Co/Mo = 1.07 during a
stability test (TOS of 50 h). Al₂O₃ supported catalysts displayed higher
anisole conversions compared to ZrO₂ ones at the tested operating conditions.
Further reaction pathway elucidation is done with the use of intrinsic
kinetic measurements varying space time (50 – 250 kg_cat s mol^-1),
temperature (523 - 623 K) and H₂/anisole inlet molar ratio (50-150
mol mol^-1) with best performing catalysts. Catalyst deactivation causes
will be explored through characterization (O₂-TPO, XRD, XPS, (S)TEM)
of spent catalyst samples.

Addition
of Co improved the catalyst stability compared to the MoO₃ catalysts
in our previous study ^7-8.
Catalyst activity-structure correlations drawn from present study can serve
significantly in guiding the synthesis of next generation catalysts with better
catalyst stability and activity during anisole HDO.

Figure
1 Time on stream (TOS) experiment with (a) CoMo/ZrO₂
and (b) CoMo/Al₂O₃ at T = 573 K, P_T = 0.5 MPa,
H₂/anisole = 50 mol mol^-1, space-time = 220 kg_cat
s mol^-1_anisole.
Co/Mo = 1.07 for both catalysts.

Conclusions

Supported
CoMo catalysts observed to be relatively stable than the MoO₃
catalysts at the tested operating conditions during anisole HDO over 50 h TOS. Al₂O₃
supported catalysts exhibited higher anisole conversions and relatively lesser
stability compared to ZrO₂ ones at the tested operating conditions. Catalysts
stability as well as HDO activity observed during an extensive experimental
campaign are correlated to the key properties such as active site dispersion,
reducibility, crystallite size, and metal-support interaction. This will
further enhance our understanding of the catalyst activity, stability and selectivity
towards anisole HDO and provide valuable insights into the corresponding
reaction pathways.

Acknowledgments

This research work is
supported by the Innovative Catalyst Design for large-scale sustainable
processes (i-CaD) project, which is a European Research Council (ERC)
consolidator grant, by the European Commission in the 7^th Framework
Programme (GA nº 615456). It also fits in the framework of the FAST
industrialization by Catalyst Research and Development (FASTCARD) project,
which is a large scale collaborative project supported by European Commission
in the 7^th Framework Programme (GA nº 604277).

Keywords:

hydrodeoxygenation,
reaction pathways, catalyst stability

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